OSCL-LXR linux-6.0.1/​fs/​btrfs/​free-space-cache.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2008 Red Hat.  All rights reserved.
  */
 
 #include <linux/pagemap.h>
 #include <linux/sched.h>
 #include <linux/sched/signal.h>
 #include <linux/slab.h>
 #include <linux/math64.h>
 #include <linux/ratelimit.h>
 #include <linux/error-injection.h>
 #include <linux/sched/mm.h>
 #include "misc.h"
 #include "ctree.h"
 #include "free-space-cache.h"
 #include "transaction.h"
 #include "disk-io.h"
 #include "extent_io.h"
 #include "volumes.h"
 #include "space-info.h"
 #include "delalloc-space.h"
 #include "block-group.h"
 #include "discard.h"
 #include "subpage.h"
 #include "inode-item.h"
 
 #define BITS_PER_BITMAP     (PAGE_SIZE * 8UL)
 #define MAX_CACHE_BYTES_PER_GIG SZ_64K
 #define FORCE_EXTENT_THRESHOLD  SZ_1M
 
 struct btrfs_trim_range {
     u64 start;
     u64 bytes;
     struct list_head list;
 };
 
 static int link_free_space(struct btrfs_free_space_ctl *ctl,
                struct btrfs_free_space *info);
 static void unlink_free_space(struct btrfs_free_space_ctl *ctl,
                   struct btrfs_free_space *info, bool update_stat);
 static int search_bitmap(struct btrfs_free_space_ctl *ctl,
              struct btrfs_free_space *bitmap_info, u64 *offset,
              u64 *bytes, bool for_alloc);
 static void free_bitmap(struct btrfs_free_space_ctl *ctl,
             struct btrfs_free_space *bitmap_info);
 static void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
                   struct btrfs_free_space *info, u64 offset,
                   u64 bytes, bool update_stats);
 
 static struct inode *__lookup_free_space_inode(struct btrfs_root *root,
                            struct btrfs_path *path,
                            u64 offset)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_key key;
     struct btrfs_key location;
     struct btrfs_disk_key disk_key;
     struct btrfs_free_space_header *header;
     struct extent_buffer *leaf;
     struct inode *inode = NULL;
     unsigned nofs_flag;
     int ret;
 
     key.objectid = BTRFS_FREE_SPACE_OBJECTID;
     key.offset = offset;
     key.type = 0;
 
     ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
     if (ret < 0)
         return ERR_PTR(ret);
     if (ret > 0) {
         btrfs_release_path(path);
         return ERR_PTR(-ENOENT);
     }
 
     leaf = path->nodes[0];
     header = btrfs_item_ptr(leaf, path->slots[0],
                 struct btrfs_free_space_header);
     btrfs_free_space_key(leaf, header, &disk_key);
     btrfs_disk_key_to_cpu(&location, &disk_key);
     btrfs_release_path(path);
 
     /*
      * We are often under a trans handle at this point, so we need to make
      * sure NOFS is set to keep us from deadlocking.
      */
     nofs_flag = memalloc_nofs_save();
     inode = btrfs_iget_path(fs_info->sb, location.objectid, root, path);
     btrfs_release_path(path);
     memalloc_nofs_restore(nofs_flag);
     if (IS_ERR(inode))
         return inode;
 
     mapping_set_gfp_mask(inode->i_mapping,
             mapping_gfp_constraint(inode->i_mapping,
             ~(__GFP_FS | __GFP_HIGHMEM)));
 
     return inode;
 }
 
 struct inode *lookup_free_space_inode(struct btrfs_block_group *block_group,
         struct btrfs_path *path)
 {
     struct btrfs_fs_info *fs_info = block_group->fs_info;
     struct inode *inode = NULL;
     u32 flags = BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;
 
     spin_lock(&block_group->lock);
     if (block_group->inode)
         inode = igrab(block_group->inode);
     spin_unlock(&block_group->lock);
     if (inode)
         return inode;
 
     inode = __lookup_free_space_inode(fs_info->tree_root, path,
                       block_group->start);
     if (IS_ERR(inode))
         return inode;
 
     spin_lock(&block_group->lock);
     if (!((BTRFS_I(inode)->flags & flags) == flags)) {
         btrfs_info(fs_info, "Old style space inode found, converting.");
         BTRFS_I(inode)->flags |= BTRFS_INODE_NODATASUM |
             BTRFS_INODE_NODATACOW;
         block_group->disk_cache_state = BTRFS_DC_CLEAR;
     }
 
     if (!block_group->iref) {
         block_group->inode = igrab(inode);
         block_group->iref = 1;
     }
     spin_unlock(&block_group->lock);
 
     return inode;
 }
 
 static int __create_free_space_inode(struct btrfs_root *root,
                      struct btrfs_trans_handle *trans,
                      struct btrfs_path *path,
                      u64 ino, u64 offset)
 {
     struct btrfs_key key;
     struct btrfs_disk_key disk_key;
     struct btrfs_free_space_header *header;
     struct btrfs_inode_item *inode_item;
     struct extent_buffer *leaf;
     /* We inline CRCs for the free disk space cache */
     const u64 flags = BTRFS_INODE_NOCOMPRESS | BTRFS_INODE_PREALLOC |
               BTRFS_INODE_NODATASUM | BTRFS_INODE_NODATACOW;
     int ret;
 
     ret = btrfs_insert_empty_inode(trans, root, path, ino);
     if (ret)
         return ret;
 
     leaf = path->nodes[0];
     inode_item = btrfs_item_ptr(leaf, path->slots[0],
                     struct btrfs_inode_item);
     btrfs_item_key(leaf, &disk_key, path->slots[0]);
     memzero_extent_buffer(leaf, (unsigned long)inode_item,
                  sizeof(*inode_item));
     btrfs_set_inode_generation(leaf, inode_item, trans->transid);
     btrfs_set_inode_size(leaf, inode_item, 0);
     btrfs_set_inode_nbytes(leaf, inode_item, 0);
     btrfs_set_inode_uid(leaf, inode_item, 0);
     btrfs_set_inode_gid(leaf, inode_item, 0);
     btrfs_set_inode_mode(leaf, inode_item, S_IFREG | 0600);
     btrfs_set_inode_flags(leaf, inode_item, flags);
     btrfs_set_inode_nlink(leaf, inode_item, 1);
     btrfs_set_inode_transid(leaf, inode_item, trans->transid);
     btrfs_set_inode_block_group(leaf, inode_item, offset);
     btrfs_mark_buffer_dirty(leaf);
     btrfs_release_path(path);
 
     key.objectid = BTRFS_FREE_SPACE_OBJECTID;
     key.offset = offset;
     key.type = 0;
     ret = btrfs_insert_empty_item(trans, root, path, &key,
                       sizeof(struct btrfs_free_space_header));
     if (ret < 0) {
         btrfs_release_path(path);
         return ret;
     }
 
     leaf = path->nodes[0];
     header = btrfs_item_ptr(leaf, path->slots[0],
                 struct btrfs_free_space_header);
     memzero_extent_buffer(leaf, (unsigned long)header, sizeof(*header));
     btrfs_set_free_space_key(leaf, header, &disk_key);
     btrfs_mark_buffer_dirty(leaf);
     btrfs_release_path(path);
 
     return 0;
 }
 
 int create_free_space_inode(struct btrfs_trans_handle *trans,
                 struct btrfs_block_group *block_group,
                 struct btrfs_path *path)
 {
     int ret;
     u64 ino;
 
     ret = btrfs_get_free_objectid(trans->fs_info->tree_root, &ino);
     if (ret < 0)
         return ret;
 
     return __create_free_space_inode(trans->fs_info->tree_root, trans, path,
                      ino, block_group->start);
 }
 
 /*
  * inode is an optional sink: if it is NULL, btrfs_remove_free_space_inode
  * handles lookup, otherwise it takes ownership and iputs the inode.
  * Don't reuse an inode pointer after passing it into this function.
  */
 int btrfs_remove_free_space_inode(struct btrfs_trans_handle *trans,
                   struct inode *inode,
                   struct btrfs_block_group *block_group)
 {
     struct btrfs_path *path;
     struct btrfs_key key;
     int ret = 0;
 
     path = btrfs_alloc_path();
     if (!path)
         return -ENOMEM;
 
     if (!inode)
         inode = lookup_free_space_inode(block_group, path);
     if (IS_ERR(inode)) {
         if (PTR_ERR(inode) != -ENOENT)
             ret = PTR_ERR(inode);
         goto out;
     }
     ret = btrfs_orphan_add(trans, BTRFS_I(inode));
     if (ret) {
         btrfs_add_delayed_iput(inode);
         goto out;
     }
     clear_nlink(inode);
     /* One for the block groups ref */
     spin_lock(&block_group->lock);
     if (block_group->iref) {
         block_group->iref = 0;
         block_group->inode = NULL;
         spin_unlock(&block_group->lock);
         iput(inode);
     } else {
         spin_unlock(&block_group->lock);
     }
     /* One for the lookup ref */
     btrfs_add_delayed_iput(inode);
 
     key.objectid = BTRFS_FREE_SPACE_OBJECTID;
     key.type = 0;
     key.offset = block_group->start;
     ret = btrfs_search_slot(trans, trans->fs_info->tree_root, &key, path,
                 -1, 1);
     if (ret) {
         if (ret > 0)
             ret = 0;
         goto out;
     }
     ret = btrfs_del_item(trans, trans->fs_info->tree_root, path);
 out:
     btrfs_free_path(path);
     return ret;
 }
 
 int btrfs_check_trunc_cache_free_space(struct btrfs_fs_info *fs_info,
                        struct btrfs_block_rsv *rsv)
 {
     u64 needed_bytes;
     int ret;
 
     /* 1 for slack space, 1 for updating the inode */
     needed_bytes = btrfs_calc_insert_metadata_size(fs_info, 1) +
         btrfs_calc_metadata_size(fs_info, 1);
 
     spin_lock(&rsv->lock);
     if (rsv->reserved < needed_bytes)
         ret = -ENOSPC;
     else
         ret = 0;
     spin_unlock(&rsv->lock);
     return ret;
 }
 
 int btrfs_truncate_free_space_cache(struct btrfs_trans_handle *trans,
                     struct btrfs_block_group *block_group,
                     struct inode *vfs_inode)
 {
     struct btrfs_truncate_control control = {
         .inode = BTRFS_I(vfs_inode),
         .new_size = 0,
         .ino = btrfs_ino(BTRFS_I(vfs_inode)),
         .min_type = BTRFS_EXTENT_DATA_KEY,
         .clear_extent_range = true,
     };
     struct btrfs_inode *inode = BTRFS_I(vfs_inode);
     struct btrfs_root *root = inode->root;
     struct extent_state *cached_state = NULL;
     int ret = 0;
     bool locked = false;
 
     if (block_group) {
         struct btrfs_path *path = btrfs_alloc_path();
 
         if (!path) {
             ret = -ENOMEM;
             goto fail;
         }
         locked = true;
         mutex_lock(&trans->transaction->cache_write_mutex);
         if (!list_empty(&block_group->io_list)) {
             list_del_init(&block_group->io_list);
 
             btrfs_wait_cache_io(trans, block_group, path);
             btrfs_put_block_group(block_group);
         }
 
         /*
          * now that we've truncated the cache away, its no longer
          * setup or written
          */
         spin_lock(&block_group->lock);
         block_group->disk_cache_state = BTRFS_DC_CLEAR;
         spin_unlock(&block_group->lock);
         btrfs_free_path(path);
     }
 
     btrfs_i_size_write(inode, 0);
     truncate_pagecache(vfs_inode, 0);
 
     lock_extent_bits(&inode->io_tree, 0, (u64)-1, &cached_state);
     btrfs_drop_extent_cache(inode, 0, (u64)-1, 0);
 
     /*
      * We skip the throttling logic for free space cache inodes, so we don't
      * need to check for -EAGAIN.
      */
     ret = btrfs_truncate_inode_items(trans, root, &control);
 
     inode_sub_bytes(&inode->vfs_inode, control.sub_bytes);
     btrfs_inode_safe_disk_i_size_write(inode, control.last_size);
 
     unlock_extent_cached(&inode->io_tree, 0, (u64)-1, &cached_state);
     if (ret)
         goto fail;
 
     ret = btrfs_update_inode(trans, root, inode);
 
 fail:
     if (locked)
         mutex_unlock(&trans->transaction->cache_write_mutex);
     if (ret)
         btrfs_abort_transaction(trans, ret);
 
     return ret;
 }
 
 static void readahead_cache(struct inode *inode)
 {
     struct file_ra_state ra;
     unsigned long last_index;
 
     file_ra_state_init(&ra, inode->i_mapping);
     last_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
 
     page_cache_sync_readahead(inode->i_mapping, &ra, NULL, 0, last_index);
 }
 
 static int io_ctl_init(struct btrfs_io_ctl *io_ctl, struct inode *inode,
                int write)
 {
     int num_pages;
 
     num_pages = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 
     /* Make sure we can fit our crcs and generation into the first page */
     if (write && (num_pages * sizeof(u32) + sizeof(u64)) > PAGE_SIZE)
         return -ENOSPC;
 
     memset(io_ctl, 0, sizeof(struct btrfs_io_ctl));
 
     io_ctl->pages = kcalloc(num_pages, sizeof(struct page *), GFP_NOFS);
     if (!io_ctl->pages)
         return -ENOMEM;
 
     io_ctl->num_pages = num_pages;
     io_ctl->fs_info = btrfs_sb(inode->i_sb);
     io_ctl->inode = inode;
 
     return 0;
 }
 ALLOW_ERROR_INJECTION(io_ctl_init, ERRNO);
 
 static void io_ctl_free(struct btrfs_io_ctl *io_ctl)
 {
     kfree(io_ctl->pages);
     io_ctl->pages = NULL;
 }
 
 static void io_ctl_unmap_page(struct btrfs_io_ctl *io_ctl)
 {
     if (io_ctl->cur) {
         io_ctl->cur = NULL;
         io_ctl->orig = NULL;
     }
 }
 
 static void io_ctl_map_page(struct btrfs_io_ctl *io_ctl, int clear)
 {
     ASSERT(io_ctl->index < io_ctl->num_pages);
     io_ctl->page = io_ctl->pages[io_ctl->index++];
     io_ctl->cur = page_address(io_ctl->page);
     io_ctl->orig = io_ctl->cur;
     io_ctl->size = PAGE_SIZE;
     if (clear)
         clear_page(io_ctl->cur);
 }
 
 static void io_ctl_drop_pages(struct btrfs_io_ctl *io_ctl)
 {
     int i;
 
     io_ctl_unmap_page(io_ctl);
 
     for (i = 0; i < io_ctl->num_pages; i++) {
         if (io_ctl->pages[i]) {
             btrfs_page_clear_checked(io_ctl->fs_info,
                     io_ctl->pages[i],
                     page_offset(io_ctl->pages[i]),
                     PAGE_SIZE);
             unlock_page(io_ctl->pages[i]);
             put_page(io_ctl->pages[i]);
         }
     }
 }
 
 static int io_ctl_prepare_pages(struct btrfs_io_ctl *io_ctl, bool uptodate)
 {
     struct page *page;
     struct inode *inode = io_ctl->inode;
     gfp_t mask = btrfs_alloc_write_mask(inode->i_mapping);
     int i;
 
     for (i = 0; i < io_ctl->num_pages; i++) {
         int ret;
 
         page = find_or_create_page(inode->i_mapping, i, mask);
         if (!page) {
             io_ctl_drop_pages(io_ctl);
             return -ENOMEM;
         }
 
         ret = set_page_extent_mapped(page);
         if (ret < 0) {
             unlock_page(page);
             put_page(page);
             io_ctl_drop_pages(io_ctl);
             return ret;
         }
 
         io_ctl->pages[i] = page;
         if (uptodate && !PageUptodate(page)) {
             btrfs_read_folio(NULL, page_folio(page));
             lock_page(page);
             if (page->mapping != inode->i_mapping) {
                 btrfs_err(BTRFS_I(inode)->root->fs_info,
                       "free space cache page truncated");
                 io_ctl_drop_pages(io_ctl);
                 return -EIO;
             }
             if (!PageUptodate(page)) {
                 btrfs_err(BTRFS_I(inode)->root->fs_info,
                        "error reading free space cache");
                 io_ctl_drop_pages(io_ctl);
                 return -EIO;
             }
         }
     }
 
     for (i = 0; i < io_ctl->num_pages; i++)
         clear_page_dirty_for_io(io_ctl->pages[i]);
 
     return 0;
 }
 
 static void io_ctl_set_generation(struct btrfs_io_ctl *io_ctl, u64 generation)
 {
     io_ctl_map_page(io_ctl, 1);
 
     /*
      * Skip the csum areas.  If we don't check crcs then we just have a
      * 64bit chunk at the front of the first page.
      */
     io_ctl->cur += (sizeof(u32) * io_ctl->num_pages);
     io_ctl->size -= sizeof(u64) + (sizeof(u32) * io_ctl->num_pages);
 
     put_unaligned_le64(generation, io_ctl->cur);
     io_ctl->cur += sizeof(u64);
 }
 
 static int io_ctl_check_generation(struct btrfs_io_ctl *io_ctl, u64 generation)
 {
     u64 cache_gen;
 
