Merge tag 'bcachefs-2024-09-21' of git://evilpiepirate.org/bcachefs

[linux.git] / mm / zswap.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * zswap.c - zswap driver file
 *
 * zswap is a cache 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/swap.h>
#include <linux/crypto.h>
#include <linux/scatterlist.h>
#include <linux/mempolicy.h>
#include <linux/mempool.h>
#include <linux/zpool.h>
#include <crypto/acompress.h>
#include <linux/zswap.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 <linux/list_lru.h>

#include "swap.h"
#include "internal.h"

/*********************************
* statistics
**********************************/
/* The number of compressed pages currently stored in zswap */
atomic_t zswap_stored_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;
/* Store failed due to compression algorithm failure */
static u64 zswap_reject_compress_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;

/* 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 ""

static int zswap_setup(void);

/* Enable/disable zswap */
static DEFINE_STATIC_KEY_MAYBE(CONFIG_ZSWAP_DEFAULT_ON, zswap_ever_enabled);
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 memory pressure-based shrinker. */
static bool zswap_shrinker_enabled = IS_ENABLED(
                CONFIG_ZSWAP_SHRINKER_DEFAULT_ON);
module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);

bool zswap_is_enabled(void)
{
        return zswap_enabled;
}

bool zswap_never_enabled(void)
{
        return !static_branch_maybe(CONFIG_ZSWAP_DEFAULT_ON, &zswap_ever_enabled);
}

/*********************************
* data structures
**********************************/

struct crypto_acomp_ctx {
        struct crypto_acomp *acomp;
        struct acomp_req *req;
        struct crypto_wait wait;
        u8 *buffer;
        struct mutex mutex;
        bool is_sleepable;
};

/*
 * The lock ordering is zswap_tree.lock -> zswap_pool.lru_lock.
 * The only case where lru_lock is not acquired while holding tree.lock is
 * when a zswap_entry is taken off the lru for writeback, in that case it
 * needs to be verified that it's still valid in the tree.
 */
struct zswap_pool {
        struct zpool *zpool;
        struct crypto_acomp_ctx __percpu *acomp_ctx;
        struct percpu_ref ref;
        struct list_head list;
        struct work_struct release_work;
        struct hlist_node node;
        char tfm_name[CRYPTO_MAX_ALG_NAME];
};

/* Global LRU lists shared by all zswap pools. */
static struct list_lru zswap_list_lru;

/* The lock protects zswap_next_shrink updates. */
static DEFINE_SPINLOCK(zswap_shrink_lock);
static struct mem_cgroup *zswap_next_shrink;
static struct work_struct zswap_shrink_work;
static struct shrinker *zswap_shrinker;

/*
 * struct zswap_entry
 *
 * This structure contains the metadata for tracking a single compressed
 * page within zswap.
 *
 * swpentry - associated swap entry, the offset indexes into the red-black tree
 * length - the length in bytes of the compressed page data.  Needed during
 *          decompression.
 * referenced - true if the entry recently entered the zswap pool. Unset by the
 *              writeback logic. The entry is only reclaimed by the writeback
 *              logic if referenced is unset. See comments in the shrinker
 *              section for context.
 * 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
 * objcg - the obj_cgroup that the compressed memory is charged to
 * lru - handle to the pool's lru used to evict pages.
 */
struct zswap_entry {
        swp_entry_t swpentry;
        unsigned int length;
        bool referenced;
        struct zswap_pool *pool;
        unsigned long handle;
        struct obj_cgroup *objcg;
        struct list_head lru;
};

static struct xarray *zswap_trees[MAX_SWAPFILES];
static unsigned int nr_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);

enum zswap_init_type {
        ZSWAP_UNINIT,
        ZSWAP_INIT_SUCCEED,
        ZSWAP_INIT_FAILED
};

static enum zswap_init_type zswap_init_state;

/* used to ensure the integrity of initialization */
static DEFINE_MUTEX(zswap_init_lock);

/* init completed, but couldn't create the initial pool */
static bool zswap_has_pool;

/*********************************
* helpers and fwd declarations
**********************************/

static inline struct xarray *swap_zswap_tree(swp_entry_t swp)
{
        return &zswap_trees[swp_type(swp)][swp_offset(swp)
                >> SWAP_ADDRESS_SPACE_SHIFT];
}

#define zswap_pool_debug(msg, p)                                \
        pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name,         \
                 zpool_get_type((p)->zpool))

/*********************************
* pool functions
**********************************/
static void __zswap_pool_empty(struct percpu_ref *ref);

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);
        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;

        /* being the current pool takes 1 ref; this func expects the
         * caller to always add the new pool as the current pool
         */
        ret = percpu_ref_init(&pool->ref, __zswap_pool_empty,
                              PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
        if (ret)
                goto ref_fail;
        INIT_LIST_HEAD(&pool->list);

        zswap_pool_debug("created", pool);

        return pool;

ref_fail:
        cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
error:
        if (pool->acomp_ctx)
                free_percpu(pool->acomp_ctx);
        if (pool->zpool)
                zpool_destroy_pool(pool->zpool);
        kfree(pool);
        return NULL;
}

static 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 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 ref... */
        WARN_ON(!percpu_ref_is_zero(&pool->ref));
        percpu_ref_exit(&pool->ref);

