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	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
 /*
  *  linux/mm/swap_state.c
  *
  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *  Swap reorganised 29.12.95, Stephen Tweedie
  *
  *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
  */
 #include <linux/mm.h>
 #include <linux/gfp.h>
 #include <linux/kernel_stat.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
 #include <linux/init.h>
 #include <linux/pagemap.h>
 #include <linux/backing-dev.h>
 #include <linux/blkdev.h>
 #include <linux/pagevec.h>
 #include <linux/migrate.h>
 #include <linux/vmalloc.h>
 #include <linux/swap_slots.h>
 #include <linux/huge_mm.h>
 #include <linux/shmem_fs.h>
 #include "internal.h"
 #include "swap.h"
 
 /*
  * swapper_space is a fiction, retained to simplify the path through
  * vmscan's shrink_page_list.
  */
 static const struct address_space_operations swap_aops = {
     .writepage  = swap_writepage,
     .dirty_folio    = noop_dirty_folio,
 #ifdef CONFIG_MIGRATION
     .migrate_folio  = migrate_folio,
 #endif
 };
 
 struct address_space *swapper_spaces[MAX_SWAPFILES] __read_mostly;
 static unsigned int nr_swapper_spaces[MAX_SWAPFILES] __read_mostly;
 static bool enable_vma_readahead __read_mostly = true;
 
 #define SWAP_RA_WIN_SHIFT   (PAGE_SHIFT / 2)
 #define SWAP_RA_HITS_MASK   ((1UL << SWAP_RA_WIN_SHIFT) - 1)
 #define SWAP_RA_HITS_MAX    SWAP_RA_HITS_MASK
 #define SWAP_RA_WIN_MASK    (~PAGE_MASK & ~SWAP_RA_HITS_MASK)
 
 #define SWAP_RA_HITS(v)     ((v) & SWAP_RA_HITS_MASK)
 #define SWAP_RA_WIN(v)      (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
 #define SWAP_RA_ADDR(v)     ((v) & PAGE_MASK)
 
 #define SWAP_RA_VAL(addr, win, hits)                \
     (((addr) & PAGE_MASK) |                 \
      (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |    \
      ((hits) & SWAP_RA_HITS_MASK))
 
 /* Initial readahead hits is 4 to start up with a small window */
 #define GET_SWAP_RA_VAL(vma)                    \
     (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)
 
 static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);
 
 void show_swap_cache_info(void)
 {
     printk("%lu pages in swap cache\n", total_swapcache_pages());
     printk("Free swap  = %ldkB\n",
         get_nr_swap_pages() << (PAGE_SHIFT - 10));
     printk("Total swap = %lukB\n", total_swap_pages << (PAGE_SHIFT - 10));
 }
 
 void *get_shadow_from_swap_cache(swp_entry_t entry)
 {
     struct address_space *address_space = swap_address_space(entry);
     pgoff_t idx = swp_offset(entry);
     struct page *page;
 
     page = xa_load(&address_space->i_pages, idx);
     if (xa_is_value(page))
         return page;
     return NULL;
 }
 
 /*
  * add_to_swap_cache resembles filemap_add_folio on swapper_space,
  * but sets SwapCache flag and private instead of mapping and index.
  */
 int add_to_swap_cache(struct page *page, swp_entry_t entry,
             gfp_t gfp, void **shadowp)
 {
     struct address_space *address_space = swap_address_space(entry);
     pgoff_t idx = swp_offset(entry);
     XA_STATE_ORDER(xas, &address_space->i_pages, idx, compound_order(page));
     unsigned long i, nr = thp_nr_pages(page);
     void *old;
 