     /*
      * Skip the crc area.  If we don't check crcs then we just have a 64bit
      * chunk at the front of the first page.
      */
     io_ctl->cur += sizeof(u32) * io_ctl->num_pages;
     io_ctl->size -= sizeof(u64) + (sizeof(u32) * io_ctl->num_pages);
 
     cache_gen = get_unaligned_le64(io_ctl->cur);
     if (cache_gen != generation) {
         btrfs_err_rl(io_ctl->fs_info,
             "space cache generation (%llu) does not match inode (%llu)",
                 cache_gen, generation);
         io_ctl_unmap_page(io_ctl);
         return -EIO;
     }
     io_ctl->cur += sizeof(u64);
     return 0;
 }
 
 static void io_ctl_set_crc(struct btrfs_io_ctl *io_ctl, int index)
 {
     u32 *tmp;
     u32 crc = ~(u32)0;
     unsigned offset = 0;
 
     if (index == 0)
         offset = sizeof(u32) * io_ctl->num_pages;
 
     crc = btrfs_crc32c(crc, io_ctl->orig + offset, PAGE_SIZE - offset);
     btrfs_crc32c_final(crc, (u8 *)&crc);
     io_ctl_unmap_page(io_ctl);
     tmp = page_address(io_ctl->pages[0]);
     tmp += index;
     *tmp = crc;
 }
 
 static int io_ctl_check_crc(struct btrfs_io_ctl *io_ctl, int index)
 {
     u32 *tmp, val;
     u32 crc = ~(u32)0;
     unsigned offset = 0;
 
     if (index == 0)
         offset = sizeof(u32) * io_ctl->num_pages;
 
     tmp = page_address(io_ctl->pages[0]);
     tmp += index;
     val = *tmp;
 
     io_ctl_map_page(io_ctl, 0);
     crc = btrfs_crc32c(crc, io_ctl->orig + offset, PAGE_SIZE - offset);
     btrfs_crc32c_final(crc, (u8 *)&crc);
     if (val != crc) {
         btrfs_err_rl(io_ctl->fs_info,
             "csum mismatch on free space cache");
         io_ctl_unmap_page(io_ctl);
         return -EIO;
     }
 
     return 0;
 }
 
 static int io_ctl_add_entry(struct btrfs_io_ctl *io_ctl, u64 offset, u64 bytes,
                 void *bitmap)
 {
     struct btrfs_free_space_entry *entry;
 
     if (!io_ctl->cur)
         return -ENOSPC;
 
     entry = io_ctl->cur;
     put_unaligned_le64(offset, &entry->offset);
     put_unaligned_le64(bytes, &entry->bytes);
     entry->type = (bitmap) ? BTRFS_FREE_SPACE_BITMAP :
         BTRFS_FREE_SPACE_EXTENT;
     io_ctl->cur += sizeof(struct btrfs_free_space_entry);
     io_ctl->size -= sizeof(struct btrfs_free_space_entry);
 
     if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
         return 0;
 
     io_ctl_set_crc(io_ctl, io_ctl->index - 1);
 
     /* No more pages to map */
     if (io_ctl->index >= io_ctl->num_pages)
         return 0;
 
     /* map the next page */
     io_ctl_map_page(io_ctl, 1);
     return 0;
 }
 
 static int io_ctl_add_bitmap(struct btrfs_io_ctl *io_ctl, void *bitmap)
 {
     if (!io_ctl->cur)
         return -ENOSPC;
 
     /*
      * If we aren't at the start of the current page, unmap this one and
      * map the next one if there is any left.
      */
     if (io_ctl->cur != io_ctl->orig) {
         io_ctl_set_crc(io_ctl, io_ctl->index - 1);
         if (io_ctl->index >= io_ctl->num_pages)
             return -ENOSPC;
         io_ctl_map_page(io_ctl, 0);
     }
 
     copy_page(io_ctl->cur, bitmap);
     io_ctl_set_crc(io_ctl, io_ctl->index - 1);
     if (io_ctl->index < io_ctl->num_pages)
         io_ctl_map_page(io_ctl, 0);
     return 0;
 }
 
 static void io_ctl_zero_remaining_pages(struct btrfs_io_ctl *io_ctl)
 {
     /*
      * If we're not on the boundary we know we've modified the page and we
      * need to crc the page.
      */
     if (io_ctl->cur != io_ctl->orig)
         io_ctl_set_crc(io_ctl, io_ctl->index - 1);
     else
         io_ctl_unmap_page(io_ctl);
 
     while (io_ctl->index < io_ctl->num_pages) {
         io_ctl_map_page(io_ctl, 1);
         io_ctl_set_crc(io_ctl, io_ctl->index - 1);
     }
 }
 
 static int io_ctl_read_entry(struct btrfs_io_ctl *io_ctl,
                 struct btrfs_free_space *entry, u8 *type)
 {
     struct btrfs_free_space_entry *e;
     int ret;
 
     if (!io_ctl->cur) {
         ret = io_ctl_check_crc(io_ctl, io_ctl->index);
         if (ret)
             return ret;
     }
 
     e = io_ctl->cur;
     entry->offset = get_unaligned_le64(&e->offset);
     entry->bytes = get_unaligned_le64(&e->bytes);
     *type = e->type;
     io_ctl->cur += sizeof(struct btrfs_free_space_entry);
     io_ctl->size -= sizeof(struct btrfs_free_space_entry);
 
     if (io_ctl->size >= sizeof(struct btrfs_free_space_entry))
         return 0;
 
     io_ctl_unmap_page(io_ctl);
 
     return 0;
 }
 
 static int io_ctl_read_bitmap(struct btrfs_io_ctl *io_ctl,
                   struct btrfs_free_space *entry)
 {
     int ret;
 
     ret = io_ctl_check_crc(io_ctl, io_ctl->index);
     if (ret)
         return ret;
 
     copy_page(entry->bitmap, io_ctl->cur);
     io_ctl_unmap_page(io_ctl);
 
     return 0;
 }
 
 static void recalculate_thresholds(struct btrfs_free_space_ctl *ctl)
 {
     struct btrfs_block_group *block_group = ctl->block_group;
     u64 max_bytes;
     u64 bitmap_bytes;
     u64 extent_bytes;
     u64 size = block_group->length;
     u64 bytes_per_bg = BITS_PER_BITMAP * ctl->unit;
     u64 max_bitmaps = div64_u64(size + bytes_per_bg - 1, bytes_per_bg);
 
     max_bitmaps = max_t(u64, max_bitmaps, 1);
 
     ASSERT(ctl->total_bitmaps <= max_bitmaps);
 
     /*
      * We are trying to keep the total amount of memory used per 1GiB of
      * space to be MAX_CACHE_BYTES_PER_GIG.  However, with a reclamation
      * mechanism of pulling extents >= FORCE_EXTENT_THRESHOLD out of
      * bitmaps, we may end up using more memory than this.
      */
     if (size < SZ_1G)
         max_bytes = MAX_CACHE_BYTES_PER_GIG;
     else
         max_bytes = MAX_CACHE_BYTES_PER_GIG * div_u64(size, SZ_1G);
 
     bitmap_bytes = ctl->total_bitmaps * ctl->unit;
 
     /*
      * we want the extent entry threshold to always be at most 1/2 the max
      * bytes we can have, or whatever is less than that.
      */
     extent_bytes = max_bytes - bitmap_bytes;
     extent_bytes = min_t(u64, extent_bytes, max_bytes >> 1);
 
     ctl->extents_thresh =
         div_u64(extent_bytes, sizeof(struct btrfs_free_space));
 }
 
 static int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
                    struct btrfs_free_space_ctl *ctl,
                    struct btrfs_path *path, u64 offset)
 {
     struct btrfs_fs_info *fs_info = root->fs_info;
     struct btrfs_free_space_header *header;
     struct extent_buffer *leaf;
     struct btrfs_io_ctl io_ctl;
     struct btrfs_key key;
     struct btrfs_free_space *e, *n;
     LIST_HEAD(bitmaps);
     u64 num_entries;
     u64 num_bitmaps;
     u64 generation;
     u8 type;
     int ret = 0;
 
     /* Nothing in the space cache, goodbye */
     if (!i_size_read(inode))
         return 0;
 
     key.objectid = BTRFS_FREE_SPACE_OBJECTID;
     key.offset = offset;
     key.type = 0;
 
     ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
     if (ret < 0)
         return 0;
     else if (ret > 0) {
         btrfs_release_path(path);
         return 0;
     }
 
     ret = -1;
 
     leaf = path->nodes[0];
     header = btrfs_item_ptr(leaf, path->slots[0],
                 struct btrfs_free_space_header);
     num_entries = btrfs_free_space_entries(leaf, header);
     num_bitmaps = btrfs_free_space_bitmaps(leaf, header);
     generation = btrfs_free_space_generation(leaf, header);
     btrfs_release_path(path);
 
     if (!BTRFS_I(inode)->generation) {
         btrfs_info(fs_info,
                "the free space cache file (%llu) is invalid, skip it",
                offset);
         return 0;
     }
 
     if (BTRFS_I(inode)->generation != generation) {
         btrfs_err(fs_info,
               "free space inode generation (%llu) did not match free space cache generation (%llu)",
               BTRFS_I(inode)->generation, generation);
         return 0;
     }
 
     if (!num_entries)
         return 0;
 
     ret = io_ctl_init(&io_ctl, inode, 0);
     if (ret)
         return ret;
 
     readahead_cache(inode);
 
     ret = io_ctl_prepare_pages(&io_ctl, true);
     if (ret)
         goto out;
 
     ret = io_ctl_check_crc(&io_ctl, 0);
     if (ret)
         goto free_cache;
 
     ret = io_ctl_check_generation(&io_ctl, generation);
     if (ret)
         goto free_cache;
 
     while (num_entries) {
         e = kmem_cache_zalloc(btrfs_free_space_cachep,
                       GFP_NOFS);
         if (!e) {
             ret = -ENOMEM;
             goto free_cache;
         }
 
         ret = io_ctl_read_entry(&io_ctl, e, &type);
         if (ret) {
             kmem_cache_free(btrfs_free_space_cachep, e);
             goto free_cache;
         }
 
         if (!e->bytes) {
             ret = -1;
             kmem_cache_free(btrfs_free_space_cachep, e);
             goto free_cache;
         }
 
         if (type == BTRFS_FREE_SPACE_EXTENT) {
             spin_lock(&ctl->tree_lock);
             ret = link_free_space(ctl, e);
             spin_unlock(&ctl->tree_lock);
             if (ret) {
                 btrfs_err(fs_info,
                     "Duplicate entries in free space cache, dumping");
                 kmem_cache_free(btrfs_free_space_cachep, e);
                 goto free_cache;
             }
         } else {
             ASSERT(num_bitmaps);
             num_bitmaps--;
             e->bitmap = kmem_cache_zalloc(
                     btrfs_free_space_bitmap_cachep, GFP_NOFS);
             if (!e->bitmap) {
                 ret = -ENOMEM;
                 kmem_cache_free(
                     btrfs_free_space_cachep, e);
                 goto free_cache;
             }
             spin_lock(&ctl->tree_lock);
             ret = link_free_space(ctl, e);
             ctl->total_bitmaps++;
             recalculate_thresholds(ctl);
             spin_unlock(&ctl->tree_lock);
             if (ret) {
                 btrfs_err(fs_info,
                     "Duplicate entries in free space cache, dumping");
                 kmem_cache_free(btrfs_free_space_cachep, e);
                 goto free_cache;
             }
             list_add_tail(&e->list, &bitmaps);
         }
 
         num_entries--;
     }
 
     io_ctl_unmap_page(&io_ctl);
 
     /*
      * We add the bitmaps at the end of the entries in order that
      * the bitmap entries are added to the cache.
      */
     list_for_each_entry_safe(e, n, &bitmaps, list) {
         list_del_init(&e->list);
         ret = io_ctl_read_bitmap(&io_ctl, e);
         if (ret)
             goto free_cache;
     }
 
     io_ctl_drop_pages(&io_ctl);
     ret = 1;
 out:
     io_ctl_free(&io_ctl);
     return ret;
 free_cache:
     io_ctl_drop_pages(&io_ctl);
     __btrfs_remove_free_space_cache(ctl);
     goto out;
 }
 
 static int copy_free_space_cache(struct btrfs_block_group *block_group,
                  struct btrfs_free_space_ctl *ctl)
 {
     struct btrfs_free_space *info;
     struct rb_node *n;
     int ret = 0;
 
     while (!ret && (n = rb_first(&ctl->free_space_offset)) != NULL) {
         info = rb_entry(n, struct btrfs_free_space, offset_index);
         if (!info->bitmap) {
             unlink_free_space(ctl, info, true);
             ret = btrfs_add_free_space(block_group, info->offset,
                            info->bytes);
             kmem_cache_free(btrfs_free_space_cachep, info);
         } else {
             u64 offset = info->offset;
             u64 bytes = ctl->unit;
 
             while (search_bitmap(ctl, info, &offset, &bytes,
                          false) == 0) {
                 ret = btrfs_add_free_space(block_group, offset,
                                bytes);
                 if (ret)
                     break;
                 bitmap_clear_bits(ctl, info, offset, bytes, true);
                 offset = info->offset;
                 bytes = ctl->unit;
             }
             free_bitmap(ctl, info);
         }
         cond_resched();
     }
     return ret;
 }
 
 int load_free_space_cache(struct btrfs_block_group *block_group)
 {
     struct btrfs_fs_info *fs_info = block_group->fs_info;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space_ctl tmp_ctl = {};
     struct inode *inode;
     struct btrfs_path *path;
     int ret = 0;
     bool matched;
     u64 used = block_group->used;
 
     /*
      * Because we could potentially discard our loaded free space, we want
      * to load everything into a temporary structure first, and then if it's
      * valid copy it all into the actual free space ctl.
      */
     btrfs_init_free_space_ctl(block_group, &tmp_ctl);
 
     /*
      * If this block group has been marked to be cleared for one reason or
      * another then we can't trust the on disk cache, so just return.
      */
     spin_lock(&block_group->lock);
     if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
         spin_unlock(&block_group->lock);
         return 0;
     }
     spin_unlock(&block_group->lock);
 
     path = btrfs_alloc_path();
     if (!path)
         return 0;
     path->search_commit_root = 1;
     path->skip_locking = 1;
 
     /*
      * We must pass a path with search_commit_root set to btrfs_iget in
      * order to avoid a deadlock when allocating extents for the tree root.
      *
      * When we are COWing an extent buffer from the tree root, when looking
      * for a free extent, at extent-tree.c:find_free_extent(), we can find
      * block group without its free space cache loaded. When we find one
      * we must load its space cache which requires reading its free space
      * cache's inode item from the root tree. If this inode item is located
      * in the same leaf that we started COWing before, then we end up in
      * deadlock on the extent buffer (trying to read lock it when we
      * previously write locked it).
      *
      * It's safe to read the inode item using the commit root because
      * block groups, once loaded, stay in memory forever (until they are
      * removed) as well as their space caches once loaded. New block groups
      * once created get their ->cached field set to BTRFS_CACHE_FINISHED so
      * we will never try to read their inode item while the fs is mounted.
      */
     inode = lookup_free_space_inode(block_group, path);
     if (IS_ERR(inode)) {
         btrfs_free_path(path);
         return 0;
     }
 
     /* We may have converted the inode and made the cache invalid. */
     spin_lock(&block_group->lock);
     if (block_group->disk_cache_state != BTRFS_DC_WRITTEN) {
         spin_unlock(&block_group->lock);
         btrfs_free_path(path);
         goto out;
     }
     spin_unlock(&block_group->lock);
 
     ret = __load_free_space_cache(fs_info->tree_root, inode, &tmp_ctl,
                       path, block_group->start);
     btrfs_free_path(path);
     if (ret <= 0)
         goto out;
 
     matched = (tmp_ctl.free_space == (block_group->length - used -
                       block_group->bytes_super));
 
     if (matched) {
         ret = copy_free_space_cache(block_group, &tmp_ctl);
         /*
          * ret == 1 means we successfully loaded the free space cache,
          * so we need to re-set it here.
          */
         if (ret == 0)
             ret = 1;
     } else {
         __btrfs_remove_free_space_cache(&tmp_ctl);
         btrfs_warn(fs_info,
                "block group %llu has wrong amount of free space",
                block_group->start);
         ret = -1;
     }
 out:
     if (ret < 0) {
         /* This cache is bogus, make sure it gets cleared */
         spin_lock(&block_group->lock);
         block_group->disk_cache_state = BTRFS_DC_CLEAR;
         spin_unlock(&block_group->lock);
         ret = 0;
 
         btrfs_warn(fs_info,
                "failed to load free space cache for block group %llu, rebuilding it now",
                block_group->start);
     }
 
     spin_lock(&ctl->tree_lock);
     btrfs_discard_update_discardable(block_group);
     spin_unlock(&ctl->tree_lock);
     iput(inode);
     return ret;
 }
 
 static noinline_for_stack
 int write_cache_extent_entries(struct btrfs_io_ctl *io_ctl,
                   struct btrfs_free_space_ctl *ctl,
                   struct btrfs_block_group *block_group,
                   int *entries, int *bitmaps,
                   struct list_head *bitmap_list)
 {
     int ret;
     struct btrfs_free_cluster *cluster = NULL;
     struct btrfs_free_cluster *cluster_locked = NULL;
     struct rb_node *node = rb_first(&ctl->free_space_offset);
     struct btrfs_trim_range *trim_entry;
 
