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OpenCloudOS-Kernel/mm/zswap.c

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// 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/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/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 "swap.h"
#include "internal.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 ""
static int zswap_setup(void);
/* 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);
static bool zswap_exclusive_loads_enabled = IS_ENABLED(
CONFIG_ZSWAP_EXCLUSIVE_LOADS_DEFAULT_ON);
module_param_named(exclusive_loads, zswap_exclusive_loads_enabled, bool, 0644);
/* Number of zpools in zswap_pool (empirically determined for scalability) */
#define ZSWAP_NR_ZPOOLS 32
/*********************************
* data structures
**********************************/
struct crypto_acomp_ctx {
struct crypto_acomp *acomp;
struct acomp_req *req;
struct crypto_wait wait;
u8 *dstmem;
struct mutex *mutex;
};
/*
* 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 *zpools[ZSWAP_NR_ZPOOLS];
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 list_head lru;
spinlock_t lru_lock;
};
/*
* 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
* swpentry - associated swap entry, the offset indexes 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, and both
* pool and lru are invalid and must be ignored.
* 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 {
struct rb_node rbnode;
swp_entry_t swpentry;
int refcount;
unsigned int length;
struct zswap_pool *pool;
union {
unsigned long handle;
unsigned long value;
};
struct obj_cgroup *objcg;
struct list_head lru;
};
/*
* 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);
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
**********************************/
#define zswap_pool_debug(msg, p) \
pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name, \
zpool_get_type((p)->zpools[0]))
static int zswap_writeback_entry(struct zswap_entry *entry,
struct zswap_tree *tree);
static int zswap_pool_get(struct zswap_pool *pool);
static void zswap_pool_put(struct zswap_pool *pool);
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;
int i;
rcu_read_lock();
list_for_each_entry_rcu(pool, &zswap_pools, list)
for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
total += zpool_get_total_size(pool->zpools[i]);
rcu_read_unlock();
zswap_pool_total_size = total;
}
/*********************************
* zswap entry functions
**********************************/
static struct kmem_cache *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;
pgoff_t entry_offset;
while (node) {
entry = rb_entry(node, struct zswap_entry, rbnode);
entry_offset = swp_offset(entry->swpentry);
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;
pgoff_t myentry_offset, entry_offset = swp_offset(entry->swpentry);
while (*link) {
parent = *link;
myentry = rb_entry(parent, struct zswap_entry, rbnode);
myentry_offset = swp_offset(myentry->swpentry);
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 bool 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);
return true;
}
return false;
}
static struct zpool *zswap_find_zpool(struct zswap_entry *entry)
{
int i = 0;
if (ZSWAP_NR_ZPOOLS > 1)
i = hash_ptr(entry, ilog2(ZSWAP_NR_ZPOOLS));
return entry->pool->zpools[i];
}
/*
* 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 {
spin_lock(&entry->pool->lru_lock);
list_del(&entry->lru);
spin_unlock(&entry->pool->lru_lock);
zpool_free(zswap_find_zpool(entry), 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;
WARN_ON_ONCE(refcount < 0);
if (refcount == 0) {
WARN_ON_ONCE(!RB_EMPTY_NODE(&entry->rbnode));
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;
/* all zpools share the same type */
if (strcmp(zpool_get_type(pool->zpools[0]), type))
continue;
/* if we can't get it, it's about to be destroyed */
if (!zswap_pool_get(pool))
continue;
return pool;
}
return NULL;
}
/*
* If the entry is still valid in the tree, drop the initial ref and remove it
* from the tree. This function must be called with an additional ref held,
* otherwise it may race with another invalidation freeing the entry.
