[PATCH 7/8] zswap: add to mm/

Seth Jennings sjenning at linux.vnet.ibm.com
Tue Dec 11 21:56:05 UTC 2012


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.

Additional, 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 at linux.vnet.ibm.com>
---
 include/linux/swap.h |    4 +
 mm/Kconfig           |   15 +
 mm/Makefile          |    1 +
 mm/page_io.c         |   22 +-
 mm/swap_state.c      |    2 +-
 mm/zswap.c           | 1077 ++++++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 1115 insertions(+), 6 deletions(-)
 create mode 100644 mm/zswap.c

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 68df9c1..98981f0 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -321,6 +321,9 @@ static inline void mem_cgroup_uncharge_swap(swp_entry_t ent)
 /* linux/mm/page_io.c */
 extern int swap_readpage(struct page *);
 extern int swap_writepage(struct page *page, struct writeback_control *wbc);
+extern void end_swap_bio_write(struct bio *bio, int err);
+extern int __swap_writepage(struct page *page, struct writeback_control *wbc,
+	void (*end_write_func)(struct bio *, int));
 extern int swap_set_page_dirty(struct page *page);
 extern void end_swap_bio_read(struct bio *bio, int err);
 
@@ -335,6 +338,7 @@ extern struct address_space swapper_space;
 extern void show_swap_cache_info(void);
 extern int add_to_swap(struct page *);
 extern int add_to_swap_cache(struct page *, swp_entry_t, gfp_t);
+extern int __add_to_swap_cache(struct page *page, swp_entry_t entry);
 extern void __delete_from_swap_cache(struct page *);
 extern void delete_from_swap_cache(struct page *);
 extern void free_page_and_swap_cache(struct page *);
diff --git a/mm/Kconfig b/mm/Kconfig
index 1680a012..68cd1b6 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -435,3 +435,18 @@ config FRONTSWAP
 	  and swap data is stored as normal on the matching swap device.
 
 	  If unsure, say Y to enable frontswap.
+
+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 3a46287..1b1ed5c 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/page_io.c b/mm/page_io.c
index 78eee32..56276fe 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -42,7 +42,7 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
 	return bio;
 }
 
-static void end_swap_bio_write(struct bio *bio, int err)
+void end_swap_bio_write(struct bio *bio, int err)
 {
 	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	struct page *page = bio->bi_io_vec[0].bv_page;
@@ -179,15 +179,16 @@ bad_bmap:
 	goto out;
 }
 
+int __swap_writepage(struct page *page, struct writeback_control *wbc,
+	void (*end_write_func)(struct bio *, int));
+
 /*
  * We may have stale swap cache pages in memory: notice
  * them here and get rid of the unnecessary final write.
  */
 int swap_writepage(struct page *page, struct writeback_control *wbc)
 {
-	struct bio *bio;
-	int ret = 0, rw = WRITE;
-	struct swap_info_struct *sis = page_swap_info(page);
+	int ret = 0;
 
 	if (try_to_free_swap(page)) {
 		unlock_page(page);
@@ -199,6 +200,17 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		end_page_writeback(page);
 		goto out;
 	}
+	ret = __swap_writepage(page, wbc, end_swap_bio_write);
+out:
+	return ret;
+}
+
+int __swap_writepage(struct page *page, struct writeback_control *wbc,
+	void (*end_write_func)(struct bio *, int))
+{
+	struct bio *bio;
+	int ret = 0, rw = WRITE;
+	struct swap_info_struct *sis = page_swap_info(page);
 
 	if (sis->flags & SWP_FILE) {
 		struct kiocb kiocb;
@@ -226,7 +238,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		return ret;
 	}
 
-	bio = get_swap_bio(GFP_NOIO, page, end_swap_bio_write);
+	bio = get_swap_bio(GFP_NOIO, page, end_write_func);
 	if (bio == NULL) {
 		set_page_dirty(page);
 		unlock_page(page);
diff --git a/mm/swap_state.c b/mm/swap_state.c
index d1f6c2d..95a8597 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -68,7 +68,7 @@ void show_swap_cache_info(void)
  * __add_to_swap_cache resembles add_to_page_cache_locked on swapper_space,
  * but sets SwapCache flag and private instead of mapping and index.
  */
-static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
+int __add_to_swap_cache(struct page *page, swp_entry_t entry)
 {
 	int error;
 