     VM_BUG_ON_PAGE(!PageLocked(page), page);
     VM_BUG_ON_PAGE(PageSwapCache(page), page);
     VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
 
     page_ref_add(page, nr);
     SetPageSwapCache(page);
 
     do {
         xas_lock_irq(&xas);
         xas_create_range(&xas);
         if (xas_error(&xas))
             goto unlock;
         for (i = 0; i < nr; i++) {
             VM_BUG_ON_PAGE(xas.xa_index != idx + i, page);
             old = xas_load(&xas);
             if (xa_is_value(old)) {
                 if (shadowp)
                     *shadowp = old;
             }
             set_page_private(page + i, entry.val + i);
             xas_store(&xas, page);
             xas_next(&xas);
         }
         address_space->nrpages += nr;
         __mod_node_page_state(page_pgdat(page), NR_FILE_PAGES, nr);
         __mod_lruvec_page_state(page, NR_SWAPCACHE, nr);
 unlock:
         xas_unlock_irq(&xas);
     } while (xas_nomem(&xas, gfp));
 
     if (!xas_error(&xas))
         return 0;
 
     ClearPageSwapCache(page);
     page_ref_sub(page, nr);
     return xas_error(&xas);
 }
 
 /*
  * This must be called only on folios that have
  * been verified to be in the swap cache.
  */
 void __delete_from_swap_cache(struct folio *folio,
             swp_entry_t entry, void *shadow)
 {
     struct address_space *address_space = swap_address_space(entry);
     int i;
     long nr = folio_nr_pages(folio);
     pgoff_t idx = swp_offset(entry);
     XA_STATE(xas, &address_space->i_pages, idx);
 
     VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
     VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
     VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
 
     for (i = 0; i < nr; i++) {
         void *entry = xas_store(&xas, shadow);
         VM_BUG_ON_PAGE(entry != folio, entry);
         set_page_private(folio_page(folio, i), 0);
         xas_next(&xas);
     }
     folio_clear_swapcache(folio);
     address_space->nrpages -= nr;
     __node_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
     __lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr);
 }
 
 /**
  * add_to_swap - allocate swap space for a folio
  * @folio: folio we want to move to swap
  *
  * Allocate swap space for the folio and add the folio to the
  * swap cache.
  *
  * Context: Caller needs to hold the folio lock.
  * Return: Whether the folio was added to the swap cache.
  */
 bool add_to_swap(struct folio *folio)
 {
     swp_entry_t entry;
     int err;
 
     VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
     VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
 
     entry = folio_alloc_swap(folio);
     if (!entry.val)
         return false;
 
     /*
      * XArray node allocations from PF_MEMALLOC contexts could
      * completely exhaust the page allocator. __GFP_NOMEMALLOC
      * stops emergency reserves from being allocated.
      *
      * TODO: this could cause a theoretical memory reclaim
      * deadlock in the swap out path.
      */
     /*
      * Add it to the swap cache.
      */
     err = add_to_swap_cache(&folio->page, entry,
             __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN, NULL);
     if (err)
         /*
          * add_to_swap_cache() doesn't return -EEXIST, so we can safely
          * clear SWAP_HAS_CACHE flag.
          */
         goto fail;
     /*
      * Normally the folio will be dirtied in unmap because its
      * pte should be dirty. A special case is MADV_FREE page. The
      * page's pte could have dirty bit cleared but the folio's
      * SwapBacked flag is still set because clearing the dirty bit
      * and SwapBacked flag has no lock protected. For such folio,
      * unmap will not set dirty bit for it, so folio reclaim will
      * not write the folio out. This can cause data corruption when
      * the folio is swapped in later. Always setting the dirty flag
      * for the folio solves the problem.
      */
     folio_mark_dirty(folio);
 
     return true;
 
 fail:
     put_swap_page(&folio->page, entry);
     return false;
 }
 
 /*
  * This must be called only on folios that have
  * been verified to be in the swap cache and locked.
  * It will never put the folio into the free list,
  * the caller has a reference on the folio.
  */
 void delete_from_swap_cache(struct folio *folio)
 {
     swp_entry_t entry = folio_swap_entry(folio);
     struct address_space *address_space = swap_address_space(entry);
 
     xa_lock_irq(&address_space->i_pages);
     __delete_from_swap_cache(folio, entry, NULL);
     xa_unlock_irq(&address_space->i_pages);
 
