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zswap.c
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/*
* zswap.c - zswap driver file
*
* zswap is a backend for frontswap that takes pages that are in the process
* of being swapped out and attempts to compress and store them in a
* RAM-based memory pool. This can result in a significant I/O reduction on
* the swap device and, in the case where decompressing from RAM is faster
* than reading from the swap device, can also improve workload performance.
*
* Copyright (C) 2012 Seth Jennings <[email protected]>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/frontswap.h>
#include <linux/rbtree.h>
#include <linux/swap.h>
#include <linux/blkdev.h>
#include <linux/swapfile.h>
#include <linux/crypto.h>
#include <linux/mempool.h>
#include <linux/zpool.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/jiffies.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#define CREATE_TRACE_POINTS
#include <trace/events/zswap.h>
/*********************************
* statistics
**********************************/
/* Total bytes used by the compressed storage */
static u64 zswap_pool_total_size;
/* Number of memory pages used by the compressed pool */
u64 zswap_pool_pages;
/* 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;
/* 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;
/* Writeback wakes up */
static u64 zswap_writebackd_wakeup;
/* The number of zero pages currently stored in zswap */
static atomic_t zswap_zero_pages = ATOMIC_INIT(0);
/*********************************
* tunables
**********************************/
/* Enable/disable zswap (disabled by default, fixed at boot for now) */
static bool zswap_enabled __read_mostly = 1;
module_param_named(enabled, zswap_enabled, bool, 0444);
/* Compressor to be used by zswap (fixed at boot for now) */
#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
#define ZSWAP_COMPRESSOR "lz4"
static char *zswap_compressor = ZSWAP_COMPRESSOR;
module_param_named(compressor, zswap_compressor, charp, 0444);
/* The maximum rate (1/1000) of memory that the compressed pool can occupy */
static unsigned int zswap_max_pool_percent = 500;
module_param_named(max_pool_percent,
zswap_max_pool_percent, uint, 0644);
static unsigned int zswap_high_pool_percent = 40;
module_param_named(high_pool_percent,
zswap_high_pool_percent, uint, 0644);
static unsigned int zswap_low_pool_percent = 38;
module_param_named(low_pool_percent,
zswap_low_pool_percent, uint, 0644);
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
/* zswap writeback related parameters */
static unsigned long zswap_writeback_resume; /* jiffies */
static unsigned int zswap_writeback_interval = 1;
module_param_named(writeback_interval, zswap_writeback_interval, uint, 0644);
#endif
/* Compressed storage to use */
#define ZSWAP_ZPOOL_DEFAULT "zsmalloc"
static char *zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
module_param_named(zpool, zswap_zpool_type, charp, 0444);
/* zswap compaction related parameters */
static unsigned int zswap_compaction_interval = 10;
module_param_named(compaction_interval, zswap_compaction_interval, uint, 0644);
static unsigned int zswap_compaction_pages = 2048;
module_param_named(compaction_pages, zswap_compaction_pages, uint, 0644);
/* zpool is shared by all of zswap backend */
static struct zpool *zswap_pool;
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
/* writeback thread */
static wait_queue_head_t zswap_writebackd_wait;
static struct task_struct *zswap_writebackd_task;
#endif
/*********************************
* compression functions
**********************************/
/* per-cpu compression transforms */
static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
enum comp_op {
ZSWAP_COMPOP_COMPRESS,
ZSWAP_COMPOP_DECOMPRESS
};
static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
u8 *dst, unsigned int *dlen)
{
struct crypto_comp *tfm;
int ret;
tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
switch (op) {
case ZSWAP_COMPOP_COMPRESS:
ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
break;
case ZSWAP_COMPOP_DECOMPRESS:
ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
break;
default:
ret = -EINVAL;
}
put_cpu();
return ret;
}
static int __init zswap_comp_init(void)
{
if (!crypto_has_comp(zswap_compressor, 0, 0)) {
pr_info("%s compressor not available\n", zswap_compressor);
/* fall back to default compressor */
zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
if (!crypto_has_comp(zswap_compressor, 0, 0))
/* can't even load the default compressor */
return -ENODEV;
}
pr_info("using %s compressor\n", zswap_compressor);
/* alloc percpu transforms */
zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
if (!zswap_comp_pcpu_tfms)
return -ENOMEM;
return 0;
}
static void __init zswap_comp_exit(void)
{
/* free percpu transforms */
free_percpu(zswap_comp_pcpu_tfms);
}
/*********************************
* data structures
**********************************/
/*
* 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
* 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.
