Message-ID: <20130225043551.GA12158@lge.com>
Date:	Mon, 25 Feb 2013 13:35:51 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>,
	Jenifer Hopper <jhopper@...ibm.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Larry Woodman <lwoodman@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Joe Perches <joe@...ches.com>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org
Subject: Re: [PATCHv6 4/8] zswap: add to mm/

Hello, Seth.
Here comes minor comments.

On Wed, Feb 20, 2013 at 04:04:44PM -0600, Seth Jennings wrote:
> zswap is a thin compression backend for frontswap. It receives
> pages from frontswap and attempts to store them in a compressed
> memory pool, resulting in an effective partial memory reclaim and
> dramatically reduced swap device I/O.
> 
> Additionally, in most cases, pages can be retrieved from this
> compressed store much more quickly than reading from tradition
> swap devices resulting in faster performance for many workloads.
> 
> This patch adds the zswap driver to mm/
> 
> Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> ---
>  mm/Kconfig  |  15 ++
>  mm/Makefile |   1 +
>  mm/zswap.c  | 665 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 681 insertions(+)
>  create mode 100644 mm/zswap.c
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 25b8f38..f9f35b7 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -470,3 +470,18 @@ config PGTABLE_MAPPING
>  
>  	  You can check speed with zsmalloc benchmark[1].
>  	  [1] https://github.com/spartacus06/zsmalloc
> +
> +config ZSWAP
> +	bool "In-kernel swap page compression"
> +	depends on FRONTSWAP && CRYPTO
> +	select CRYPTO_LZO
> +	select ZSMALLOC
> +	default n
> +	help
> +	  Zswap is a backend for the frontswap mechanism in the VMM.
> +	  It receives pages from frontswap and attempts to store them
> +	  in a compressed memory pool, resulting in an effective
> +	  partial memory reclaim.  In addition, pages and be retrieved
> +	  from this compressed store much faster than most tradition
> +	  swap devices resulting in reduced I/O and faster performance
> +	  for many workloads.
> diff --git a/mm/Makefile b/mm/Makefile
> index 0f6ef0a..1e0198f 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -32,6 +32,7 @@ obj-$(CONFIG_HAVE_MEMBLOCK) += memblock.o
>  obj-$(CONFIG_BOUNCE)	+= bounce.o
>  obj-$(CONFIG_SWAP)	+= page_io.o swap_state.o swapfile.o
>  obj-$(CONFIG_FRONTSWAP)	+= frontswap.o
> +obj-$(CONFIG_ZSWAP)	+= zswap.o
>  obj-$(CONFIG_HAS_DMA)	+= dmapool.o
>  obj-$(CONFIG_HUGETLBFS)	+= hugetlb.o
>  obj-$(CONFIG_NUMA) 	+= mempolicy.o
> diff --git a/mm/zswap.c b/mm/zswap.c
> new file mode 100644
> index 0000000..d3b4943
> --- /dev/null
> +++ b/mm/zswap.c
> @@ -0,0 +1,665 @@
> +/*
> + * 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 them and store
> + * them in a RAM-based memory pool.  This results in a significant I/O
> + * reduction on the real swap device and, in the case of a slow swap
> + * device, can also improve workload performance.
> + *
> + * Copyright (C) 2012  Seth Jennings <sjenning@...ux.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/crypto.h>
> +#include <linux/mempool.h>
> +#include <linux/zsmalloc.h>
> +
> +/*********************************
> +* statistics
> +**********************************/
> +/* Number of memory pages used by the compressed pool */
> +static atomic_t zswap_pool_pages = ATOMIC_INIT(0);
> +/* The number of compressed pages currently stored in zswap */
> +static 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.
> +*/
> +static u64 zswap_pool_limit_hit;
> +static u64 zswap_reject_compress_poor;
> +static u64 zswap_reject_zsmalloc_fail;
> +static u64 zswap_reject_kmemcache_fail;
> +static u64 zswap_duplicate_entry;
> +
> +/*********************************
> +* tunables
> +**********************************/
> +/* Enable/disable zswap (disabled by default, fixed at boot for now) */
> +static bool zswap_enabled;
> +module_param_named(enabled, zswap_enabled, bool, 0);
> +
> +/* 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, 0);
> +
> +/* 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);
> +
> +/*
> + * Maximum compression ratio, as as percentage, for an acceptable
> + * compressed page. Any pages that do not compress by at least
> + * this ratio will be rejected.
> +*/
> +static unsigned int zswap_max_compression_ratio = 80;
> +module_param_named(max_compression_ratio,
> +			zswap_max_compression_ratio, uint, 0644);
> +
> +/*********************************
> +* 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 zswap_comp_exit(void)
> +{
> +	/* free percpu transforms */
> +	if (zswap_comp_pcpu_tfms)
> +		free_percpu(zswap_comp_pcpu_tfms);
> +}
> +
> +/*********************************
> +* data structures
> +**********************************/
> +struct zswap_entry {
> +	struct rb_node rbnode;
> +	unsigned type;
> +	pgoff_t offset;
> +	unsigned long handle;
> +	unsigned int length;
> +};
> +
> +struct zswap_tree {
> +	struct rb_root rbroot;
> +	spinlock_t lock;
> +	struct zs_pool *pool;
> +};
> +
> +static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
> +
> +/*********************************
> +* zswap entry functions
> +**********************************/
> +#define ZSWAP_KMEM_CACHE_NAME "zswap_entry_cache"
> +static struct kmem_cache *zswap_entry_cache;
> +
> +static inline int zswap_entry_cache_create(void)
> +{
> +	zswap_entry_cache =
> +		kmem_cache_create(ZSWAP_KMEM_CACHE_NAME,
> +			sizeof(struct zswap_entry), 0, 0, NULL);
> +	return (zswap_entry_cache == NULL);
> +}
> +
> +static inline void zswap_entry_cache_destory(void)
> +{
> +	kmem_cache_destroy(zswap_entry_cache);
> +}
> +
> +static inline 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;
> +	return entry;
> +}
> +
> +static inline 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, it 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;
> +}
> +
> +/*********************************
> +* 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 = (u8 *)__get_free_pages(GFP_KERNEL, 1);