     /* Get the cluster for this block_group if it exists */
     if (block_group && !list_empty(&block_group->cluster_list)) {
         cluster = list_entry(block_group->cluster_list.next,
                      struct btrfs_free_cluster,
                      block_group_list);
     }
 
     if (!node && cluster) {
         cluster_locked = cluster;
         spin_lock(&cluster_locked->lock);
         node = rb_first(&cluster->root);
         cluster = NULL;
     }
 
     /* Write out the extent entries */
     while (node) {
         struct btrfs_free_space *e;
 
         e = rb_entry(node, struct btrfs_free_space, offset_index);
         *entries += 1;
 
         ret = io_ctl_add_entry(io_ctl, e->offset, e->bytes,
                        e->bitmap);
         if (ret)
             goto fail;
 
         if (e->bitmap) {
             list_add_tail(&e->list, bitmap_list);
             *bitmaps += 1;
         }
         node = rb_next(node);
         if (!node && cluster) {
             node = rb_first(&cluster->root);
             cluster_locked = cluster;
             spin_lock(&cluster_locked->lock);
             cluster = NULL;
         }
     }
     if (cluster_locked) {
         spin_unlock(&cluster_locked->lock);
         cluster_locked = NULL;
     }
 
     /*
      * Make sure we don't miss any range that was removed from our rbtree
      * because trimming is running. Otherwise after a umount+mount (or crash
      * after committing the transaction) we would leak free space and get
      * an inconsistent free space cache report from fsck.
      */
     list_for_each_entry(trim_entry, &ctl->trimming_ranges, list) {
         ret = io_ctl_add_entry(io_ctl, trim_entry->start,
                        trim_entry->bytes, NULL);
         if (ret)
             goto fail;
         *entries += 1;
     }
 
     return 0;
 fail:
     if (cluster_locked)
         spin_unlock(&cluster_locked->lock);
     return -ENOSPC;
 }
 
 static noinline_for_stack int
 update_cache_item(struct btrfs_trans_handle *trans,
           struct btrfs_root *root,
           struct inode *inode,
           struct btrfs_path *path, u64 offset,
           int entries, int bitmaps)
 {
     struct btrfs_key key;
     struct btrfs_free_space_header *header;
     struct extent_buffer *leaf;
     int ret;
 
     key.objectid = BTRFS_FREE_SPACE_OBJECTID;
     key.offset = offset;
     key.type = 0;
 
     ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
     if (ret < 0) {
         clear_extent_bit(&BTRFS_I(inode)->io_tree, 0, inode->i_size - 1,
                  EXTENT_DELALLOC, 0, 0, NULL);
         goto fail;
     }
     leaf = path->nodes[0];
     if (ret > 0) {
         struct btrfs_key found_key;
         ASSERT(path->slots[0]);
         path->slots[0]--;
         btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
         if (found_key.objectid != BTRFS_FREE_SPACE_OBJECTID ||
             found_key.offset != offset) {
             clear_extent_bit(&BTRFS_I(inode)->io_tree, 0,
                      inode->i_size - 1, EXTENT_DELALLOC, 0,
                      0, NULL);
             btrfs_release_path(path);
             goto fail;
         }
     }
 
     BTRFS_I(inode)->generation = trans->transid;
     header = btrfs_item_ptr(leaf, path->slots[0],
                 struct btrfs_free_space_header);
     btrfs_set_free_space_entries(leaf, header, entries);
     btrfs_set_free_space_bitmaps(leaf, header, bitmaps);
     btrfs_set_free_space_generation(leaf, header, trans->transid);
     btrfs_mark_buffer_dirty(leaf);
     btrfs_release_path(path);
 
     return 0;
 
 fail:
     return -1;
 }
 
 static noinline_for_stack int write_pinned_extent_entries(
                 struct btrfs_trans_handle *trans,
                 struct btrfs_block_group *block_group,
                 struct btrfs_io_ctl *io_ctl,
                 int *entries)
 {
     u64 start, extent_start, extent_end, len;
     struct extent_io_tree *unpin = NULL;
     int ret;
 
     if (!block_group)
         return 0;
 
     /*
      * We want to add any pinned extents to our free space cache
      * so we don't leak the space
      *
      * We shouldn't have switched the pinned extents yet so this is the
      * right one
      */
     unpin = &trans->transaction->pinned_extents;
 
     start = block_group->start;
 
     while (start < block_group->start + block_group->length) {
         ret = find_first_extent_bit(unpin, start,
                         &extent_start, &extent_end,
                         EXTENT_DIRTY, NULL);
         if (ret)
             return 0;
 
         /* This pinned extent is out of our range */
         if (extent_start >= block_group->start + block_group->length)
             return 0;
 
         extent_start = max(extent_start, start);
         extent_end = min(block_group->start + block_group->length,
                  extent_end + 1);
         len = extent_end - extent_start;
 
         *entries += 1;
         ret = io_ctl_add_entry(io_ctl, extent_start, len, NULL);
         if (ret)
             return -ENOSPC;
 
         start = extent_end;
     }
 
     return 0;
 }
 
 static noinline_for_stack int
 write_bitmap_entries(struct btrfs_io_ctl *io_ctl, struct list_head *bitmap_list)
 {
     struct btrfs_free_space *entry, *next;
     int ret;
 
     /* Write out the bitmaps */
     list_for_each_entry_safe(entry, next, bitmap_list, list) {
         ret = io_ctl_add_bitmap(io_ctl, entry->bitmap);
         if (ret)
             return -ENOSPC;
         list_del_init(&entry->list);
     }
 
     return 0;
 }
 
 static int flush_dirty_cache(struct inode *inode)
 {
     int ret;
 
     ret = btrfs_wait_ordered_range(inode, 0, (u64)-1);
     if (ret)
         clear_extent_bit(&BTRFS_I(inode)->io_tree, 0, inode->i_size - 1,
                  EXTENT_DELALLOC, 0, 0, NULL);
 
     return ret;
 }
 
 static void noinline_for_stack
 cleanup_bitmap_list(struct list_head *bitmap_list)
 {
     struct btrfs_free_space *entry, *next;
 
     list_for_each_entry_safe(entry, next, bitmap_list, list)
         list_del_init(&entry->list);
 }
 
 static void noinline_for_stack
 cleanup_write_cache_enospc(struct inode *inode,
                struct btrfs_io_ctl *io_ctl,
                struct extent_state **cached_state)
 {
     io_ctl_drop_pages(io_ctl);
     unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
                  i_size_read(inode) - 1, cached_state);
 }
 
 static int __btrfs_wait_cache_io(struct btrfs_root *root,
                  struct btrfs_trans_handle *trans,
                  struct btrfs_block_group *block_group,
                  struct btrfs_io_ctl *io_ctl,
                  struct btrfs_path *path, u64 offset)
 {
     int ret;
     struct inode *inode = io_ctl->inode;
 
     if (!inode)
         return 0;
 
     /* Flush the dirty pages in the cache file. */
     ret = flush_dirty_cache(inode);
     if (ret)
         goto out;
 
     /* Update the cache item to tell everyone this cache file is valid. */
     ret = update_cache_item(trans, root, inode, path, offset,
                 io_ctl->entries, io_ctl->bitmaps);
 out:
     if (ret) {
         invalidate_inode_pages2(inode->i_mapping);
         BTRFS_I(inode)->generation = 0;
         if (block_group)
             btrfs_debug(root->fs_info,
       "failed to write free space cache for block group %llu error %d",
                   block_group->start, ret);
     }
     btrfs_update_inode(trans, root, BTRFS_I(inode));
 
     if (block_group) {
         /* the dirty list is protected by the dirty_bgs_lock */
         spin_lock(&trans->transaction->dirty_bgs_lock);
 
         /* the disk_cache_state is protected by the block group lock */
         spin_lock(&block_group->lock);
 
         /*
          * only mark this as written if we didn't get put back on
          * the dirty list while waiting for IO.   Otherwise our
          * cache state won't be right, and we won't get written again
          */
         if (!ret && list_empty(&block_group->dirty_list))
             block_group->disk_cache_state = BTRFS_DC_WRITTEN;
         else if (ret)
             block_group->disk_cache_state = BTRFS_DC_ERROR;
 
         spin_unlock(&block_group->lock);
         spin_unlock(&trans->transaction->dirty_bgs_lock);
         io_ctl->inode = NULL;
         iput(inode);
     }
 
     return ret;
 
 }
 
 int btrfs_wait_cache_io(struct btrfs_trans_handle *trans,
             struct btrfs_block_group *block_group,
             struct btrfs_path *path)
 {
     return __btrfs_wait_cache_io(block_group->fs_info->tree_root, trans,
                      block_group, &block_group->io_ctl,
                      path, block_group->start);
 }
 
 /**
  * Write out cached info to an inode
  *
  * @root:        root the inode belongs to
  * @inode:       freespace inode we are writing out
  * @ctl:         free space cache we are going to write out
  * @block_group: block_group for this cache if it belongs to a block_group
  * @io_ctl:      holds context for the io
  * @trans:       the trans handle
  *
  * This function writes out a free space cache struct to disk for quick recovery
  * on mount.  This will return 0 if it was successful in writing the cache out,
  * or an errno if it was not.
  */
 static int __btrfs_write_out_cache(struct btrfs_root *root, struct inode *inode,
                    struct btrfs_free_space_ctl *ctl,
                    struct btrfs_block_group *block_group,
                    struct btrfs_io_ctl *io_ctl,
                    struct btrfs_trans_handle *trans)
 {
     struct extent_state *cached_state = NULL;
     LIST_HEAD(bitmap_list);
     int entries = 0;
     int bitmaps = 0;
     int ret;
     int must_iput = 0;
 
     if (!i_size_read(inode))
         return -EIO;
 
     WARN_ON(io_ctl->pages);
     ret = io_ctl_init(io_ctl, inode, 1);
     if (ret)
         return ret;
 
     if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA)) {
         down_write(&block_group->data_rwsem);
         spin_lock(&block_group->lock);
         if (block_group->delalloc_bytes) {
             block_group->disk_cache_state = BTRFS_DC_WRITTEN;
             spin_unlock(&block_group->lock);
             up_write(&block_group->data_rwsem);
             BTRFS_I(inode)->generation = 0;
             ret = 0;
             must_iput = 1;
             goto out;
         }
         spin_unlock(&block_group->lock);
     }
 
     /* Lock all pages first so we can lock the extent safely. */
     ret = io_ctl_prepare_pages(io_ctl, false);
     if (ret)
         goto out_unlock;
 
     lock_extent_bits(&BTRFS_I(inode)->io_tree, 0, i_size_read(inode) - 1,
              &cached_state);
 
     io_ctl_set_generation(io_ctl, trans->transid);
 
     mutex_lock(&ctl->cache_writeout_mutex);
     /* Write out the extent entries in the free space cache */
     spin_lock(&ctl->tree_lock);
     ret = write_cache_extent_entries(io_ctl, ctl,
                      block_group, &entries, &bitmaps,
                      &bitmap_list);
     if (ret)
         goto out_nospc_locked;
 
     /*
      * Some spaces that are freed in the current transaction are pinned,
      * they will be added into free space cache after the transaction is
      * committed, we shouldn't lose them.
      *
      * If this changes while we are working we'll get added back to
      * the dirty list and redo it.  No locking needed
      */
     ret = write_pinned_extent_entries(trans, block_group, io_ctl, &entries);
     if (ret)
         goto out_nospc_locked;
 
     /*
      * At last, we write out all the bitmaps and keep cache_writeout_mutex
      * locked while doing it because a concurrent trim can be manipulating
      * or freeing the bitmap.
      */
     ret = write_bitmap_entries(io_ctl, &bitmap_list);
     spin_unlock(&ctl->tree_lock);
     mutex_unlock(&ctl->cache_writeout_mutex);
     if (ret)
         goto out_nospc;
 
     /* Zero out the rest of the pages just to make sure */
     io_ctl_zero_remaining_pages(io_ctl);
 
     /* Everything is written out, now we dirty the pages in the file. */
     ret = btrfs_dirty_pages(BTRFS_I(inode), io_ctl->pages,
                 io_ctl->num_pages, 0, i_size_read(inode),
                 &cached_state, false);
     if (ret)
         goto out_nospc;
 
     if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA))
         up_write(&block_group->data_rwsem);
     /*
      * Release the pages and unlock the extent, we will flush
      * them out later
      */
     io_ctl_drop_pages(io_ctl);
     io_ctl_free(io_ctl);
 
     unlock_extent_cached(&BTRFS_I(inode)->io_tree, 0,
                  i_size_read(inode) - 1, &cached_state);
 
     /*
      * at this point the pages are under IO and we're happy,
      * The caller is responsible for waiting on them and updating
      * the cache and the inode
      */
     io_ctl->entries = entries;
     io_ctl->bitmaps = bitmaps;
 
     ret = btrfs_fdatawrite_range(inode, 0, (u64)-1);
     if (ret)
         goto out;
 
     return 0;
 
 out_nospc_locked:
     cleanup_bitmap_list(&bitmap_list);
     spin_unlock(&ctl->tree_lock);
     mutex_unlock(&ctl->cache_writeout_mutex);
 
 out_nospc:
     cleanup_write_cache_enospc(inode, io_ctl, &cached_state);
 
 out_unlock:
     if (block_group && (block_group->flags & BTRFS_BLOCK_GROUP_DATA))
         up_write(&block_group->data_rwsem);
 
 out:
     io_ctl->inode = NULL;
     io_ctl_free(io_ctl);
     if (ret) {
         invalidate_inode_pages2(inode->i_mapping);
         BTRFS_I(inode)->generation = 0;
     }
     btrfs_update_inode(trans, root, BTRFS_I(inode));
     if (must_iput)
         iput(inode);
     return ret;
 }
 
 int btrfs_write_out_cache(struct btrfs_trans_handle *trans,
               struct btrfs_block_group *block_group,
               struct btrfs_path *path)
 {
     struct btrfs_fs_info *fs_info = trans->fs_info;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct inode *inode;
     int ret = 0;
 
     spin_lock(&block_group->lock);
     if (block_group->disk_cache_state < BTRFS_DC_SETUP) {
         spin_unlock(&block_group->lock);
         return 0;
     }
     spin_unlock(&block_group->lock);
 
     inode = lookup_free_space_inode(block_group, path);
     if (IS_ERR(inode))
         return 0;
 
     ret = __btrfs_write_out_cache(fs_info->tree_root, inode, ctl,
                 block_group, &block_group->io_ctl, trans);
     if (ret) {
         btrfs_debug(fs_info,
       "failed to write free space cache for block group %llu error %d",
               block_group->start, ret);
         spin_lock(&block_group->lock);
         block_group->disk_cache_state = BTRFS_DC_ERROR;
         spin_unlock(&block_group->lock);
 
         block_group->io_ctl.inode = NULL;
         iput(inode);
     }
 
     /*
      * if ret == 0 the caller is expected to call btrfs_wait_cache_io
      * to wait for IO and put the inode
      */
 
     return ret;
 }
 
 static inline unsigned long offset_to_bit(u64 bitmap_start, u32 unit,
                       u64 offset)
 {
     ASSERT(offset >= bitmap_start);
     offset -= bitmap_start;
     return (unsigned long)(div_u64(offset, unit));
 }
 
 static inline unsigned long bytes_to_bits(u64 bytes, u32 unit)
 {
     return (unsigned long)(div_u64(bytes, unit));
 }
 
 static inline u64 offset_to_bitmap(struct btrfs_free_space_ctl *ctl,
                    u64 offset)
 {
     u64 bitmap_start;
     u64 bytes_per_bitmap;
 
     bytes_per_bitmap = BITS_PER_BITMAP * ctl->unit;
     bitmap_start = offset - ctl->start;
     bitmap_start = div64_u64(bitmap_start, bytes_per_bitmap);
     bitmap_start *= bytes_per_bitmap;
     bitmap_start += ctl->start;
 
     return bitmap_start;
 }
 
 static int tree_insert_offset(struct rb_root *root, u64 offset,
                   struct rb_node *node, int bitmap)
 {
     struct rb_node **p = &root->rb_node;
     struct rb_node *parent = NULL;
     struct btrfs_free_space *info;
 
     while (*p) {
         parent = *p;
         info = rb_entry(parent, struct btrfs_free_space, offset_index);
 
         if (offset < info->offset) {
             p = &(*p)->rb_left;
         } else if (offset > info->offset) {
             p = &(*p)->rb_right;
         } else {
             /*
              * we could have a bitmap entry and an extent entry
              * share the same offset.  If this is the case, we want
              * the extent entry to always be found first if we do a
              * linear search through the tree, since we want to have
              * the quickest allocation time, and allocating from an
              * extent is faster than allocating from a bitmap.  So
              * if we're inserting a bitmap and we find an entry at
              * this offset, we want to go right, or after this entry
              * logically.  If we are inserting an extent and we've
              * found a bitmap, we want to go left, or before
              * logically.
              */
             if (bitmap) {
                 if (info->bitmap) {
                     WARN_ON_ONCE(1);
                     return -EEXIST;
                 }
                 p = &(*p)->rb_right;
             } else {
                 if (!info->bitmap) {
                     WARN_ON_ONCE(1);
                     return -EEXIST;
                 }
                 p = &(*p)->rb_left;
             }
         }
     }
 
     rb_link_node(node, parent, p);
     rb_insert_color(node, root);
 
     return 0;
 }
 
 /*
  * This is a little subtle.  We *only* have ->max_extent_size set if we actually
  * searched through the bitmap and figured out the largest ->max_extent_size,
  * otherwise it's 0.  In the case that it's 0 we don't want to tell the
  * allocator the wrong thing, we want to use the actual real max_extent_size
  * we've found already if it's larger, or we want to use ->bytes.
  *
  * This matters because find_free_space() will skip entries who's ->bytes is
  * less than the required bytes.  So if we didn't search down this bitmap, we
  * may pick some previous entry that has a smaller ->max_extent_size than we
  * have.  For example, assume we have two entries, one that has
  * ->max_extent_size set to 4K and ->bytes set to 1M.  A second entry hasn't set
  * ->max_extent_size yet, has ->bytes set to 8K and it's contiguous.  We will
  *  call into find_free_space(), and return with max_extent_size == 4K, because
  *  that first bitmap entry had ->max_extent_size set, but the second one did
  *  not.  If instead we returned 8K we'd come in searching for 8K, and find the
  *  8K contiguous range.
  *
  *  Consider the other case, we have 2 8K chunks in that second entry and still
  *  don't have ->max_extent_size set.  We'll return 16K, and the next time the
  *  allocator comes in it'll fully search our second bitmap, and this time it'll
  *  get an uptodate value of 8K as the maximum chunk size.  Then we'll get the
  *  right allocation the next loop through.
  */
 static inline u64 get_max_extent_size(const struct btrfs_free_space *entry)
 {
     if (entry->bitmap && entry->max_extent_size)
         return entry->max_extent_size;
     return entry->bytes;
 }
 
