zcache-main.c

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/*
 * zcache.c
 *
 * Copyright (c) 2010,2011, Dan Magenheimer, Oracle Corp.
 * Copyright (c) 2010,2011, Nitin Gupta
 *
 * Zcache provides an in-kernel "host implementation" for transcendent memory
 * and, thus indirectly, for cleancache and frontswap.  Zcache includes two
 * page-accessible memory [1] interfaces, both utilizing the crypto compression
 * API:
 * 1) "compression buddies" ("zbud") is used for ephemeral pages
 * 2) zsmalloc is used for persistent pages.
 * Xvmalloc (based on the TLSF allocator) has very low fragmentation
 * so maximizes space efficiency, while zbud allows pairs (and potentially,
 * in the future, more than a pair of) compressed pages to be closely linked
 * so that reclaiming can be done via the kernel's physical-page-oriented
 * "shrinker" interface.
 *
 * [1] For a definition of page-accessible memory (aka PAM), see:
 *   http://marc.info/?l=linux-mm&m=127811271605009
 */

#include <linux/module.h>
#include <linux/cpu.h>
#include <linux/highmem.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/math64.h>
#include <linux/crypto.h>
#include <linux/string.h>
#include <linux/idr.h>
#include "tmem.h"

#include "../zsmalloc/zsmalloc.h"

#ifdef CONFIG_CLEANCACHE
#include <linux/cleancache.h>
#endif
#ifdef CONFIG_FRONTSWAP
#include <linux/frontswap.h>
#endif

#if 0
/* this is more aggressive but may cause other problems? */
#define ZCACHE_GFP_MASK (GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN)
#else
#define ZCACHE_GFP_MASK \
    (__GFP_FS | __GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC)
#endif

#define MAX_CLIENTS 16
#define LOCAL_CLIENT ((uint16_t)-1)

MODULE_LICENSE("GPL");

struct zcache_client {
    struct idr tmem_pools;
    struct zs_pool *zspool;
    bool allocated;
    atomic_t refcount;
};

static struct zcache_client zcache_host;
static struct zcache_client zcache_clients[MAX_CLIENTS];

static inline uint16_t get_client_id_from_client(struct zcache_client *cli)
{
    BUG_ON(cli == NULL);
    if (cli == &zcache_host)
        return LOCAL_CLIENT;
    return cli - &zcache_clients[0];
}

static struct zcache_client *get_zcache_client(uint16_t cli_id)
{
    if (cli_id == LOCAL_CLIENT)
        return &zcache_host;

    if ((unsigned int)cli_id < MAX_CLIENTS)
        return &zcache_clients[cli_id];

    return NULL;
}

static inline bool is_local_client(struct zcache_client *cli)
{
    return cli == &zcache_host;
}

/* crypto API for zcache  */
#define ZCACHE_COMP_NAME_SZ CRYPTO_MAX_ALG_NAME
static char zcache_comp_name[ZCACHE_COMP_NAME_SZ];
static struct crypto_comp * __percpu *zcache_comp_pcpu_tfms;

enum comp_op {
    ZCACHE_COMPOP_COMPRESS,
    ZCACHE_COMPOP_DECOMPRESS
};

static inline int zcache_comp_op(enum comp_op op,
                const u8 *src, unsigned int slen,
                u8 *dst, unsigned int *dlen)
{
    struct crypto_comp *tfm;
    int ret;

    BUG_ON(!zcache_comp_pcpu_tfms);
    tfm = *per_cpu_ptr(zcache_comp_pcpu_tfms, get_cpu());
    BUG_ON(!tfm);
    switch (op) {
    case ZCACHE_COMPOP_COMPRESS:
        ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
        break;
    case ZCACHE_COMPOP_DECOMPRESS:
        ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
        break;
    default:
        ret = -EINVAL;
    }
    put_cpu();
    return ret;
}