* offset - the swap offset for the entry. Index into the red-black tree.
* handle - zpool allocation handle that stores the compressed page data
* length - the length in bytes of the compressed page data. Needed during
* decompression
* zero_flag - the flag indicating the page for the zswap_entry is a zero page.
* zswap does not store the page during compression.
* It memsets the page with 0 during decompression.
*/
struct zswap_entry {
struct rb_node rbnode;
pgoff_t offset;
int refcount;
unsigned int length;
unsigned long handle;
unsigned char zero_flag;
};
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
struct zswap_header {
swp_entry_t swpentry;
};
#endif
/*
* 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];
/*********************************
* zswap entry functions
**********************************/
static struct kmem_cache *zswap_entry_cache;
static int __init zswap_entry_cache_create(void)
{
zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
return zswap_entry_cache == NULL;
}
static void __init zswap_entry_cache_destroy(void)
{
kmem_cache_destroy(zswap_entry_cache);
}
static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
{
struct zswap_entry *entry;
entry = kmem_cache_alloc(zswap_entry_cache, gfp);
if (!entry)
return NULL;
entry->refcount = 1;
entry->zero_flag = 0;
RB_CLEAR_NODE(&entry->rbnode);
return entry;
}
static void zswap_entry_cache_free(struct zswap_entry *entry)
{
kmem_cache_free(zswap_entry_cache, entry);
}
/*********************************
* rbtree functions
**********************************/
static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
{
struct rb_node *node = root->rb_node;
struct zswap_entry *entry;
while (node) {
entry = rb_entry(node, struct zswap_entry, rbnode);
if (entry->offset > offset)
node = node->rb_left;
else if (entry->offset < offset)
node = node->rb_right;
else
return entry;
}
return NULL;
}
/*
* In the case that a entry with the same offset is found, a pointer to
* the existing entry is stored in dupentry and the function returns -EEXIST
*/
static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
struct zswap_entry **dupentry)
{
struct rb_node **link = &root->rb_node, *parent = NULL;
struct zswap_entry *myentry;
while (*link) {
parent = *link;
myentry = rb_entry(parent, struct zswap_entry, rbnode);
if (myentry->offset > entry->offset)
link = &(*link)->rb_left;
else if (myentry->offset < entry->offset)
link = &(*link)->rb_right;
else {
*dupentry = myentry;
return -EEXIST;
}
}
rb_link_node(&entry->rbnode, parent, link);
rb_insert_color(&entry->rbnode, root);
return 0;
}
static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)
{
if (!RB_EMPTY_NODE(&entry->rbnode)) {
rb_erase(&entry->rbnode, root);
RB_CLEAR_NODE(&entry->rbnode);
}
}
/*
* Carries out the common pattern of freeing and entry's zpool allocation,
* freeing the entry itself, and decrementing the number of stored pages.