 /*
  * We want the largest entry to be leftmost, so this is inverted from what you'd
  * normally expect.
  */
 static bool entry_less(struct rb_node *node, const struct rb_node *parent)
 {
     const struct btrfs_free_space *entry, *exist;
 
     entry = rb_entry(node, struct btrfs_free_space, bytes_index);
     exist = rb_entry(parent, struct btrfs_free_space, bytes_index);
     return get_max_extent_size(exist) < get_max_extent_size(entry);
 }
 
 /*
  * searches the tree for the given offset.
  *
  * fuzzy - If this is set, then we are trying to make an allocation, and we just
  * want a section that has at least bytes size and comes at or after the given
  * offset.
  */
 static struct btrfs_free_space *
 tree_search_offset(struct btrfs_free_space_ctl *ctl,
            u64 offset, int bitmap_only, int fuzzy)
 {
     struct rb_node *n = ctl->free_space_offset.rb_node;
     struct btrfs_free_space *entry = NULL, *prev = NULL;
 
     /* find entry that is closest to the 'offset' */
     while (n) {
         entry = rb_entry(n, struct btrfs_free_space, offset_index);
         prev = entry;
 
         if (offset < entry->offset)
             n = n->rb_left;
         else if (offset > entry->offset)
             n = n->rb_right;
         else
             break;
 
         entry = NULL;
     }
 
     if (bitmap_only) {
         if (!entry)
             return NULL;
         if (entry->bitmap)
             return entry;
 
         /*
          * bitmap entry and extent entry may share same offset,
          * in that case, bitmap entry comes after extent entry.
          */
         n = rb_next(n);
         if (!n)
             return NULL;
         entry = rb_entry(n, struct btrfs_free_space, offset_index);
         if (entry->offset != offset)
             return NULL;
 
         WARN_ON(!entry->bitmap);
         return entry;
     } else if (entry) {
         if (entry->bitmap) {
             /*
              * if previous extent entry covers the offset,
              * we should return it instead of the bitmap entry
              */
             n = rb_prev(&entry->offset_index);
             if (n) {
                 prev = rb_entry(n, struct btrfs_free_space,
                         offset_index);
                 if (!prev->bitmap &&
                     prev->offset + prev->bytes > offset)
                     entry = prev;
             }
         }
         return entry;
     }
 
     if (!prev)
         return NULL;
 
     /* find last entry before the 'offset' */
     entry = prev;
     if (entry->offset > offset) {
         n = rb_prev(&entry->offset_index);
         if (n) {
             entry = rb_entry(n, struct btrfs_free_space,
                     offset_index);
             ASSERT(entry->offset <= offset);
         } else {
             if (fuzzy)
                 return entry;
             else
                 return NULL;
         }
     }
 
     if (entry->bitmap) {
         n = rb_prev(&entry->offset_index);
         if (n) {
             prev = rb_entry(n, struct btrfs_free_space,
                     offset_index);
             if (!prev->bitmap &&
                 prev->offset + prev->bytes > offset)
                 return prev;
         }
         if (entry->offset + BITS_PER_BITMAP * ctl->unit > offset)
             return entry;
     } else if (entry->offset + entry->bytes > offset)
         return entry;
 
     if (!fuzzy)
         return NULL;
 
     while (1) {
         n = rb_next(&entry->offset_index);
         if (!n)
             return NULL;
         entry = rb_entry(n, struct btrfs_free_space, offset_index);
         if (entry->bitmap) {
             if (entry->offset + BITS_PER_BITMAP *
                 ctl->unit > offset)
                 break;
         } else {
             if (entry->offset + entry->bytes > offset)
                 break;
         }
     }
     return entry;
 }
 
 static inline void unlink_free_space(struct btrfs_free_space_ctl *ctl,
                      struct btrfs_free_space *info,
                      bool update_stat)
 {
     rb_erase(&info->offset_index, &ctl->free_space_offset);
     rb_erase_cached(&info->bytes_index, &ctl->free_space_bytes);
     ctl->free_extents--;
 
     if (!info->bitmap && !btrfs_free_space_trimmed(info)) {
         ctl->discardable_extents[BTRFS_STAT_CURR]--;
         ctl->discardable_bytes[BTRFS_STAT_CURR] -= info->bytes;
     }
 
     if (update_stat)
         ctl->free_space -= info->bytes;
 }
 
 static int link_free_space(struct btrfs_free_space_ctl *ctl,
                struct btrfs_free_space *info)
 {
     int ret = 0;
 
     ASSERT(info->bytes || info->bitmap);
     ret = tree_insert_offset(&ctl->free_space_offset, info->offset,
                  &info->offset_index, (info->bitmap != NULL));
     if (ret)
         return ret;
 
     rb_add_cached(&info->bytes_index, &ctl->free_space_bytes, entry_less);
 
     if (!info->bitmap && !btrfs_free_space_trimmed(info)) {
         ctl->discardable_extents[BTRFS_STAT_CURR]++;
         ctl->discardable_bytes[BTRFS_STAT_CURR] += info->bytes;
     }
 
     ctl->free_space += info->bytes;
     ctl->free_extents++;
     return ret;
 }
 
 static void relink_bitmap_entry(struct btrfs_free_space_ctl *ctl,
                 struct btrfs_free_space *info)
 {
     ASSERT(info->bitmap);
 
     /*
      * If our entry is empty it's because we're on a cluster and we don't
      * want to re-link it into our ctl bytes index.
      */
     if (RB_EMPTY_NODE(&info->bytes_index))
         return;
 
     rb_erase_cached(&info->bytes_index, &ctl->free_space_bytes);
     rb_add_cached(&info->bytes_index, &ctl->free_space_bytes, entry_less);
 }
 
 static inline void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
                      struct btrfs_free_space *info,
                      u64 offset, u64 bytes, bool update_stat)
 {
     unsigned long start, count, end;
     int extent_delta = -1;
 
     start = offset_to_bit(info->offset, ctl->unit, offset);
     count = bytes_to_bits(bytes, ctl->unit);
     end = start + count;
     ASSERT(end <= BITS_PER_BITMAP);
 
     bitmap_clear(info->bitmap, start, count);
 
     info->bytes -= bytes;
     if (info->max_extent_size > ctl->unit)
         info->max_extent_size = 0;
 
     relink_bitmap_entry(ctl, info);
 
     if (start && test_bit(start - 1, info->bitmap))
         extent_delta++;
 
     if (end < BITS_PER_BITMAP && test_bit(end, info->bitmap))
         extent_delta++;
 
     info->bitmap_extents += extent_delta;
     if (!btrfs_free_space_trimmed(info)) {
         ctl->discardable_extents[BTRFS_STAT_CURR] += extent_delta;
         ctl->discardable_bytes[BTRFS_STAT_CURR] -= bytes;
     }
 
     if (update_stat)
         ctl->free_space -= bytes;
 }
 
 static void bitmap_set_bits(struct btrfs_free_space_ctl *ctl,
                 struct btrfs_free_space *info, u64 offset,
                 u64 bytes)
 {
     unsigned long start, count, end;
     int extent_delta = 1;
 
     start = offset_to_bit(info->offset, ctl->unit, offset);
     count = bytes_to_bits(bytes, ctl->unit);
     end = start + count;
     ASSERT(end <= BITS_PER_BITMAP);
 
     bitmap_set(info->bitmap, start, count);
 
     /*
      * We set some bytes, we have no idea what the max extent size is
      * anymore.
      */
     info->max_extent_size = 0;
     info->bytes += bytes;
     ctl->free_space += bytes;
 
     relink_bitmap_entry(ctl, info);
 
     if (start && test_bit(start - 1, info->bitmap))
         extent_delta--;
 
     if (end < BITS_PER_BITMAP && test_bit(end, info->bitmap))
         extent_delta--;
 
     info->bitmap_extents += extent_delta;
     if (!btrfs_free_space_trimmed(info)) {
         ctl->discardable_extents[BTRFS_STAT_CURR] += extent_delta;
         ctl->discardable_bytes[BTRFS_STAT_CURR] += bytes;
     }
 }
 
 /*
  * If we can not find suitable extent, we will use bytes to record
  * the size of the max extent.
  */
 static int search_bitmap(struct btrfs_free_space_ctl *ctl,
              struct btrfs_free_space *bitmap_info, u64 *offset,
              u64 *bytes, bool for_alloc)
 {
     unsigned long found_bits = 0;
     unsigned long max_bits = 0;
     unsigned long bits, i;
     unsigned long next_zero;
     unsigned long extent_bits;
 
     /*
      * Skip searching the bitmap if we don't have a contiguous section that
      * is large enough for this allocation.
      */
     if (for_alloc &&
         bitmap_info->max_extent_size &&
         bitmap_info->max_extent_size < *bytes) {
         *bytes = bitmap_info->max_extent_size;
         return -1;
     }
 
     i = offset_to_bit(bitmap_info->offset, ctl->unit,
               max_t(u64, *offset, bitmap_info->offset));
     bits = bytes_to_bits(*bytes, ctl->unit);
 
     for_each_set_bit_from(i, bitmap_info->bitmap, BITS_PER_BITMAP) {
         if (for_alloc && bits == 1) {
             found_bits = 1;
             break;
         }
         next_zero = find_next_zero_bit(bitmap_info->bitmap,
                            BITS_PER_BITMAP, i);
         extent_bits = next_zero - i;
         if (extent_bits >= bits) {
             found_bits = extent_bits;
             break;
         } else if (extent_bits > max_bits) {
             max_bits = extent_bits;
         }
         i = next_zero;
     }
 
     if (found_bits) {
         *offset = (u64)(i * ctl->unit) + bitmap_info->offset;
         *bytes = (u64)(found_bits) * ctl->unit;
         return 0;
     }
 
     *bytes = (u64)(max_bits) * ctl->unit;
     bitmap_info->max_extent_size = *bytes;
     relink_bitmap_entry(ctl, bitmap_info);
     return -1;
 }
 
 /* Cache the size of the max extent in bytes */
 static struct btrfs_free_space *
 find_free_space(struct btrfs_free_space_ctl *ctl, u64 *offset, u64 *bytes,
         unsigned long align, u64 *max_extent_size, bool use_bytes_index)
 {
     struct btrfs_free_space *entry;
     struct rb_node *node;
     u64 tmp;
     u64 align_off;
     int ret;
 
     if (!ctl->free_space_offset.rb_node)
         goto out;
 again:
     if (use_bytes_index) {
         node = rb_first_cached(&ctl->free_space_bytes);
     } else {
         entry = tree_search_offset(ctl, offset_to_bitmap(ctl, *offset),
                        0, 1);
         if (!entry)
             goto out;
         node = &entry->offset_index;
     }
 
     for (; node; node = rb_next(node)) {
         if (use_bytes_index)
             entry = rb_entry(node, struct btrfs_free_space,
                      bytes_index);
         else
             entry = rb_entry(node, struct btrfs_free_space,
                      offset_index);
 
         /*
          * If we are using the bytes index then all subsequent entries
          * in this tree are going to be < bytes, so simply set the max
          * extent size and exit the loop.
          *
          * If we're using the offset index then we need to keep going
          * through the rest of the tree.
          */
         if (entry->bytes < *bytes) {
             *max_extent_size = max(get_max_extent_size(entry),
                            *max_extent_size);
             if (use_bytes_index)
                 break;
             continue;
         }
 
         /* make sure the space returned is big enough
          * to match our requested alignment
          */
         if (*bytes >= align) {
             tmp = entry->offset - ctl->start + align - 1;
             tmp = div64_u64(tmp, align);
             tmp = tmp * align + ctl->start;
             align_off = tmp - entry->offset;
         } else {
             align_off = 0;
             tmp = entry->offset;
         }
 
         /*
          * We don't break here if we're using the bytes index because we
          * may have another entry that has the correct alignment that is
          * the right size, so we don't want to miss that possibility.
          * At worst this adds another loop through the logic, but if we
          * broke here we could prematurely ENOSPC.
          */
         if (entry->bytes < *bytes + align_off) {
             *max_extent_size = max(get_max_extent_size(entry),
                            *max_extent_size);
             continue;
         }
 
         if (entry->bitmap) {
             struct rb_node *old_next = rb_next(node);
             u64 size = *bytes;
 
             ret = search_bitmap(ctl, entry, &tmp, &size, true);
             if (!ret) {
                 *offset = tmp;
                 *bytes = size;
                 return entry;
             } else {
                 *max_extent_size =
                     max(get_max_extent_size(entry),
                         *max_extent_size);
             }
 
             /*
              * The bitmap may have gotten re-arranged in the space
              * index here because the max_extent_size may have been
              * updated.  Start from the beginning again if this
              * happened.
              */
             if (use_bytes_index && old_next != rb_next(node))
                 goto again;
             continue;
         }
 
         *offset = tmp;
         *bytes = entry->bytes - align_off;
         return entry;
     }
 out:
     return NULL;
 }
 
 static void add_new_bitmap(struct btrfs_free_space_ctl *ctl,
                struct btrfs_free_space *info, u64 offset)
 {
     info->offset = offset_to_bitmap(ctl, offset);
     info->bytes = 0;
     info->bitmap_extents = 0;
     INIT_LIST_HEAD(&info->list);
     link_free_space(ctl, info);
     ctl->total_bitmaps++;
     recalculate_thresholds(ctl);
 }
 
 static void free_bitmap(struct btrfs_free_space_ctl *ctl,
             struct btrfs_free_space *bitmap_info)
 {
     /*
      * Normally when this is called, the bitmap is completely empty. However,
      * if we are blowing up the free space cache for one reason or another
      * via __btrfs_remove_free_space_cache(), then it may not be freed and
      * we may leave stats on the table.
      */
     if (bitmap_info->bytes && !btrfs_free_space_trimmed(bitmap_info)) {
         ctl->discardable_extents[BTRFS_STAT_CURR] -=
             bitmap_info->bitmap_extents;
         ctl->discardable_bytes[BTRFS_STAT_CURR] -= bitmap_info->bytes;
 
     }
     unlink_free_space(ctl, bitmap_info, true);
     kmem_cache_free(btrfs_free_space_bitmap_cachep, bitmap_info->bitmap);
     kmem_cache_free(btrfs_free_space_cachep, bitmap_info);
     ctl->total_bitmaps--;
     recalculate_thresholds(ctl);
 }
 
 static noinline int remove_from_bitmap(struct btrfs_free_space_ctl *ctl,
                   struct btrfs_free_space *bitmap_info,
                   u64 *offset, u64 *bytes)
 {
     u64 end;
     u64 search_start, search_bytes;
     int ret;
 
 again:
     end = bitmap_info->offset + (u64)(BITS_PER_BITMAP * ctl->unit) - 1;
 
     /*
      * We need to search for bits in this bitmap.  We could only cover some
      * of the extent in this bitmap thanks to how we add space, so we need
      * to search for as much as it as we can and clear that amount, and then
      * go searching for the next bit.
      */
     search_start = *offset;
     search_bytes = ctl->unit;
     search_bytes = min(search_bytes, end - search_start + 1);
     ret = search_bitmap(ctl, bitmap_info, &search_start, &search_bytes,
                 false);
     if (ret < 0 || search_start != *offset)
         return -EINVAL;
 