/**********
 * Compression buddies ("zbud") provides for packing two (or, possibly
 * in the future, more) compressed ephemeral pages into a single "raw"
 * (physical) page and tracking them with data structures so that
 * the raw pages can be easily reclaimed.
 *
 * A zbud page ("zbpg") is an aligned page containing a list_head,
 * a lock, and two "zbud headers".  The remainder of the physical
 * page is divided up into aligned 64-byte "chunks" which contain
 * the compressed data for zero, one, or two zbuds.  Each zbpg
 * resides on: (1) an "unused list" if it has no zbuds; (2) a
 * "buddied" list if it is fully populated  with two zbuds; or
 * (3) one of PAGE_SIZE/64 "unbuddied" lists indexed by how many chunks
 * the one unbuddied zbud uses.  The data inside a zbpg cannot be
 * read or written unless the zbpg's lock is held.
 */

#define ZBH_SENTINEL  0x43214321
#define ZBPG_SENTINEL  0xdeadbeef

#define ZBUD_MAX_BUDS 2

struct zbud_hdr {
    uint16_t client_id;
    uint16_t pool_id;
    struct tmem_oid oid;
    uint32_t index;
    uint16_t size; /* compressed size in bytes, zero means unused */
    DECL_SENTINEL
};

struct zbud_page {
    struct list_head bud_list;
    spinlock_t lock;
    struct zbud_hdr buddy[ZBUD_MAX_BUDS];
    DECL_SENTINEL
    /* followed by NUM_CHUNK aligned CHUNK_SIZE-byte chunks */
};

#define CHUNK_SHIFT 6
#define CHUNK_SIZE  (1 << CHUNK_SHIFT)
#define CHUNK_MASK  (~(CHUNK_SIZE-1))
#define NCHUNKS     (((PAGE_SIZE - sizeof(struct zbud_page)) & \
                CHUNK_MASK) >> CHUNK_SHIFT)
#define MAX_CHUNK   (NCHUNKS-1)

static struct {
    struct list_head list;
    unsigned count;
} zbud_unbuddied[NCHUNKS];
/* list N contains pages with N chunks USED and NCHUNKS-N unused */
/* element 0 is never used but optimizing that isn't worth it */
static unsigned long zbud_cumul_chunk_counts[NCHUNKS];

struct list_head zbud_buddied_list;
static unsigned long zcache_zbud_buddied_count;

/* protects the buddied list and all unbuddied lists */
static DEFINE_SPINLOCK(zbud_budlists_spinlock);

static LIST_HEAD(zbpg_unused_list);
static unsigned long zcache_zbpg_unused_list_count;

/* protects the unused page list */
static DEFINE_SPINLOCK(zbpg_unused_list_spinlock);

static atomic_t zcache_zbud_curr_raw_pages;
static atomic_t zcache_zbud_curr_zpages;
static unsigned long zcache_zbud_curr_zbytes;
static unsigned long zcache_zbud_cumul_zpages;
static unsigned long zcache_zbud_cumul_zbytes;
static unsigned long zcache_compress_poor;
static unsigned long zcache_mean_compress_poor;

/* forward references */
static void *zcache_get_free_page(void);
static void zcache_free_page(void *p);

/*
 * zbud helper functions
 */

static inline unsigned zbud_max_buddy_size(void)
{
    return MAX_CHUNK << CHUNK_SHIFT;
}

static inline unsigned zbud_size_to_chunks(unsigned size)
{
    BUG_ON(size == 0 || size > zbud_max_buddy_size());
    return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
}

static inline int zbud_budnum(struct zbud_hdr *zh)
{
    unsigned offset = (unsigned long)zh & (PAGE_SIZE - 1);
    struct zbud_page *zbpg = NULL;
    unsigned budnum = -1U;
    int i;

    for (i = 0; i < ZBUD_MAX_BUDS; i++)
        if (offset == offsetof(typeof(*zbpg), buddy[i])) {
            budnum = i;
            break;
        }
    BUG_ON(budnum == -1U);
    return budnum;
}

static char *zbud_data(struct zbud_hdr *zh, unsigned size)
{
    struct zbud_page *zbpg;
    char *p;
    unsigned budnum;