        /* pool is now off zswap_pools list and has no references. */
        zswap_pool_destroy(pool);
}

static struct zswap_pool *zswap_pool_current(void);

static void __zswap_pool_empty(struct percpu_ref *ref)
{
        struct zswap_pool *pool;

        pool = container_of(ref, typeof(*pool), ref);

        spin_lock_bh(&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_bh(&zswap_pools_lock);
}

static int __must_check zswap_pool_get(struct zswap_pool *pool)
{
        if (!pool)
                return 0;

        return percpu_ref_tryget(&pool->ref);
}

static void zswap_pool_put(struct zswap_pool *pool)
{
        percpu_ref_put(&pool->ref);
}

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;
}

/* 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 unsigned long zswap_max_pages(void)
{
        return totalram_pages() * zswap_max_pool_percent / 100;
}

static unsigned long zswap_accept_thr_pages(void)
{
        return zswap_max_pages() * zswap_accept_thr_percent / 100;
}

unsigned long zswap_total_pages(void)
{
        struct zswap_pool *pool;
        unsigned long total = 0;

        rcu_read_lock();
        list_for_each_entry_rcu(pool, &zswap_pools, list)
                total += zpool_get_total_pages(pool->zpool);
        rcu_read_unlock();

        return total;
}

static bool zswap_check_limits(void)
{
        unsigned long cur_pages = zswap_total_pages();
        unsigned long max_pages = zswap_max_pages();

        if (cur_pages >= max_pages) {
                zswap_pool_limit_hit++;
                zswap_pool_reached_full = true;
        } else if (zswap_pool_reached_full &&
                   cur_pages <= zswap_accept_thr_pages()) {
                        zswap_pool_reached_full = false;
        }
        return zswap_pool_reached_full;
}

/*********************************
* param callbacks
**********************************/

static bool zswap_pool_changed(const char *s, const struct kernel_param *kp)
{
        /* no change required */
        if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
                return false;
        return true;
}

/* 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 = 0;
        bool new_pool = false;

        mutex_lock(&zswap_init_lock);
        switch (zswap_init_state) {
        case ZSWAP_UNINIT:
                /* if this is load-time (pre-init) param setting,
                 * don't create a pool; that's done during init.
                 */
                ret = param_set_charp(s, kp);
                break;
        case ZSWAP_INIT_SUCCEED:
                new_pool = zswap_pool_changed(s, kp);
                break;
        case ZSWAP_INIT_FAILED:
                pr_err("can't set param, initialization failed\n");
                ret = -ENODEV;
        }
        mutex_unlock(&zswap_init_lock);

        /* no need to create a new pool, return directly */
        if (!new_pool)
                return ret;

        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_bh(&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_bh(&zswap_pools_lock);

        if (!pool)
                pool = zswap_pool_create(type, compressor);
        else {
                /*
                 * Restore the initial ref dropped by percpu_ref_kill()
                 * when the pool was decommissioned and switch it again
                 * to percpu mode.
                 */
                percpu_ref_resurrect(&pool->ref);

                /* Drop the ref from zswap_pool_find_get(). */
                zswap_pool_put(pool);
        }

        if (pool)
                ret = param_set_charp(s, kp);
        else
                ret = -EINVAL;

        spin_lock_bh(&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_bh(&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)
                percpu_ref_kill(&put_pool->ref);

        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)
{
        int ret = -ENODEV;

        /* if this is load-time (pre-init) param setting, only set param. */
        if (system_state != SYSTEM_RUNNING)
                return param_set_bool(val, kp);

        mutex_lock(&zswap_init_lock);
        switch (zswap_init_state) {
        case ZSWAP_UNINIT:
                if (zswap_setup())
                        break;
                fallthrough;
        case ZSWAP_INIT_SUCCEED:
                if (!zswap_has_pool)
                        pr_err("can't enable, no pool configured\n");
                else
                        ret = param_set_bool(val, kp);
                break;
        case ZSWAP_INIT_FAILED:
                pr_err("can't enable, initialization failed\n");
        }
        mutex_unlock(&zswap_init_lock);

        return ret;
}

/*********************************
* lru functions
**********************************/

/* should be called under RCU */
#ifdef CONFIG_MEMCG
static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
{
        return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
}
#else
static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
{
        return NULL;
}
#endif

static inline int entry_to_nid(struct zswap_entry *entry)
{
        return page_to_nid(virt_to_page(entry));
}

static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
{
        int nid = entry_to_nid(entry);
        struct mem_cgroup *memcg;