*/
static void zswap_invalidate_entry(struct zswap_tree *tree,
struct zswap_entry *entry)
{
if (zswap_rb_erase(&tree->rbroot, entry))
zswap_entry_put(tree, entry);
}
static int zswap_reclaim_entry(struct zswap_pool *pool)
{
struct zswap_entry *entry;
struct zswap_tree *tree;
pgoff_t swpoffset;
int ret;
/* Get an entry off the LRU */
spin_lock(&pool->lru_lock);
if (list_empty(&pool->lru)) {
spin_unlock(&pool->lru_lock);
return -EINVAL;
}
entry = list_last_entry(&pool->lru, struct zswap_entry, lru);
list_del_init(&entry->lru);
/*
* Once the lru lock is dropped, the entry might get freed. The
* swpoffset is copied to the stack, and entry isn't deref'd again
* until the entry is verified to still be alive in the tree.
*/
swpoffset = swp_offset(entry->swpentry);
tree = zswap_trees[swp_type(entry->swpentry)];
spin_unlock(&pool->lru_lock);
/* Check for invalidate() race */
spin_lock(&tree->lock);
if (entry != zswap_rb_search(&tree->rbroot, swpoffset)) {
ret = -EAGAIN;
goto unlock;
}
/* Hold a reference to prevent a free during writeback */
zswap_entry_get(entry);
spin_unlock(&tree->lock);
ret = zswap_writeback_entry(entry, tree);
spin_lock(&tree->lock);
if (ret) {
/* Writeback failed, put entry back on LRU */
spin_lock(&pool->lru_lock);
list_move(&entry->lru, &pool->lru);
spin_unlock(&pool->lru_lock);
goto put_unlock;
}
/*
* Writeback started successfully, the page now belongs to the
* swapcache. Drop the entry from zswap - unless invalidate already
* took it out while we had the tree->lock released for IO.
*/
zswap_invalidate_entry(tree, entry);
put_unlock:
/* Drop local reference */
zswap_entry_put(tree, entry);
unlock:
spin_unlock(&tree->lock);
return ret ? -EAGAIN : 0;
}
static void shrink_worker(struct work_struct *w)
{
struct zswap_pool *pool = container_of(w, typeof(*pool),
shrink_work);
int ret, failures = 0;
do {
ret = zswap_reclaim_entry(pool);
if (ret) {
zswap_reject_reclaim_fail++;
if (ret != -EAGAIN)
break;
if (++failures == MAX_RECLAIM_RETRIES)
break;
}
cond_resched();
} while (!zswap_can_accept());
zswap_pool_put(pool);
}
static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
{
int i;
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;
for (i = 0; i < ZSWAP_NR_ZPOOLS; i++) {
/* unique name for each pool specifically required by zsmalloc */
snprintf(name, 38, "zswap%x",
atomic_inc_return(&zswap_pools_count));
pool->zpools[i] = zpool_create_pool(type, name, gfp);
if (!pool->zpools[i]) {
pr_err("%s zpool not available\n", type);
goto error;
}
}
pr_debug("using %s zpool\n", zpool_get_type(pool->zpools[0]));
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_LIST_HEAD(&pool->lru);
spin_lock_init(&pool->lru_lock);
INIT_WORK(&pool->shrink_work, shrink_worker);
zswap_pool_debug("created", pool);
return pool;
error:
if (pool->acomp_ctx)
free_percpu(pool->acomp_ctx);
while (i--)
zpool_destroy_pool(pool->zpools[i]);
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)
{
int i;
zswap_pool_debug("destroying", pool);
cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
free_percpu(pool->acomp_ctx);
for (i = 0; i < ZSWAP_NR_ZPOOLS; i++)
zpool_destroy_pool(pool->zpools[i]);
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
**********************************/
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(&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)
{
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;
}
/*********************************
* writeback code
**********************************/
/*
* 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 zswap_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 zswap_entry *entry,
struct zswap_tree *tree)
{
swp_entry_t swpentry = entry->swpentry;
struct page *page;
struct scatterlist input, output;
struct crypto_acomp_ctx *acomp_ctx;
struct zpool *pool = zswap_find_zpool(entry);
bool page_was_allocated;
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_KERNEL);
if (!tmp)
return -ENOMEM;
}
/* try to allocate swap cache page */
page = __read_swap_cache_async(swpentry, GFP_KERNEL, NULL, 0,
&page_was_allocated);
if (!page) {
ret = -ENOMEM;
goto fail;
}
/* Found an existing page, we raced with load/swapin */
if (!page_was_allocated) {
put_page(page);
ret = -EEXIST;
goto fail;
}
/*
* Page is locked, and the swapcache is now secured against
* concurrent swapping to and from the slot. Verify that the
* swap entry hasn't been invalidated and recycled behind our
* backs (our zswap_entry reference doesn't prevent that), to
* avoid overwriting a new swap page with old compressed data.