    ASSERT_SENTINEL(zh, ZBH);
    budnum = zbud_budnum(zh);
    BUG_ON(size == 0 || size > zbud_max_buddy_size());
    zbpg = container_of(zh, struct zbud_page, buddy[budnum]);
    ASSERT_SPINLOCK(&zbpg->lock);
    p = (char *)zbpg;
    if (budnum == 0)
        p += ((sizeof(struct zbud_page) + CHUNK_SIZE - 1) &
                            CHUNK_MASK);
    else if (budnum == 1)
        p += PAGE_SIZE - ((size + CHUNK_SIZE - 1) & CHUNK_MASK);
    return p;
}

/*
 * zbud raw page management
 */

static struct zbud_page *zbud_alloc_raw_page(void)
{
    struct zbud_page *zbpg = NULL;
    struct zbud_hdr *zh0, *zh1;
    bool recycled = 0;

    /* if any pages on the zbpg list, use one */
    spin_lock(&zbpg_unused_list_spinlock);
    if (!list_empty(&zbpg_unused_list)) {
        zbpg = list_first_entry(&zbpg_unused_list,
                struct zbud_page, bud_list);
        list_del_init(&zbpg->bud_list);
        zcache_zbpg_unused_list_count--;
        recycled = 1;
    }
    spin_unlock(&zbpg_unused_list_spinlock);
    if (zbpg == NULL)
        /* none on zbpg list, try to get a kernel page */
        zbpg = zcache_get_free_page();
    if (likely(zbpg != NULL)) {
        INIT_LIST_HEAD(&zbpg->bud_list);
        zh0 = &zbpg->buddy[0]; zh1 = &zbpg->buddy[1];
        spin_lock_init(&zbpg->lock);
        if (recycled) {
            ASSERT_INVERTED_SENTINEL(zbpg, ZBPG);
            SET_SENTINEL(zbpg, ZBPG);
            BUG_ON(zh0->size != 0 || tmem_oid_valid(&zh0->oid));
            BUG_ON(zh1->size != 0 || tmem_oid_valid(&zh1->oid));
        } else {
            atomic_inc(&zcache_zbud_curr_raw_pages);
            INIT_LIST_HEAD(&zbpg->bud_list);
            SET_SENTINEL(zbpg, ZBPG);
            zh0->size = 0; zh1->size = 0;
            tmem_oid_set_invalid(&zh0->oid);
            tmem_oid_set_invalid(&zh1->oid);
        }
    }
    return zbpg;
}

static void zbud_free_raw_page(struct zbud_page *zbpg)
{
    struct zbud_hdr *zh0 = &zbpg->buddy[0], *zh1 = &zbpg->buddy[1];

    ASSERT_SENTINEL(zbpg, ZBPG);
    BUG_ON(!list_empty(&zbpg->bud_list));
    ASSERT_SPINLOCK(&zbpg->lock);
    BUG_ON(zh0->size != 0 || tmem_oid_valid(&zh0->oid));
    BUG_ON(zh1->size != 0 || tmem_oid_valid(&zh1->oid));
    INVERT_SENTINEL(zbpg, ZBPG);
    spin_unlock(&zbpg->lock);
    spin_lock(&zbpg_unused_list_spinlock);
    list_add(&zbpg->bud_list, &zbpg_unused_list);
    zcache_zbpg_unused_list_count++;
    spin_unlock(&zbpg_unused_list_spinlock);
}

/*
 * core zbud handling routines
 */

static unsigned zbud_free(struct zbud_hdr *zh)
{
    unsigned size;

    ASSERT_SENTINEL(zh, ZBH);
    BUG_ON(!tmem_oid_valid(&zh->oid));
    size = zh->size;
    BUG_ON(zh->size == 0 || zh->size > zbud_max_buddy_size());
    zh->size = 0;
    tmem_oid_set_invalid(&zh->oid);
    INVERT_SENTINEL(zh, ZBH);
    zcache_zbud_curr_zbytes -= size;
    atomic_dec(&zcache_zbud_curr_zpages);
    return size;
}