        /*
         * Note that it is safe to use rcu_read_lock() here, even in the face of
         * concurrent memcg offlining. Thanks to the memcg->kmemcg_id indirection
         * used in list_lru lookup, only two scenarios are possible:
         *
         * 1. list_lru_add() is called before memcg->kmemcg_id is updated. The
         *    new entry will be reparented to memcg's parent's list_lru.
         * 2. list_lru_add() is called after memcg->kmemcg_id is updated. The
         *    new entry will be added directly to memcg's parent's list_lru.
         *
         * Similar reasoning holds for list_lru_del().
         */
        rcu_read_lock();
        memcg = mem_cgroup_from_entry(entry);
        /* will always succeed */
        list_lru_add(list_lru, &entry->lru, nid, memcg);
        rcu_read_unlock();
}

static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry)
{
        int nid = entry_to_nid(entry);
        struct mem_cgroup *memcg;

        rcu_read_lock();
        memcg = mem_cgroup_from_entry(entry);
        /* will always succeed */
        list_lru_del(list_lru, &entry->lru, nid, memcg);
        rcu_read_unlock();
}

void zswap_lruvec_state_init(struct lruvec *lruvec)
{
        atomic_long_set(&lruvec->zswap_lruvec_state.nr_disk_swapins, 0);
}

void zswap_folio_swapin(struct folio *folio)
{
        struct lruvec *lruvec;

        if (folio) {
                lruvec = folio_lruvec(folio);
                atomic_long_inc(&lruvec->zswap_lruvec_state.nr_disk_swapins);
        }
}

/*
 * This function should be called when a memcg is being offlined.
 *
 * Since the global shrinker shrink_worker() may hold a reference
 * of the memcg, we must check and release the reference in
 * zswap_next_shrink.
 *
 * shrink_worker() must handle the case where this function releases
 * the reference of memcg being shrunk.
 */
void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg)
{
        /* lock out zswap shrinker walking memcg tree */
        spin_lock(&zswap_shrink_lock);
        if (zswap_next_shrink == memcg) {
                do {
                        zswap_next_shrink = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
                } while (zswap_next_shrink && !mem_cgroup_online(zswap_next_shrink));
        }
        spin_unlock(&zswap_shrink_lock);
}

/*********************************
* zswap entry functions
**********************************/
static struct kmem_cache *zswap_entry_cache;

static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int nid)
{
        struct zswap_entry *entry;
        entry = kmem_cache_alloc_node(zswap_entry_cache, gfp, nid);
        if (!entry)
                return NULL;
        return entry;
}

static void zswap_entry_cache_free(struct zswap_entry *entry)
{
        kmem_cache_free(zswap_entry_cache, entry);
}

/*
 * 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_entry_free(struct zswap_entry *entry)
{
        zswap_lru_del(&zswap_list_lru, entry);
        zpool_free(entry->pool->zpool, entry->handle);
        zswap_pool_put(entry->pool);
        if (entry->objcg) {
                obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
                obj_cgroup_put(entry->objcg);
        }
        zswap_entry_cache_free(entry);
        atomic_dec(&zswap_stored_pages);
}

/*********************************
* compressed storage functions
**********************************/
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;
        int ret;

        mutex_init(&acomp_ctx->mutex);

        acomp_ctx->buffer = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
        if (!acomp_ctx->buffer)
                return -ENOMEM;

        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));
                ret = PTR_ERR(acomp);
                goto acomp_fail;
        }
        acomp_ctx->acomp = acomp;
        acomp_ctx->is_sleepable = acomp_is_async(acomp);

        req = acomp_request_alloc(acomp_ctx->acomp);
        if (!req) {
                pr_err("could not alloc crypto acomp_request %s\n",
                       pool->tfm_name);
                ret = -ENOMEM;
                goto req_fail;
        }
        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);

        return 0;

req_fail:
        crypto_free_acomp(acomp_ctx->acomp);
acomp_fail:
        kfree(acomp_ctx->buffer);
        return ret;
}

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);
                kfree(acomp_ctx->buffer);
        }

        return 0;
}

static bool zswap_compress(struct folio *folio, struct zswap_entry *entry)
{
        struct crypto_acomp_ctx *acomp_ctx;
        struct scatterlist input, output;
        int comp_ret = 0, alloc_ret = 0;
        unsigned int dlen = PAGE_SIZE;
        unsigned long handle;
        struct zpool *zpool;
        char *buf;
        gfp_t gfp;
        u8 *dst;

        acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);

        mutex_lock(&acomp_ctx->mutex);

        dst = acomp_ctx->buffer;
        sg_init_table(&input, 1);
        sg_set_folio(&input, folio, PAGE_SIZE, 0);

