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 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * zswap.c - zswap driver file
  *
  * zswap is a backend for frontswap that takes pages that are in the process
  * of being swapped out and attempts to compress and store them in a
  * RAM-based memory pool.  This can result in a significant I/O reduction on
  * the swap device and, in the case where decompressing from RAM is faster
  * than reading from the swap device, can also improve workload performance.
  *
  * Copyright (C) 2012  Seth Jennings <sjenning@linux.vnet.ibm.com>
 */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/module.h>
 #include <linux/cpu.h>
 #include <linux/highmem.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/types.h>
 #include <linux/atomic.h>
 #include <linux/frontswap.h>
 #include <linux/rbtree.h>
 #include <linux/swap.h>
 #include <linux/crypto.h>
 #include <linux/scatterlist.h>
 #include <linux/mempool.h>
 #include <linux/zpool.h>
 #include <crypto/acompress.h>
 
 #include <linux/mm_types.h>
 #include <linux/page-flags.h>
 #include <linux/swapops.h>
 #include <linux/writeback.h>
 #include <linux/pagemap.h>
 #include <linux/workqueue.h>
 
 #include "swap.h"
 
 /*********************************
 * statistics
 **********************************/
 /* Total bytes used by the compressed storage */
 u64 zswap_pool_total_size;
 /* The number of compressed pages currently stored in zswap */
 atomic_t zswap_stored_pages = ATOMIC_INIT(0);
 /* The number of same-value filled pages currently stored in zswap */
 static atomic_t zswap_same_filled_pages = ATOMIC_INIT(0);
 
 /*
  * The statistics below are not protected from concurrent access for
  * performance reasons so they may not be a 100% accurate.  However,
  * they do provide useful information on roughly how many times a
  * certain event is occurring.
 */
 
 /* Pool limit was hit (see zswap_max_pool_percent) */
 static u64 zswap_pool_limit_hit;
 /* Pages written back when pool limit was reached */
 static u64 zswap_written_back_pages;
 /* Store failed due to a reclaim failure after pool limit was reached */
 static u64 zswap_reject_reclaim_fail;
 /* Compressed page was too big for the allocator to (optimally) store */
 static u64 zswap_reject_compress_poor;
 /* Store failed because underlying allocator could not get memory */
 static u64 zswap_reject_alloc_fail;
 /* Store failed because the entry metadata could not be allocated (rare) */
 static u64 zswap_reject_kmemcache_fail;
 /* Duplicate store was encountered (rare) */
 static u64 zswap_duplicate_entry;
 
 /* Shrinker work queue */
 static struct workqueue_struct *shrink_wq;
 /* Pool limit was hit, we need to calm down */
 static bool zswap_pool_reached_full;
 
 /*********************************
 * tunables
 **********************************/
 
 #define ZSWAP_PARAM_UNSET ""
 
 /* Enable/disable zswap */
 static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
 static int zswap_enabled_param_set(const char *,
                    const struct kernel_param *);
 static const struct kernel_param_ops zswap_enabled_param_ops = {
     .set =      zswap_enabled_param_set,
     .get =      param_get_bool,
 };
 module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);
 
 /* Crypto compressor to use */
 static char *zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
 static int zswap_compressor_param_set(const char *,
                       const struct kernel_param *);
 static const struct kernel_param_ops zswap_compressor_param_ops = {
     .set =      zswap_compressor_param_set,
     .get =      param_get_charp,
     .free =     param_free_charp,
 };
 module_param_cb(compressor, &zswap_compressor_param_ops,
         &zswap_compressor, 0644);
 
 /* Compressed storage zpool to use */
 static char *zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
 static int zswap_zpool_param_set(const char *, const struct kernel_param *);
 static const struct kernel_param_ops zswap_zpool_param_ops = {
     .set =      zswap_zpool_param_set,
     .get =      param_get_charp,
     .free =     param_free_charp,
 };
 module_param_cb(zpool, &zswap_zpool_param_ops, &zswap_zpool_type, 0644);
 
 /* The maximum percentage of memory that the compressed pool can occupy */
 static unsigned int zswap_max_pool_percent = 20;
 module_param_named(max_pool_percent, zswap_max_pool_percent, uint, 0644);
 
 /* The threshold for accepting new pages after the max_pool_percent was hit */
 static unsigned int zswap_accept_thr_percent = 90; /* of max pool size */
 module_param_named(accept_threshold_percent, zswap_accept_thr_percent,
            uint, 0644);
 
 /*
  * Enable/disable handling same-value filled pages (enabled by default).
  * If disabled every page is considered non-same-value filled.
  */
 static bool zswap_same_filled_pages_enabled = true;
 module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled,
            bool, 0644);
 
 /* Enable/disable handling non-same-value filled pages (enabled by default) */
 static bool zswap_non_same_filled_pages_enabled = true;
 module_param_named(non_same_filled_pages_enabled, zswap_non_same_filled_pages_enabled,
            bool, 0644);
 
 /*********************************
 * data structures
 **********************************/
 
 struct crypto_acomp_ctx {
     struct crypto_acomp *acomp;
     struct acomp_req *req;
     struct crypto_wait wait;
     u8 *dstmem;
     struct mutex *mutex;
 };
 
 struct zswap_pool {
     struct zpool *zpool;
     struct crypto_acomp_ctx __percpu *acomp_ctx;
     struct kref kref;
     struct list_head list;
     struct work_struct release_work;
     struct work_struct shrink_work;
     struct hlist_node node;
     char tfm_name[CRYPTO_MAX_ALG_NAME];
 };
 