     /* We may have found more bits than what we need */
     search_bytes = min(search_bytes, *bytes);
 
     /* Cannot clear past the end of the bitmap */
     search_bytes = min(search_bytes, end - search_start + 1);
 
     bitmap_clear_bits(ctl, bitmap_info, search_start, search_bytes, true);
     *offset += search_bytes;
     *bytes -= search_bytes;
 
     if (*bytes) {
         struct rb_node *next = rb_next(&bitmap_info->offset_index);
         if (!bitmap_info->bytes)
             free_bitmap(ctl, bitmap_info);
 
         /*
          * no entry after this bitmap, but we still have bytes to
          * remove, so something has gone wrong.
          */
         if (!next)
             return -EINVAL;
 
         bitmap_info = rb_entry(next, struct btrfs_free_space,
                        offset_index);
 
         /*
          * if the next entry isn't a bitmap we need to return to let the
          * extent stuff do its work.
          */
         if (!bitmap_info->bitmap)
             return -EAGAIN;
 
         /*
          * Ok the next item is a bitmap, but it may not actually hold
          * the information for the rest of this free space stuff, so
          * look for it, and if we don't find it return so we can try
          * everything over again.
          */
         search_start = *offset;
         search_bytes = ctl->unit;
         ret = search_bitmap(ctl, bitmap_info, &search_start,
                     &search_bytes, false);
         if (ret < 0 || search_start != *offset)
             return -EAGAIN;
 
         goto again;
     } else if (!bitmap_info->bytes)
         free_bitmap(ctl, bitmap_info);
 
     return 0;
 }
 
 static u64 add_bytes_to_bitmap(struct btrfs_free_space_ctl *ctl,
                    struct btrfs_free_space *info, u64 offset,
                    u64 bytes, enum btrfs_trim_state trim_state)
 {
     u64 bytes_to_set = 0;
     u64 end;
 
     /*
      * This is a tradeoff to make bitmap trim state minimal.  We mark the
      * whole bitmap untrimmed if at any point we add untrimmed regions.
      */
     if (trim_state == BTRFS_TRIM_STATE_UNTRIMMED) {
         if (btrfs_free_space_trimmed(info)) {
             ctl->discardable_extents[BTRFS_STAT_CURR] +=
                 info->bitmap_extents;
             ctl->discardable_bytes[BTRFS_STAT_CURR] += info->bytes;
         }
         info->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
     }
 
     end = info->offset + (u64)(BITS_PER_BITMAP * ctl->unit);
 
     bytes_to_set = min(end - offset, bytes);
 
     bitmap_set_bits(ctl, info, offset, bytes_to_set);
 
     return bytes_to_set;
 
 }
 
 static bool use_bitmap(struct btrfs_free_space_ctl *ctl,
               struct btrfs_free_space *info)
 {
     struct btrfs_block_group *block_group = ctl->block_group;
     struct btrfs_fs_info *fs_info = block_group->fs_info;
     bool forced = false;
 
 #ifdef CONFIG_BTRFS_DEBUG
     if (btrfs_should_fragment_free_space(block_group))
         forced = true;
 #endif
 
     /* This is a way to reclaim large regions from the bitmaps. */
     if (!forced && info->bytes >= FORCE_EXTENT_THRESHOLD)
         return false;
 
     /*
      * If we are below the extents threshold then we can add this as an
      * extent, and don't have to deal with the bitmap
      */
     if (!forced && ctl->free_extents < ctl->extents_thresh) {
         /*
          * If this block group has some small extents we don't want to
          * use up all of our free slots in the cache with them, we want
          * to reserve them to larger extents, however if we have plenty
          * of cache left then go ahead an dadd them, no sense in adding
          * the overhead of a bitmap if we don't have to.
          */
         if (info->bytes <= fs_info->sectorsize * 8) {
             if (ctl->free_extents * 3 <= ctl->extents_thresh)
                 return false;
         } else {
             return false;
         }
     }
 
     /*
      * The original block groups from mkfs can be really small, like 8
      * megabytes, so don't bother with a bitmap for those entries.  However
      * some block groups can be smaller than what a bitmap would cover but
      * are still large enough that they could overflow the 32k memory limit,
      * so allow those block groups to still be allowed to have a bitmap
      * entry.
      */
     if (((BITS_PER_BITMAP * ctl->unit) >> 1) > block_group->length)
         return false;
 
     return true;
 }
 
 static const struct btrfs_free_space_op free_space_op = {
     .use_bitmap     = use_bitmap,
 };
 
 static int insert_into_bitmap(struct btrfs_free_space_ctl *ctl,
                   struct btrfs_free_space *info)
 {
     struct btrfs_free_space *bitmap_info;
     struct btrfs_block_group *block_group = NULL;
     int added = 0;
     u64 bytes, offset, bytes_added;
     enum btrfs_trim_state trim_state;
     int ret;
 
     bytes = info->bytes;
     offset = info->offset;
     trim_state = info->trim_state;
 
     if (!ctl->op->use_bitmap(ctl, info))
         return 0;
 
     if (ctl->op == &free_space_op)
         block_group = ctl->block_group;
 again:
     /*
      * Since we link bitmaps right into the cluster we need to see if we
      * have a cluster here, and if so and it has our bitmap we need to add
      * the free space to that bitmap.
      */
     if (block_group && !list_empty(&block_group->cluster_list)) {
         struct btrfs_free_cluster *cluster;
         struct rb_node *node;
         struct btrfs_free_space *entry;
 
         cluster = list_entry(block_group->cluster_list.next,
                      struct btrfs_free_cluster,
                      block_group_list);
         spin_lock(&cluster->lock);
         node = rb_first(&cluster->root);
         if (!node) {
             spin_unlock(&cluster->lock);
             goto no_cluster_bitmap;
         }
 
         entry = rb_entry(node, struct btrfs_free_space, offset_index);
         if (!entry->bitmap) {
             spin_unlock(&cluster->lock);
             goto no_cluster_bitmap;
         }
 
         if (entry->offset == offset_to_bitmap(ctl, offset)) {
             bytes_added = add_bytes_to_bitmap(ctl, entry, offset,
                               bytes, trim_state);
             bytes -= bytes_added;
             offset += bytes_added;
         }
         spin_unlock(&cluster->lock);
         if (!bytes) {
             ret = 1;
             goto out;
         }
     }
 
 no_cluster_bitmap:
     bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                      1, 0);
     if (!bitmap_info) {
         ASSERT(added == 0);
         goto new_bitmap;
     }
 
     bytes_added = add_bytes_to_bitmap(ctl, bitmap_info, offset, bytes,
                       trim_state);
     bytes -= bytes_added;
     offset += bytes_added;
     added = 0;
 
     if (!bytes) {
         ret = 1;
         goto out;
     } else
         goto again;
 
 new_bitmap:
     if (info && info->bitmap) {
         add_new_bitmap(ctl, info, offset);
         added = 1;
         info = NULL;
         goto again;
     } else {
         spin_unlock(&ctl->tree_lock);
 
         /* no pre-allocated info, allocate a new one */
         if (!info) {
             info = kmem_cache_zalloc(btrfs_free_space_cachep,
                          GFP_NOFS);
             if (!info) {
                 spin_lock(&ctl->tree_lock);
                 ret = -ENOMEM;
                 goto out;
             }
         }
 
         /* allocate the bitmap */
         info->bitmap = kmem_cache_zalloc(btrfs_free_space_bitmap_cachep,
                          GFP_NOFS);
         info->trim_state = BTRFS_TRIM_STATE_TRIMMED;
         spin_lock(&ctl->tree_lock);
         if (!info->bitmap) {
             ret = -ENOMEM;
             goto out;
         }
         goto again;
     }
 
 out:
     if (info) {
         if (info->bitmap)
             kmem_cache_free(btrfs_free_space_bitmap_cachep,
                     info->bitmap);
         kmem_cache_free(btrfs_free_space_cachep, info);
     }
 
     return ret;
 }
 
 /*
  * Free space merging rules:
  *  1) Merge trimmed areas together
  *  2) Let untrimmed areas coalesce with trimmed areas
  *  3) Always pull neighboring regions from bitmaps
  *
  * The above rules are for when we merge free space based on btrfs_trim_state.
  * Rules 2 and 3 are subtle because they are suboptimal, but are done for the
  * same reason: to promote larger extent regions which makes life easier for
  * find_free_extent().  Rule 2 enables coalescing based on the common path
  * being returning free space from btrfs_finish_extent_commit().  So when free
  * space is trimmed, it will prevent aggregating trimmed new region and
  * untrimmed regions in the rb_tree.  Rule 3 is purely to obtain larger extents
  * and provide find_free_extent() with the largest extents possible hoping for
  * the reuse path.
  */
 static bool try_merge_free_space(struct btrfs_free_space_ctl *ctl,
               struct btrfs_free_space *info, bool update_stat)
 {
     struct btrfs_free_space *left_info = NULL;
     struct btrfs_free_space *right_info;
     bool merged = false;
     u64 offset = info->offset;
     u64 bytes = info->bytes;
     const bool is_trimmed = btrfs_free_space_trimmed(info);
 
     /*
      * first we want to see if there is free space adjacent to the range we
      * are adding, if there is remove that struct and add a new one to
      * cover the entire range
      */
     right_info = tree_search_offset(ctl, offset + bytes, 0, 0);
     if (right_info && rb_prev(&right_info->offset_index))
         left_info = rb_entry(rb_prev(&right_info->offset_index),
                      struct btrfs_free_space, offset_index);
     else if (!right_info)
         left_info = tree_search_offset(ctl, offset - 1, 0, 0);
 
     /* See try_merge_free_space() comment. */
     if (right_info && !right_info->bitmap &&
         (!is_trimmed || btrfs_free_space_trimmed(right_info))) {
         unlink_free_space(ctl, right_info, update_stat);
         info->bytes += right_info->bytes;
         kmem_cache_free(btrfs_free_space_cachep, right_info);
         merged = true;
     }
 
     /* See try_merge_free_space() comment. */
     if (left_info && !left_info->bitmap &&
         left_info->offset + left_info->bytes == offset &&
         (!is_trimmed || btrfs_free_space_trimmed(left_info))) {
         unlink_free_space(ctl, left_info, update_stat);
         info->offset = left_info->offset;
         info->bytes += left_info->bytes;
         kmem_cache_free(btrfs_free_space_cachep, left_info);
         merged = true;
     }
 
     return merged;
 }
 
 static bool steal_from_bitmap_to_end(struct btrfs_free_space_ctl *ctl,
                      struct btrfs_free_space *info,
                      bool update_stat)
 {
     struct btrfs_free_space *bitmap;
     unsigned long i;
     unsigned long j;
     const u64 end = info->offset + info->bytes;
     const u64 bitmap_offset = offset_to_bitmap(ctl, end);
     u64 bytes;
 
     bitmap = tree_search_offset(ctl, bitmap_offset, 1, 0);
     if (!bitmap)
         return false;
 
     i = offset_to_bit(bitmap->offset, ctl->unit, end);
     j = find_next_zero_bit(bitmap->bitmap, BITS_PER_BITMAP, i);
     if (j == i)
         return false;
     bytes = (j - i) * ctl->unit;
     info->bytes += bytes;
 
     /* See try_merge_free_space() comment. */
     if (!btrfs_free_space_trimmed(bitmap))
         info->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
 
     bitmap_clear_bits(ctl, bitmap, end, bytes, update_stat);
 
     if (!bitmap->bytes)
         free_bitmap(ctl, bitmap);
 
     return true;
 }
 
 static bool steal_from_bitmap_to_front(struct btrfs_free_space_ctl *ctl,
                        struct btrfs_free_space *info,
                        bool update_stat)
 {
     struct btrfs_free_space *bitmap;
     u64 bitmap_offset;
     unsigned long i;
     unsigned long j;
     unsigned long prev_j;
     u64 bytes;
 
     bitmap_offset = offset_to_bitmap(ctl, info->offset);
     /* If we're on a boundary, try the previous logical bitmap. */
     if (bitmap_offset == info->offset) {
         if (info->offset == 0)
             return false;
         bitmap_offset = offset_to_bitmap(ctl, info->offset - 1);
     }
 
     bitmap = tree_search_offset(ctl, bitmap_offset, 1, 0);
     if (!bitmap)
         return false;
 
     i = offset_to_bit(bitmap->offset, ctl->unit, info->offset) - 1;
     j = 0;
     prev_j = (unsigned long)-1;
     for_each_clear_bit_from(j, bitmap->bitmap, BITS_PER_BITMAP) {
         if (j > i)
             break;
         prev_j = j;
     }
     if (prev_j == i)
         return false;
 
     if (prev_j == (unsigned long)-1)
         bytes = (i + 1) * ctl->unit;
     else
         bytes = (i - prev_j) * ctl->unit;
 
     info->offset -= bytes;
     info->bytes += bytes;
 
     /* See try_merge_free_space() comment. */
     if (!btrfs_free_space_trimmed(bitmap))
         info->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
 
     bitmap_clear_bits(ctl, bitmap, info->offset, bytes, update_stat);
 
     if (!bitmap->bytes)
         free_bitmap(ctl, bitmap);
 
     return true;
 }
 
 /*
  * We prefer always to allocate from extent entries, both for clustered and
  * non-clustered allocation requests. So when attempting to add a new extent
  * entry, try to see if there's adjacent free space in bitmap entries, and if
  * there is, migrate that space from the bitmaps to the extent.
  * Like this we get better chances of satisfying space allocation requests
  * because we attempt to satisfy them based on a single cache entry, and never
  * on 2 or more entries - even if the entries represent a contiguous free space
  * region (e.g. 1 extent entry + 1 bitmap entry starting where the extent entry
  * ends).
  */
 static void steal_from_bitmap(struct btrfs_free_space_ctl *ctl,
                   struct btrfs_free_space *info,
                   bool update_stat)
 {
     /*
      * Only work with disconnected entries, as we can change their offset,
      * and must be extent entries.
      */
     ASSERT(!info->bitmap);
     ASSERT(RB_EMPTY_NODE(&info->offset_index));
 
     if (ctl->total_bitmaps > 0) {
         bool stole_end;
         bool stole_front = false;
 
         stole_end = steal_from_bitmap_to_end(ctl, info, update_stat);
         if (ctl->total_bitmaps > 0)
             stole_front = steal_from_bitmap_to_front(ctl, info,
                                  update_stat);
 
         if (stole_end || stole_front)
             try_merge_free_space(ctl, info, update_stat);
     }
 }
 
 int __btrfs_add_free_space(struct btrfs_block_group *block_group,
                u64 offset, u64 bytes,
                enum btrfs_trim_state trim_state)
 {
     struct btrfs_fs_info *fs_info = block_group->fs_info;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *info;
     int ret = 0;
     u64 filter_bytes = bytes;
 
     ASSERT(!btrfs_is_zoned(fs_info));
 
     info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
     if (!info)
         return -ENOMEM;
 
     info->offset = offset;
     info->bytes = bytes;
     info->trim_state = trim_state;
     RB_CLEAR_NODE(&info->offset_index);
     RB_CLEAR_NODE(&info->bytes_index);
 
     spin_lock(&ctl->tree_lock);
 
     if (try_merge_free_space(ctl, info, true))
         goto link;
 
     /*
      * There was no extent directly to the left or right of this new
      * extent then we know we're going to have to allocate a new extent, so
      * before we do that see if we need to drop this into a bitmap
      */
     ret = insert_into_bitmap(ctl, info);
     if (ret < 0) {
         goto out;
     } else if (ret) {
         ret = 0;
         goto out;
     }
 link:
     /*
      * Only steal free space from adjacent bitmaps if we're sure we're not
      * going to add the new free space to existing bitmap entries - because
      * that would mean unnecessary work that would be reverted. Therefore
      * attempt to steal space from bitmaps if we're adding an extent entry.
      */
     steal_from_bitmap(ctl, info, true);
 
     filter_bytes = max(filter_bytes, info->bytes);
 
     ret = link_free_space(ctl, info);
     if (ret)
         kmem_cache_free(btrfs_free_space_cachep, info);
 out:
     btrfs_discard_update_discardable(block_group);
     spin_unlock(&ctl->tree_lock);
 
     if (ret) {
         btrfs_crit(fs_info, "unable to add free space :%d", ret);
         ASSERT(ret != -EEXIST);
     }
 
     if (trim_state != BTRFS_TRIM_STATE_TRIMMED) {
         btrfs_discard_check_filter(block_group, filter_bytes);
         btrfs_discard_queue_work(&fs_info->discard_ctl, block_group);
     }
 
     return ret;
 }
 
 static int __btrfs_add_free_space_zoned(struct btrfs_block_group *block_group,
                     u64 bytenr, u64 size, bool used)
 {
     struct btrfs_space_info *sinfo = block_group->space_info;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     u64 offset = bytenr - block_group->start;
     u64 to_free, to_unusable;
     int bg_reclaim_threshold = 0;
     bool initial = (size == block_group->length);
     u64 reclaimable_unusable;
 