        /*
         * We need PAGE_SIZE * 2 here since there maybe over-compression case,
         * and hardware-accelerators may won't check the dst buffer size, so
         * giving the dst buffer with enough length to avoid buffer overflow.
         */
        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, zswap 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 zwap.
         * but in different threads running on different cpu, we have different
         * acomp instance, so multiple threads can do (de)compression in parallel.
         */
        comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
        dlen = acomp_ctx->req->dlen;
        if (comp_ret)
                goto unlock;

        zpool = entry->pool->zpool;
        gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
        if (zpool_malloc_support_movable(zpool))
                gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
        alloc_ret = zpool_malloc(zpool, dlen, gfp, &handle);
        if (alloc_ret)
                goto unlock;

        buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
        memcpy(buf, dst, dlen);
        zpool_unmap_handle(zpool, handle);

        entry->handle = handle;
        entry->length = dlen;

unlock:
        if (comp_ret == -ENOSPC || alloc_ret == -ENOSPC)
                zswap_reject_compress_poor++;
        else if (comp_ret)
                zswap_reject_compress_fail++;
        else if (alloc_ret)
                zswap_reject_alloc_fail++;

        mutex_unlock(&acomp_ctx->mutex);
        return comp_ret == 0 && alloc_ret == 0;
}

static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
{
        struct zpool *zpool = entry->pool->zpool;
        struct scatterlist input, output;
        struct crypto_acomp_ctx *acomp_ctx;
        u8 *src;

        acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
        mutex_lock(&acomp_ctx->mutex);

        src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
        /*
         * If zpool_map_handle is atomic, we cannot reliably utilize its mapped buffer
         * to do crypto_acomp_decompress() which might sleep. In such cases, we must
         * resort to copying the buffer to a temporary one.
         * Meanwhile, zpool_map_handle() might return a non-linearly mapped buffer,
         * such as a kmap address of high memory or even ever a vmap address.
         * However, sg_init_one is only equipped to handle linearly mapped low memory.
         * In such cases, we also must copy the buffer to a temporary and lowmem one.
         */
        if ((acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) ||
            !virt_addr_valid(src)) {
                memcpy(acomp_ctx->buffer, src, entry->length);
                src = acomp_ctx->buffer;
                zpool_unmap_handle(zpool, entry->handle);
        }

        sg_init_one(&input, src, entry->length);
        sg_init_table(&output, 1);
        sg_set_folio(&output, folio, PAGE_SIZE, 0);
        acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, PAGE_SIZE);
        BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
        BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
        mutex_unlock(&acomp_ctx->mutex);

        if (src != acomp_ctx->buffer)
                zpool_unmap_handle(zpool, entry->handle);
}

/*********************************
* writeback code
**********************************/
/*
 * Attempts to free an entry by adding a folio to the swap cache,
 * decompressing the entry data into the folio, and issuing a
 * bio write to write the folio back to the swap device.
 *
 * This can be thought of as a "resumed writeback" of the folio
 * to the swap device.  We are basically resuming the same swap
 * writeback path that was intercepted with the zswap_store()
 * in the first place.  After the folio has been decompressed into
 * the swap cache, the compressed version stored by zswap can be
 * freed.
 */
static int zswap_writeback_entry(struct zswap_entry *entry,
                                 swp_entry_t swpentry)
{
        struct xarray *tree;
        pgoff_t offset = swp_offset(swpentry);
        struct folio *folio;
        struct mempolicy *mpol;
        bool folio_was_allocated;
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_NONE,
        };

        /* try to allocate swap cache folio */
        mpol = get_task_policy(current);
        folio = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
                                NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
        if (!folio)
                return -ENOMEM;

        /*
         * Found an existing folio, we raced with swapin or concurrent
         * shrinker. We generally writeback cold folios from zswap, and
         * swapin means the folio just became hot, so skip this folio.
         * For unlikely concurrent shrinker case, it will be unlinked
         * and freed when invalidated by the concurrent shrinker anyway.
         */
        if (!folio_was_allocated) {
                folio_put(folio);
                return -EEXIST;
        }

        /*
         * folio is locked, and the swapcache is now secured against
         * concurrent swapping to and from the slot, and concurrent
         * swapoff so we can safely dereference the zswap tree here.
         * Verify that the swap entry hasn't been invalidated and recycled
         * behind our backs, to avoid overwriting a new swap folio with
         * old compressed data. Only when this is successful can the entry
         * be dereferenced.
         */
        tree = swap_zswap_tree(swpentry);
        if (entry != xa_cmpxchg(tree, offset, entry, NULL, GFP_KERNEL)) {
                delete_from_swap_cache(folio);
                folio_unlock(folio);
                folio_put(folio);
                return -ENOMEM;
        }

        zswap_decompress(entry, folio);

        count_vm_event(ZSWPWB);
        if (entry->objcg)
                count_objcg_event(entry->objcg, ZSWPWB);

        zswap_entry_free(entry);

        /* folio is up to date */
        folio_mark_uptodate(folio);

        /* move it to the tail of the inactive list after end_writeback */
        folio_set_reclaim(folio);