 /*
  * struct zswap_entry
  *
  * This structure contains the metadata for tracking a single compressed
  * page within zswap.
  *
  * rbnode - links the entry into red-black tree for the appropriate swap type
  * offset - the swap offset for the entry.  Index into the red-black tree.
  * refcount - the number of outstanding reference to the entry. This is needed
  *            to protect against premature freeing of the entry by code
  *            concurrent calls to load, invalidate, and writeback.  The lock
  *            for the zswap_tree structure that contains the entry must
  *            be held while changing the refcount.  Since the lock must
  *            be held, there is no reason to also make refcount atomic.
  * length - the length in bytes of the compressed page data.  Needed during
  *          decompression. For a same value filled page length is 0.
  * pool - the zswap_pool the entry's data is in
  * handle - zpool allocation handle that stores the compressed page data
  * value - value of the same-value filled pages which have same content
  */
 struct zswap_entry {
     struct rb_node rbnode;
     pgoff_t offset;
     int refcount;
     unsigned int length;
     struct zswap_pool *pool;
     union {
         unsigned long handle;
         unsigned long value;
     };
     struct obj_cgroup *objcg;
 };
 
 struct zswap_header {
     swp_entry_t swpentry;
 };
 
 /*
  * The tree lock in the zswap_tree struct protects a few things:
  * - the rbtree
  * - the refcount field of each entry in the tree
  */
 struct zswap_tree {
     struct rb_root rbroot;
     spinlock_t lock;
 };
 
 static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
 
 /* RCU-protected iteration */
 static LIST_HEAD(zswap_pools);
 /* protects zswap_pools list modification */
 static DEFINE_SPINLOCK(zswap_pools_lock);
 /* pool counter to provide unique names to zpool */
 static atomic_t zswap_pools_count = ATOMIC_INIT(0);
 
 /* used by param callback function */
 static bool zswap_init_started;
 
 /* fatal error during init */
 static bool zswap_init_failed;
 
 /* init completed, but couldn't create the initial pool */
 static bool zswap_has_pool;
 
 /*********************************
 * helpers and fwd declarations
 **********************************/
 
 #define zswap_pool_debug(msg, p)                \
     pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name,     \
          zpool_get_type((p)->zpool))
 
 static int zswap_writeback_entry(struct zpool *pool, unsigned long handle);
 static int zswap_pool_get(struct zswap_pool *pool);
 static void zswap_pool_put(struct zswap_pool *pool);
 
 static const struct zpool_ops zswap_zpool_ops = {
     .evict = zswap_writeback_entry
 };
 
 static bool zswap_is_full(void)
 {
     return totalram_pages() * zswap_max_pool_percent / 100 <
             DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
 }
 
 static bool zswap_can_accept(void)
 {
     return totalram_pages() * zswap_accept_thr_percent / 100 *
                 zswap_max_pool_percent / 100 >
             DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
 }
 
 static void zswap_update_total_size(void)
 {
     struct zswap_pool *pool;
     u64 total = 0;
 
     rcu_read_lock();
 
     list_for_each_entry_rcu(pool, &zswap_pools, list)
         total += zpool_get_total_size(pool->zpool);
 
     rcu_read_unlock();
 
     zswap_pool_total_size = total;
 }
 
 /*********************************
 * zswap entry functions
 **********************************/
 static struct kmem_cache *zswap_entry_cache;
 
 static int __init zswap_entry_cache_create(void)
 {
     zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
     return zswap_entry_cache == NULL;
 }
 
 static void __init zswap_entry_cache_destroy(void)
 {
     kmem_cache_destroy(zswap_entry_cache);
 }
 
 static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
 {
     struct zswap_entry *entry;
     entry = kmem_cache_alloc(zswap_entry_cache, gfp);
     if (!entry)
         return NULL;
     entry->refcount = 1;
     RB_CLEAR_NODE(&entry->rbnode);
     return entry;
 }
 
 static void zswap_entry_cache_free(struct zswap_entry *entry)
 {
     kmem_cache_free(zswap_entry_cache, entry);
 }
 
 /*********************************
 * rbtree functions
 **********************************/
 static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
 {
     struct rb_node *node = root->rb_node;
     struct zswap_entry *entry;
 
     while (node) {
         entry = rb_entry(node, struct zswap_entry, rbnode);
         if (entry->offset > offset)
             node = node->rb_left;
         else if (entry->offset < offset)
             node = node->rb_right;
         else
             return entry;
     }
     return NULL;
 }
 
 /*
  * In the case that a entry with the same offset is found, a pointer to
  * the existing entry is stored in dupentry and the function returns -EEXIST
  */
 static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
             struct zswap_entry **dupentry)
 {
     struct rb_node **link = &root->rb_node, *parent = NULL;
     struct zswap_entry *myentry;
 
     while (*link) {
         parent = *link;
         myentry = rb_entry(parent, struct zswap_entry, rbnode);
         if (myentry->offset > entry->offset)
             link = &(*link)->rb_left;
         else if (myentry->offset < entry->offset)
             link = &(*link)->rb_right;
         else {
             *dupentry = myentry;
             return -EEXIST;
         }
     }
     rb_link_node(&entry->rbnode, parent, link);
     rb_insert_color(&entry->rbnode, root);
     return 0;
 }
 
 static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)
 {
     if (!RB_EMPTY_NODE(&entry->rbnode)) {
         rb_erase(&entry->rbnode, root);
         RB_CLEAR_NODE(&entry->rbnode);
     }
 }
 
 /*
  * Carries out the common pattern of freeing and entry's zpool allocation,
  * freeing the entry itself, and decrementing the number of stored pages.
  */
 static void zswap_free_entry(struct zswap_entry *entry)
 {
     if (entry->objcg) {
         obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
         obj_cgroup_put(entry->objcg);
     }
     if (!entry->length)
         atomic_dec(&zswap_same_filled_pages);
     else {
         zpool_free(entry->pool->zpool, entry->handle);
         zswap_pool_put(entry->pool);
     }
     zswap_entry_cache_free(entry);
     atomic_dec(&zswap_stored_pages);
     zswap_update_total_size();
 }
 
 /* caller must hold the tree lock */
 static void zswap_entry_get(struct zswap_entry *entry)
 {
     entry->refcount++;
 }
 