*/
static void zswap_free_entry(struct zswap_entry *entry)
{
if (entry->zero_flag == 1) {
atomic_dec(&zswap_zero_pages);
goto zeropage_out;
}
zpool_free(zswap_pool, entry->handle);
zeropage_out:
zswap_entry_cache_free(entry);
atomic_dec(&zswap_stored_pages);
zswap_pool_total_size = zpool_get_total_size(zswap_pool);
zswap_pool_pages = zpool_get_total_size(zswap_pool) >> PAGE_SHIFT;
}
/* caller must hold the tree lock */
static void zswap_entry_get(struct zswap_entry *entry)
{
entry->refcount++;
}
/* caller must hold the tree lock
* remove from the tree and free it, if nobody reference the entry
*/
static void zswap_entry_put(struct zswap_tree *tree,
struct zswap_entry *entry)
{
int refcount = --entry->refcount;
BUG_ON(refcount < 0);
if (refcount == 0) {
zswap_rb_erase(&tree->rbroot, entry);
zswap_free_entry(entry);
}
}
/* caller must hold the tree lock */
static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
pgoff_t offset)
{
struct zswap_entry *entry = NULL;
entry = zswap_rb_search(root, offset);
if (entry)
zswap_entry_get(entry);
return entry;
}
/*********************************
* per-cpu code
**********************************/
static DEFINE_PER_CPU(u8 *, zswap_dstmem);
static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
{
struct crypto_comp *tfm;
u8 *dst;
switch (action) {
case CPU_UP_PREPARE:
tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
if (IS_ERR(tfm)) {
pr_err("can't allocate compressor transform\n");
return NOTIFY_BAD;
}
*per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
if (!dst) {
pr_err("can't allocate compressor buffer\n");
crypto_free_comp(tfm);
*per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
return NOTIFY_BAD;
}
per_cpu(zswap_dstmem, cpu) = dst;
break;
case CPU_DEAD:
case CPU_UP_CANCELED:
tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
if (tfm) {
crypto_free_comp(tfm);
*per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
}
dst = per_cpu(zswap_dstmem, cpu);
kfree(dst);
per_cpu(zswap_dstmem, cpu) = NULL;
break;
default:
break;
}
return NOTIFY_OK;
}
static int zswap_cpu_notifier(struct notifier_block *nb,
unsigned long action, void *pcpu)
{
unsigned long cpu = (unsigned long)pcpu;
return __zswap_cpu_notifier(action, cpu);
}
static struct notifier_block zswap_cpu_notifier_block = {
.notifier_call = zswap_cpu_notifier
};
static int __init zswap_cpu_init(void)
{
unsigned long cpu;
cpu_notifier_register_begin();
for_each_online_cpu(cpu)
if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
goto cleanup;
__register_cpu_notifier(&zswap_cpu_notifier_block);
cpu_notifier_register_done();
return 0;
cleanup:
for_each_online_cpu(cpu)
__zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
cpu_notifier_register_done();
return -ENOMEM;
}
/*********************************
* helpers
**********************************/
enum zswap_pool_status {
ZSWAP_POOL_MAX,
ZSWAP_POOL_HIGH,
ZSWAP_POOL_LOW,
};
static bool zswap_is_full(enum zswap_pool_status zps)
{
unsigned int percent;
switch (zps) {
case ZSWAP_POOL_LOW:
percent = zswap_low_pool_percent;
break;
case ZSWAP_POOL_HIGH:
percent = zswap_high_pool_percent;
break;
case ZSWAP_POOL_MAX:
default:
percent = zswap_max_pool_percent;
break;
}
return ((totalram_pages * percent) / 1000) <
DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
}
/*********************************
* writeback code
**********************************/
/* return enum for zswap_get_swap_cache_page */
enum zswap_get_swap_ret {
ZSWAP_SWAPCACHE_NEW,
ZSWAP_SWAPCACHE_EXIST,
ZSWAP_SWAPCACHE_FAIL,
};
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
/*
* zswap_get_swap_cache_page
*
* This is an adaption of read_swap_cache_async()
*
* This function tries to find a page with the given swap entry
* in the swapper_space address space (the swap cache). If the page
* is found, it is returned in retpage. Otherwise, a page is allocated,
* added to the swap cache, and returned in retpage.
*
* If success, the swap cache page is returned in retpage
* Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache
* Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,
* the new page is added to swapcache and locked
* Returns ZSWAP_SWAPCACHE_FAIL on error
*/
static int zswap_get_swap_cache_page(swp_entry_t entry,
struct page **retpage)
{
struct page *found_page, *new_page = NULL;
struct address_space *swapper_space = swap_address_space(entry);
int err;
*retpage = NULL;
do {
/*
* First check the swap cache. Since this is normally
* called after lookup_swap_cache() failed, re-calling
* that would confuse statistics.