     put_swap_page(&folio->page, entry);
     folio_ref_sub(folio, folio_nr_pages(folio));
 }
 
 void clear_shadow_from_swap_cache(int type, unsigned long begin,
                 unsigned long end)
 {
     unsigned long curr = begin;
     void *old;
 
     for (;;) {
         swp_entry_t entry = swp_entry(type, curr);
         struct address_space *address_space = swap_address_space(entry);
         XA_STATE(xas, &address_space->i_pages, curr);
 
         xa_lock_irq(&address_space->i_pages);
         xas_for_each(&xas, old, end) {
             if (!xa_is_value(old))
                 continue;
             xas_store(&xas, NULL);
         }
         xa_unlock_irq(&address_space->i_pages);
 
         /* search the next swapcache until we meet end */
         curr >>= SWAP_ADDRESS_SPACE_SHIFT;
         curr++;
         curr <<= SWAP_ADDRESS_SPACE_SHIFT;
         if (curr > end)
             break;
     }
 }
 
 /* 
  * If we are the only user, then try to free up the swap cache. 
  * 
  * Its ok to check for PageSwapCache without the page lock
  * here because we are going to recheck again inside
  * try_to_free_swap() _with_ the lock.
  *                  - Marcelo
  */
 void free_swap_cache(struct page *page)
 {
     if (PageSwapCache(page) && !page_mapped(page) && trylock_page(page)) {
         try_to_free_swap(page);
         unlock_page(page);
     }
 }
 
 /* 
  * Perform a free_page(), also freeing any swap cache associated with
  * this page if it is the last user of the page.
  */
 void free_page_and_swap_cache(struct page *page)
 {
     free_swap_cache(page);
     if (!is_huge_zero_page(page))
         put_page(page);
 }
 
 /*
  * Passed an array of pages, drop them all from swapcache and then release
  * them.  They are removed from the LRU and freed if this is their last use.
  */
 void free_pages_and_swap_cache(struct page **pages, int nr)
 {
     struct page **pagep = pages;
     int i;
 
     lru_add_drain();
     for (i = 0; i < nr; i++)
         free_swap_cache(pagep[i]);
     release_pages(pagep, nr);
 }
 
 static inline bool swap_use_vma_readahead(void)
 {
     return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
 }
 
 /*
  * Lookup a swap entry in the swap cache. A found page will be returned
  * unlocked and with its refcount incremented - we rely on the kernel
  * lock getting page table operations atomic even if we drop the page
  * lock before returning.
  */
 struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
                    unsigned long addr)
 {
     struct page *page;
     struct swap_info_struct *si;
 
     si = get_swap_device(entry);
     if (!si)
         return NULL;
     page = find_get_page(swap_address_space(entry), swp_offset(entry));
     put_swap_device(si);
 
     if (page) {
         bool vma_ra = swap_use_vma_readahead();
         bool readahead;
 
         /*
          * At the moment, we don't support PG_readahead for anon THP
          * so let's bail out rather than confusing the readahead stat.
          */
         if (unlikely(PageTransCompound(page)))
             return page;
 
         readahead = TestClearPageReadahead(page);
         if (vma && vma_ra) {
             unsigned long ra_val;
             int win, hits;
 
             ra_val = GET_SWAP_RA_VAL(vma);
             win = SWAP_RA_WIN(ra_val);
             hits = SWAP_RA_HITS(ra_val);
             if (readahead)
                 hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
             atomic_long_set(&vma->swap_readahead_info,
                     SWAP_RA_VAL(addr, win, hits));
         }
 
         if (readahead) {
             count_vm_event(SWAP_RA_HIT);
             if (!vma || !vma_ra)
                 atomic_inc(&swapin_readahead_hits);
         }
     }
 
     return page;
 }
 
 /**
  * find_get_incore_page - Find and get a page from the page or swap caches.
  * @mapping: The address_space to search.
  * @index: The page cache index.
  *
  * This differs from find_get_page() in that it will also look for the
  * page in the swap cache.
  *
  * Return: The found page or %NULL.
  */
 struct page *find_get_incore_page(struct address_space *mapping, pgoff_t index)
 {
     swp_entry_t swp;
     struct swap_info_struct *si;
     struct page *page = pagecache_get_page(mapping, index,
                         FGP_ENTRY | FGP_HEAD, 0);
 