 /* caller must hold the tree lock
 * remove from the tree and free it, if nobody reference the entry
 */
 static void zswap_entry_put(struct zswap_tree *tree,
             struct zswap_entry *entry)
 {
     int refcount = --entry->refcount;
 
     BUG_ON(refcount < 0);
     if (refcount == 0) {
         zswap_rb_erase(&tree->rbroot, entry);
         zswap_free_entry(entry);
     }
 }
 
 /* caller must hold the tree lock */
 static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
                 pgoff_t offset)
 {
     struct zswap_entry *entry;
 
     entry = zswap_rb_search(root, offset);
     if (entry)
         zswap_entry_get(entry);
 
     return entry;
 }
 
 /*********************************
 * per-cpu code
 **********************************/
 static DEFINE_PER_CPU(u8 *, zswap_dstmem);
 /*
  * If users dynamically change the zpool type and compressor at runtime, i.e.
  * zswap is running, zswap can have more than one zpool on one cpu, but they
  * are sharing dtsmem. So we need this mutex to be per-cpu.
  */
 static DEFINE_PER_CPU(struct mutex *, zswap_mutex);
 
 static int zswap_dstmem_prepare(unsigned int cpu)
 {
     struct mutex *mutex;
     u8 *dst;
 
     dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
     if (!dst)
         return -ENOMEM;
 
     mutex = kmalloc_node(sizeof(*mutex), GFP_KERNEL, cpu_to_node(cpu));
     if (!mutex) {
         kfree(dst);
         return -ENOMEM;
     }
 
     mutex_init(mutex);
     per_cpu(zswap_dstmem, cpu) = dst;
     per_cpu(zswap_mutex, cpu) = mutex;
     return 0;
 }
 
 static int zswap_dstmem_dead(unsigned int cpu)
 {
     struct mutex *mutex;
     u8 *dst;
 
     mutex = per_cpu(zswap_mutex, cpu);
     kfree(mutex);
     per_cpu(zswap_mutex, cpu) = NULL;
 
     dst = per_cpu(zswap_dstmem, cpu);
     kfree(dst);
     per_cpu(zswap_dstmem, cpu) = NULL;
 
     return 0;
 }
 
 static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 {
     struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
     struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
     struct crypto_acomp *acomp;
     struct acomp_req *req;
 
     acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu));
     if (IS_ERR(acomp)) {
         pr_err("could not alloc crypto acomp %s : %ld\n",
                 pool->tfm_name, PTR_ERR(acomp));
         return PTR_ERR(acomp);
     }
     acomp_ctx->acomp = acomp;
 
     req = acomp_request_alloc(acomp_ctx->acomp);
     if (!req) {
         pr_err("could not alloc crypto acomp_request %s\n",
                pool->tfm_name);
         crypto_free_acomp(acomp_ctx->acomp);
         return -ENOMEM;
     }
     acomp_ctx->req = req;
 
     crypto_init_wait(&acomp_ctx->wait);
     /*
      * if the backend of acomp is async zip, crypto_req_done() will wakeup
      * crypto_wait_req(); if the backend of acomp is scomp, the callback
      * won't be called, crypto_wait_req() will return without blocking.
      */
     acomp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
                    crypto_req_done, &acomp_ctx->wait);
 
     acomp_ctx->mutex = per_cpu(zswap_mutex, cpu);
     acomp_ctx->dstmem = per_cpu(zswap_dstmem, cpu);
 
     return 0;
 }
 
 static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
 {
     struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
     struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
 
     if (!IS_ERR_OR_NULL(acomp_ctx)) {
         if (!IS_ERR_OR_NULL(acomp_ctx->req))
             acomp_request_free(acomp_ctx->req);
         if (!IS_ERR_OR_NULL(acomp_ctx->acomp))
             crypto_free_acomp(acomp_ctx->acomp);
     }
 
     return 0;
 }
 
 /*********************************
 * pool functions
 **********************************/
 
 static struct zswap_pool *__zswap_pool_current(void)
 {
     struct zswap_pool *pool;
 
     pool = list_first_or_null_rcu(&zswap_pools, typeof(*pool), list);
     WARN_ONCE(!pool && zswap_has_pool,
           "%s: no page storage pool!\n", __func__);
 
     return pool;
 }
 
 static struct zswap_pool *zswap_pool_current(void)
 {
     assert_spin_locked(&zswap_pools_lock);
 
     return __zswap_pool_current();
 }
 
 static struct zswap_pool *zswap_pool_current_get(void)
 {
     struct zswap_pool *pool;
 
     rcu_read_lock();
 
     pool = __zswap_pool_current();
     if (!zswap_pool_get(pool))
         pool = NULL;
 
     rcu_read_unlock();
 
     return pool;
 }
 
 static struct zswap_pool *zswap_pool_last_get(void)
 {
     struct zswap_pool *pool, *last = NULL;
 
     rcu_read_lock();
 
     list_for_each_entry_rcu(pool, &zswap_pools, list)
         last = pool;
     WARN_ONCE(!last && zswap_has_pool,
           "%s: no page storage pool!\n", __func__);
     if (!zswap_pool_get(last))
         last = NULL;
 
     rcu_read_unlock();
 
     return last;
 }
 
 /* type and compressor must be null-terminated */
 static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
 {
     struct zswap_pool *pool;
 
     assert_spin_locked(&zswap_pools_lock);
 
     list_for_each_entry_rcu(pool, &zswap_pools, list) {
         if (strcmp(pool->tfm_name, compressor))
             continue;
         if (strcmp(zpool_get_type(pool->zpool), type))
             continue;
         /* if we can't get it, it's about to be destroyed */
         if (!zswap_pool_get(pool))
             continue;
         return pool;
     }
 
     return NULL;
 }
 
 static void shrink_worker(struct work_struct *w)
 {
     struct zswap_pool *pool = container_of(w, typeof(*pool),
                         shrink_work);
 
     if (zpool_shrink(pool->zpool, 1, NULL))
         zswap_reject_reclaim_fail++;
     zswap_pool_put(pool);
 }
 
 static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
 {
     struct zswap_pool *pool;
     char name[38]; /* 'zswap' + 32 char (max) num + \0 */
     gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
     int ret;
 
     if (!zswap_has_pool) {
         /* if either are unset, pool initialization failed, and we
          * need both params to be set correctly before trying to
          * create a pool.
          */
         if (!strcmp(type, ZSWAP_PARAM_UNSET))
             return NULL;
         if (!strcmp(compressor, ZSWAP_PARAM_UNSET))
             return NULL;
     }
 
     pool = kzalloc(sizeof(*pool), GFP_KERNEL);
     if (!pool)
         return NULL;
 