Order 1 is really needed?
Following code uses only PAGE_SIZE, not 2 * PAGE_SIZE.

> +		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);
> +		if (dst) {
> +			free_pages((unsigned long)dst, 1);
> +			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 zswap_cpu_init(void)
> +{
> +	unsigned long cpu;
> +
> +	get_online_cpus();
> +	for_each_online_cpu(cpu)
> +		if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
> +			goto cleanup;
> +	register_cpu_notifier(&zswap_cpu_notifier_block);
> +	put_online_cpus();
> +	return 0;
> +
> +cleanup:
> +	for_each_online_cpu(cpu)
> +		__zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
> +	put_online_cpus();
> +	return -ENOMEM;
> +}
> +
> +/*********************************
> +* zsmalloc callbacks
> +**********************************/
> +static mempool_t *zswap_page_pool;
> +
> +static inline unsigned int zswap_max_pool_pages(void)
> +{
> +	return zswap_max_pool_percent * totalram_pages / 100;
> +}
> +
> +static inline int zswap_page_pool_create(void)
> +{
> +	/* TODO: dynamically size mempool */
> +	zswap_page_pool = mempool_create_page_pool(256, 0);
> +	if (!zswap_page_pool)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
> +static inline void zswap_page_pool_destroy(void)
> +{
> +	mempool_destroy(zswap_page_pool);
> +}
> +
> +static struct page *zswap_alloc_page(gfp_t flags)
> +{
> +	struct page *page;
> +
> +	if (atomic_read(&zswap_pool_pages) >= zswap_max_pool_pages()) {
> +		zswap_pool_limit_hit++;
> +		return NULL;
> +	}
> +	page = mempool_alloc(zswap_page_pool, flags);
> +	if (page)
> +		atomic_inc(&zswap_pool_pages);
> +	return page;
> +}
> +
> +static void zswap_free_page(struct page *page)
> +{
> +	if (!page)
> +		return;
> +	mempool_free(page, zswap_page_pool);
> +	atomic_dec(&zswap_pool_pages);
> +}
> +
> +static struct zs_ops zswap_zs_ops = {
> +	.alloc = zswap_alloc_page,
> +	.free = zswap_free_page
> +};
> +
> +/*********************************
> +* 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;
> +	unsigned long handle;
> +	char *buf;
> +	u8 *src, *dst;
> +
> +	if (!tree) {
> +		ret = -ENODEV;
> +		goto reject;
> +	}
> +
> +	/* compress */
> +	dst = get_cpu_var(zswap_dstmem);
> +	src = kmap_atomic(page);
> +	ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
> +	kunmap_atomic(src);
> +	if (ret) {
> +		ret = -EINVAL;
> +		goto putcpu;
> +	}
> +	if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
> +		zswap_reject_compress_poor++;
> +		ret = -E2BIG;
> +		goto putcpu;
> +	}
> +
> +	/* store */
> +	handle = zs_malloc(tree->pool, dlen,
> +		__GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
> +			__GFP_NOWARN);
> +	if (!handle) {
> +		zswap_reject_zsmalloc_fail++;
> +		ret = -ENOMEM;
> +		goto putcpu;
> +	}
> +
> +	buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
> +	memcpy(buf, dst, dlen);
> +	zs_unmap_object(tree->pool, handle);