        /* start writeback */
        __swap_writepage(folio, &wbc);
        folio_put(folio);

        return 0;
}

/*********************************
* shrinker functions
**********************************/
/*
 * The dynamic shrinker is modulated by the following factors:
 *
 * 1. Each zswap entry has a referenced bit, which the shrinker unsets (giving
 *    the entry a second chance) before rotating it in the LRU list. If the
 *    entry is considered again by the shrinker, with its referenced bit unset,
 *    it is written back. The writeback rate as a result is dynamically
 *    adjusted by the pool activities - if the pool is dominated by new entries
 *    (i.e lots of recent zswapouts), these entries will be protected and
 *    the writeback rate will slow down. On the other hand, if the pool has a
 *    lot of stagnant entries, these entries will be reclaimed immediately,
 *    effectively increasing the writeback rate.
 *
 * 2. Swapins counter: If we observe swapins, it is a sign that we are
 *    overshrinking and should slow down. We maintain a swapins counter, which
 *    is consumed and subtract from the number of eligible objects on the LRU
 *    in zswap_shrinker_count().
 *
 * 3. Compression ratio. The better the workload compresses, the less gains we
 *    can expect from writeback. We scale down the number of objects available
 *    for reclaim by this ratio.
 */
static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
                                       spinlock_t *lock, void *arg)
{
        struct zswap_entry *entry = container_of(item, struct zswap_entry, lru);
        bool *encountered_page_in_swapcache = (bool *)arg;
        swp_entry_t swpentry;
        enum lru_status ret = LRU_REMOVED_RETRY;
        int writeback_result;

        /*
         * Second chance algorithm: if the entry has its referenced bit set, give it
         * a second chance. Only clear the referenced bit and rotate it in the
         * zswap's LRU list.
         */
        if (entry->referenced) {
                entry->referenced = false;
                return LRU_ROTATE;
        }

        /*
         * As soon as we drop the LRU lock, the entry can be freed by
         * a concurrent invalidation. This means the following:
         *
         * 1. We extract the swp_entry_t to the stack, allowing
         *    zswap_writeback_entry() to pin the swap entry and
         *    then validate the zwap entry against that swap entry's
         *    tree using pointer value comparison. Only when that
         *    is successful can the entry be dereferenced.
         *
         * 2. Usually, objects are taken off the LRU for reclaim. In
         *    this case this isn't possible, because if reclaim fails
         *    for whatever reason, we have no means of knowing if the
         *    entry is alive to put it back on the LRU.
         *
         *    So rotate it before dropping the lock. If the entry is
         *    written back or invalidated, the free path will unlink
         *    it. For failures, rotation is the right thing as well.
         *
         *    Temporary failures, where the same entry should be tried
         *    again immediately, almost never happen for this shrinker.
         *    We don't do any trylocking; -ENOMEM comes closest,
         *    but that's extremely rare and doesn't happen spuriously
         *    either. Don't bother distinguishing this case.
         */
        list_move_tail(item, &l->list);

        /*
         * Once the lru lock is dropped, the entry might get freed. The
         * swpentry is copied to the stack, and entry isn't deref'd again
         * until the entry is verified to still be alive in the tree.
         */
        swpentry = entry->swpentry;

        /*
         * It's safe to drop the lock here because we return either
         * LRU_REMOVED_RETRY or LRU_RETRY.
         */
        spin_unlock(lock);

        writeback_result = zswap_writeback_entry(entry, swpentry);

        if (writeback_result) {
                zswap_reject_reclaim_fail++;
                ret = LRU_RETRY;

                /*
                 * Encountering a page already in swap cache is a sign that we are shrinking
                 * into the warmer region. We should terminate shrinking (if we're in the dynamic
                 * shrinker context).
                 */
                if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
                        ret = LRU_STOP;
                        *encountered_page_in_swapcache = true;
                }
        } else {
                zswap_written_back_pages++;
        }

        spin_lock(lock);
        return ret;
}

static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,
                struct shrink_control *sc)
{
        unsigned long shrink_ret;
        bool encountered_page_in_swapcache = false;

        if (!zswap_shrinker_enabled ||
                        !mem_cgroup_zswap_writeback_enabled(sc->memcg)) {
                sc->nr_scanned = 0;
                return SHRINK_STOP;
        }

        shrink_ret = list_lru_shrink_walk(&zswap_list_lru, sc, &shrink_memcg_cb,
                &encountered_page_in_swapcache);

        if (encountered_page_in_swapcache)
                return SHRINK_STOP;

        return shrink_ret ? shrink_ret : SHRINK_STOP;
}

static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
                struct shrink_control *sc)
{
        struct mem_cgroup *memcg = sc->memcg;
        struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid));
        atomic_long_t *nr_disk_swapins =
                &lruvec->zswap_lruvec_state.nr_disk_swapins;
        unsigned long nr_backing, nr_stored, nr_freeable, nr_disk_swapins_cur,
                nr_remain;

        if (!zswap_shrinker_enabled || !mem_cgroup_zswap_writeback_enabled(memcg))
                return 0;

        /*
         * The shrinker resumes swap writeback, which will enter block
         * and may enter fs. XXX: Harmonize with vmscan.c __GFP_FS
         * rules (may_enter_fs()), which apply on a per-folio basis.
         */
        if (!gfp_has_io_fs(sc->gfp_mask))
                return 0;