     if (!page)
         return page;
     if (!xa_is_value(page))
         return find_subpage(page, index);
     if (!shmem_mapping(mapping))
         return NULL;
 
     swp = radix_to_swp_entry(page);
     /* There might be swapin error entries in shmem mapping. */
     if (non_swap_entry(swp))
         return NULL;
     /* Prevent swapoff from happening to us */
     si = get_swap_device(swp);
     if (!si)
         return NULL;
     page = find_get_page(swap_address_space(swp), swp_offset(swp));
     put_swap_device(si);
     return page;
 }
 
 struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
             struct vm_area_struct *vma, unsigned long addr,
             bool *new_page_allocated)
 {
     struct swap_info_struct *si;
     struct page *page;
     void *shadow = NULL;
 
     *new_page_allocated = false;
 
     for (;;) {
         int err;
         /*
          * First check the swap cache.  Since this is normally
          * called after lookup_swap_cache() failed, re-calling
          * that would confuse statistics.
          */
         si = get_swap_device(entry);
         if (!si)
             return NULL;
         page = find_get_page(swap_address_space(entry),
                      swp_offset(entry));
         put_swap_device(si);
         if (page)
             return page;
 
         /*
          * Just skip read ahead for unused swap slot.
          * During swap_off when swap_slot_cache is disabled,
          * we have to handle the race between putting
          * swap entry in swap cache and marking swap slot
          * as SWAP_HAS_CACHE.  That's done in later part of code or
          * else swap_off will be aborted if we return NULL.
          */
         if (!__swp_swapcount(entry) && swap_slot_cache_enabled)
             return NULL;
 
         /*
          * Get a new page to read into from swap.  Allocate it now,
          * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
          * cause any racers to loop around until we add it to cache.
          */
         page = alloc_page_vma(gfp_mask, vma, addr);
         if (!page)
             return NULL;
 
         /*
          * Swap entry may have been freed since our caller observed it.
          */
         err = swapcache_prepare(entry);
         if (!err)
             break;
 
         put_page(page);
         if (err != -EEXIST)
             return NULL;
 
         /*
          * We might race against __delete_from_swap_cache(), and
          * stumble across a swap_map entry whose SWAP_HAS_CACHE
          * has not yet been cleared.  Or race against another
          * __read_swap_cache_async(), which has set SWAP_HAS_CACHE
          * in swap_map, but not yet added its page to swap cache.
          */
         schedule_timeout_uninterruptible(1);
     }
 
     /*
      * The swap entry is ours to swap in. Prepare the new page.
      */
 
     __SetPageLocked(page);
     __SetPageSwapBacked(page);
 
     if (mem_cgroup_swapin_charge_page(page, NULL, gfp_mask, entry))
         goto fail_unlock;
 
     /* May fail (-ENOMEM) if XArray node allocation failed. */
     if (add_to_swap_cache(page, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
         goto fail_unlock;
 
     mem_cgroup_swapin_uncharge_swap(entry);
 
     if (shadow)
         workingset_refault(page_folio(page), shadow);
 
     /* Caller will initiate read into locked page */
     lru_cache_add(page);
     *new_page_allocated = true;
     return page;
 
 fail_unlock:
     put_swap_page(page, entry);
     unlock_page(page);
     put_page(page);
     return NULL;
 }
 
 /*
  * Locate a page of swap in physical memory, reserving swap cache space
  * and reading the disk if it is not already cached.
  * A failure return means that either the page allocation failed or that
  * the swap entry is no longer in use.
  */
 struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                    struct vm_area_struct *vma,
                    unsigned long addr, bool do_poll,
                    struct swap_iocb **plug)
 {
     bool page_was_allocated;
     struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
             vma, addr, &page_was_allocated);
 
     if (page_was_allocated)
         swap_readpage(retpage, do_poll, plug);
 
     return retpage;
 }
 
 static unsigned int __swapin_nr_pages(unsigned long prev_offset,
                       unsigned long offset,
                       int hits,
                       int max_pages,
                       int prev_win)
 {
     unsigned int pages, last_ra;
 
