3 files changed, 964 insertions, 0 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index 45503ed5f3aa..8028dcc6615c 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -488,6 +488,26 @@ config ZBUD
           deterministic reclaim properties that make it preferable to a higher
           density approach when reclaim will be used.
 
+config ZSWAP
+        bool "Compressed cache for swap pages (EXPERIMENTAL)"
+        depends on FRONTSWAP && CRYPTO=y
+        select CRYPTO_LZO
+        select ZBUD
+        default n
+        help
+          A lightweight compressed cache for swap pages.  It takes
+          pages that are in the process of being swapped out and attempts to
+          compress them into a dynamically allocated RAM-based memory pool.
+          This can result in a significant I/O reduction on swap device and,
+          in the case where decompressing from RAM is faster that swap device
+          reads, can also improve workload performance.
+
+          This is marked experimental because it is a new feature (as of
+          v3.11) that interacts heavily with memory reclaim.  While these
+          interactions don't cause any known issues on simple memory setups,
+          they have not be fully explored on the large set of potential
+          configurations and workloads that exist.
+
 config MEM_SOFT_DIRTY
         bool "Track memory changes"
         depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY
diff --git a/mm/Makefile b/mm/Makefile
index 95f0197ce3d3..f00803386a67 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 000000000000..deda2b671e12
--- /dev/null
+++ b/mm/zswap.c
@@ -0,0 +1,943 @@
+/*
+ * 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/crypto.h>
+#include <linux/mempool.h>
+#include <linux/zbud.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 u64 zswap_pool_pages;
+/* 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.
+*/
+
+/* 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;
+
+/*********************************
+* tunables
+**********************************/
+/* Enable/disable zswap (disabled by default, fixed at boot for now) */
+static bool zswap_enabled __read_mostly;
+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);
+
+/*********************************
+* 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
+ *
+ * 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
+ *            concurent 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 - zsmalloc allocation handle that stores the compressed page data
+ * length - the length in bytes of the compressed page data.  Needed during
+ *           decompression
+ */
+struct zswap_entry {
+        struct rb_node rbnode;
+        pgoff_t offset;
+        int refcount;
+        unsigned int length;
+        unsigned long handle;
+};
+
+struct zswap_header {
+        swp_entry_t swpentry;
+};
+
+/*
+ * 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;
+        struct zbud_pool *pool;
+};
+
+static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
+
+/*********************************
+* zswap entry functions
+**********************************/
+static struct kmem_cache *zswap_entry_cache;
+
+static int zswap_entry_cache_create(void)
+{
+        zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
+        return (zswap_entry_cache == NULL);
+}
+
+static void zswap_entry_cache_destory(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;
+        return entry;
+}
+
+static void zswap_entry_cache_free(struct zswap_entry *entry)
+{
+        kmem_cache_free(zswap_entry_cache, entry);
+}
+
+/* caller must hold the tree lock */
+static void zswap_entry_get(struct zswap_entry *entry)
+{
+        entry->refcount++;
+}
+
+/* caller must hold the tree lock */
+static 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, 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 = kmalloc(PAGE_SIZE * 2, GFP_KERNEL);
+                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 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;
+}
+
+/*********************************
+* helpers
+**********************************/
+static bool zswap_is_full(void)
+{
+        return (totalram_pages * zswap_max_pool_percent / 100 <
+                zswap_pool_pages);
+}
+
+/*
+ * Carries out the common pattern of freeing and entry's zsmalloc allocation,
+ * freeing the entry itself, and decrementing the number of stored pages.
+ */
+static void zswap_free_entry(struct zswap_tree *tree, struct zswap_entry *entry)
+{
+        zbud_free(tree->pool, entry->handle);
+        zswap_entry_cache_free(entry);
+        atomic_dec(&zswap_stored_pages);
+        zswap_pool_pages = zbud_get_pool_size(tree->pool);
+}
+
+/*********************************
+* writeback code
+**********************************/
+/* return enum for zswap_get_swap_cache_page */
+enum zswap_get_swap_ret {
+        ZSWAP_SWAPCACHE_NEW,
+        ZSWAP_SWAPCACHE_EXIST,
+        ZSWAP_SWAPCACHE_NOMEM
+};
+
+/*
+ * 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 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
+ * Returns <0 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 = &swapper_spaces[swp_type(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_NOMEM;
+        *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.