diff --git a/mm/zswap.c b/mm/zswap.c
new file mode 100644
index 0000000..f05b26b
--- /dev/null
+++ b/mm/zswap.c
@@ -0,0 +1,1077 @@
+/*
+ * zswap-drv.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 at 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.
+*/
+
+#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>
+
+#include <linux/mm_types.h>
+#include <linux/page-flags.h>
+#include <linux/swapops.h>
+#include <linux/writeback.h>
+#include <linux/pagemap.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 number of outstanding pages awaiting writeback */
+static atomic_t zswap_outstanding_flushes = ATOMIC_INIT(0);
+
+/*
+ * The statistics below are not protected from concurrent access for
+ * performance reasons so they may not be a 100% accurate.  However,
+ * the do provide useful information on roughly how many times a
+ * certain event is occurring.
+*/
+static u64 zswap_flushed_pages;
+static u64 zswap_reject_compress_poor;
+static u64 zswap_flush_attempted;
+static u64 zswap_reject_tmppage_fail;
+static u64 zswap_reject_flush_fail;
+static u64 zswap_reject_zsmalloc_fail;
+static u64 zswap_reject_kmemcache_fail;
+static u64 zswap_saved_by_flush;
+static u64 zswap_duplicate_entry;
+
+/*********************************
+* tunables
+**********************************/
+/* Enable/disable zswap (enabled 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("zswap: %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("zswap: 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;
+	struct list_head lru;
+	int refcount;
+	unsigned type;
+	pgoff_t offset;
+	unsigned long handle;
+	unsigned int length;
+};
+
+struct zswap_tree {
+	struct rb_root rbroot;
+	struct list_head lru;
+	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;
+	INIT_LIST_HEAD(&entry->lru);
+	entry->refcount = 1;
+	return entry;
+}
+
+static inline void zswap_entry_cache_free(struct zswap_entry *entry)
+{
+	kmem_cache_free(zswap_entry_cache, entry);
+}
+
+static inline void zswap_entry_get(struct zswap_entry *entry)
+{
+	entry->refcount++;
+}
+
+static inline int zswap_entry_put(struct zswap_entry *entry)
+{
+	entry->refcount--;
+	return entry->refcount;
+}
+
+/*********************************
+* 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("zswap: 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);
+		if (!dst) {
+			pr_err("zswap: 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;
+}
+
+#if 0
+/*
+ * #define out for now to avoid unused function warning
+ * but keep around in case future development needs it
+*/
+static void zswap_cpu_exit(void)
+{
+	unsigned long cpu;
+
+	get_online_cpus();
+	unregister_cpu_notifier(&zswap_cpu_notifier_block);
+	for_each_online_cpu(cpu)
+		(void)__zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
+	put_online_cpus();
+}
+#endif
+
+/*********************************
+* zsmalloc callbacks
+**********************************/
+static mempool_t *zswap_page_pool;
+
+static u64 zswap_pool_limit_hit;
+
+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)
+{
+	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)
+{
+	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
+};
+
+/*********************************
+* flush code
+**********************************/
+static void zswap_end_swap_write(struct bio *bio, int err)
+{
+	end_swap_bio_write(bio, err);
+	atomic_dec(&zswap_outstanding_flushes);
+	zswap_flushed_pages++;
+}
+
+/*
+ * zswap_get_swap_cache_page
+ *
+ * This is an adaption of read_swap_cache_async()
+ *
+ * If success, page is returned in retpage
+ * Returns 0 if page was already in the swap cache, page is not locked
+ * Returns 1 if the new page needs to be populated, page is locked
+ */
+static int zswap_get_swap_cache_page(swp_entry_t entry,
+				struct page **retpage)
+{
+	struct page *found_page, *new_page = NULL;
+	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 1;
+		}