*/
spin_lock(&tree->lock);
if (zswap_rb_search(&tree->rbroot, swp_offset(entry->swpentry)) != entry) {
spin_unlock(&tree->lock);
delete_from_swap_cache(page_folio(page));
ret = -ENOMEM;
goto fail;
}
spin_unlock(&tree->lock);
/* decompress */
acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
dlen = PAGE_SIZE;
src = zpool_map_handle(pool, entry->handle, ZPOOL_MM_RO);
if (!zpool_can_sleep_mapped(pool)) {
memcpy(tmp, src, entry->length);
src = tmp;
zpool_unmap_handle(pool, entry->handle);
}
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);
if (!zpool_can_sleep_mapped(pool))
kfree(tmp);
else
zpool_unmap_handle(pool, entry->handle);
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);
put_page(page);
zswap_written_back_pages++;
return ret;
fail:
if (!zpool_can_sleep_mapped(pool))
kfree(tmp);
/*
* If we get here because the page is already in swapcache, a
* load may be happening concurrently. It is safe and okay to
* not free the entry. It is also okay to return !0.
*/
return ret;
}
static int zswap_is_page_same_filled(void *ptr, unsigned long *value)
{
unsigned long *page;
unsigned long val;
unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1;
page = (unsigned long *)ptr;
val = page[0];
if (val != page[last_pos])
return 0;
for (pos = 1; pos < last_pos; pos++) {
if (val != page[pos])
return 0;
}
*value = val;
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));
}
bool zswap_store(struct folio *folio)
{
swp_entry_t swp = folio->swap;
int type = swp_type(swp);
pgoff_t offset = swp_offset(swp);
struct page *page = &folio->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;
struct zpool *zpool;
unsigned int dlen = PAGE_SIZE;
unsigned long handle, value;
char *buf;
u8 *src, *dst;
gfp_t gfp;
int ret;
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 || !tree)
return false;
/*
* If this is a duplicate, it must be removed before attempting to store
* it, otherwise, if the store fails the old page won't be removed from
* the tree, and it might be written back overriding the new data.
*/
spin_lock(&tree->lock);
dupentry = zswap_rb_search(&tree->rbroot, offset);
if (dupentry) {
zswap_duplicate_entry++;
zswap_invalidate_entry(tree, dupentry);
}
spin_unlock(&tree->lock);
/*
* XXX: zswap reclaim does not work with cgroups yet. Without a
* cgroup-aware entry LRU, we will push out entries system-wide based on
* local cgroup limits.
*/
objcg = get_obj_cgroup_from_folio(folio);
if (objcg && !obj_cgroup_may_zswap(objcg))
goto reject;
/* 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())
goto shrink;
else
zswap_pool_reached_full = false;
}
/* allocate entry */
entry = zswap_entry_cache_alloc(GFP_KERNEL);
if (!entry) {
zswap_reject_kmemcache_fail++;
goto reject;
}
if (zswap_same_filled_pages_enabled) {
src = kmap_atomic(page);
if (zswap_is_page_same_filled(src, &value)) {
kunmap_atomic(src);
entry->swpentry = swp_entry(type, 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)
goto freepage;
/* if entry is successfully added, it keeps the reference */
entry->pool = zswap_pool_current_get();
if (!entry->pool)
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, 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.