     /*
      * This heuristic has been found to work well on both sequential and
      * random loads, swapping to hard disk or to SSD: please don't ask
      * what the "+ 2" means, it just happens to work well, that's all.
      */
     pages = hits + 2;
     if (pages == 2) {
         /*
          * We can have no readahead hits to judge by: but must not get
          * stuck here forever, so check for an adjacent offset instead
          * (and don't even bother to check whether swap type is same).
          */
         if (offset != prev_offset + 1 && offset != prev_offset - 1)
             pages = 1;
     } else {
         unsigned int roundup = 4;
         while (roundup < pages)
             roundup <<= 1;
         pages = roundup;
     }
 
     if (pages > max_pages)
         pages = max_pages;
 
     /* Don't shrink readahead too fast */
     last_ra = prev_win / 2;
     if (pages < last_ra)
         pages = last_ra;
 
     return pages;
 }
 
 static unsigned long swapin_nr_pages(unsigned long offset)
 {
     static unsigned long prev_offset;
     unsigned int hits, pages, max_pages;
     static atomic_t last_readahead_pages;
 
     max_pages = 1 << READ_ONCE(page_cluster);
     if (max_pages <= 1)
         return 1;
 
     hits = atomic_xchg(&swapin_readahead_hits, 0);
     pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
                   max_pages,
                   atomic_read(&last_readahead_pages));
     if (!hits)
         WRITE_ONCE(prev_offset, offset);
     atomic_set(&last_readahead_pages, pages);
 
     return pages;
 }
 
 /**
  * swap_cluster_readahead - swap in pages in hope we need them soon
  * @entry: swap entry of this memory
  * @gfp_mask: memory allocation flags
  * @vmf: fault information
  *
  * Returns the struct page for entry and addr, after queueing swapin.
  *
  * Primitive swap readahead code. We simply read an aligned block of
  * (1 << page_cluster) entries in the swap area. This method is chosen
  * because it doesn't cost us any seek time.  We also make sure to queue
  * the 'original' request together with the readahead ones...
  *
  * This has been extended to use the NUMA policies from the mm triggering
  * the readahead.
  *
  * Caller must hold read mmap_lock if vmf->vma is not NULL.
  */
 struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
                 struct vm_fault *vmf)
 {
     struct page *page;
     unsigned long entry_offset = swp_offset(entry);
     unsigned long offset = entry_offset;
     unsigned long start_offset, end_offset;
     unsigned long mask;
     struct swap_info_struct *si = swp_swap_info(entry);
     struct blk_plug plug;
     struct swap_iocb *splug = NULL;
     bool do_poll = true, page_allocated;
     struct vm_area_struct *vma = vmf->vma;
     unsigned long addr = vmf->address;
 
     mask = swapin_nr_pages(offset) - 1;
     if (!mask)
         goto skip;
 
     do_poll = false;
     /* Read a page_cluster sized and aligned cluster around offset. */
     start_offset = offset & ~mask;
     end_offset = offset | mask;
     if (!start_offset)  /* First page is swap header. */
         start_offset++;
     if (end_offset >= si->max)
         end_offset = si->max - 1;
 
     blk_start_plug(&plug);
     for (offset = start_offset; offset <= end_offset ; offset++) {
         /* Ok, do the async read-ahead now */
         page = __read_swap_cache_async(
             swp_entry(swp_type(entry), offset),
             gfp_mask, vma, addr, &page_allocated);
         if (!page)
             continue;
         if (page_allocated) {
             swap_readpage(page, false, &splug);
             if (offset != entry_offset) {
                 SetPageReadahead(page);
                 count_vm_event(SWAP_RA);
             }
         }
         put_page(page);
     }
     blk_finish_plug(&plug);
     swap_read_unplug(splug);
 