+		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 -ENOMEM;
+	*retpage = found_page;
+	return 0;
+}
+
+static int zswap_flush_entry(struct zswap_entry *entry)
+{
+	unsigned long type = entry->type;
+	struct zswap_tree *tree = zswap_trees[type];
+	struct page *page;
+	swp_entry_t swpentry;
+	u8 *src, *dst;
+	unsigned int dlen;
+	int ret, refcount;
+	struct writeback_control wbc = {
+		.sync_mode = WB_SYNC_NONE,
+	};
+
+	/* get/allocate page in the swap cache */
+	swpentry = swp_entry(type, entry->offset);
+	ret = zswap_get_swap_cache_page(swpentry, &page);
+	if (ret < 0)
+		return ret;
+	else if (ret) {
+		/* decompress */
+		dlen = PAGE_SIZE;
+		src = zs_map_object(tree->pool, entry->handle, ZS_MM_RO);
+		dst = kmap_atomic(page);
+		ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
+				dst, &dlen);
+		kunmap_atomic(dst);
+		zs_unmap_object(tree->pool, entry->handle);
+		BUG_ON(ret);
+		BUG_ON(dlen != PAGE_SIZE);
+		SetPageUptodate(page);
+	} else {
+		/* page is already in the swap cache, ignore for now */
+		spin_lock(&tree->lock);
+		refcount = zswap_entry_put(entry);
+		spin_unlock(&tree->lock);
+
+		if (likely(refcount))
+			return 0;
+
+		/* if the refcount is zero, invalidate must have come in */
+		/* free */
+		zs_free(tree->pool, entry->handle);
+		zswap_entry_cache_free(entry);
+		atomic_dec(&zswap_stored_pages);
+
+		return 0;
+	}
+
+	/* start writeback */
+	SetPageReclaim(page);
+	/*
+	 * Return value is ignored here because it doesn't change anything
+	 * for us.  Page is returned unlocked.
+	 */
+	(void)__swap_writepage(page, &wbc, zswap_end_swap_write);
+	page_cache_release(page);
+	atomic_inc(&zswap_outstanding_flushes);
+
+	/* remove */
+	spin_lock(&tree->lock);
+	refcount = zswap_entry_put(entry);
+	if (refcount > 1) {
+		/* load in progress, load will free */
+		spin_unlock(&tree->lock);
+		return 0;
+	}
+	if (refcount == 1)
+		/* no invalidate yet, 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);
+
+	return 0;
+}
+
+static void zswap_flush_entries(unsigned type, int nr)
+{
+	struct zswap_tree *tree = zswap_trees[type];
+	struct zswap_entry *entry;
+	int i, ret;
+
+/*
+ * This limits is arbitrary for now until a better
+ * policy can be implemented. This is so we don't
+ * eat all of RAM decompressing pages for writeback.
+ */
+#define ZSWAP_MAX_OUTSTANDING_FLUSHES 64
+	if (atomic_read(&zswap_outstanding_flushes) >
+		ZSWAP_MAX_OUTSTANDING_FLUSHES)
+		return;
+
+	for (i = 0; i < nr; i++) {
+		/* dequeue from lru */
+		spin_lock(&tree->lock);
+		if (list_empty(&tree->lru)) {
+			spin_unlock(&tree->lock);
+			break;
+		}
+		entry = list_first_entry(&tree->lru,
+				struct zswap_entry, lru);
+		list_del(&entry->lru);
+		zswap_entry_get(entry);
+		spin_unlock(&tree->lock);
+		ret = zswap_flush_entry(entry);
+		if (ret) {
+			/* put back on the lru */
+			spin_lock(&tree->lock);
+			list_add(&entry->lru, &tree->lru);
+			spin_unlock(&tree->lock);
+		} else {
+			if (atomic_read(&zswap_outstanding_flushes) >
+				ZSWAP_MAX_OUTSTANDING_FLUSHES)
+				break;
+		}
+	}
+}
+
+/*******************************************
+* page pool for temporary compression result
+********************************************/
+#define ZSWAP_TMPPAGE_POOL_PAGES 16
+static LIST_HEAD(zswap_tmppage_list);
+static DEFINE_SPINLOCK(zswap_tmppage_lock);
+
+static void zswap_tmppage_pool_destroy(void)
+{
+	struct page *page, *tmppage;
+
+	spin_lock(&zswap_tmppage_lock);
+	list_for_each_entry_safe(page, tmppage, &zswap_tmppage_list, lru) {
+		list_del(&page->lru);
+		__free_pages(page, 1);
+	}
+	spin_unlock(&zswap_tmppage_lock);
+}
+
+static int zswap_tmppage_pool_create(void)
+{
+	int i;
+	struct page *page;
+
+	for (i = 0; i < ZSWAP_TMPPAGE_POOL_PAGES; i++) {
+		page = alloc_pages(GFP_KERNEL, 1);
+		if (!page) {
+			zswap_tmppage_pool_destroy();
+			return -ENOMEM;
+		}
+		spin_lock(&zswap_tmppage_lock);
+		list_add(&page->lru, &zswap_tmppage_list);