        /*
         * For memcg, use the cgroup-wide ZSWAP stats since we don't
         * have them per-node and thus per-lruvec. Careful if memcg is
         * runtime-disabled: we can get sc->memcg == NULL, which is ok
         * for the lruvec, but not for memcg_page_state().
         *
         * Without memcg, use the zswap pool-wide metrics.
         */
        if (!mem_cgroup_disabled()) {
                mem_cgroup_flush_stats(memcg);
                nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
                nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
        } else {
                nr_backing = zswap_total_pages();
                nr_stored = atomic_read(&zswap_stored_pages);
        }

        if (!nr_stored)
                return 0;

        nr_freeable = list_lru_shrink_count(&zswap_list_lru, sc);
        if (!nr_freeable)
                return 0;

        /*
         * Subtract from the lru size the number of pages that are recently swapped
         * in from disk. The idea is that had we protect the zswap's LRU by this
         * amount of pages, these disk swapins would not have happened.
         */
        nr_disk_swapins_cur = atomic_long_read(nr_disk_swapins);
        do {
                if (nr_freeable >= nr_disk_swapins_cur)
                        nr_remain = 0;
                else
                        nr_remain = nr_disk_swapins_cur - nr_freeable;
        } while (!atomic_long_try_cmpxchg(
                nr_disk_swapins, &nr_disk_swapins_cur, nr_remain));

        nr_freeable -= nr_disk_swapins_cur - nr_remain;
        if (!nr_freeable)
                return 0;

        /*
         * Scale the number of freeable pages by the memory saving factor.
         * This ensures that the better zswap compresses memory, the fewer
         * pages we will evict to swap (as it will otherwise incur IO for
         * relatively small memory saving).
         */
        return mult_frac(nr_freeable, nr_backing, nr_stored);
}

static struct shrinker *zswap_alloc_shrinker(void)
{
        struct shrinker *shrinker;

        shrinker =
                shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap");
        if (!shrinker)
                return NULL;

        shrinker->scan_objects = zswap_shrinker_scan;
        shrinker->count_objects = zswap_shrinker_count;
        shrinker->batch = 0;
        shrinker->seeks = DEFAULT_SEEKS;
        return shrinker;
}

static int shrink_memcg(struct mem_cgroup *memcg)
{
        int nid, shrunk = 0, scanned = 0;

        if (!mem_cgroup_zswap_writeback_enabled(memcg))
                return -ENOENT;

        /*
         * Skip zombies because their LRUs are reparented and we would be
         * reclaiming from the parent instead of the dead memcg.
         */
        if (memcg && !mem_cgroup_online(memcg))
                return -ENOENT;

        for_each_node_state(nid, N_NORMAL_MEMORY) {
                unsigned long nr_to_walk = 1;

                shrunk += list_lru_walk_one(&zswap_list_lru, nid, memcg,
                                            &shrink_memcg_cb, NULL, &nr_to_walk);
                scanned += 1 - nr_to_walk;
        }

        if (!scanned)
                return -ENOENT;

        return shrunk ? 0 : -EAGAIN;
}

static void shrink_worker(struct work_struct *w)
{
        struct mem_cgroup *memcg;
        int ret, failures = 0, attempts = 0;
        unsigned long thr;

        /* Reclaim down to the accept threshold */
        thr = zswap_accept_thr_pages();

        /*
         * Global reclaim will select cgroup in a round-robin fashion from all
         * online memcgs, but memcgs that have no pages in zswap and
         * writeback-disabled memcgs (memory.zswap.writeback=0) are not
         * candidates for shrinking.
         *
         * Shrinking will be aborted if we encounter the following
         * MAX_RECLAIM_RETRIES times:
         * - No writeback-candidate memcgs found in a memcg tree walk.
         * - Shrinking a writeback-candidate memcg failed.
         *
         * We save iteration cursor memcg into zswap_next_shrink,
         * which can be modified by the offline memcg cleaner
         * zswap_memcg_offline_cleanup().
         *
         * Since the offline cleaner is called only once, we cannot leave an
         * offline memcg reference in zswap_next_shrink.
         * We can rely on the cleaner only if we get online memcg under lock.
         *
         * If we get an offline memcg, we cannot determine if the cleaner has
         * already been called or will be called later. We must put back the
         * reference before returning from this function. Otherwise, the
         * offline memcg left in zswap_next_shrink will hold the reference
         * until the next run of shrink_worker().
         */
        do {
                /*
                 * Start shrinking from the next memcg after zswap_next_shrink.
                 * When the offline cleaner has already advanced the cursor,
                 * advancing the cursor here overlooks one memcg, but this
                 * should be negligibly rare.
                 *
                 * If we get an online memcg, keep the extra reference in case
                 * the original one obtained by mem_cgroup_iter() is dropped by
                 * zswap_memcg_offline_cleanup() while we are shrinking the
                 * memcg.
                 */
                spin_lock(&zswap_shrink_lock);
                do {
                        memcg = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
                        zswap_next_shrink = memcg;
                } while (memcg && !mem_cgroup_tryget_online(memcg));
                spin_unlock(&zswap_shrink_lock);

                if (!memcg) {
                        /*
                         * Continue shrinking without incrementing failures if
                         * we found candidate memcgs in the last tree walk.
                         */
                        if (!attempts && ++failures == MAX_RECLAIM_RETRIES)
                                break;

