/*
 * 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;
        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 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);
}

/* 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(tree, 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(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);
}

/*********************************
* writeback code
**********************************/
/* return enum for zswap_get_swap_cache_page */
enum zswap_get_swap_ret {
        ZSWAP_SWAPCACHE_NEW,
        ZSWAP_SWAPCACHE_EXIST,
        ZSWAP_SWAPCACHE_FAIL,
};

/*
 * 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.
 */
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;
        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_entry_find_get(&tree->rbroot, offset);
        if (!entry) {
                /* entry was invalidated */
                spin_unlock(&tree->lock);
                return 0;
        }
        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 *)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);
        }

        /* 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;
}

/*********************************
* 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 */
                        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_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 ret;

        /* 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);

        /* 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);
        zswap_entry_put(tree, entry);
        spin_unlock(&tree->lock);

        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;

        /* 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);
}

/* 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(tree, entry);
        tree->rbroot = RB_ROOT;
        spin_unlock(&tree->lock);

        zbud_destroy_pool(tree->pool);
        kfree(tree);
        zswap_trees[type] = NULL;
}

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");