     /* unique name for each pool specifically required by zsmalloc */
     snprintf(name, 38, "zswap%x", atomic_inc_return(&zswap_pools_count));
 
     pool->zpool = zpool_create_pool(type, name, gfp, &zswap_zpool_ops);
     if (!pool->zpool) {
         pr_err("%s zpool not available\n", type);
         goto error;
     }
     pr_debug("using %s zpool\n", zpool_get_type(pool->zpool));
 
     strscpy(pool->tfm_name, compressor, sizeof(pool->tfm_name));
 
     pool->acomp_ctx = alloc_percpu(*pool->acomp_ctx);
     if (!pool->acomp_ctx) {
         pr_err("percpu alloc failed\n");
         goto error;
     }
 
     ret = cpuhp_state_add_instance(CPUHP_MM_ZSWP_POOL_PREPARE,
                        &pool->node);
     if (ret)
         goto error;
     pr_debug("using %s compressor\n", pool->tfm_name);
 
     /* being the current pool takes 1 ref; this func expects the
      * caller to always add the new pool as the current pool
      */
     kref_init(&pool->kref);
     INIT_LIST_HEAD(&pool->list);
     INIT_WORK(&pool->shrink_work, shrink_worker);
 
     zswap_pool_debug("created", pool);
 
     return pool;
 
 error:
     if (pool->acomp_ctx)
         free_percpu(pool->acomp_ctx);
     if (pool->zpool)
         zpool_destroy_pool(pool->zpool);
     kfree(pool);
     return NULL;
 }
 
 static __init struct zswap_pool *__zswap_pool_create_fallback(void)
 {
     bool has_comp, has_zpool;
 
     has_comp = crypto_has_acomp(zswap_compressor, 0, 0);
     if (!has_comp && strcmp(zswap_compressor,
                 CONFIG_ZSWAP_COMPRESSOR_DEFAULT)) {
         pr_err("compressor %s not available, using default %s\n",
                zswap_compressor, CONFIG_ZSWAP_COMPRESSOR_DEFAULT);
         param_free_charp(&zswap_compressor);
         zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
         has_comp = crypto_has_acomp(zswap_compressor, 0, 0);
     }
     if (!has_comp) {
         pr_err("default compressor %s not available\n",
                zswap_compressor);
         param_free_charp(&zswap_compressor);
         zswap_compressor = ZSWAP_PARAM_UNSET;
     }
 
     has_zpool = zpool_has_pool(zswap_zpool_type);
     if (!has_zpool && strcmp(zswap_zpool_type,
                  CONFIG_ZSWAP_ZPOOL_DEFAULT)) {
         pr_err("zpool %s not available, using default %s\n",
                zswap_zpool_type, CONFIG_ZSWAP_ZPOOL_DEFAULT);
         param_free_charp(&zswap_zpool_type);
         zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
         has_zpool = zpool_has_pool(zswap_zpool_type);
     }
     if (!has_zpool) {
         pr_err("default zpool %s not available\n",
                zswap_zpool_type);
         param_free_charp(&zswap_zpool_type);
         zswap_zpool_type = ZSWAP_PARAM_UNSET;
     }
 
     if (!has_comp || !has_zpool)
         return NULL;
 
     return zswap_pool_create(zswap_zpool_type, zswap_compressor);
 }
 
 static void zswap_pool_destroy(struct zswap_pool *pool)
 {
     zswap_pool_debug("destroying", pool);
 
     cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
     free_percpu(pool->acomp_ctx);
     zpool_destroy_pool(pool->zpool);
     kfree(pool);
 }
 
 static int __must_check zswap_pool_get(struct zswap_pool *pool)
 {
     if (!pool)
         return 0;
 
     return kref_get_unless_zero(&pool->kref);
 }
 
 static void __zswap_pool_release(struct work_struct *work)
 {
     struct zswap_pool *pool = container_of(work, typeof(*pool),
                         release_work);
 
     synchronize_rcu();
 
     /* nobody should have been able to get a kref... */
     WARN_ON(kref_get_unless_zero(&pool->kref));
 
     /* pool is now off zswap_pools list and has no references. */
     zswap_pool_destroy(pool);
 }
 
 static void __zswap_pool_empty(struct kref *kref)
 {
     struct zswap_pool *pool;
 
     pool = container_of(kref, typeof(*pool), kref);
 
     spin_lock(&zswap_pools_lock);
 
     WARN_ON(pool == zswap_pool_current());
 
     list_del_rcu(&pool->list);
 
     INIT_WORK(&pool->release_work, __zswap_pool_release);
     schedule_work(&pool->release_work);
 
     spin_unlock(&zswap_pools_lock);
 }
 
 static void zswap_pool_put(struct zswap_pool *pool)
 {
     kref_put(&pool->kref, __zswap_pool_empty);
 }
 
 /*********************************
 * param callbacks
 **********************************/
 
 /* val must be a null-terminated string */
 static int __zswap_param_set(const char *val, const struct kernel_param *kp,
                  char *type, char *compressor)
 {
     struct zswap_pool *pool, *put_pool = NULL;
     char *s = strstrip((char *)val);
     int ret;
 
     if (zswap_init_failed) {
         pr_err("can't set param, initialization failed\n");
         return -ENODEV;
     }
 