*/
found_page = find_get_page(swapper_space, entry.val);
if (found_page)
break;
/*
* Get a new page to read into from swap.
*/
if (!new_page) {
new_page = alloc_page(GFP_KERNEL);
if (!new_page)
break; /* Out of memory */
}
/*
* call radix_tree_preload() while we can wait.
*/
err = radix_tree_preload(GFP_KERNEL);
if (err)
break;
/*
* Swap entry may have been freed since our caller observed it.
*/
err = swapcache_prepare(entry);
if (err == -EEXIST) { /* seems racy */
radix_tree_preload_end();
continue;
}
if (err) { /* swp entry is obsolete ? */
radix_tree_preload_end();
break;
}
/* May fail (-ENOMEM) if radix-tree node allocation failed. */
__set_page_locked(new_page);
SetPageSwapBacked(new_page);
err = __add_to_swap_cache(new_page, entry);
if (likely(!err)) {
radix_tree_preload_end();
lru_cache_add_anon(new_page);
*retpage = new_page;
return ZSWAP_SWAPCACHE_NEW;
}
radix_tree_preload_end();
ClearPageSwapBacked(new_page);
__clear_page_locked(new_page);
/*
* add_to_swap_cache() doesn't return -EEXIST, so we can safely
* clear SWAP_HAS_CACHE flag.
*/
swapcache_free(entry);
} while (err != -ENOMEM);
if (new_page)
page_cache_release(new_page);
if (!found_page)
return ZSWAP_SWAPCACHE_FAIL;
*retpage = found_page;
return ZSWAP_SWAPCACHE_EXIST;
}
/*
* Attempts to free an entry by adding a page to the swap cache,
* decompressing the entry data into the page, and issuing a
* bio write to write the page back to the swap device.
*
* This can be thought of as a "resumed writeback" of the page
* to the swap device. We are basically resuming the same swap
* writeback path that was intercepted with the frontswap_store()
* in the first place. After the page has been decompressed into
* the swap cache, the compressed version stored by zswap can be
* freed.
*/
#define ZSWAP_RECLAIM_MAGIC 0xf1f2f3f45f6f7f8fUL
static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
{
struct zswap_header *zhdr;
swp_entry_t swpentry;
struct zswap_tree *tree;
pgoff_t offset;
struct zswap_entry *entry;
struct page *page;
u8 *src, *dst;
unsigned int dlen;
int ret;
struct writeback_control wbc = {
.sync_mode = WB_SYNC_NONE,
};
/* extract swpentry from data */
zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
swpentry = zhdr->swpentry; /* here */
zpool_unmap_handle(pool, handle);
if (swpentry.val == ZSWAP_RECLAIM_MAGIC)
return -EAGAIN;
tree = zswap_trees[swp_type(swpentry)];
offset = swp_offset(swpentry);
/* find and ref zswap entry */
spin_lock(&tree->lock);
entry = zswap_entry_find_get(&tree->rbroot, offset);
if (!entry) {
/* entry was invalidated */
spin_unlock(&tree->lock);
return -EAGAIN;
}
if (entry->handle != handle) {
/* entry is not valid */
zswap_entry_put(tree, entry);
spin_unlock(&tree->lock);
return -EAGAIN;
}
spin_unlock(&tree->lock);
BUG_ON(offset != entry->offset);
/* try to allocate swap cache page */
switch (zswap_get_swap_cache_page(swpentry, &page)) {
case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
ret = -ENOMEM;
goto fail;
case ZSWAP_SWAPCACHE_EXIST:
/* page is already in the swap cache, ignore for now */
page_cache_release(page);
ret = -EEXIST;
goto fail;
case ZSWAP_SWAPCACHE_NEW: /* page is locked */
/* decompress */
dlen = PAGE_SIZE;
src = (u8 *)zpool_map_handle(zswap_pool, entry->handle,
ZPOOL_MM_RO) + sizeof(struct zswap_header);