*/
ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
dlen = acomp_ctx->req->dlen;
if (ret)
goto put_dstmem;
/* store */
zpool = zswap_find_zpool(entry);
gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
if (zpool_malloc_support_movable(zpool))
gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
ret = zpool_malloc(zpool, 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(zpool, handle, ZPOOL_MM_WO);
memcpy(buf, dst, dlen);
zpool_unmap_handle(zpool, handle);
mutex_unlock(acomp_ctx->mutex);
/* populate entry */
entry->swpentry = swp_entry(type, 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);
/*
* A duplicate entry should have been removed at the beginning of this
* function. Since the swap entry should be pinned, if a duplicate is
* found again here it means that something went wrong in the swap
* cache.
*/
while (zswap_rb_insert(&tree->rbroot, entry, &dupentry) == -EEXIST) {
WARN_ON(1);
zswap_duplicate_entry++;
zswap_invalidate_entry(tree, dupentry);
}
if (entry->length) {
spin_lock(&entry->pool->lru_lock);
list_add(&entry->lru, &entry->pool->lru);
spin_unlock(&entry->pool->lru_lock);
}
spin_unlock(&tree->lock);
/* update stats */
atomic_inc(&zswap_stored_pages);
zswap_update_total_size();
count_vm_event(ZSWPOUT);
return true;
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 false;
shrink:
pool = zswap_pool_last_get();
if (pool && !queue_work(shrink_wq, &pool->shrink_work))
zswap_pool_put(pool);
goto reject;
}
bool zswap_load(struct folio *folio)
{
swp_entry_t swp = folio->swap;
int type = swp_type(swp);
pgoff_t offset = swp_offset(swp);
struct page *page = &folio->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;
struct zpool *zpool;
unsigned int dlen;
bool ret;
VM_WARN_ON_ONCE(!folio_test_locked(folio));
/* find */
spin_lock(&tree->lock);
entry = zswap_entry_find_get(&tree->rbroot, offset);
if (!entry) {
spin_unlock(&tree->lock);
return false;
}
spin_unlock(&tree->lock);
if (!entry->length) {
dst = kmap_atomic(page);
zswap_fill_page(dst, entry->value);
kunmap_atomic(dst);
ret = true;
goto stats;
}
zpool = zswap_find_zpool(entry);
if (!zpool_can_sleep_mapped(zpool)) {
tmp = kmalloc(entry->length, GFP_KERNEL);
if (!tmp) {
ret = false;
goto freeentry;
}
}
/* decompress */
dlen = PAGE_SIZE;
src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
if (!zpool_can_sleep_mapped(zpool)) {
memcpy(tmp, src, entry->length);
src = tmp;
zpool_unmap_handle(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);
if (crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait))
WARN_ON(1);
mutex_unlock(acomp_ctx->mutex);
if (zpool_can_sleep_mapped(zpool))
zpool_unmap_handle(zpool, entry->handle);
else
kfree(tmp);
ret = true;
stats:
count_vm_event(ZSWPIN);
if (entry->objcg)
count_objcg_event(entry->objcg, ZSWPIN);
freeentry:
spin_lock(&tree->lock);
if (ret && zswap_exclusive_loads_enabled) {
zswap_invalidate_entry(tree, entry);
folio_mark_dirty(folio);
} else if (entry->length) {
spin_lock(&entry->pool->lru_lock);
list_move(&entry->lru, &entry->pool->lru);
spin_unlock(&entry->pool->lru_lock);
}
zswap_entry_put(tree, entry);
spin_unlock(&tree->lock);
return ret;
}
void zswap_invalidate(int 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;
}
zswap_invalidate_entry(tree, entry);
spin_unlock(&tree->lock);
}
void zswap_swapon(int 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;
}
void zswap_swapoff(int 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;
}
/*********************************
* debugfs functions
**********************************/
#ifdef CONFIG_DEBUG_FS
#include <linux/debugfs.h>
static struct dentry *zswap_debugfs_root;
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_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 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(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->zpools[0]));
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;
if (zswap_debugfs_init())
pr_warn("debugfs initialization failed\n");
zswap_init_state = ZSWAP_INIT_SUCCEED;
return 0;
fallback_fail:
if (pool)
zswap_pool_destroy(pool);
hp_fail:
cpuhp_remove_state(CPUHP_MM_ZSWP_MEM_PREPARE);
dstmem_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");
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