     lru_add_drain();    /* Push any new pages onto the LRU now */
 skip:
     /* The page was likely read above, so no need for plugging here */
     return read_swap_cache_async(entry, gfp_mask, vma, addr, do_poll, NULL);
 }
 
 int init_swap_address_space(unsigned int type, unsigned long nr_pages)
 {
     struct address_space *spaces, *space;
     unsigned int i, nr;
 
     nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
     spaces = kvcalloc(nr, sizeof(struct address_space), GFP_KERNEL);
     if (!spaces)
         return -ENOMEM;
     for (i = 0; i < nr; i++) {
         space = spaces + i;
         xa_init_flags(&space->i_pages, XA_FLAGS_LOCK_IRQ);
         atomic_set(&space->i_mmap_writable, 0);
         space->a_ops = &swap_aops;
         /* swap cache doesn't use writeback related tags */
         mapping_set_no_writeback_tags(space);
     }
     nr_swapper_spaces[type] = nr;
     swapper_spaces[type] = spaces;
 
     return 0;
 }
 
 void exit_swap_address_space(unsigned int type)
 {
     int i;
     struct address_space *spaces = swapper_spaces[type];
 
     for (i = 0; i < nr_swapper_spaces[type]; i++)
         VM_WARN_ON_ONCE(!mapping_empty(&spaces[i]));
     kvfree(spaces);
     nr_swapper_spaces[type] = 0;
     swapper_spaces[type] = NULL;
 }
 
 static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
                      unsigned long faddr,
                      unsigned long lpfn,
                      unsigned long rpfn,
                      unsigned long *start,
                      unsigned long *end)
 {
     *start = max3(lpfn, PFN_DOWN(vma->vm_start),
               PFN_DOWN(faddr & PMD_MASK));
     *end = min3(rpfn, PFN_DOWN(vma->vm_end),
             PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
 }
 
 static void swap_ra_info(struct vm_fault *vmf,
             struct vma_swap_readahead *ra_info)
 {
     struct vm_area_struct *vma = vmf->vma;
     unsigned long ra_val;
     unsigned long faddr, pfn, fpfn;
     unsigned long start, end;
     pte_t *pte, *orig_pte;
     unsigned int max_win, hits, prev_win, win, left;
 #ifndef CONFIG_64BIT
     pte_t *tpte;
 #endif
 
     max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
                  SWAP_RA_ORDER_CEILING);
     if (max_win == 1) {
         ra_info->win = 1;
         return;
     }
 
     faddr = vmf->address;
     orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
 
     fpfn = PFN_DOWN(faddr);
     ra_val = GET_SWAP_RA_VAL(vma);
     pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
     prev_win = SWAP_RA_WIN(ra_val);
     hits = SWAP_RA_HITS(ra_val);
     ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
                            max_win, prev_win);
     atomic_long_set(&vma->swap_readahead_info,
             SWAP_RA_VAL(faddr, win, 0));
 
     if (win == 1) {
         pte_unmap(orig_pte);
         return;
     }
 
     /* Copy the PTEs because the page table may be unmapped */
     if (fpfn == pfn + 1)
         swap_ra_clamp_pfn(vma, faddr, fpfn, fpfn + win, &start, &end);
     else if (pfn == fpfn + 1)
         swap_ra_clamp_pfn(vma, faddr, fpfn - win + 1, fpfn + 1,
                   &start, &end);
     else {
         left = (win - 1) / 2;
         swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
                   &start, &end);
     }
     ra_info->nr_pte = end - start;
     ra_info->offset = fpfn - start;
     pte -= ra_info->offset;
 #ifdef CONFIG_64BIT
     ra_info->ptes = pte;
 #else
     tpte = ra_info->ptes;
     for (pfn = start; pfn != end; pfn++)
         *tpte++ = *pte++;
 #endif
     pte_unmap(orig_pte);
 }
 