dst = kmap_atomic(page);
ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src,
entry->length, dst, &dlen);
kunmap_atomic(dst);
zpool_unmap_handle(zswap_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, end_swap_bio_write);
page_cache_release(page);
zswap_written_back_pages++;
spin_lock(&tree->lock);
/* drop local reference */
zswap_entry_put(tree, entry);
/*
* There are two possible situations for entry here:
* (1) refcount is 1(normal case), entry is valid and on the tree
* (2) refcount is 0, entry is freed and not on the tree
* because invalidate happened during writeback
* search the tree and free the entry if find entry
*/
if (entry == zswap_rb_search(&tree->rbroot, offset))
zswap_entry_put(tree, entry);
spin_unlock(&tree->lock);
goto end;
/*
* if we get here due to ZSWAP_SWAPCACHE_EXIST
* a load may happening concurrently
* it is safe and okay to not free the entry
* if we free the entry in the following put
* it it either okay to return !0
*/
fail:
spin_lock(&tree->lock);
zswap_entry_put(tree, entry);
spin_unlock(&tree->lock);
end:
return ret;
}
#else
static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
{
return -EINVAL;
}
#endif /* CONFIG_ZSWAP_ENABLE_WRITEBACK */
static int page_zero_filled(void *ptr)
{
unsigned int pos;
unsigned long *page;
page = (unsigned long *)ptr;
for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) {
if (page[pos])
return 0;
}
return 1;
}
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
static bool __zswap_writeback_ok(struct swap_info_struct *sis)
{
struct gendisk *disk = NULL;
bool ret = false;
spin_lock(&sis->lock);
if (!(sis->flags & SWP_USED))
goto out;
if (sis->bdev)
disk = sis->bdev->bd_disk;
if (disk && disk->fops && disk->fops->ioctl &&
disk->fops->ioctl(sis->bdev, 0, 0, 32))
ret = true;
out:
spin_unlock(&sis->lock);
return ret;
}
static bool zswap_writeback_ok(void)
{
int i;
if (time_is_after_jiffies(zswap_writeback_resume))
return false;
for (i = 0; i < MAX_SWAPFILES; i++)
if (swap_info[i] && __zswap_writeback_ok(swap_info[i]))
return true;
return false;
}
static bool zswap_prepare_writebackd_sleep(long remaining)
{
if (remaining)
return false;
if (!zswap_writeback_ok())
return true;
return !zswap_is_full(ZSWAP_POOL_LOW);
}
static void zswap_writebackd_try_to_sleep(void)
{
long remaining = 0;
DEFINE_WAIT(wait);
if (freezing(current) || kthread_should_stop())
return;
prepare_to_wait(&zswap_writebackd_wait, &wait, TASK_INTERRUPTIBLE);
if (zswap_prepare_writebackd_sleep(remaining)) {
remaining = schedule_timeout(HZ/10);
finish_wait(&zswap_writebackd_wait, &wait);
prepare_to_wait(&zswap_writebackd_wait, &wait,
TASK_INTERRUPTIBLE);
}
if (zswap_prepare_writebackd_sleep(remaining)) {
trace_mm_zswap_writebackd_sleep(zswap_pool_pages);
if (!kthread_should_stop())
schedule();
}
finish_wait(&zswap_writebackd_wait, &wait);
}
static int zswap_writebackd(void *arg)
{
set_freezable();
for (;;) {
bool ret;
/* try to sleep */
zswap_writebackd_try_to_sleep();
ret = try_to_freeze();
if (kthread_should_stop())
break;
/*
* like kswapd kthread, don't call zpool_shrink
* after returning from the refrigerator
*/
if (!ret) {
trace_mm_zswap_writebackd_wake(zswap_pool_pages);
if (zpool_shrink(zswap_pool, 32, NULL)) {
zswap_reject_reclaim_fail++;