+ */
+static int zswap_writeback_entry(struct zbud_pool *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, refcount;
+        struct writeback_control wbc = {
+                .sync_mode = WB_SYNC_NONE,
+        };
+
+        /* extract swpentry from data */
+        zhdr = zbud_map(pool, handle);
+        swpentry = zhdr->swpentry; /* here */
+        zbud_unmap(pool, handle);
+        tree = zswap_trees[swp_type(swpentry)];
+        offset = swp_offset(swpentry);
+        BUG_ON(pool != tree->pool);
+
+        /* find and ref zswap entry */
+        spin_lock(&tree->lock);
+        entry = zswap_rb_search(&tree->rbroot, offset);
+        if (!entry) {
+                /* entry was invalidated */
+                spin_unlock(&tree->lock);
+                return 0;
+        }
+        zswap_entry_get(entry);
+        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_NOMEM: /* no memory */
+                ret = -ENOMEM;
+                goto fail;
+
+        case ZSWAP_SWAPCACHE_EXIST: /* page is unlocked */
+                /* 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 *)zbud_map(tree->pool, entry->handle) +
+                        sizeof(struct zswap_header);
+                dst = kmap_atomic(page);
+                ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src,
+                                entry->length, dst, &dlen);
+                kunmap_atomic(dst);
+                zbud_unmap(tree->pool, entry->handle);
+                BUG_ON(ret);
+                BUG_ON(dlen != PAGE_SIZE);
+
+                /* page is up to date */
+                SetPageUptodate(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(entry);
+        /* drop the initial reference from entry creation */
+        refcount = zswap_entry_put(entry);
+
+        /*
+         * There are three possible values for refcount here:
+         * (1) refcount is 1, load is in progress, unlink from rbtree,
+         *     load will free
+         * (2) refcount is 0, (normal case) entry is valid,
+         *     remove from rbtree and free entry
+         * (3) refcount is -1, invalidate happened during writeback,
+         *     free entry
+         */
+        if (refcount >= 0) {
+                /* no invalidate yet, remove from rbtree */
+                rb_erase(&entry->rbnode, &tree->rbroot);
+        }
+        spin_unlock(&tree->lock);
+        if (refcount <= 0) {
+                /* free the entry */
+                zswap_free_entry(tree, entry);
+                return 0;
+        }
+        return -EAGAIN;
+
+fail:
+        spin_lock(&tree->lock);
+        zswap_entry_put(entry);
+        spin_unlock(&tree->lock);
+        return ret;
+}
+
+/*********************************
+* 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;
+        struct zswap_header *zhdr;
+
+        if (!tree) {
+                ret = -ENODEV;
+                goto reject;
+        }
+
+        /* reclaim space if needed */
+        if (zswap_is_full()) {
+                zswap_pool_limit_hit++;
+                if (zbud_reclaim_page(tree->pool, 8)) {
+                        zswap_reject_reclaim_fail++;
+                        ret = -ENOMEM;
+                        goto reject;
+                }
+        }
+
+        /* allocate entry */
+        entry = zswap_entry_cache_alloc(GFP_KERNEL);
+        if (!entry) {
+                zswap_reject_kmemcache_fail++;
+                ret = -ENOMEM;
+                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;
+        }
+
+        /* store */
+        len = dlen + sizeof(struct zswap_header);
+        ret = zbud_alloc(tree->pool, len, __GFP_NORETRY | __GFP_NOWARN,
+                &handle);
+        if (ret == -ENOSPC) {
+                zswap_reject_compress_poor++;
+                goto freepage;
+        }
+        if (ret) {
+                zswap_reject_alloc_fail++;
+                goto freepage;
+        }
+        zhdr = zbud_map(tree->pool, handle);
+        zhdr->swpentry = swp_entry(type, offset);
+        buf = (u8 *)(zhdr + 1);
+        memcpy(buf, dst, dlen);
+        zbud_unmap(tree->pool, handle);
+        put_cpu_var(zswap_dstmem);
+
+        /* 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 */
+                        rb_erase(&dupentry->rbnode, &tree->rbroot);
+                        if (!zswap_entry_put(dupentry)) {
+                                /* free */
+                                zswap_free_entry(tree, dupentry);
+                        }
+                }
+        } while (ret == -EEXIST);
+        spin_unlock(&tree->lock);
+
+        /* update stats */
+        atomic_inc(&zswap_stored_pages);
+        zswap_pool_pages = zbud_get_pool_size(tree->pool);
+
+        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 refcount, ret;
+
+        /* find */
+        spin_lock(&tree->lock);
+        entry = zswap_rb_search(&tree->rbroot, offset);
+        if (!entry) {
+                /* entry was written back */
+                spin_unlock(&tree->lock);
+                return -1;
+        }
+        zswap_entry_get(entry);
+        spin_unlock(&tree->lock);
+
+        /* decompress */
+        dlen = PAGE_SIZE;
+        src = (u8 *)zbud_map(tree->pool, entry->handle) +
+                        sizeof(struct zswap_header);
+        dst = kmap_atomic(page);
+        ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
+                dst, &dlen);
+        kunmap_atomic(dst);
+        zbud_unmap(tree->pool, entry->handle);
+        BUG_ON(ret);
+
+        spin_lock(&tree->lock);
+        refcount = zswap_entry_put(entry);
+        if (likely(refcount)) {
+                spin_unlock(&tree->lock);
+                return 0;
+        }
+        spin_unlock(&tree->lock);
+
+        /*
+         * We don't have to unlink from the rbtree because
+         * zswap_writeback_entry() or zswap_frontswap_invalidate page()
+         * has already done this for us if we are the last reference.
+         */
+        /* free */
+
+        zswap_free_entry(tree, entry);
+
+        return 0;
+}
+
+/* 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;
+        int refcount;
+
+        /* 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 */
+        rb_erase(&entry->rbnode, &tree->rbroot);
+
+        /* drop the initial reference from entry creation */
+        refcount = zswap_entry_put(entry);
+
+        spin_unlock(&tree->lock);
+
+        if (refcount) {
+                /* writeback in progress, writeback will free */
+                return;
+        }
+
+        /* free */
+        zswap_free_entry(tree, entry);
+}
+
+/* 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 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);
+                zbud_free(tree->pool, entry->handle);
+                zswap_entry_cache_free(entry);
+                atomic_dec(&zswap_stored_pages);
+        }
+        tree->rbroot = RB_ROOT;
+        spin_unlock(&tree->lock);
+}
+
+static struct zbud_ops zswap_zbud_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)
+                goto err;
+        tree->pool = zbud_create_pool(GFP_KERNEL, &zswap_zbud_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_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_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 int __init zswap_debugfs_init(void)
+{
+        return 0;
+}
+
+static 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_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_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@linux.vnet.ibm.com>");
+MODULE_DESCRIPTION("Compressed cache for swap pages");