     /* no change required */
     if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
         return 0;
 
     /* if this is load-time (pre-init) param setting,
      * don't create a pool; that's done during init.
      */
     if (!zswap_init_started)
         return param_set_charp(s, kp);
 
     if (!type) {
         if (!zpool_has_pool(s)) {
             pr_err("zpool %s not available\n", s);
             return -ENOENT;
         }
         type = s;
     } else if (!compressor) {
         if (!crypto_has_acomp(s, 0, 0)) {
             pr_err("compressor %s not available\n", s);
             return -ENOENT;
         }
         compressor = s;
     } else {
         WARN_ON(1);
         return -EINVAL;
     }
 
     spin_lock(&zswap_pools_lock);
 
     pool = zswap_pool_find_get(type, compressor);
     if (pool) {
         zswap_pool_debug("using existing", pool);
         WARN_ON(pool == zswap_pool_current());
         list_del_rcu(&pool->list);
     }
 
     spin_unlock(&zswap_pools_lock);
 
     if (!pool)
         pool = zswap_pool_create(type, compressor);
 
     if (pool)
         ret = param_set_charp(s, kp);
     else
         ret = -EINVAL;
 
     spin_lock(&zswap_pools_lock);
 
     if (!ret) {
         put_pool = zswap_pool_current();
         list_add_rcu(&pool->list, &zswap_pools);
         zswap_has_pool = true;
     } else if (pool) {
         /* add the possibly pre-existing pool to the end of the pools
          * list; if it's new (and empty) then it'll be removed and
          * destroyed by the put after we drop the lock
          */
         list_add_tail_rcu(&pool->list, &zswap_pools);
         put_pool = pool;
     }
 
     spin_unlock(&zswap_pools_lock);
 
     if (!zswap_has_pool && !pool) {
         /* if initial pool creation failed, and this pool creation also
          * failed, maybe both compressor and zpool params were bad.
          * Allow changing this param, so pool creation will succeed
          * when the other param is changed. We already verified this
          * param is ok in the zpool_has_pool() or crypto_has_acomp()
          * checks above.
          */
         ret = param_set_charp(s, kp);
     }
 
     /* drop the ref from either the old current pool,
      * or the new pool we failed to add
      */
     if (put_pool)
         zswap_pool_put(put_pool);
 
     return ret;
 }
 
 static int zswap_compressor_param_set(const char *val,
                       const struct kernel_param *kp)
 {
     return __zswap_param_set(val, kp, zswap_zpool_type, NULL);
 }
 
 static int zswap_zpool_param_set(const char *val,
                  const struct kernel_param *kp)
 {
     return __zswap_param_set(val, kp, NULL, zswap_compressor);
 }
 
 static int zswap_enabled_param_set(const char *val,
                    const struct kernel_param *kp)
 {
     if (zswap_init_failed) {
         pr_err("can't enable, initialization failed\n");
         return -ENODEV;
     }
     if (!zswap_has_pool && zswap_init_started) {
         pr_err("can't enable, no pool configured\n");
         return -ENODEV;
     }
 
     return param_set_bool(val, kp);
 }
 
 /*********************************
 * writeback code
 **********************************/
 /* return enum for zswap_get_swap_cache_page */
 enum zswap_get_swap_ret {
     ZSWAP_SWAPCACHE_NEW,
     ZSWAP_SWAPCACHE_EXIST,
     ZSWAP_SWAPCACHE_FAIL,
 };
 
 /*
  * zswap_get_swap_cache_page
  *
  * This is an adaption of read_swap_cache_async()
  *
  * This function tries to find a page with the given swap entry
  * in the swapper_space address space (the swap cache).  If the page
  * is found, it is returned in retpage.  Otherwise, a page is allocated,
  * added to the swap cache, and returned in retpage.
  *
  * If success, the swap cache page is returned in retpage
  * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache
  * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,
  *     the new page is added to swapcache and locked
  * Returns ZSWAP_SWAPCACHE_FAIL on error
  */
 static int zswap_get_swap_cache_page(swp_entry_t entry,
                 struct page **retpage)
 {
     bool page_was_allocated;
 
     *retpage = __read_swap_cache_async(entry, GFP_KERNEL,
             NULL, 0, &page_was_allocated);
     if (page_was_allocated)
         return ZSWAP_SWAPCACHE_NEW;
     if (!*retpage)
         return ZSWAP_SWAPCACHE_FAIL;
     return ZSWAP_SWAPCACHE_EXIST;
 }
 
 /*
  * Attempts to free an entry by adding a page to the swap cache,
  * decompressing the entry data into the page, and issuing a
  * bio write to write the page back to the swap device.
  *
  * This can be thought of as a "resumed writeback" of the page
  * to the swap device.  We are basically resuming the same swap
  * writeback path that was intercepted with the frontswap_store()
  * in the first place.  After the page has been decompressed into
  * the swap cache, the compressed version stored by zswap can be
  * freed.
  */
 static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
 {
     struct zswap_header *zhdr;
     swp_entry_t swpentry;
     struct zswap_tree *tree;
     pgoff_t offset;
     struct zswap_entry *entry;
     struct page *page;
     struct scatterlist input, output;
     struct crypto_acomp_ctx *acomp_ctx;
 
     u8 *src, *tmp = NULL;
     unsigned int dlen;
     int ret;
     struct writeback_control wbc = {
         .sync_mode = WB_SYNC_NONE,
     };
 
     if (!zpool_can_sleep_mapped(pool)) {
         tmp = kmalloc(PAGE_SIZE, GFP_ATOMIC);
         if (!tmp)
             return -ENOMEM;
     }
 
     /* extract swpentry from data */
     zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
     swpentry = zhdr->swpentry; /* here */
     tree = zswap_trees[swp_type(swpentry)];
     offset = swp_offset(swpentry);
 
