android_kernel_samsung_msm8976/mm/zswap.c

/*
 * zswap.c - zswap driver file
 *
 * zswap is a backend for frontswap that takes pages that are in the process
 * of being swapped out and attempts to compress and store them in a
 * RAM-based memory pool.  This can result in a significant I/O reduction on
 * the swap device and, in the case where decompressing from RAM is faster
 * than reading from the swap device, can also improve workload performance.
 *
 * Copyright (C) 2012  Seth Jennings <sjenning@linux.vnet.ibm.com>
 *
 * 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>
#include <linux/show_mem_notifier.h>

#define CREATE_TRACE_POINTS
#include <trace/events/zswap.h>

/*********************************
* statistics
**********************************/
/* Total bytes used by the compressed storage */
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"
static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
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 = 30;
module_param_named(high_pool_percent,
			zswap_high_pool_percent, uint, 0644);

static unsigned int zswap_low_pool_percent = 25;
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, NULL);
	} 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) {
			zswap_duplicate_entry++;
			/* remove from rbtree */
			zswap_rb_erase(&tree->rbroot, dupentry);
			zswap_entry_put(tree, dupentry);
		}
	} while (ret == -EEXIST);
	spin_unlock(&tree->lock);

	/* update stats */
	atomic_inc(&zswap_stored_pages);
	zswap_pool_total_size = zpool_get_total_size(zswap_pool);
	zswap_pool_pages = zswap_pool_total_size >> PAGE_SHIFT;

	return 0;

freepage:
	put_cpu_var(zswap_dstmem);
	zswap_entry_cache_free(entry);
reject:
	return ret;
}

/*
 * returns 0 if the page was successfully decompressed
 * return -1 on entry not found or error
*/
static int zswap_frontswap_load(unsigned type, pgoff_t offset,
				struct page *page)
{
	struct zswap_tree *tree = zswap_trees[type];
	struct zswap_entry *entry;
	u8 *src, *dst;
	unsigned int dlen;
	int ret = 0;

	/* find */
	spin_lock(&tree->lock);
	entry = zswap_entry_find_get(&tree->rbroot, offset);
	if (!entry) {
		/* entry was written back */
		spin_unlock(&tree->lock);
		return -1;
	}
	spin_unlock(&tree->lock);

	if (entry->zero_flag == 1) {
		dst = kmap_atomic(page);
		memset(dst, 0, PAGE_SIZE);
		kunmap_atomic(dst);
		goto zeropage_out;
	}

	/* decompress */
	dlen = PAGE_SIZE;
	src = (u8 *)zpool_map_handle(zswap_pool, entry->handle,
			ZPOOL_MM_RO);
	dst = kmap_atomic(page);
#ifdef CONFIG_ZSWAP_ENABLE_WRITEBACK
	src += sizeof(struct zswap_header);
	ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
		dst, &dlen);
#else
	if (entry->length == PAGE_SIZE)
		copy_page(dst, src);
	else
		ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
			dst, &dlen);
#endif
	kunmap_atomic(dst);
	zpool_unmap_handle(zswap_pool, entry->handle);
	BUG_ON(ret);

zeropage_out:
	spin_lock(&tree->lock);
	zswap_entry_put(tree, entry);
	spin_unlock(&tree->lock);

	return 0;
}

int sysctl_zswap_compact;

int sysctl_zswap_compaction_handler(struct ctl_table *table, int write,
			void __user *buffer, size_t *length, loff_t *ppos)
{
	if (write) {
		sysctl_zswap_compact++;
		zpool_compact(zswap_pool);
		pr_info("zswap_compact: (%d times so far)\n",
			sysctl_zswap_compact);
	} else
		proc_dointvec(table, write, buffer, length, ppos);

	return 0;
}

static void zswap_compact_zpool(struct work_struct *work)
{
	sysctl_zswap_compact++;
	zpool_compact(zswap_pool);
	pr_info("zswap_compact: (%d times so far)\n",
		sysctl_zswap_compact);
}
static DECLARE_WORK(zswap_compaction_work, zswap_compact_zpool);

/* frees an entry in zswap */
static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
	struct zswap_tree *tree = zswap_trees[type];
	struct zswap_entry *entry;
#ifdef CONFIG_ZSWAP_COMPACTION
	static unsigned long resume = 0;
#endif

	/* find */
	spin_lock(&tree->lock);
	entry = zswap_rb_search(&tree->rbroot, offset);
	if (!entry) {
		/* entry was written back */
		spin_unlock(&tree->lock);
		return;
	}

	/* remove from rbtree */
	zswap_rb_erase(&tree->rbroot, entry);

	/* drop the initial reference from entry creation */
	zswap_entry_put(tree, entry);

	spin_unlock(&tree->lock);

#ifdef CONFIG_ZSWAP_COMPACTION
	if (time_is_before_jiffies(resume) &&
		!work_pending(&zswap_compaction_work) &&
		zpool_compactable(zswap_pool, zswap_compaction_pages)) {
		resume = jiffies + zswap_compaction_interval * HZ;
		schedule_work(&zswap_compaction_work);
	}
#endif
}

/* frees all zswap entries for the given swap type */
static void zswap_frontswap_invalidate_area(unsigned type)
{
	struct zswap_tree *tree = zswap_trees[type];
	struct zswap_entry *entry, *n;

	if (!tree)
		return;