+		spin_unlock(&zswap_tmppage_lock);
+	}
+	return 0;
+}
+
+static inline struct page *zswap_tmppage_alloc(void)
+{
+	struct page *page;
+
+	spin_lock(&zswap_tmppage_lock);
+	if (list_empty(&zswap_tmppage_list)) {
+		spin_unlock(&zswap_tmppage_lock);
+		return NULL;
+	}
+	page = list_first_entry(&zswap_tmppage_list, struct page, lru);
+	list_del(&page->lru);
+	spin_unlock(&zswap_tmppage_lock);
+	return page;
+}
+
+static inline void zswap_tmppage_free(struct page *page)
+{
+	spin_lock(&zswap_tmppage_lock);
+	list_add(&page->lru, &zswap_tmppage_list);
+	spin_unlock(&zswap_tmppage_lock);
+}
+
+/*********************************
+* frontswap hooks
+**********************************/
+/* attempts to compress and store an single page */
+static int zswap_fs_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, *tmpdst;
+	struct page *tmppage;
+	bool flush_attempted = 0;
+
+	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 freepage;
+	}
+	if ((dlen * 100 / PAGE_SIZE) > zswap_max_compression_ratio) {
+		zswap_reject_compress_poor++;
+		ret = -E2BIG;
+		goto freepage;
+	}
+
+	/* store */
+	handle = zs_malloc(tree->pool, dlen,
+		__GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
+			__GFP_NOWARN);
+	if (!handle) {
+		zswap_flush_attempted++;
+		/*
+		 * Copy compressed buffer out of per-cpu storage so
+		 * we can re-enable preemption.
+		*/
+		tmppage = zswap_tmppage_alloc();
+		if (!tmppage) {
+			zswap_reject_tmppage_fail++;
+			ret = -ENOMEM;
+			goto freepage;
+		}
+		flush_attempted = 1;
+		tmpdst = page_address(tmppage);
+		memcpy(tmpdst, dst, dlen);
+		dst = tmpdst;
+		put_cpu_var(zswap_dstmem);
+
+		/* try to free up some space */
+		/* TODO: replace with more targeted policy */
+		zswap_flush_entries(type, 16);
+		/* try again, allowing wait */
+		handle = zs_malloc(tree->pool, dlen,
+			__GFP_NORETRY | __GFP_HIGHMEM | __GFP_NOMEMALLOC |
+				__GFP_NOWARN);
+		if (!handle) {
+			/* still no space, fail */
+			zswap_reject_zsmalloc_fail++;
+			ret = -ENOMEM;
+			goto freepage;
+		}
+		zswap_saved_by_flush++;
+	}
+
+	buf = zs_map_object(tree->pool, handle, ZS_MM_WO);
+	memcpy(buf, dst, dlen);
+	zs_unmap_object(tree->pool, handle);
+	if (flush_attempted)
+		zswap_tmppage_free(tmppage);
+	else
+		put_cpu_var(zswap_dstmem);
+
+	/* allocate entry */
+	entry = zswap_entry_cache_alloc(GFP_KERNEL);
+	if (!entry) {
+		zswap_reject_kmemcache_fail++;
+		ret = -ENOMEM;
+		goto reject;
+	}
+
+	/* 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 and lru */
+			rb_erase(&dupentry->rbnode, &tree->rbroot);
+			if (dupentry->lru.next != LIST_POISON1)
+				list_del(&dupentry->lru);
+			if (!zswap_entry_put(dupentry)) {
+				/* free */
+				zs_free(tree->pool, dupentry->handle);
+				zswap_entry_cache_free(dupentry);
+				atomic_dec(&zswap_stored_pages);
+			}
+		}
+	} while (ret == -EEXIST);
+	list_add_tail(&entry->lru, &tree->lru);
+	spin_unlock(&tree->lock);
+
+	/* update stats */
+	atomic_inc(&zswap_stored_pages);
+
+	return 0;
+
+freepage:
+	if (flush_attempted)
+		zswap_tmppage_free(tmppage);
+	else
+		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_fs_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 refcount;
+
+	/* find */
+	spin_lock(&tree->lock);
+	entry = zswap_rb_search(&tree->rbroot, offset);
+	if (!entry) {
+		/* entry was flushed */
+		spin_unlock(&tree->lock);
+		return -1;
+	}
+	zswap_entry_get(entry);
+
+	/* remove from lru */
+	if (entry->lru.next != LIST_POISON1)
+		list_del(&entry->lru);
+	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);
+
+	spin_lock(&tree->lock);
+	refcount = zswap_entry_put(entry);
+	if (likely(refcount)) {
+		list_add_tail(&entry->lru, &tree->lru);
+		spin_unlock(&tree->lock);
+		return 0;
+	}
+	spin_unlock(&tree->lock);
+
+	/*
+	 * We don't have to unlink from the rbtree because zswap_flush_entry()
+	 * or zswap_fs_invalidate page() has already done this for us if we
+	 * are the last reference.
+	 */