     /* find and ref zswap entry */
     spin_lock(&tree->lock);
     entry = zswap_entry_find_get(&tree->rbroot, offset);
     if (!entry) {
         /* entry was invalidated */
         spin_unlock(&tree->lock);
         zpool_unmap_handle(pool, handle);
         kfree(tmp);
         return 0;
     }
     spin_unlock(&tree->lock);
     BUG_ON(offset != entry->offset);
 
     src = (u8 *)zhdr + sizeof(struct zswap_header);
     if (!zpool_can_sleep_mapped(pool)) {
         memcpy(tmp, src, entry->length);
         src = tmp;
         zpool_unmap_handle(pool, handle);
     }
 
     /* try to allocate swap cache page */
     switch (zswap_get_swap_cache_page(swpentry, &page)) {
     case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
         ret = -ENOMEM;
         goto fail;
 
     case ZSWAP_SWAPCACHE_EXIST:
         /* page is already in the swap cache, ignore for now */
         put_page(page);
         ret = -EEXIST;
         goto fail;
 
     case ZSWAP_SWAPCACHE_NEW: /* page is locked */
         /* decompress */
         acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
         dlen = PAGE_SIZE;
 
         mutex_lock(acomp_ctx->mutex);
         sg_init_one(&input, src, entry->length);
         sg_init_table(&output, 1);
         sg_set_page(&output, page, PAGE_SIZE, 0);
         acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
         ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
         dlen = acomp_ctx->req->dlen;
         mutex_unlock(acomp_ctx->mutex);
 
         BUG_ON(ret);
         BUG_ON(dlen != PAGE_SIZE);
 
         /* page is up to date */
         SetPageUptodate(page);
     }
 
     /* move it to the tail of the inactive list after end_writeback */
     SetPageReclaim(page);
 
     /* start writeback */
     __swap_writepage(page, &wbc, end_swap_bio_write);
     put_page(page);
     zswap_written_back_pages++;
 
     spin_lock(&tree->lock);
     /* drop local reference */
     zswap_entry_put(tree, entry);
 
     /*
     * There are two possible situations for entry here:
     * (1) refcount is 1(normal case),  entry is valid and on the tree
     * (2) refcount is 0, entry is freed and not on the tree
     *     because invalidate happened during writeback
     *  search the tree and free the entry if find entry
     */
     if (entry == zswap_rb_search(&tree->rbroot, offset))
         zswap_entry_put(tree, entry);
     spin_unlock(&tree->lock);
 
     goto end;
 
     /*
     * if we get here due to ZSWAP_SWAPCACHE_EXIST
     * a load may be happening concurrently.
     * it is safe and okay to not free the entry.
     * if we free the entry in the following put
     * it is also okay to return !0
     */
 fail:
     spin_lock(&tree->lock);
     zswap_entry_put(tree, entry);
     spin_unlock(&tree->lock);
 
 end:
     if (zpool_can_sleep_mapped(pool))
         zpool_unmap_handle(pool, handle);
     else
         kfree(tmp);
 
     return ret;
 }
 
 static int zswap_is_page_same_filled(void *ptr, unsigned long *value)
 {
     unsigned int pos;
     unsigned long *page;
 
     page = (unsigned long *)ptr;
     for (pos = 1; pos < PAGE_SIZE / sizeof(*page); pos++) {
         if (page[pos] != page[0])
             return 0;
     }
     *value = page[0];
     return 1;
 }
 
 static void zswap_fill_page(void *ptr, unsigned long value)
 {
     unsigned long *page;
 
     page = (unsigned long *)ptr;
     memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
 }
 
 /*********************************
 * frontswap hooks
 **********************************/
 /* attempts to compress and store an single page */
 static int zswap_frontswap_store(unsigned type, pgoff_t offset,
                 struct page *page)
 {
     struct zswap_tree *tree = zswap_trees[type];
     struct zswap_entry *entry, *dupentry;
     struct scatterlist input, output;
     struct crypto_acomp_ctx *acomp_ctx;
     struct obj_cgroup *objcg = NULL;
     struct zswap_pool *pool;
     int ret;
     unsigned int hlen, dlen = PAGE_SIZE;
     unsigned long handle, value;
     char *buf;
     u8 *src, *dst;
     struct zswap_header zhdr = { .swpentry = swp_entry(type, offset) };
     gfp_t gfp;
 
     /* THP isn't supported */
     if (PageTransHuge(page)) {
         ret = -EINVAL;
         goto reject;
     }
 
     if (!zswap_enabled || !tree) {
         ret = -ENODEV;
         goto reject;
     }
 
     objcg = get_obj_cgroup_from_page(page);
     if (objcg && !obj_cgroup_may_zswap(objcg))
         goto shrink;
 
     /* reclaim space if needed */
     if (zswap_is_full()) {
         zswap_pool_limit_hit++;
         zswap_pool_reached_full = true;
         goto shrink;
     }
 
     if (zswap_pool_reached_full) {
            if (!zswap_can_accept()) {
             ret = -ENOMEM;
             goto reject;
         } else
             zswap_pool_reached_full = false;
     }
 
     /* allocate entry */
     entry = zswap_entry_cache_alloc(GFP_KERNEL);
     if (!entry) {
         zswap_reject_kmemcache_fail++;
         ret = -ENOMEM;
         goto reject;
     }
 
     if (zswap_same_filled_pages_enabled) {
         src = kmap_atomic(page);
         if (zswap_is_page_same_filled(src, &value)) {
             kunmap_atomic(src);
             entry->offset = offset;
             entry->length = 0;
             entry->value = value;
             atomic_inc(&zswap_same_filled_pages);
             goto insert_entry;
         }
         kunmap_atomic(src);
     }
 
     if (!zswap_non_same_filled_pages_enabled) {
         ret = -EINVAL;
         goto freepage;
     }
 