	/* walk the tree and free everything */
	spin_lock(&tree->lock);
	rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
		zswap_free_entry(entry);
	tree->rbroot = RB_ROOT;
	spin_unlock(&tree->lock);
	kfree(tree);
	zswap_trees[type] = NULL;
}

static struct zpool_ops zswap_zpool_ops = {
	.evict = zswap_writeback_entry
};

static void zswap_frontswap_init(unsigned type)
{
	struct zswap_tree *tree;

	tree = kzalloc(sizeof(struct zswap_tree), GFP_KERNEL);
	if (!tree) {
		pr_err("alloc failed, zswap disabled for swap type %d\n", type);
		return;
	}

	tree->rbroot = RB_ROOT;
	spin_lock_init(&tree->lock);
	zswap_trees[type] = tree;
}

static struct frontswap_ops zswap_frontswap_ops = {
	.store = zswap_frontswap_store,
	.load = zswap_frontswap_load,
	.invalidate_page = zswap_frontswap_invalidate_page,
	.invalidate_area = zswap_frontswap_invalidate_area,
	.init = zswap_frontswap_init
};

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

static struct dentry *zswap_debugfs_root;

static int __init zswap_debugfs_init(void)
{
	if (!debugfs_initialized())
		return -ENODEV;

	zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
	if (!zswap_debugfs_root)
		return -ENOMEM;

	debugfs_create_u64("pool_limit_hit", S_IRUGO,
			zswap_debugfs_root, &zswap_pool_limit_hit);
	debugfs_create_u64("reject_reclaim_fail", S_IRUGO,
			zswap_debugfs_root, &zswap_reject_reclaim_fail);
	debugfs_create_u64("reject_alloc_fail", S_IRUGO,
			zswap_debugfs_root, &zswap_reject_alloc_fail);
	debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
			zswap_debugfs_root, &zswap_reject_kmemcache_fail);
	debugfs_create_u64("reject_compress_poor", S_IRUGO,
			zswap_debugfs_root, &zswap_reject_compress_poor);
	debugfs_create_u64("written_back_pages", S_IRUGO,
			zswap_debugfs_root, &zswap_written_back_pages);
	debugfs_create_u64("duplicate_entry", S_IRUGO,
			zswap_debugfs_root, &zswap_duplicate_entry);
	debugfs_create_u64("pool_total_size", S_IRUGO,
			zswap_debugfs_root, &zswap_pool_total_size);
	debugfs_create_u64("pool_pages", S_IRUGO,
			zswap_debugfs_root, &zswap_pool_pages);
	debugfs_create_atomic_t("stored_pages", S_IRUGO,
			zswap_debugfs_root, &zswap_stored_pages);
	debugfs_create_atomic_t("zero_pages", S_IRUGO,
			zswap_debugfs_root, &zswap_zero_pages);
	debugfs_create_u64("writebackd_wakeup", S_IRUGO,
			zswap_debugfs_root, &zswap_writebackd_wakeup);

	return 0;
}

static void __exit zswap_debugfs_exit(void)
{
	debugfs_remove_recursive(zswap_debugfs_root);
}
#else
static int __init zswap_debugfs_init(void)
{
	return 0;
}

static void __exit zswap_debugfs_exit(void) { }
#endif

static int zswap_size_notifier(struct notifier_block *nb,
					unsigned long is_simple, void *data)
{
	struct seq_file *s;

	s = (struct seq_file *)data;
	if (!is_simple)
		return 0;
	if (s != NULL)
		seq_printf(s, "ZSwapDevice:    %8lu kB\n",
			(unsigned long)zswap_pool_pages << (PAGE_SHIFT - 10));
	else
		printk("ZSwapDevice:%lukB ",
			(unsigned long)zswap_pool_pages << (PAGE_SHIFT - 10));
	return 0;
}

static struct notifier_block zswap_size_nb = {
	.notifier_call = zswap_size_notifier,
};

/*********************************
* module init and exit
**********************************/
static int __init init_zswap(void)
{
	gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_HIGHMEM;

	if (!zswap_enabled)
		return 0;

	pr_info("loading zswap\n");
	zswap_writebackd_run();

	zswap_pool = zpool_create_pool(zswap_zpool_type, "zswap", gfp,
					&zswap_zpool_ops);
	if (!zswap_pool && strcmp(zswap_zpool_type, ZSWAP_ZPOOL_DEFAULT)) {
		pr_info("%s zpool not available\n", zswap_zpool_type);
		zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
		zswap_pool = zpool_create_pool(zswap_zpool_type, "zswap", gfp,
					&zswap_zpool_ops);
	}
	if (!zswap_pool) {
		pr_err("%s zpool not available\n", zswap_zpool_type);
		pr_err("zpool creation failed\n");
		goto error;
	}
	pr_info("using %s pool\n", zswap_zpool_type);

	if (zswap_entry_cache_create()) {
		pr_err("entry cache creation failed\n");
		goto cachefail;
	}
	if (zswap_comp_init()) {
		pr_err("compressor initialization failed\n");
		goto compfail;
	}
	if (zswap_cpu_init()) {
		pr_err("per-cpu initialization failed\n");
		goto pcpufail;
	}

	frontswap_register_ops(&zswap_frontswap_ops);
	if (zswap_debugfs_init())
		pr_warn("debugfs initialization failed\n");

	show_mem_notifier_register(&zswap_size_nb);
	return 0;
pcpufail:
	zswap_comp_exit();
compfail:
	zswap_entry_cache_destroy();
cachefail:
	zpool_destroy_pool(zswap_pool);
error:
	return -ENOMEM;
}
/* must be late so crypto has time to come up */
late_initcall(init_zswap);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
MODULE_DESCRIPTION("Compressed cache for swap pages");