                        attempts = 0;
                        goto resched;
                }

                ret = shrink_memcg(memcg);
                /* drop the extra reference */
                mem_cgroup_put(memcg);

                /*
                 * There are no writeback-candidate pages in the memcg.
                 * This is not an issue as long as we can find another memcg
                 * with pages in zswap. Skip this without incrementing attempts
                 * and failures.
                 */
                if (ret == -ENOENT)
                        continue;
                ++attempts;

                if (ret && ++failures == MAX_RECLAIM_RETRIES)
                        break;
resched:
                cond_resched();
        } while (zswap_total_pages() > thr);
}

/*********************************
* main API
**********************************/
bool zswap_store(struct folio *folio)
{
        swp_entry_t swp = folio->swap;
        pgoff_t offset = swp_offset(swp);
        struct xarray *tree = swap_zswap_tree(swp);
        struct zswap_entry *entry, *old;
        struct obj_cgroup *objcg = NULL;
        struct mem_cgroup *memcg = NULL;

        VM_WARN_ON_ONCE(!folio_test_locked(folio));
        VM_WARN_ON_ONCE(!folio_test_swapcache(folio));

        /* Large folios aren't supported */
        if (folio_test_large(folio))
                return false;

        if (!zswap_enabled)
                goto check_old;

        /* Check cgroup limits */
        objcg = get_obj_cgroup_from_folio(folio);
        if (objcg && !obj_cgroup_may_zswap(objcg)) {
                memcg = get_mem_cgroup_from_objcg(objcg);
                if (shrink_memcg(memcg)) {
                        mem_cgroup_put(memcg);
                        goto reject;
                }
                mem_cgroup_put(memcg);
        }

        if (zswap_check_limits())
                goto reject;

        /* allocate entry */
        entry = zswap_entry_cache_alloc(GFP_KERNEL, folio_nid(folio));
        if (!entry) {
                zswap_reject_kmemcache_fail++;
                goto reject;
        }

        /* if entry is successfully added, it keeps the reference */
        entry->pool = zswap_pool_current_get();
        if (!entry->pool)
                goto freepage;

        if (objcg) {
                memcg = get_mem_cgroup_from_objcg(objcg);
                if (memcg_list_lru_alloc(memcg, &zswap_list_lru, GFP_KERNEL)) {
                        mem_cgroup_put(memcg);
                        goto put_pool;
                }
                mem_cgroup_put(memcg);
        }

        if (!zswap_compress(folio, entry))
                goto put_pool;

        entry->swpentry = swp;
        entry->objcg = objcg;
        entry->referenced = true;

        old = xa_store(tree, offset, entry, GFP_KERNEL);
        if (xa_is_err(old)) {
                int err = xa_err(old);

                WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err);
                zswap_reject_alloc_fail++;
                goto store_failed;
        }

        /*
         * We may have had an existing entry that became stale when
         * the folio was redirtied and now the new version is being
         * swapped out. Get rid of the old.
         */
        if (old)
                zswap_entry_free(old);

        if (objcg) {
                obj_cgroup_charge_zswap(objcg, entry->length);
                count_objcg_event(objcg, ZSWPOUT);
        }

        /*
         * We finish initializing the entry while it's already in xarray.
         * This is safe because:
         *
         * 1. Concurrent stores and invalidations are excluded by folio lock.
         *
         * 2. Writeback is excluded by the entry not being on the LRU yet.
         *    The publishing order matters to prevent writeback from seeing
         *    an incoherent entry.
         */
        if (entry->length) {
                INIT_LIST_HEAD(&entry->lru);
                zswap_lru_add(&zswap_list_lru, entry);
        }

        /* update stats */
        atomic_inc(&zswap_stored_pages);
        count_vm_event(ZSWPOUT);

        return true;

store_failed:
        zpool_free(entry->pool->zpool, entry->handle);
put_pool:
        zswap_pool_put(entry->pool);
freepage:
        zswap_entry_cache_free(entry);
reject:
        obj_cgroup_put(objcg);
        if (zswap_pool_reached_full)
                queue_work(shrink_wq, &zswap_shrink_work);
check_old:
        /*
         * If the zswap store fails or zswap is disabled, we must invalidate the
         * possibly stale entry which was previously stored at this offset.
         * Otherwise, writeback could overwrite the new data in the swapfile.
         */
        entry = xa_erase(tree, offset);
        if (entry)
                zswap_entry_free(entry);
        return false;
}

bool zswap_load(struct folio *folio)
{
        swp_entry_t swp = folio->swap;
        pgoff_t offset = swp_offset(swp);
        bool swapcache = folio_test_swapcache(folio);
        struct xarray *tree = swap_zswap_tree(swp);
        struct zswap_entry *entry;

        VM_WARN_ON_ONCE(!folio_test_locked(folio));

        if (zswap_never_enabled())
                return false;

        /*
         * Large folios should not be swapped in while zswap is being used, as
         * they are not properly handled. Zswap does not properly load large
         * folios, and a large folio may only be partially in zswap.
         *
         * Return true without marking the folio uptodate so that an IO error is
         * emitted (e.g. do_swap_page() will sigbus).
         */
        if (WARN_ON_ONCE(folio_test_large(folio)))
                return true;