     WARN_ON(!initial && offset + size > block_group->zone_capacity);
 
     if (!initial)
         bg_reclaim_threshold = READ_ONCE(sinfo->bg_reclaim_threshold);
 
     spin_lock(&ctl->tree_lock);
     if (!used)
         to_free = size;
     else if (initial)
         to_free = block_group->zone_capacity;
     else if (offset >= block_group->alloc_offset)
         to_free = size;
     else if (offset + size <= block_group->alloc_offset)
         to_free = 0;
     else
         to_free = offset + size - block_group->alloc_offset;
     to_unusable = size - to_free;
 
     ctl->free_space += to_free;
     /*
      * If the block group is read-only, we should account freed space into
      * bytes_readonly.
      */
     if (!block_group->ro)
         block_group->zone_unusable += to_unusable;
     spin_unlock(&ctl->tree_lock);
     if (!used) {
         spin_lock(&block_group->lock);
         block_group->alloc_offset -= size;
         spin_unlock(&block_group->lock);
     }
 
     reclaimable_unusable = block_group->zone_unusable -
                    (block_group->length - block_group->zone_capacity);
     /* All the region is now unusable. Mark it as unused and reclaim */
     if (block_group->zone_unusable == block_group->length) {
         btrfs_mark_bg_unused(block_group);
     } else if (bg_reclaim_threshold &&
            reclaimable_unusable >=
            div_factor_fine(block_group->zone_capacity,
                    bg_reclaim_threshold)) {
         btrfs_mark_bg_to_reclaim(block_group);
     }
 
     return 0;
 }
 
 int btrfs_add_free_space(struct btrfs_block_group *block_group,
              u64 bytenr, u64 size)
 {
     enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
 
     if (btrfs_is_zoned(block_group->fs_info))
         return __btrfs_add_free_space_zoned(block_group, bytenr, size,
                             true);
 
     if (btrfs_test_opt(block_group->fs_info, DISCARD_SYNC))
         trim_state = BTRFS_TRIM_STATE_TRIMMED;
 
     return __btrfs_add_free_space(block_group, bytenr, size, trim_state);
 }
 
 int btrfs_add_free_space_unused(struct btrfs_block_group *block_group,
                 u64 bytenr, u64 size)
 {
     if (btrfs_is_zoned(block_group->fs_info))
         return __btrfs_add_free_space_zoned(block_group, bytenr, size,
                             false);
 
     return btrfs_add_free_space(block_group, bytenr, size);
 }
 
 /*
  * This is a subtle distinction because when adding free space back in general,
  * we want it to be added as untrimmed for async. But in the case where we add
  * it on loading of a block group, we want to consider it trimmed.
  */
 int btrfs_add_free_space_async_trimmed(struct btrfs_block_group *block_group,
                        u64 bytenr, u64 size)
 {
     enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
 
     if (btrfs_is_zoned(block_group->fs_info))
         return __btrfs_add_free_space_zoned(block_group, bytenr, size,
                             true);
 
     if (btrfs_test_opt(block_group->fs_info, DISCARD_SYNC) ||
         btrfs_test_opt(block_group->fs_info, DISCARD_ASYNC))
         trim_state = BTRFS_TRIM_STATE_TRIMMED;
 
     return __btrfs_add_free_space(block_group, bytenr, size, trim_state);
 }
 
 int btrfs_remove_free_space(struct btrfs_block_group *block_group,
                 u64 offset, u64 bytes)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *info;
     int ret;
     bool re_search = false;
 
     if (btrfs_is_zoned(block_group->fs_info)) {
         /*
          * This can happen with conventional zones when replaying log.
          * Since the allocation info of tree-log nodes are not recorded
          * to the extent-tree, calculate_alloc_pointer() failed to
          * advance the allocation pointer after last allocated tree log
          * node blocks.
          *
          * This function is called from
          * btrfs_pin_extent_for_log_replay() when replaying the log.
          * Advance the pointer not to overwrite the tree-log nodes.
          */
         if (block_group->start + block_group->alloc_offset <
             offset + bytes) {
             block_group->alloc_offset =
                 offset + bytes - block_group->start;
         }
         return 0;
     }
 
     spin_lock(&ctl->tree_lock);
 
 again:
     ret = 0;
     if (!bytes)
         goto out_lock;
 
     info = tree_search_offset(ctl, offset, 0, 0);
     if (!info) {
         /*
          * oops didn't find an extent that matched the space we wanted
          * to remove, look for a bitmap instead
          */
         info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                       1, 0);
         if (!info) {
             /*
              * If we found a partial bit of our free space in a
              * bitmap but then couldn't find the other part this may
              * be a problem, so WARN about it.
              */
             WARN_ON(re_search);
             goto out_lock;
         }
     }
 
     re_search = false;
     if (!info->bitmap) {
         unlink_free_space(ctl, info, true);
         if (offset == info->offset) {
             u64 to_free = min(bytes, info->bytes);
 
             info->bytes -= to_free;
             info->offset += to_free;
             if (info->bytes) {
                 ret = link_free_space(ctl, info);
                 WARN_ON(ret);
             } else {
                 kmem_cache_free(btrfs_free_space_cachep, info);
             }
 
             offset += to_free;
             bytes -= to_free;
             goto again;
         } else {
             u64 old_end = info->bytes + info->offset;
 
             info->bytes = offset - info->offset;
             ret = link_free_space(ctl, info);
             WARN_ON(ret);
             if (ret)
                 goto out_lock;
 
             /* Not enough bytes in this entry to satisfy us */
             if (old_end < offset + bytes) {
                 bytes -= old_end - offset;
                 offset = old_end;
                 goto again;
             } else if (old_end == offset + bytes) {
                 /* all done */
                 goto out_lock;
             }
             spin_unlock(&ctl->tree_lock);
 
             ret = __btrfs_add_free_space(block_group,
                              offset + bytes,
                              old_end - (offset + bytes),
                              info->trim_state);
             WARN_ON(ret);
             goto out;
         }
     }
 
     ret = remove_from_bitmap(ctl, info, &offset, &bytes);
     if (ret == -EAGAIN) {
         re_search = true;
         goto again;
     }
 out_lock:
     btrfs_discard_update_discardable(block_group);
     spin_unlock(&ctl->tree_lock);
 out:
     return ret;
 }
 
 void btrfs_dump_free_space(struct btrfs_block_group *block_group,
                u64 bytes)
 {
     struct btrfs_fs_info *fs_info = block_group->fs_info;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *info;
     struct rb_node *n;
     int count = 0;
 
     /*
      * Zoned btrfs does not use free space tree and cluster. Just print
      * out the free space after the allocation offset.
      */
     if (btrfs_is_zoned(fs_info)) {
         btrfs_info(fs_info, "free space %llu active %d",
                block_group->zone_capacity - block_group->alloc_offset,
                block_group->zone_is_active);
         return;
     }
 
     spin_lock(&ctl->tree_lock);
     for (n = rb_first(&ctl->free_space_offset); n; n = rb_next(n)) {
         info = rb_entry(n, struct btrfs_free_space, offset_index);
         if (info->bytes >= bytes && !block_group->ro)
             count++;
         btrfs_crit(fs_info, "entry offset %llu, bytes %llu, bitmap %s",
                info->offset, info->bytes,
                (info->bitmap) ? "yes" : "no");
     }
     spin_unlock(&ctl->tree_lock);
     btrfs_info(fs_info, "block group has cluster?: %s",
            list_empty(&block_group->cluster_list) ? "no" : "yes");
     btrfs_info(fs_info,
            "%d blocks of free space at or bigger than bytes is", count);
 }
 
 void btrfs_init_free_space_ctl(struct btrfs_block_group *block_group,
                    struct btrfs_free_space_ctl *ctl)
 {
     struct btrfs_fs_info *fs_info = block_group->fs_info;
 
     spin_lock_init(&ctl->tree_lock);
     ctl->unit = fs_info->sectorsize;
     ctl->start = block_group->start;
     ctl->block_group = block_group;
     ctl->op = &free_space_op;
     ctl->free_space_bytes = RB_ROOT_CACHED;
     INIT_LIST_HEAD(&ctl->trimming_ranges);
     mutex_init(&ctl->cache_writeout_mutex);
 
     /*
      * we only want to have 32k of ram per block group for keeping
      * track of free space, and if we pass 1/2 of that we want to
      * start converting things over to using bitmaps
      */
     ctl->extents_thresh = (SZ_32K / 2) / sizeof(struct btrfs_free_space);
 }
 
 /*
  * for a given cluster, put all of its extents back into the free
  * space cache.  If the block group passed doesn't match the block group
  * pointed to by the cluster, someone else raced in and freed the
  * cluster already.  In that case, we just return without changing anything
  */
 static void __btrfs_return_cluster_to_free_space(
                  struct btrfs_block_group *block_group,
                  struct btrfs_free_cluster *cluster)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *entry;
     struct rb_node *node;
 
     spin_lock(&cluster->lock);
     if (cluster->block_group != block_group) {
         spin_unlock(&cluster->lock);
         return;
     }
 
     cluster->block_group = NULL;
     cluster->window_start = 0;
     list_del_init(&cluster->block_group_list);
 
     node = rb_first(&cluster->root);
     while (node) {
         bool bitmap;
 
         entry = rb_entry(node, struct btrfs_free_space, offset_index);
         node = rb_next(&entry->offset_index);
         rb_erase(&entry->offset_index, &cluster->root);
         RB_CLEAR_NODE(&entry->offset_index);
 
         bitmap = (entry->bitmap != NULL);
         if (!bitmap) {
             /* Merging treats extents as if they were new */
             if (!btrfs_free_space_trimmed(entry)) {
                 ctl->discardable_extents[BTRFS_STAT_CURR]--;
                 ctl->discardable_bytes[BTRFS_STAT_CURR] -=
                     entry->bytes;
             }
 
             try_merge_free_space(ctl, entry, false);
             steal_from_bitmap(ctl, entry, false);
 
             /* As we insert directly, update these statistics */
             if (!btrfs_free_space_trimmed(entry)) {
                 ctl->discardable_extents[BTRFS_STAT_CURR]++;
                 ctl->discardable_bytes[BTRFS_STAT_CURR] +=
                     entry->bytes;
             }
         }
         tree_insert_offset(&ctl->free_space_offset,
                    entry->offset, &entry->offset_index, bitmap);
         rb_add_cached(&entry->bytes_index, &ctl->free_space_bytes,
                   entry_less);
     }
     cluster->root = RB_ROOT;
     spin_unlock(&cluster->lock);
     btrfs_put_block_group(block_group);
 }
 
 static void __btrfs_remove_free_space_cache_locked(
                 struct btrfs_free_space_ctl *ctl)
 {
     struct btrfs_free_space *info;
     struct rb_node *node;
 
     while ((node = rb_last(&ctl->free_space_offset)) != NULL) {
         info = rb_entry(node, struct btrfs_free_space, offset_index);
         if (!info->bitmap) {
             unlink_free_space(ctl, info, true);
             kmem_cache_free(btrfs_free_space_cachep, info);
         } else {
             free_bitmap(ctl, info);
         }
 
         cond_resched_lock(&ctl->tree_lock);
     }
 }
 
 void __btrfs_remove_free_space_cache(struct btrfs_free_space_ctl *ctl)
 {
     spin_lock(&ctl->tree_lock);
     __btrfs_remove_free_space_cache_locked(ctl);
     if (ctl->block_group)
         btrfs_discard_update_discardable(ctl->block_group);
     spin_unlock(&ctl->tree_lock);
 }
 
 void btrfs_remove_free_space_cache(struct btrfs_block_group *block_group)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_cluster *cluster;
     struct list_head *head;
 
     spin_lock(&ctl->tree_lock);
     while ((head = block_group->cluster_list.next) !=
            &block_group->cluster_list) {
         cluster = list_entry(head, struct btrfs_free_cluster,
                      block_group_list);
 
         WARN_ON(cluster->block_group != block_group);
         __btrfs_return_cluster_to_free_space(block_group, cluster);
 
         cond_resched_lock(&ctl->tree_lock);
     }
     __btrfs_remove_free_space_cache_locked(ctl);
     btrfs_discard_update_discardable(block_group);
     spin_unlock(&ctl->tree_lock);
 
 }
 
 /**
  * btrfs_is_free_space_trimmed - see if everything is trimmed
  * @block_group: block_group of interest
  *
  * Walk @block_group's free space rb_tree to determine if everything is trimmed.
  */
 bool btrfs_is_free_space_trimmed(struct btrfs_block_group *block_group)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *info;
     struct rb_node *node;
     bool ret = true;
 
     spin_lock(&ctl->tree_lock);
     node = rb_first(&ctl->free_space_offset);
 
     while (node) {
         info = rb_entry(node, struct btrfs_free_space, offset_index);
 
         if (!btrfs_free_space_trimmed(info)) {
             ret = false;
             break;
         }
 
         node = rb_next(node);
     }
 
     spin_unlock(&ctl->tree_lock);
     return ret;
 }
 
 u64 btrfs_find_space_for_alloc(struct btrfs_block_group *block_group,
                    u64 offset, u64 bytes, u64 empty_size,
                    u64 *max_extent_size)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_discard_ctl *discard_ctl =
                     &block_group->fs_info->discard_ctl;
     struct btrfs_free_space *entry = NULL;
     u64 bytes_search = bytes + empty_size;
     u64 ret = 0;
     u64 align_gap = 0;
     u64 align_gap_len = 0;
     enum btrfs_trim_state align_gap_trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
     bool use_bytes_index = (offset == block_group->start);
 
     ASSERT(!btrfs_is_zoned(block_group->fs_info));
 
     spin_lock(&ctl->tree_lock);
     entry = find_free_space(ctl, &offset, &bytes_search,
                 block_group->full_stripe_len, max_extent_size,
                 use_bytes_index);
     if (!entry)
         goto out;
 
     ret = offset;
     if (entry->bitmap) {
         bitmap_clear_bits(ctl, entry, offset, bytes, true);
 
         if (!btrfs_free_space_trimmed(entry))
             atomic64_add(bytes, &discard_ctl->discard_bytes_saved);
 
         if (!entry->bytes)
             free_bitmap(ctl, entry);
     } else {
         unlink_free_space(ctl, entry, true);
         align_gap_len = offset - entry->offset;
         align_gap = entry->offset;
         align_gap_trim_state = entry->trim_state;
 
         if (!btrfs_free_space_trimmed(entry))
             atomic64_add(bytes, &discard_ctl->discard_bytes_saved);
 
         entry->offset = offset + bytes;
         WARN_ON(entry->bytes < bytes + align_gap_len);
 
         entry->bytes -= bytes + align_gap_len;
         if (!entry->bytes)
             kmem_cache_free(btrfs_free_space_cachep, entry);
         else
             link_free_space(ctl, entry);
     }
 out:
     btrfs_discard_update_discardable(block_group);
     spin_unlock(&ctl->tree_lock);
 
     if (align_gap_len)
         __btrfs_add_free_space(block_group, align_gap, align_gap_len,
                        align_gap_trim_state);
     return ret;
 }
 
 /*
  * given a cluster, put all of its extents back into the free space
  * cache.  If a block group is passed, this function will only free
  * a cluster that belongs to the passed block group.
  *
  * Otherwise, it'll get a reference on the block group pointed to by the
  * cluster and remove the cluster from it.
  */
 void btrfs_return_cluster_to_free_space(
                    struct btrfs_block_group *block_group,
                    struct btrfs_free_cluster *cluster)
 {
     struct btrfs_free_space_ctl *ctl;
 
     /* first, get a safe pointer to the block group */
     spin_lock(&cluster->lock);
     if (!block_group) {
         block_group = cluster->block_group;
         if (!block_group) {
             spin_unlock(&cluster->lock);
             return;
         }
     } else if (cluster->block_group != block_group) {
         /* someone else has already freed it don't redo their work */
         spin_unlock(&cluster->lock);
         return;
     }
     btrfs_get_block_group(block_group);
     spin_unlock(&cluster->lock);
 
     ctl = block_group->free_space_ctl;
 
     /* now return any extents the cluster had on it */
     spin_lock(&ctl->tree_lock);
     __btrfs_return_cluster_to_free_space(block_group, cluster);
     spin_unlock(&ctl->tree_lock);
 
     btrfs_discard_queue_work(&block_group->fs_info->discard_ctl, block_group);
 
     /* finally drop our ref */
     btrfs_put_block_group(block_group);
 }
 
 static u64 btrfs_alloc_from_bitmap(struct btrfs_block_group *block_group,
                    struct btrfs_free_cluster *cluster,
                    struct btrfs_free_space *entry,
                    u64 bytes, u64 min_start,
                    u64 *max_extent_size)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     int err;
     u64 search_start = cluster->window_start;
     u64 search_bytes = bytes;
     u64 ret = 0;
 
     search_start = min_start;
     search_bytes = bytes;
 
     err = search_bitmap(ctl, entry, &search_start, &search_bytes, true);
     if (err) {
         *max_extent_size = max(get_max_extent_size(entry),
                        *max_extent_size);
         return 0;
     }
 
     ret = search_start;
     bitmap_clear_bits(ctl, entry, ret, bytes, false);
 
     return ret;
 }
 
 /*
  * given a cluster, try to allocate 'bytes' from it, returns 0
  * if it couldn't find anything suitably large, or a logical disk offset
  * if things worked out
  */
 u64 btrfs_alloc_from_cluster(struct btrfs_block_group *block_group,
                  struct btrfs_free_cluster *cluster, u64 bytes,
                  u64 min_start, u64 *max_extent_size)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_discard_ctl *discard_ctl =
                     &block_group->fs_info->discard_ctl;
     struct btrfs_free_space *entry = NULL;
     struct rb_node *node;
     u64 ret = 0;
 