> +	put_cpu_var(zswap_dstmem);
> +
> +	/* allocate entry */
> +	entry = zswap_entry_cache_alloc(GFP_KERNEL);
> +	if (!entry) {
> +		zs_free(tree->pool, handle);
> +		zswap_reject_kmemcache_fail++;
> +		ret = -ENOMEM;
> +		goto reject;
> +	}

How about moving up zswap_entry_cache_alloc()?
It can save compression processing time
if zswap_entry_cache_alloc() is failed.

> +
> +	/* populate entry */
> +	entry->type = type;
> +	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 */
> +			rb_erase(&dupentry->rbnode, &tree->rbroot);
> +			
> +			/* free */
> +			zs_free(tree->pool, dupentry->handle);
> +			zswap_entry_cache_free(dupentry);
> +			atomic_dec(&zswap_stored_pages);
> +		}
> +	} while (ret == -EEXIST);
> +	spin_unlock(&tree->lock);
> +
> +	/* update stats */
> +	atomic_inc(&zswap_stored_pages);
> +
> +	return 0;
> +
> +putcpu:
> +	put_cpu_var(zswap_dstmem);
> +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;
> +
> +	/* find */
> +	spin_lock(&tree->lock);
> +	entry = zswap_rb_search(&tree->rbroot, offset);
> +	spin_unlock(&tree->lock);
> +
> +	/* decompress */
> +	dlen = PAGE_SIZE;
> +	src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
> +	dst = kmap_atomic(page);
> +	zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
> +		dst, &dlen);
> +	kunmap_atomic(dst);
> +	zs_unmap_object(tree->pool, entry->handle);
> +
> +	return 0;
> +}
> +
> +/* invalidates a single page */
> +static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
> +{
> +	struct zswap_tree *tree = zswap_trees[type];
> +	struct zswap_entry *entry;
> +
> +	/* find */
> +	spin_lock(&tree->lock);
> +	entry = zswap_rb_search(&tree->rbroot, offset);
> +
> +	/* remove from rbtree */
> +	rb_erase(&entry->rbnode, &tree->rbroot);
> +	spin_unlock(&tree->lock);
> +
> +	/* free */
> +	zs_free(tree->pool, entry->handle);
> +	zswap_entry_cache_free(entry);
> +	atomic_dec(&zswap_stored_pages);
> +}
> +
> +/* invalidates all pages for the given swap type */
> +static void zswap_frontswap_invalidate_area(unsigned type)
> +{
> +	struct zswap_tree *tree = zswap_trees[type];
> +	struct rb_node *node;
> +	struct zswap_entry *entry;
> +
> +	if (!tree)
> +		return;
> +
> +	/* walk the tree and free everything */
> +	spin_lock(&tree->lock);
> +	/*
> +	 * TODO: Even though this code should not be executed because
> +	 * the try_to_unuse() in swapoff should have emptied the tree,
> +	 * it is very wasteful to rebalance the tree after every
> +	 * removal when we are freeing the whole tree.
> +	 *
> +	 * If post-order traversal code is ever added to the rbtree
> +	 * implementation, it should be used here.
> +	 */
> +	while ((node = rb_first(&tree->rbroot))) {
> +		entry = rb_entry(node, struct zswap_entry, rbnode);
> +		rb_erase(&entry->rbnode, &tree->rbroot);
> +		zs_free(tree->pool, entry->handle);
> +		zswap_entry_cache_free(entry);
> +	}