        /*
         * When reading into the swapcache, invalidate our entry. The
         * swapcache can be the authoritative owner of the page and
         * its mappings, and the pressure that results from having two
         * in-memory copies outweighs any benefits of caching the
         * compression work.
         *
         * (Most swapins go through the swapcache. The notable
         * exception is the singleton fault on SWP_SYNCHRONOUS_IO
         * files, which reads into a private page and may free it if
         * the fault fails. We remain the primary owner of the entry.)
         */
        if (swapcache)
                entry = xa_erase(tree, offset);
        else
                entry = xa_load(tree, offset);

        if (!entry)
                return false;

        zswap_decompress(entry, folio);

        count_vm_event(ZSWPIN);
        if (entry->objcg)
                count_objcg_event(entry->objcg, ZSWPIN);

        if (swapcache) {
                zswap_entry_free(entry);
                folio_mark_dirty(folio);
        }

        folio_mark_uptodate(folio);
        return true;
}

void zswap_invalidate(swp_entry_t swp)
{
        pgoff_t offset = swp_offset(swp);
        struct xarray *tree = swap_zswap_tree(swp);
        struct zswap_entry *entry;

        entry = xa_erase(tree, offset);
        if (entry)
                zswap_entry_free(entry);
}

int zswap_swapon(int type, unsigned long nr_pages)
{
        struct xarray *trees, *tree;
        unsigned int nr, i;

        nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
        trees = kvcalloc(nr, sizeof(*tree), GFP_KERNEL);
        if (!trees) {
                pr_err("alloc failed, zswap disabled for swap type %d\n", type);
                return -ENOMEM;
        }

        for (i = 0; i < nr; i++)
                xa_init(trees + i);

        nr_zswap_trees[type] = nr;
        zswap_trees[type] = trees;
        return 0;
}

void zswap_swapoff(int type)
{
        struct xarray *trees = zswap_trees[type];
        unsigned int i;

        if (!trees)
                return;

        /* try_to_unuse() invalidated all the entries already */
        for (i = 0; i < nr_zswap_trees[type]; i++)
                WARN_ON_ONCE(!xa_empty(trees + i));

        kvfree(trees);
        nr_zswap_trees[type] = 0;
        zswap_trees[type] = NULL;
}

/*********************************
* debugfs functions
**********************************/
#ifdef CONFIG_DEBUG_FS
#include <linux/debugfs.h>

static struct dentry *zswap_debugfs_root;

static int debugfs_get_total_size(void *data, u64 *val)
{
        *val = zswap_total_pages() * PAGE_SIZE;
        return 0;
}
DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu\n");

static int 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_fail", 0444,
                           zswap_debugfs_root, &zswap_reject_compress_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_file("pool_total_size", 0444,
                            zswap_debugfs_root, NULL, &total_size_fops);
        debugfs_create_atomic_t("stored_pages", 0444,
                                zswap_debugfs_root, &zswap_stored_pages);

        return 0;
}
#else
static int zswap_debugfs_init(void)
{
        return 0;
}
#endif

/*********************************
* module init and exit
**********************************/
static int zswap_setup(void)
{
        struct zswap_pool *pool;
        int ret;

        zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
        if (!zswap_entry_cache) {
                pr_err("entry cache creation failed\n");
                goto cache_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;

        shrink_wq = alloc_workqueue("zswap-shrink",
                        WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
        if (!shrink_wq)
                goto shrink_wq_fail;

        zswap_shrinker = zswap_alloc_shrinker();
        if (!zswap_shrinker)
                goto shrinker_fail;
        if (list_lru_init_memcg(&zswap_list_lru, zswap_shrinker))
                goto lru_fail;
        shrinker_register(zswap_shrinker);

        INIT_WORK(&zswap_shrink_work, shrink_worker);

        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;
                static_branch_enable(&zswap_ever_enabled);
        } else {
                pr_err("pool creation failed\n");
                zswap_enabled = false;
        }

        if (zswap_debugfs_init())
                pr_warn("debugfs initialization failed\n");
        zswap_init_state = ZSWAP_INIT_SUCCEED;
        return 0;

lru_fail:
        shrinker_free(zswap_shrinker);
shrinker_fail:
        destroy_workqueue(shrink_wq);
shrink_wq_fail:
        cpuhp_remove_multi_state(CPUHP_MM_ZSWP_POOL_PREPARE);
hp_fail:
        kmem_cache_destroy(zswap_entry_cache);
cache_fail:
        /* if built-in, we aren't unloaded on failure; don't allow use */
        zswap_init_state = ZSWAP_INIT_FAILED;
        zswap_enabled = false;
        return -ENOMEM;
}

static int __init zswap_init(void)
{
        if (!zswap_enabled)
                return 0;
        return zswap_setup();
}
/* must be late so crypto has time to come up */
late_initcall(zswap_init);

MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>");
MODULE_DESCRIPTION("Compressed cache for swap pages");