zswap_writeback_resume =
jiffies + zswap_writeback_interval * HZ;
}
}
}
return 0;
}
static void zswap_wakeup_writebackd(void)
{
if (!waitqueue_active(&zswap_writebackd_wait))
return;
if (!zswap_is_full(ZSWAP_POOL_HIGH))
return;
if (!zswap_writeback_ok())
return;
trace_mm_zswap_wakeup_writebackd(zswap_pool_pages);
wake_up_interruptible(&zswap_writebackd_wait);
zswap_writebackd_wakeup++;
}
static int zswap_writebackd_run(void)
{
int ret = 0;
if (zswap_writebackd_task)
return 0;
init_waitqueue_head(&zswap_writebackd_wait);
zswap_writebackd_task = kthread_run(zswap_writebackd, 0, "writebackd");
if (IS_ERR(zswap_writebackd_task)) {
pr_err("failed to start writebackd for zswap\n");
ret = PTR_ERR(zswap_writebackd_task);
zswap_writebackd_task = NULL;
}
return ret;
}
#else
static int zswap_writebackd_run(void)
{
return 0;
}
#endif
/*********************************
* frontswap hooks
**********************************/
/* attempts to compress and store an single page */
static int zswap_frontswap_store(unsigned type, pgoff_t offset,
struct page *page)
{
struct zswap_tree *tree = zswap_trees[type];
struct zswap_entry *entry, *dupentry;
int ret;
unsigned int dlen = PAGE_SIZE, len;
unsigned long handle;
char *buf;
u8 *src, *dst;
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
struct zswap_header *zhdr;
#endif
if (!tree) {
ret = -ENODEV;
goto reject;
}
/* if this page got EIO on pageout before, give up immediately */
if (PageError(page)) {
ret = -ENOMEM;
goto reject;
}
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
/* reclaim space if needed */
if (zswap_is_full(ZSWAP_POOL_HIGH)) {
zswap_wakeup_writebackd();
}
#endif
if (zswap_is_full(ZSWAP_POOL_MAX)) {
zswap_pool_limit_hit++;
ret = -ENOMEM;
goto reject;
}
/* allocate entry */
entry = zswap_entry_cache_alloc(GFP_KERNEL);
if (!entry) {
zswap_reject_kmemcache_fail++;
ret = -ENOMEM;
goto reject;
}
/* compress */
src = kmap_atomic(page);
if (page_zero_filled(src)) {
atomic_inc(&zswap_zero_pages);
entry->zero_flag = 1;
kunmap_atomic(src);
handle = 0;
dlen = PAGE_SIZE;
goto zeropage_out;
}
dst = get_cpu_var(zswap_dstmem);
ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
kunmap_atomic(src);
if (ret) {
ret = -EINVAL;
goto freepage;
}
/* store */
if (dlen > PAGE_SIZE)
dlen = PAGE_SIZE;
len = dlen;
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
len += sizeof(struct zswap_header);
#endif
ret = zpool_malloc(zswap_pool, len, __GFP_NORETRY | __GFP_NOWARN,
&handle);
if (ret == -ENOSPC) {
zswap_reject_compress_poor++;
goto freepage;
}
if (ret) {
zswap_reject_alloc_fail++;
goto freepage;
}
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
zhdr = zpool_map_handle(zswap_pool, handle, ZPOOL_MM_RW);
zhdr->swpentry = swp_entry(type, offset);
buf = (u8 *)(zhdr + 1);
memcpy(buf, dst, dlen);
#else
buf = (u8 *)zpool_map_handle(zswap_pool, handle, ZPOOL_MM_RW);
if (dlen == PAGE_SIZE) {
src = kmap_atomic(page);
copy_page(buf, src);
kunmap_atomic(src);
} else
memcpy(buf, dst, dlen);
#endif
zpool_unmap_handle(zswap_pool, handle);
put_cpu_var(zswap_dstmem);
zeropage_out:
/* populate entry */
entry->offset = offset;
entry->handle = handle;
entry->length = dlen;
/* map */
spin_lock(&tree->lock);
do {
ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
if (ret == -EEXIST) {