You should decrease zswap_stored_pages in while loop.

> +	tree->rbroot = RB_ROOT;
> +	spin_unlock(&tree->lock);
> +}
> +
> +/* NOTE: this is called in atomic context from swapon and must not sleep */
> +static void zswap_frontswap_init(unsigned type)
> +{
> +	struct zswap_tree *tree;
> +
> +	tree = kzalloc(sizeof(struct zswap_tree), GFP_NOWAIT);
> +	if (!tree)
> +		goto err;
> +	tree->pool = zs_create_pool(GFP_NOWAIT, &zswap_zs_ops);
> +	if (!tree->pool)
> +		goto freetree;
> +	tree->rbroot = RB_ROOT;
> +	spin_lock_init(&tree->lock);
> +	zswap_trees[type] = tree;
> +	return;
> +
> +freetree:
> +	kfree(tree);
> +err:
> +	pr_err("alloc failed, zswap disabled for swap type %d\n", type);
> +}
> +
> +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_zsmalloc_fail", S_IRUGO,
> +			zswap_debugfs_root, &zswap_reject_zsmalloc_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("duplicate_entry", S_IRUGO,
> +			zswap_debugfs_root, &zswap_duplicate_entry);
> +	debugfs_create_atomic_t("pool_pages", S_IRUGO,
> +			zswap_debugfs_root, &zswap_pool_pages);
> +	debugfs_create_atomic_t("stored_pages", S_IRUGO,
> +			zswap_debugfs_root, &zswap_stored_pages);
> +
> +	return 0;
> +}
> +
> +static void __exit zswap_debugfs_exit(void)
> +{
> +	debugfs_remove_recursive(zswap_debugfs_root);
> +}
> +#else
> +static inline int __init zswap_debugfs_init(void)
> +{
> +	return 0;
> +}
> +
> +static inline void __exit zswap_debugfs_exit(void) { }
> +#endif
> +
> +/*********************************
> +* module init and exit
> +**********************************/
> +static int __init init_zswap(void)
> +{
> +	if (!zswap_enabled)
> +		return 0;
> +
> +	pr_info("loading zswap\n");
> +	if (zswap_entry_cache_create()) {
> +		pr_err("entry cache creation failed\n");
> +		goto error;
> +	}
> +	if (zswap_page_pool_create()) {
> +		pr_err("page pool initialization failed\n");
> +		goto pagepoolfail;
> +	}
> +	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");
> +	return 0;
> +pcpufail:
> +	zswap_comp_exit();
> +compfail:
> +	zswap_page_pool_destroy();
> +pagepoolfail:
> +	zswap_entry_cache_destory();
> +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@...ux.vnet.ibm.com>");
> +MODULE_DESCRIPTION("Compressed cache for swap pages");
> -- 
> 1.8.1.1
> 
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