     ASSERT(!btrfs_is_zoned(block_group->fs_info));
 
     spin_lock(&cluster->lock);
     if (bytes > cluster->max_size)
         goto out;
 
     if (cluster->block_group != block_group)
         goto out;
 
     node = rb_first(&cluster->root);
     if (!node)
         goto out;
 
     entry = rb_entry(node, struct btrfs_free_space, offset_index);
     while (1) {
         if (entry->bytes < bytes)
             *max_extent_size = max(get_max_extent_size(entry),
                            *max_extent_size);
 
         if (entry->bytes < bytes ||
             (!entry->bitmap && entry->offset < min_start)) {
             node = rb_next(&entry->offset_index);
             if (!node)
                 break;
             entry = rb_entry(node, struct btrfs_free_space,
                      offset_index);
             continue;
         }
 
         if (entry->bitmap) {
             ret = btrfs_alloc_from_bitmap(block_group,
                               cluster, entry, bytes,
                               cluster->window_start,
                               max_extent_size);
             if (ret == 0) {
                 node = rb_next(&entry->offset_index);
                 if (!node)
                     break;
                 entry = rb_entry(node, struct btrfs_free_space,
                          offset_index);
                 continue;
             }
             cluster->window_start += bytes;
         } else {
             ret = entry->offset;
 
             entry->offset += bytes;
             entry->bytes -= bytes;
         }
 
         break;
     }
 out:
     spin_unlock(&cluster->lock);
 
     if (!ret)
         return 0;
 
     spin_lock(&ctl->tree_lock);
 
     if (!btrfs_free_space_trimmed(entry))
         atomic64_add(bytes, &discard_ctl->discard_bytes_saved);
 
     ctl->free_space -= bytes;
     if (!entry->bitmap && !btrfs_free_space_trimmed(entry))
         ctl->discardable_bytes[BTRFS_STAT_CURR] -= bytes;
 
     spin_lock(&cluster->lock);
     if (entry->bytes == 0) {
         rb_erase(&entry->offset_index, &cluster->root);
         ctl->free_extents--;
         if (entry->bitmap) {
             kmem_cache_free(btrfs_free_space_bitmap_cachep,
                     entry->bitmap);
             ctl->total_bitmaps--;
             recalculate_thresholds(ctl);
         } else if (!btrfs_free_space_trimmed(entry)) {
             ctl->discardable_extents[BTRFS_STAT_CURR]--;
         }
         kmem_cache_free(btrfs_free_space_cachep, entry);
     }
 
     spin_unlock(&cluster->lock);
     spin_unlock(&ctl->tree_lock);
 
     return ret;
 }
 
 static int btrfs_bitmap_cluster(struct btrfs_block_group *block_group,
                 struct btrfs_free_space *entry,
                 struct btrfs_free_cluster *cluster,
                 u64 offset, u64 bytes,
                 u64 cont1_bytes, u64 min_bytes)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     unsigned long next_zero;
     unsigned long i;
     unsigned long want_bits;
     unsigned long min_bits;
     unsigned long found_bits;
     unsigned long max_bits = 0;
     unsigned long start = 0;
     unsigned long total_found = 0;
     int ret;
 
     i = offset_to_bit(entry->offset, ctl->unit,
               max_t(u64, offset, entry->offset));
     want_bits = bytes_to_bits(bytes, ctl->unit);
     min_bits = bytes_to_bits(min_bytes, ctl->unit);
 
     /*
      * Don't bother looking for a cluster in this bitmap if it's heavily
      * fragmented.
      */
     if (entry->max_extent_size &&
         entry->max_extent_size < cont1_bytes)
         return -ENOSPC;
 again:
     found_bits = 0;
     for_each_set_bit_from(i, entry->bitmap, BITS_PER_BITMAP) {
         next_zero = find_next_zero_bit(entry->bitmap,
                            BITS_PER_BITMAP, i);
         if (next_zero - i >= min_bits) {
             found_bits = next_zero - i;
             if (found_bits > max_bits)
                 max_bits = found_bits;
             break;
         }
         if (next_zero - i > max_bits)
             max_bits = next_zero - i;
         i = next_zero;
     }
 
     if (!found_bits) {
         entry->max_extent_size = (u64)max_bits * ctl->unit;
         return -ENOSPC;
     }
 
     if (!total_found) {
         start = i;
         cluster->max_size = 0;
     }
 
     total_found += found_bits;
 
     if (cluster->max_size < found_bits * ctl->unit)
         cluster->max_size = found_bits * ctl->unit;
 
     if (total_found < want_bits || cluster->max_size < cont1_bytes) {
         i = next_zero + 1;
         goto again;
     }
 
     cluster->window_start = start * ctl->unit + entry->offset;
     rb_erase(&entry->offset_index, &ctl->free_space_offset);
     rb_erase_cached(&entry->bytes_index, &ctl->free_space_bytes);
 
     /*
      * We need to know if we're currently on the normal space index when we
      * manipulate the bitmap so that we know we need to remove and re-insert
      * it into the space_index tree.  Clear the bytes_index node here so the
      * bitmap manipulation helpers know not to mess with the space_index
      * until this bitmap entry is added back into the normal cache.
      */
     RB_CLEAR_NODE(&entry->bytes_index);
 
     ret = tree_insert_offset(&cluster->root, entry->offset,
                  &entry->offset_index, 1);
     ASSERT(!ret); /* -EEXIST; Logic error */
 
     trace_btrfs_setup_cluster(block_group, cluster,
                   total_found * ctl->unit, 1);
     return 0;
 }
 
 /*
  * This searches the block group for just extents to fill the cluster with.
  * Try to find a cluster with at least bytes total bytes, at least one
  * extent of cont1_bytes, and other clusters of at least min_bytes.
  */
 static noinline int
 setup_cluster_no_bitmap(struct btrfs_block_group *block_group,
             struct btrfs_free_cluster *cluster,
             struct list_head *bitmaps, u64 offset, u64 bytes,
             u64 cont1_bytes, u64 min_bytes)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *first = NULL;
     struct btrfs_free_space *entry = NULL;
     struct btrfs_free_space *last;
     struct rb_node *node;
     u64 window_free;
     u64 max_extent;
     u64 total_size = 0;
 
     entry = tree_search_offset(ctl, offset, 0, 1);
     if (!entry)
         return -ENOSPC;
 
     /*
      * We don't want bitmaps, so just move along until we find a normal
      * extent entry.
      */
     while (entry->bitmap || entry->bytes < min_bytes) {
         if (entry->bitmap && list_empty(&entry->list))
             list_add_tail(&entry->list, bitmaps);
         node = rb_next(&entry->offset_index);
         if (!node)
             return -ENOSPC;
         entry = rb_entry(node, struct btrfs_free_space, offset_index);
     }
 
     window_free = entry->bytes;
     max_extent = entry->bytes;
     first = entry;
     last = entry;
 
     for (node = rb_next(&entry->offset_index); node;
          node = rb_next(&entry->offset_index)) {
         entry = rb_entry(node, struct btrfs_free_space, offset_index);
 
         if (entry->bitmap) {
             if (list_empty(&entry->list))
                 list_add_tail(&entry->list, bitmaps);
             continue;
         }
 
         if (entry->bytes < min_bytes)
             continue;
 
         last = entry;
         window_free += entry->bytes;
         if (entry->bytes > max_extent)
             max_extent = entry->bytes;
     }
 
     if (window_free < bytes || max_extent < cont1_bytes)
         return -ENOSPC;
 
     cluster->window_start = first->offset;
 
     node = &first->offset_index;
 
     /*
      * now we've found our entries, pull them out of the free space
      * cache and put them into the cluster rbtree
      */
     do {
         int ret;
 
         entry = rb_entry(node, struct btrfs_free_space, offset_index);
         node = rb_next(&entry->offset_index);
         if (entry->bitmap || entry->bytes < min_bytes)
             continue;
 
         rb_erase(&entry->offset_index, &ctl->free_space_offset);
         rb_erase_cached(&entry->bytes_index, &ctl->free_space_bytes);
         ret = tree_insert_offset(&cluster->root, entry->offset,
                      &entry->offset_index, 0);
         total_size += entry->bytes;
         ASSERT(!ret); /* -EEXIST; Logic error */
     } while (node && entry != last);
 
     cluster->max_size = max_extent;
     trace_btrfs_setup_cluster(block_group, cluster, total_size, 0);
     return 0;
 }
 
 /*
  * This specifically looks for bitmaps that may work in the cluster, we assume
  * that we have already failed to find extents that will work.
  */
 static noinline int
 setup_cluster_bitmap(struct btrfs_block_group *block_group,
              struct btrfs_free_cluster *cluster,
              struct list_head *bitmaps, u64 offset, u64 bytes,
              u64 cont1_bytes, u64 min_bytes)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *entry = NULL;
     int ret = -ENOSPC;
     u64 bitmap_offset = offset_to_bitmap(ctl, offset);
 
     if (ctl->total_bitmaps == 0)
         return -ENOSPC;
 
     /*
      * The bitmap that covers offset won't be in the list unless offset
      * is just its start offset.
      */
     if (!list_empty(bitmaps))
         entry = list_first_entry(bitmaps, struct btrfs_free_space, list);
 
     if (!entry || entry->offset != bitmap_offset) {
         entry = tree_search_offset(ctl, bitmap_offset, 1, 0);
         if (entry && list_empty(&entry->list))
             list_add(&entry->list, bitmaps);
     }
 
     list_for_each_entry(entry, bitmaps, list) {
         if (entry->bytes < bytes)
             continue;
         ret = btrfs_bitmap_cluster(block_group, entry, cluster, offset,
                        bytes, cont1_bytes, min_bytes);
         if (!ret)
             return 0;
     }
 
     /*
      * The bitmaps list has all the bitmaps that record free space
      * starting after offset, so no more search is required.
      */
     return -ENOSPC;
 }
 
 /*
  * here we try to find a cluster of blocks in a block group.  The goal
  * is to find at least bytes+empty_size.
  * We might not find them all in one contiguous area.
  *
  * returns zero and sets up cluster if things worked out, otherwise
  * it returns -enospc
  */
 int btrfs_find_space_cluster(struct btrfs_block_group *block_group,
                  struct btrfs_free_cluster *cluster,
                  u64 offset, u64 bytes, u64 empty_size)
 {
     struct btrfs_fs_info *fs_info = block_group->fs_info;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *entry, *tmp;
     LIST_HEAD(bitmaps);
     u64 min_bytes;
     u64 cont1_bytes;
     int ret;
 
     /*
      * Choose the minimum extent size we'll require for this
      * cluster.  For SSD_SPREAD, don't allow any fragmentation.
      * For metadata, allow allocates with smaller extents.  For
      * data, keep it dense.
      */
     if (btrfs_test_opt(fs_info, SSD_SPREAD)) {
         cont1_bytes = bytes + empty_size;
         min_bytes = cont1_bytes;
     } else if (block_group->flags & BTRFS_BLOCK_GROUP_METADATA) {
         cont1_bytes = bytes;
         min_bytes = fs_info->sectorsize;
     } else {
         cont1_bytes = max(bytes, (bytes + empty_size) >> 2);
         min_bytes = fs_info->sectorsize;
     }
 
     spin_lock(&ctl->tree_lock);
 
     /*
      * If we know we don't have enough space to make a cluster don't even
      * bother doing all the work to try and find one.
      */
     if (ctl->free_space < bytes) {
         spin_unlock(&ctl->tree_lock);
         return -ENOSPC;
     }
 
     spin_lock(&cluster->lock);
 
     /* someone already found a cluster, hooray */
     if (cluster->block_group) {
         ret = 0;
         goto out;
     }
 
     trace_btrfs_find_cluster(block_group, offset, bytes, empty_size,
                  min_bytes);
 
     ret = setup_cluster_no_bitmap(block_group, cluster, &bitmaps, offset,
                       bytes + empty_size,
                       cont1_bytes, min_bytes);
     if (ret)
         ret = setup_cluster_bitmap(block_group, cluster, &bitmaps,
                        offset, bytes + empty_size,
                        cont1_bytes, min_bytes);
 
     /* Clear our temporary list */
     list_for_each_entry_safe(entry, tmp, &bitmaps, list)
         list_del_init(&entry->list);
 
     if (!ret) {
         btrfs_get_block_group(block_group);
         list_add_tail(&cluster->block_group_list,
                   &block_group->cluster_list);
         cluster->block_group = block_group;
     } else {
         trace_btrfs_failed_cluster_setup(block_group);
     }
 out:
     spin_unlock(&cluster->lock);
     spin_unlock(&ctl->tree_lock);
 
     return ret;
 }
 
 /*
  * simple code to zero out a cluster
  */
 void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
 {
     spin_lock_init(&cluster->lock);
     spin_lock_init(&cluster->refill_lock);
     cluster->root = RB_ROOT;
     cluster->max_size = 0;
     cluster->fragmented = false;
     INIT_LIST_HEAD(&cluster->block_group_list);
     cluster->block_group = NULL;
 }
 
 static int do_trimming(struct btrfs_block_group *block_group,
                u64 *total_trimmed, u64 start, u64 bytes,
                u64 reserved_start, u64 reserved_bytes,
                enum btrfs_trim_state reserved_trim_state,
                struct btrfs_trim_range *trim_entry)
 {
     struct btrfs_space_info *space_info = block_group->space_info;
     struct btrfs_fs_info *fs_info = block_group->fs_info;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     int ret;
     int update = 0;
     const u64 end = start + bytes;
     const u64 reserved_end = reserved_start + reserved_bytes;
     enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
     u64 trimmed = 0;
 
     spin_lock(&space_info->lock);
     spin_lock(&block_group->lock);
     if (!block_group->ro) {
         block_group->reserved += reserved_bytes;
         space_info->bytes_reserved += reserved_bytes;
         update = 1;
     }
     spin_unlock(&block_group->lock);
     spin_unlock(&space_info->lock);
 
     ret = btrfs_discard_extent(fs_info, start, bytes, &trimmed);
     if (!ret) {
         *total_trimmed += trimmed;
         trim_state = BTRFS_TRIM_STATE_TRIMMED;
     }
 
     mutex_lock(&ctl->cache_writeout_mutex);
     if (reserved_start < start)
         __btrfs_add_free_space(block_group, reserved_start,
                        start - reserved_start,
                        reserved_trim_state);
     if (start + bytes < reserved_start + reserved_bytes)
         __btrfs_add_free_space(block_group, end, reserved_end - end,
                        reserved_trim_state);
     __btrfs_add_free_space(block_group, start, bytes, trim_state);
     list_del(&trim_entry->list);
     mutex_unlock(&ctl->cache_writeout_mutex);
 
     if (update) {
         spin_lock(&space_info->lock);
         spin_lock(&block_group->lock);
         if (block_group->ro)
             space_info->bytes_readonly += reserved_bytes;
         block_group->reserved -= reserved_bytes;
         space_info->bytes_reserved -= reserved_bytes;
         spin_unlock(&block_group->lock);
         spin_unlock(&space_info->lock);
     }
 
     return ret;
 }
 
 /*
  * If @async is set, then we will trim 1 region and return.
  */
 static int trim_no_bitmap(struct btrfs_block_group *block_group,
               u64 *total_trimmed, u64 start, u64 end, u64 minlen,
               bool async)
 {
     struct btrfs_discard_ctl *discard_ctl =
                     &block_group->fs_info->discard_ctl;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *entry;
     struct rb_node *node;
     int ret = 0;
     u64 extent_start;
     u64 extent_bytes;
     enum btrfs_trim_state extent_trim_state;
     u64 bytes;
     const u64 max_discard_size = READ_ONCE(discard_ctl->max_discard_size);
 
     while (start < end) {
         struct btrfs_trim_range trim_entry;
 
         mutex_lock(&ctl->cache_writeout_mutex);
         spin_lock(&ctl->tree_lock);
 
         if (ctl->free_space < minlen)
             goto out_unlock;
 
         entry = tree_search_offset(ctl, start, 0, 1);
         if (!entry)
             goto out_unlock;
 