+	/* free */
+	zs_free(tree->pool, entry->handle);
+	zswap_entry_cache_free(entry);
+	atomic_dec(&zswap_stored_pages);
+
+	return 0;
+}
+
+/* invalidates a single page */
+static void zswap_fs_invalidate_page(unsigned type, pgoff_t offset)
+{
+	struct zswap_tree *tree = zswap_trees[type];
+	struct zswap_entry *entry;
+	int refcount;
+
+	if (!tree)
+		return;
+
+	/* find */
+	spin_lock(&tree->lock);
+	entry = zswap_rb_search(&tree->rbroot, offset);
+	if (!entry) {
+		/* entry was flushed */
+		spin_unlock(&tree->lock);
+		return;
+	}
+
+	/* remove from rbtree and lru */
+	rb_erase(&entry->rbnode, &tree->rbroot);
+	if (entry->lru.next != LIST_POISON1)
+		list_del(&entry->lru);
+	refcount = zswap_entry_put(entry);
+	spin_unlock(&tree->lock);
+	if (refcount) {
+		/* must be flushing */
+		return;
+	}
+
+	/* 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_fs_invalidate_area(unsigned type)
+{
+	struct zswap_tree *tree = zswap_trees[type];
+	struct rb_node *node, *next;
+	struct zswap_entry *entry;
+
+	if (!tree)
+		return;
+
+	/* walk the tree and free everything */
+	spin_lock(&tree->lock);
+	node = rb_first(&tree->rbroot);
+	while (node) {
+		entry = rb_entry(node, struct zswap_entry, rbnode);
+		zs_free(tree->pool, entry->handle);
+		next = rb_next(node);
+		zswap_entry_cache_free(entry);
+		node = next;
+	}
+	tree->rbroot = RB_ROOT;
+	INIT_LIST_HEAD(&tree->lru);
+	spin_unlock(&tree->lock);
+}
+
+/* NOTE: this is called in atomic context from swapon and must not sleep */
+static void zswap_fs_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;
+	INIT_LIST_HEAD(&tree->lru);
+	spin_lock_init(&tree->lock);
+	zswap_trees[type] = tree;
+	return;
+
+freetree:
+	kfree(tree);
+err:
+	pr_err("zswap: alloc failed, zswap disabled for swap type %d\n", type);
+}
+
+static struct frontswap_ops zswap_fs_ops = {
+	.store = zswap_fs_store,
+	.load = zswap_fs_load,
+	.invalidate_page = zswap_fs_invalidate_page,
+	.invalidate_area = zswap_fs_invalidate_area,
+	.init = zswap_fs_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("saved_by_flush", S_IRUGO,
+			zswap_debugfs_root, &zswap_saved_by_flush);
+	debugfs_create_u64("pool_limit_hit", S_IRUGO,
+			zswap_debugfs_root, &zswap_pool_limit_hit);
+	debugfs_create_u64("reject_flush_attempted", S_IRUGO,
+			zswap_debugfs_root, &zswap_flush_attempted);
+	debugfs_create_u64("reject_tmppage_fail", S_IRUGO,
+			zswap_debugfs_root, &zswap_reject_tmppage_fail);
+	debugfs_create_u64("reject_flush_fail", S_IRUGO,
+			zswap_debugfs_root, &zswap_reject_flush_fail);
+	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("flushed_pages", S_IRUGO,
+			zswap_debugfs_root, &zswap_flushed_pages);
+	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);
+	debugfs_create_atomic_t("outstanding_flushes", S_IRUGO,
+			zswap_debugfs_root, &zswap_outstanding_flushes);
+
+	return 0;
+}
+
+static void __exit zswap_debugfs_exit(void)
+{
+	if (zswap_debugfs_root)
+		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("zswap: entry cache creation failed\n");
+		goto error;
+	}
+	if (zswap_page_pool_create()) {
+		pr_err("zswap: page pool initialization failed\n");
+		goto pagepoolfail;
+	}
+	if (zswap_tmppage_pool_create()) {
+		pr_err("zswap: workmem pool initialization failed\n");
+		goto tmppoolfail;
+	}
+	if (zswap_comp_init()) {
+		pr_err("zswap: compressor initialization failed\n");
+		goto compfail;
+	}
+	if (zswap_cpu_init()) {
+		pr_err("zswap: per-cpu initialization failed\n");
+		goto pcpufail;
+	}
+	frontswap_register_ops(&zswap_fs_ops);
+	if (zswap_debugfs_init())
+		pr_warn("zswap: debugfs initialization failed\n");
+	return 0;
+pcpufail:
+	zswap_comp_exit();
+compfail:
+	zswap_tmppage_pool_destroy();
+tmppoolfail:
+	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 at linux.vnet.ibm.com>");
+MODULE_DESCRIPTION("Compression backend for frontswap pages");
-- 
1.7.9.5




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