     /* if entry is successfully added, it keeps the reference */
     entry->pool = zswap_pool_current_get();
     if (!entry->pool) {
         ret = -EINVAL;
         goto freepage;
     }
 
     /* compress */
     acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
 
     mutex_lock(acomp_ctx->mutex);
 
     dst = acomp_ctx->dstmem;
     sg_init_table(&input, 1);
     sg_set_page(&input, page, PAGE_SIZE, 0);
 
     /* zswap_dstmem is of size (PAGE_SIZE * 2). Reflect same in sg_list */
     sg_init_one(&output, dst, PAGE_SIZE * 2);
     acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
     /*
      * it maybe looks a little bit silly that we send an asynchronous request,
      * then wait for its completion synchronously. This makes the process look
      * synchronous in fact.
      * Theoretically, acomp supports users send multiple acomp requests in one
      * acomp instance, then get those requests done simultaneously. but in this
      * case, frontswap actually does store and load page by page, there is no
      * existing method to send the second page before the first page is done
      * in one thread doing frontswap.
      * but in different threads running on different cpu, we have different
      * acomp instance, so multiple threads can do (de)compression in parallel.
      */
     ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
     dlen = acomp_ctx->req->dlen;
 
     if (ret) {
         ret = -EINVAL;
         goto put_dstmem;
     }
 
     /* store */
     hlen = zpool_evictable(entry->pool->zpool) ? sizeof(zhdr) : 0;
     gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
     if (zpool_malloc_support_movable(entry->pool->zpool))
         gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
     ret = zpool_malloc(entry->pool->zpool, hlen + dlen, gfp, &handle);
     if (ret == -ENOSPC) {
         zswap_reject_compress_poor++;
         goto put_dstmem;
     }
     if (ret) {
         zswap_reject_alloc_fail++;
         goto put_dstmem;
     }
     buf = zpool_map_handle(entry->pool->zpool, handle, ZPOOL_MM_WO);
     memcpy(buf, &zhdr, hlen);
     memcpy(buf + hlen, dst, dlen);
     zpool_unmap_handle(entry->pool->zpool, handle);
     mutex_unlock(acomp_ctx->mutex);
 
     /* populate entry */
     entry->offset = offset;
     entry->handle = handle;
     entry->length = dlen;
 
 insert_entry:
     entry->objcg = objcg;
     if (objcg) {
         obj_cgroup_charge_zswap(objcg, entry->length);
         /* Account before objcg ref is moved to tree */
         count_objcg_event(objcg, ZSWPOUT);
     }
 
     /* map */
     spin_lock(&tree->lock);
     do {
         ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
         if (ret == -EEXIST) {
             zswap_duplicate_entry++;
             /* remove from rbtree */
             zswap_rb_erase(&tree->rbroot, dupentry);
             zswap_entry_put(tree, dupentry);
         }
     } while (ret == -EEXIST);
     spin_unlock(&tree->lock);
 
     /* update stats */
     atomic_inc(&zswap_stored_pages);
     zswap_update_total_size();
     count_vm_event(ZSWPOUT);
 
     return 0;
 
 put_dstmem:
     mutex_unlock(acomp_ctx->mutex);
     zswap_pool_put(entry->pool);
 freepage:
     zswap_entry_cache_free(entry);
 reject:
     if (objcg)
         obj_cgroup_put(objcg);
     return ret;
 
 shrink:
     pool = zswap_pool_last_get();
     if (pool)
         queue_work(shrink_wq, &pool->shrink_work);
     ret = -ENOMEM;
     goto reject;
 }
 
 /*
  * returns 0 if the page was successfully decompressed
  * return -1 on entry not found or error
 */
 static int zswap_frontswap_load(unsigned type, pgoff_t offset,
                 struct page *page)
 {
     struct zswap_tree *tree = zswap_trees[type];
     struct zswap_entry *entry;
     struct scatterlist input, output;
     struct crypto_acomp_ctx *acomp_ctx;
     u8 *src, *dst, *tmp;
     unsigned int dlen;
     int ret;
 
     /* find */
     spin_lock(&tree->lock);
     entry = zswap_entry_find_get(&tree->rbroot, offset);
     if (!entry) {
         /* entry was written back */
         spin_unlock(&tree->lock);
         return -1;
     }
     spin_unlock(&tree->lock);
 
     if (!entry->length) {
         dst = kmap_atomic(page);
         zswap_fill_page(dst, entry->value);
         kunmap_atomic(dst);
         ret = 0;
         goto stats;
     }
 
     if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
         tmp = kmalloc(entry->length, GFP_ATOMIC);
         if (!tmp) {
             ret = -ENOMEM;
             goto freeentry;
         }
     }
 
     /* decompress */
     dlen = PAGE_SIZE;
     src = zpool_map_handle(entry->pool->zpool, entry->handle, ZPOOL_MM_RO);
     if (zpool_evictable(entry->pool->zpool))
         src += sizeof(struct zswap_header);
 
     if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
         memcpy(tmp, src, entry->length);
         src = tmp;
         zpool_unmap_handle(entry->pool->zpool, entry->handle);
     }
 
     acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
     mutex_lock(acomp_ctx->mutex);
     sg_init_one(&input, src, entry->length);
     sg_init_table(&output, 1);
     sg_set_page(&output, page, PAGE_SIZE, 0);
     acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, dlen);
     ret = crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait);
     mutex_unlock(acomp_ctx->mutex);
 
     if (zpool_can_sleep_mapped(entry->pool->zpool))
         zpool_unmap_handle(entry->pool->zpool, entry->handle);
     else
         kfree(tmp);
 
     BUG_ON(ret);
 stats:
     count_vm_event(ZSWPIN);
     if (entry->objcg)
         count_objcg_event(entry->objcg, ZSWPIN);
 freeentry:
     spin_lock(&tree->lock);
     zswap_entry_put(tree, entry);
     spin_unlock(&tree->lock);
 
     return ret;
 }
 
 /* frees an entry in zswap */
 static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
 {
     struct zswap_tree *tree = zswap_trees[type];
     struct zswap_entry *entry;
 