         /* Skip bitmaps and if async, already trimmed entries */
         while (entry->bitmap ||
                (async && btrfs_free_space_trimmed(entry))) {
             node = rb_next(&entry->offset_index);
             if (!node)
                 goto out_unlock;
             entry = rb_entry(node, struct btrfs_free_space,
                      offset_index);
         }
 
         if (entry->offset >= end)
             goto out_unlock;
 
         extent_start = entry->offset;
         extent_bytes = entry->bytes;
         extent_trim_state = entry->trim_state;
         if (async) {
             start = entry->offset;
             bytes = entry->bytes;
             if (bytes < minlen) {
                 spin_unlock(&ctl->tree_lock);
                 mutex_unlock(&ctl->cache_writeout_mutex);
                 goto next;
             }
             unlink_free_space(ctl, entry, true);
             /*
              * Let bytes = BTRFS_MAX_DISCARD_SIZE + X.
              * If X < BTRFS_ASYNC_DISCARD_MIN_FILTER, we won't trim
              * X when we come back around.  So trim it now.
              */
             if (max_discard_size &&
                 bytes >= (max_discard_size +
                       BTRFS_ASYNC_DISCARD_MIN_FILTER)) {
                 bytes = max_discard_size;
                 extent_bytes = max_discard_size;
                 entry->offset += max_discard_size;
                 entry->bytes -= max_discard_size;
                 link_free_space(ctl, entry);
             } else {
                 kmem_cache_free(btrfs_free_space_cachep, entry);
             }
         } else {
             start = max(start, extent_start);
             bytes = min(extent_start + extent_bytes, end) - start;
             if (bytes < minlen) {
                 spin_unlock(&ctl->tree_lock);
                 mutex_unlock(&ctl->cache_writeout_mutex);
                 goto next;
             }
 
             unlink_free_space(ctl, entry, true);
             kmem_cache_free(btrfs_free_space_cachep, entry);
         }
 
         spin_unlock(&ctl->tree_lock);
         trim_entry.start = extent_start;
         trim_entry.bytes = extent_bytes;
         list_add_tail(&trim_entry.list, &ctl->trimming_ranges);
         mutex_unlock(&ctl->cache_writeout_mutex);
 
         ret = do_trimming(block_group, total_trimmed, start, bytes,
                   extent_start, extent_bytes, extent_trim_state,
                   &trim_entry);
         if (ret) {
             block_group->discard_cursor = start + bytes;
             break;
         }
 next:
         start += bytes;
         block_group->discard_cursor = start;
         if (async && *total_trimmed)
             break;
 
         if (fatal_signal_pending(current)) {
             ret = -ERESTARTSYS;
             break;
         }
 
         cond_resched();
     }
 
     return ret;
 
 out_unlock:
     block_group->discard_cursor = btrfs_block_group_end(block_group);
     spin_unlock(&ctl->tree_lock);
     mutex_unlock(&ctl->cache_writeout_mutex);
 
     return ret;
 }
 
 /*
  * If we break out of trimming a bitmap prematurely, we should reset the
  * trimming bit.  In a rather contrieved case, it's possible to race here so
  * reset the state to BTRFS_TRIM_STATE_UNTRIMMED.
  *
  * start = start of bitmap
  * end = near end of bitmap
  *
  * Thread 1:            Thread 2:
  * trim_bitmaps(start)
  *              trim_bitmaps(end)
  *              end_trimming_bitmap()
  * reset_trimming_bitmap()
  */
 static void reset_trimming_bitmap(struct btrfs_free_space_ctl *ctl, u64 offset)
 {
     struct btrfs_free_space *entry;
 
     spin_lock(&ctl->tree_lock);
     entry = tree_search_offset(ctl, offset, 1, 0);
     if (entry) {
         if (btrfs_free_space_trimmed(entry)) {
             ctl->discardable_extents[BTRFS_STAT_CURR] +=
                 entry->bitmap_extents;
             ctl->discardable_bytes[BTRFS_STAT_CURR] += entry->bytes;
         }
         entry->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
     }
 
     spin_unlock(&ctl->tree_lock);
 }
 
 static void end_trimming_bitmap(struct btrfs_free_space_ctl *ctl,
                 struct btrfs_free_space *entry)
 {
     if (btrfs_free_space_trimming_bitmap(entry)) {
         entry->trim_state = BTRFS_TRIM_STATE_TRIMMED;
         ctl->discardable_extents[BTRFS_STAT_CURR] -=
             entry->bitmap_extents;
         ctl->discardable_bytes[BTRFS_STAT_CURR] -= entry->bytes;
     }
 }
 
 /*
  * If @async is set, then we will trim 1 region and return.
  */
 static int trim_bitmaps(struct btrfs_block_group *block_group,
             u64 *total_trimmed, u64 start, u64 end, u64 minlen,
             u64 maxlen, bool async)
 {
     struct btrfs_discard_ctl *discard_ctl =
                     &block_group->fs_info->discard_ctl;
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     struct btrfs_free_space *entry;
     int ret = 0;
     int ret2;
     u64 bytes;
     u64 offset = offset_to_bitmap(ctl, start);
     const u64 max_discard_size = READ_ONCE(discard_ctl->max_discard_size);
 
     while (offset < end) {
         bool next_bitmap = false;
         struct btrfs_trim_range trim_entry;
 
         mutex_lock(&ctl->cache_writeout_mutex);
         spin_lock(&ctl->tree_lock);
 
         if (ctl->free_space < minlen) {
             block_group->discard_cursor =
                 btrfs_block_group_end(block_group);
             spin_unlock(&ctl->tree_lock);
             mutex_unlock(&ctl->cache_writeout_mutex);
             break;
         }
 
         entry = tree_search_offset(ctl, offset, 1, 0);
         /*
          * Bitmaps are marked trimmed lossily now to prevent constant
          * discarding of the same bitmap (the reason why we are bound
          * by the filters).  So, retrim the block group bitmaps when we
          * are preparing to punt to the unused_bgs list.  This uses
          * @minlen to determine if we are in BTRFS_DISCARD_INDEX_UNUSED
          * which is the only discard index which sets minlen to 0.
          */
         if (!entry || (async && minlen && start == offset &&
                    btrfs_free_space_trimmed(entry))) {
             spin_unlock(&ctl->tree_lock);
             mutex_unlock(&ctl->cache_writeout_mutex);
             next_bitmap = true;
             goto next;
         }
 
         /*
          * Async discard bitmap trimming begins at by setting the start
          * to be key.objectid and the offset_to_bitmap() aligns to the
          * start of the bitmap.  This lets us know we are fully
          * scanning the bitmap rather than only some portion of it.
          */
         if (start == offset)
             entry->trim_state = BTRFS_TRIM_STATE_TRIMMING;
 
         bytes = minlen;
         ret2 = search_bitmap(ctl, entry, &start, &bytes, false);
         if (ret2 || start >= end) {
             /*
              * We lossily consider a bitmap trimmed if we only skip
              * over regions <= BTRFS_ASYNC_DISCARD_MIN_FILTER.
              */
             if (ret2 && minlen <= BTRFS_ASYNC_DISCARD_MIN_FILTER)
                 end_trimming_bitmap(ctl, entry);
             else
                 entry->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
             spin_unlock(&ctl->tree_lock);
             mutex_unlock(&ctl->cache_writeout_mutex);
             next_bitmap = true;
             goto next;
         }
 
         /*
          * We already trimmed a region, but are using the locking above
          * to reset the trim_state.
          */
         if (async && *total_trimmed) {
             spin_unlock(&ctl->tree_lock);
             mutex_unlock(&ctl->cache_writeout_mutex);
             goto out;
         }
 
         bytes = min(bytes, end - start);
         if (bytes < minlen || (async && maxlen && bytes > maxlen)) {
             spin_unlock(&ctl->tree_lock);
             mutex_unlock(&ctl->cache_writeout_mutex);
             goto next;
         }
 
         /*
          * Let bytes = BTRFS_MAX_DISCARD_SIZE + X.
          * If X < @minlen, we won't trim X when we come back around.
          * So trim it now.  We differ here from trimming extents as we
          * don't keep individual state per bit.
          */
         if (async &&
             max_discard_size &&
             bytes > (max_discard_size + minlen))
             bytes = max_discard_size;
 
         bitmap_clear_bits(ctl, entry, start, bytes, true);
         if (entry->bytes == 0)
             free_bitmap(ctl, entry);
 
         spin_unlock(&ctl->tree_lock);
         trim_entry.start = start;
         trim_entry.bytes = bytes;
         list_add_tail(&trim_entry.list, &ctl->trimming_ranges);
         mutex_unlock(&ctl->cache_writeout_mutex);
 
         ret = do_trimming(block_group, total_trimmed, start, bytes,
                   start, bytes, 0, &trim_entry);
         if (ret) {
             reset_trimming_bitmap(ctl, offset);
             block_group->discard_cursor =
                 btrfs_block_group_end(block_group);
             break;
         }
 next:
         if (next_bitmap) {
             offset += BITS_PER_BITMAP * ctl->unit;
             start = offset;
         } else {
             start += bytes;
         }
         block_group->discard_cursor = start;
 
         if (fatal_signal_pending(current)) {
             if (start != offset)
                 reset_trimming_bitmap(ctl, offset);
             ret = -ERESTARTSYS;
             break;
         }
 
         cond_resched();
     }
 
     if (offset >= end)
         block_group->discard_cursor = end;
 
 out:
     return ret;
 }
 
 int btrfs_trim_block_group(struct btrfs_block_group *block_group,
                u64 *trimmed, u64 start, u64 end, u64 minlen)
 {
     struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
     int ret;
     u64 rem = 0;
 
     ASSERT(!btrfs_is_zoned(block_group->fs_info));
 
     *trimmed = 0;
 
     spin_lock(&block_group->lock);
     if (block_group->removed) {
         spin_unlock(&block_group->lock);
         return 0;
     }
     btrfs_freeze_block_group(block_group);
     spin_unlock(&block_group->lock);
 
     ret = trim_no_bitmap(block_group, trimmed, start, end, minlen, false);
     if (ret)
         goto out;
 
     ret = trim_bitmaps(block_group, trimmed, start, end, minlen, 0, false);
     div64_u64_rem(end, BITS_PER_BITMAP * ctl->unit, &rem);
     /* If we ended in the middle of a bitmap, reset the trimming flag */
     if (rem)
         reset_trimming_bitmap(ctl, offset_to_bitmap(ctl, end));
 out:
     btrfs_unfreeze_block_group(block_group);
     return ret;
 }
 
 int btrfs_trim_block_group_extents(struct btrfs_block_group *block_group,
                    u64 *trimmed, u64 start, u64 end, u64 minlen,
                    bool async)
 {
     int ret;
 
     *trimmed = 0;
 
     spin_lock(&block_group->lock);
     if (block_group->removed) {
         spin_unlock(&block_group->lock);
         return 0;
     }
     btrfs_freeze_block_group(block_group);
     spin_unlock(&block_group->lock);
 
     ret = trim_no_bitmap(block_group, trimmed, start, end, minlen, async);
     btrfs_unfreeze_block_group(block_group);
 
     return ret;
 }
 
 int btrfs_trim_block_group_bitmaps(struct btrfs_block_group *block_group,
                    u64 *trimmed, u64 start, u64 end, u64 minlen,
                    u64 maxlen, bool async)
 {
     int ret;
 
     *trimmed = 0;
 
     spin_lock(&block_group->lock);
     if (block_group->removed) {
         spin_unlock(&block_group->lock);
         return 0;
     }
     btrfs_freeze_block_group(block_group);
     spin_unlock(&block_group->lock);
 
     ret = trim_bitmaps(block_group, trimmed, start, end, minlen, maxlen,
                async);
 
     btrfs_unfreeze_block_group(block_group);
 
     return ret;
 }
 
 bool btrfs_free_space_cache_v1_active(struct btrfs_fs_info *fs_info)
 {
     return btrfs_super_cache_generation(fs_info->super_copy);
 }
 
 static int cleanup_free_space_cache_v1(struct btrfs_fs_info *fs_info,
                        struct btrfs_trans_handle *trans)
 {
     struct btrfs_block_group *block_group;
     struct rb_node *node;
     int ret = 0;
 
     btrfs_info(fs_info, "cleaning free space cache v1");
 
     node = rb_first_cached(&fs_info->block_group_cache_tree);
     while (node) {
         block_group = rb_entry(node, struct btrfs_block_group, cache_node);
         ret = btrfs_remove_free_space_inode(trans, NULL, block_group);
         if (ret)
             goto out;
         node = rb_next(node);
     }
 out:
     return ret;
 }
 
 int btrfs_set_free_space_cache_v1_active(struct btrfs_fs_info *fs_info, bool active)
 {
     struct btrfs_trans_handle *trans;
     int ret;
 
     /*
      * update_super_roots will appropriately set or unset
      * super_copy->cache_generation based on SPACE_CACHE and
      * BTRFS_FS_CLEANUP_SPACE_CACHE_V1. For this reason, we need a
      * transaction commit whether we are enabling space cache v1 and don't
      * have any other work to do, or are disabling it and removing free
      * space inodes.
      */
     trans = btrfs_start_transaction(fs_info->tree_root, 0);
     if (IS_ERR(trans))
         return PTR_ERR(trans);
 
     if (!active) {
         set_bit(BTRFS_FS_CLEANUP_SPACE_CACHE_V1, &fs_info->flags);
         ret = cleanup_free_space_cache_v1(fs_info, trans);
         if (ret) {
             btrfs_abort_transaction(trans, ret);
             btrfs_end_transaction(trans);
             goto out;
         }
     }
 
     ret = btrfs_commit_transaction(trans);
 out:
     clear_bit(BTRFS_FS_CLEANUP_SPACE_CACHE_V1, &fs_info->flags);
 
     return ret;
 }
 
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 /*
  * Use this if you need to make a bitmap or extent entry specifically, it
  * doesn't do any of the merging that add_free_space does, this acts a lot like
  * how the free space cache loading stuff works, so you can get really weird
  * configurations.
  */
 int test_add_free_space_entry(struct btrfs_block_group *cache,
                   u64 offset, u64 bytes, bool bitmap)
 {
     struct btrfs_free_space_ctl *ctl = cache->free_space_ctl;
     struct btrfs_free_space *info = NULL, *bitmap_info;
     void *map = NULL;
     enum btrfs_trim_state trim_state = BTRFS_TRIM_STATE_TRIMMED;
     u64 bytes_added;
     int ret;
 
 again:
     if (!info) {
         info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
         if (!info)
             return -ENOMEM;
     }
 
     if (!bitmap) {
         spin_lock(&ctl->tree_lock);
         info->offset = offset;
         info->bytes = bytes;
         info->max_extent_size = 0;
         ret = link_free_space(ctl, info);
         spin_unlock(&ctl->tree_lock);
         if (ret)
             kmem_cache_free(btrfs_free_space_cachep, info);
         return ret;
     }
 
     if (!map) {
         map = kmem_cache_zalloc(btrfs_free_space_bitmap_cachep, GFP_NOFS);
         if (!map) {
             kmem_cache_free(btrfs_free_space_cachep, info);
             return -ENOMEM;
         }
     }
 
     spin_lock(&ctl->tree_lock);
     bitmap_info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                      1, 0);
     if (!bitmap_info) {
         info->bitmap = map;
         map = NULL;
         add_new_bitmap(ctl, info, offset);
         bitmap_info = info;
         info = NULL;
     }
 
     bytes_added = add_bytes_to_bitmap(ctl, bitmap_info, offset, bytes,
                       trim_state);
 
     bytes -= bytes_added;
     offset += bytes_added;
     spin_unlock(&ctl->tree_lock);
 
     if (bytes)
         goto again;
 
     if (info)
         kmem_cache_free(btrfs_free_space_cachep, info);
     if (map)
         kmem_cache_free(btrfs_free_space_bitmap_cachep, map);
     return 0;
 }
 
 /*
  * Checks to see if the given range is in the free space cache.  This is really
  * just used to check the absence of space, so if there is free space in the
  * range at all we will return 1.
  */
 int test_check_exists(struct btrfs_block_group *cache,
               u64 offset, u64 bytes)
 {
     struct btrfs_free_space_ctl *ctl = cache->free_space_ctl;
     struct btrfs_free_space *info;
     int ret = 0;
 
     spin_lock(&ctl->tree_lock);
     info = tree_search_offset(ctl, offset, 0, 0);
     if (!info) {
         info = tree_search_offset(ctl, offset_to_bitmap(ctl, offset),
                       1, 0);
         if (!info)
             goto out;
     }
 
 have_info:
     if (info->bitmap) {
         u64 bit_off, bit_bytes;
         struct rb_node *n;
         struct btrfs_free_space *tmp;
 
         bit_off = offset;
         bit_bytes = ctl->unit;
         ret = search_bitmap(ctl, info, &bit_off, &bit_bytes, false);
         if (!ret) {
             if (bit_off == offset) {
                 ret = 1;
                 goto out;
             } else if (bit_off > offset &&
                    offset + bytes > bit_off) {
                 ret = 1;
                 goto out;
             }
         }
 
         n = rb_prev(&info->offset_index);
         while (n) {
             tmp = rb_entry(n, struct btrfs_free_space,
                        offset_index);
             if (tmp->offset + tmp->bytes < offset)
                 break;
             if (offset + bytes < tmp->offset) {
                 n = rb_prev(&tmp->offset_index);
                 continue;
             }
             info = tmp;
             goto have_info;
         }
 
         n = rb_next(&info->offset_index);
         while (n) {
             tmp = rb_entry(n, struct btrfs_free_space,
                        offset_index);
             if (offset + bytes < tmp->offset)
                 break;
             if (tmp->offset + tmp->bytes < offset) {
                 n = rb_next(&tmp->offset_index);
                 continue;
             }
             info = tmp;
             goto have_info;
         }
 
         ret = 0;
         goto out;
     }
 
     if (info->offset == offset) {
         ret = 1;
         goto out;
     }
 
     if (offset > info->offset && offset < info->offset + info->bytes)
         ret = 1;
 out:
     spin_unlock(&ctl->tree_lock);
     return ret;
 }
 #endif /* CONFIG_BTRFS_FS_RUN_SANITY_TESTS */