 /**
  * swap_vma_readahead - swap in pages in hope we need them soon
  * @fentry: swap entry of this memory
  * @gfp_mask: memory allocation flags
  * @vmf: fault information
  *
  * Returns the struct page for entry and addr, after queueing swapin.
  *
  * Primitive swap readahead code. We simply read in a few pages whose
  * virtual addresses are around the fault address in the same vma.
  *
  * Caller must hold read mmap_lock if vmf->vma is not NULL.
  *
  */
 static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask,
                        struct vm_fault *vmf)
 {
     struct blk_plug plug;
     struct swap_iocb *splug = NULL;
     struct vm_area_struct *vma = vmf->vma;
     struct page *page;
     pte_t *pte, pentry;
     swp_entry_t entry;
     unsigned int i;
     bool page_allocated;
     struct vma_swap_readahead ra_info = {
         .win = 1,
     };
 
     swap_ra_info(vmf, &ra_info);
     if (ra_info.win == 1)
         goto skip;
 
     blk_start_plug(&plug);
     for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
          i++, pte++) {
         pentry = *pte;
         if (!is_swap_pte(pentry))
             continue;
         entry = pte_to_swp_entry(pentry);
         if (unlikely(non_swap_entry(entry)))
             continue;
         page = __read_swap_cache_async(entry, gfp_mask, vma,
                            vmf->address, &page_allocated);
         if (!page)
             continue;
         if (page_allocated) {
             swap_readpage(page, false, &splug);
             if (i != ra_info.offset) {
                 SetPageReadahead(page);
                 count_vm_event(SWAP_RA);
             }
         }
         put_page(page);
     }
     blk_finish_plug(&plug);
     swap_read_unplug(splug);
     lru_add_drain();
 skip:
     /* The page was likely read above, so no need for plugging here */
     return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
                      ra_info.win == 1, NULL);
 }
 
 /**
  * swapin_readahead - swap in pages in hope we need them soon
  * @entry: swap entry of this memory
  * @gfp_mask: memory allocation flags
  * @vmf: fault information
  *
  * Returns the struct page for entry and addr, after queueing swapin.
  *
  * It's a main entry function for swap readahead. By the configuration,
  * it will read ahead blocks by cluster-based(ie, physical disk based)
  * or vma-based(ie, virtual address based on faulty address) readahead.
  */
 struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
                 struct vm_fault *vmf)
 {
     return swap_use_vma_readahead() ?
             swap_vma_readahead(entry, gfp_mask, vmf) :
             swap_cluster_readahead(entry, gfp_mask, vmf);
 }
 
 #ifdef CONFIG_SYSFS
 static ssize_t vma_ra_enabled_show(struct kobject *kobj,
                      struct kobj_attribute *attr, char *buf)
 {
     return sysfs_emit(buf, "%s\n",
               enable_vma_readahead ? "true" : "false");
 }
 static ssize_t vma_ra_enabled_store(struct kobject *kobj,
                       struct kobj_attribute *attr,
                       const char *buf, size_t count)
 {
     ssize_t ret;
 
     ret = kstrtobool(buf, &enable_vma_readahead);
     if (ret)
         return ret;
 
     return count;
 }
 static struct kobj_attribute vma_ra_enabled_attr = __ATTR_RW(vma_ra_enabled);
 
 static struct attribute *swap_attrs[] = {
     &vma_ra_enabled_attr.attr,
     NULL,
 };
 
 static const struct attribute_group swap_attr_group = {
     .attrs = swap_attrs,
 };
 
 static int __init swap_init_sysfs(void)
 {
     int err;
     struct kobject *swap_kobj;
 
     swap_kobj = kobject_create_and_add("swap", mm_kobj);
     if (!swap_kobj) {
         pr_err("failed to create swap kobject\n");
         return -ENOMEM;
     }
     err = sysfs_create_group(swap_kobj, &swap_attr_group);
     if (err) {
         pr_err("failed to register swap group\n");
         goto delete_obj;
     }
     return 0;
 
 delete_obj:
     kobject_put(swap_kobj);
     return err;
 }
 subsys_initcall(swap_init_sysfs);
 #endif

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