     /* find */
     spin_lock(&tree->lock);
     entry = zswap_rb_search(&tree->rbroot, offset);
     if (!entry) {
         /* entry was written back */
         spin_unlock(&tree->lock);
         return;
     }
 
     /* remove from rbtree */
     zswap_rb_erase(&tree->rbroot, entry);
 
     /* drop the initial reference from entry creation */
     zswap_entry_put(tree, entry);
 
     spin_unlock(&tree->lock);
 }
 
 /* frees all zswap entries for the given swap type */
 static void zswap_frontswap_invalidate_area(unsigned type)
 {
     struct zswap_tree *tree = zswap_trees[type];
     struct zswap_entry *entry, *n;
 
     if (!tree)
         return;
 
     /* walk the tree and free everything */
     spin_lock(&tree->lock);
     rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
         zswap_free_entry(entry);
     tree->rbroot = RB_ROOT;
     spin_unlock(&tree->lock);
     kfree(tree);
     zswap_trees[type] = NULL;
 }
 
 static void zswap_frontswap_init(unsigned type)
 {
     struct zswap_tree *tree;
 
     tree = kzalloc(sizeof(*tree), GFP_KERNEL);
     if (!tree) {
         pr_err("alloc failed, zswap disabled for swap type %d\n", type);
         return;
     }
 
     tree->rbroot = RB_ROOT;
     spin_lock_init(&tree->lock);
     zswap_trees[type] = tree;
 }
 
 static const struct frontswap_ops zswap_frontswap_ops = {
     .store = zswap_frontswap_store,
     .load = zswap_frontswap_load,
     .invalidate_page = zswap_frontswap_invalidate_page,
     .invalidate_area = zswap_frontswap_invalidate_area,
     .init = zswap_frontswap_init
 };
 
 /*********************************
 * debugfs functions
 **********************************/
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 
 static struct dentry *zswap_debugfs_root;
 
 static int __init zswap_debugfs_init(void)
 {
     if (!debugfs_initialized())
         return -ENODEV;
 
     zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
 
     debugfs_create_u64("pool_limit_hit", 0444,
                zswap_debugfs_root, &zswap_pool_limit_hit);
     debugfs_create_u64("reject_reclaim_fail", 0444,
                zswap_debugfs_root, &zswap_reject_reclaim_fail);
     debugfs_create_u64("reject_alloc_fail", 0444,
                zswap_debugfs_root, &zswap_reject_alloc_fail);
     debugfs_create_u64("reject_kmemcache_fail", 0444,
                zswap_debugfs_root, &zswap_reject_kmemcache_fail);
     debugfs_create_u64("reject_compress_poor", 0444,
                zswap_debugfs_root, &zswap_reject_compress_poor);
     debugfs_create_u64("written_back_pages", 0444,
                zswap_debugfs_root, &zswap_written_back_pages);
     debugfs_create_u64("duplicate_entry", 0444,
                zswap_debugfs_root, &zswap_duplicate_entry);
     debugfs_create_u64("pool_total_size", 0444,
                zswap_debugfs_root, &zswap_pool_total_size);
     debugfs_create_atomic_t("stored_pages", 0444,
                 zswap_debugfs_root, &zswap_stored_pages);
     debugfs_create_atomic_t("same_filled_pages", 0444,
                 zswap_debugfs_root, &zswap_same_filled_pages);
 
     return 0;
 }
 #else
 static int __init zswap_debugfs_init(void)
 {
     return 0;
 }
 #endif
 
 /*********************************
 * module init and exit
 **********************************/
 static int __init init_zswap(void)
 {
     struct zswap_pool *pool;
     int ret;
 
     zswap_init_started = true;
 
     if (zswap_entry_cache_create()) {
         pr_err("entry cache creation failed\n");
         goto cache_fail;
     }
 
     ret = cpuhp_setup_state(CPUHP_MM_ZSWP_MEM_PREPARE, "mm/zswap:prepare",
                 zswap_dstmem_prepare, zswap_dstmem_dead);
     if (ret) {
         pr_err("dstmem alloc failed\n");
         goto dstmem_fail;
     }
 
     ret = cpuhp_setup_state_multi(CPUHP_MM_ZSWP_POOL_PREPARE,
                       "mm/zswap_pool:prepare",
                       zswap_cpu_comp_prepare,
                       zswap_cpu_comp_dead);
     if (ret)
         goto hp_fail;
 
     pool = __zswap_pool_create_fallback();
     if (pool) {
         pr_info("loaded using pool %s/%s\n", pool->tfm_name,
             zpool_get_type(pool->zpool));
         list_add(&pool->list, &zswap_pools);
         zswap_has_pool = true;
     } else {
         pr_err("pool creation failed\n");
         zswap_enabled = false;
     }
 
     shrink_wq = create_workqueue("zswap-shrink");
     if (!shrink_wq)
         goto fallback_fail;
 
     ret = frontswap_register_ops(&zswap_frontswap_ops);
     if (ret)
         goto destroy_wq;
     if (zswap_debugfs_init())
         pr_warn("debugfs initialization failed\n");
     return 0;
 
 destroy_wq:
     destroy_workqueue(shrink_wq);
 fallback_fail:
     if (pool)
         zswap_pool_destroy(pool);
 hp_fail:
     cpuhp_remove_state(CPUHP_MM_ZSWP_MEM_PREPARE);
 dstmem_fail:
     zswap_entry_cache_destroy();
 cache_fail:
     /* if built-in, we aren't unloaded on failure; don't allow use */
     zswap_init_failed = true;
     zswap_enabled = false;
     return -ENOMEM;
 }
 /* must be late so crypto has time to come up */
 late_initcall(init_zswap);
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>");
 MODULE_DESCRIPTION("Compressed cache for swap pages");

This page was automatically generated by the 2.1.0 LXR engine. The LXR team