static void zbud_free_and_delist(struct zbud_hdr *zh)
{
    unsigned chunks;
    struct zbud_hdr *zh_other;
    unsigned budnum = zbud_budnum(zh), size;
    struct zbud_page *zbpg =
        container_of(zh, struct zbud_page, buddy[budnum]);

    spin_lock(&zbud_budlists_spinlock);
    spin_lock(&zbpg->lock);
    if (list_empty(&zbpg->bud_list)) {
        /* ignore zombie page... see zbud_evict_pages() */
        spin_unlock(&zbpg->lock);
        spin_unlock(&zbud_budlists_spinlock);
        return;
    }
    size = zbud_free(zh);
    ASSERT_SPINLOCK(&zbpg->lock);
    zh_other = &zbpg->buddy[(budnum == 0) ? 1 : 0];
    if (zh_other->size == 0) { /* was unbuddied: unlist and free */
        chunks = zbud_size_to_chunks(size) ;
        BUG_ON(list_empty(&zbud_unbuddied[chunks].list));
        list_del_init(&zbpg->bud_list);
        zbud_unbuddied[chunks].count--;
        spin_unlock(&zbud_budlists_spinlock);
        zbud_free_raw_page(zbpg);
    } else { /* was buddied: move remaining buddy to unbuddied list */
        chunks = zbud_size_to_chunks(zh_other->size) ;
        list_del_init(&zbpg->bud_list);
        zcache_zbud_buddied_count--;
        list_add_tail(&zbpg->bud_list, &zbud_unbuddied[chunks].list);
        zbud_unbuddied[chunks].count++;
        spin_unlock(&zbud_budlists_spinlock);
        spin_unlock(&zbpg->lock);
    }
}

static struct zbud_hdr *zbud_create(uint16_t client_id, uint16_t pool_id,
                    struct tmem_oid *oid,
                    uint32_t index, struct page *page,
                    void *cdata, unsigned size)
{
    struct zbud_hdr *zh0, *zh1, *zh = NULL;
    struct zbud_page *zbpg = NULL, *ztmp;
    unsigned nchunks;
    char *to;
    int i, found_good_buddy = 0;

    nchunks = zbud_size_to_chunks(size) ;
    for (i = MAX_CHUNK - nchunks + 1; i > 0; i--) {
        spin_lock(&zbud_budlists_spinlock);
        if (!list_empty(&zbud_unbuddied[i].list)) {
            list_for_each_entry_safe(zbpg, ztmp,
                    &zbud_unbuddied[i].list, bud_list) {
                if (spin_trylock(&zbpg->lock)) {
                    found_good_buddy = i;
                    goto found_unbuddied;
                }
            }
        }
        spin_unlock(&zbud_budlists_spinlock);
    }
    /* didn't find a good buddy, try allocating a new page */
    zbpg = zbud_alloc_raw_page();
    if (unlikely(zbpg == NULL))
        goto out;
    /* ok, have a page, now compress the data before taking locks */
    spin_lock(&zbud_budlists_spinlock);
    spin_lock(&zbpg->lock);
    list_add_tail(&zbpg->bud_list, &zbud_unbuddied[nchunks].list);
    zbud_unbuddied[nchunks].count++;
    zh = &zbpg->buddy[0];
    goto init_zh;

found_unbuddied:
    ASSERT_SPINLOCK(&zbpg->lock);
    zh0 = &zbpg->buddy[0]; zh1 = &zbpg->buddy[1];
    BUG_ON(!((zh0->size == 0) ^ (zh1->size == 0)));
    if (zh0->size != 0) { /* buddy0 in use, buddy1 is vacant */
        ASSERT_SENTINEL(zh0, ZBH);
        zh = zh1;
    } else if (zh1->size != 0) { /* buddy1 in use, buddy0 is vacant */
        ASSERT_SENTINEL(zh1, ZBH);
        zh = zh0;
    } else
        BUG();
    list_del_init(&zbpg->bud_list);
    zbud_unbuddied[found_good_buddy].count--;
    list_add_tail(&zbpg->bud_list, &zbud_buddied_list);
    zcache_zbud_buddied_count++;

init_zh:
    SET_SENTINEL(zh, ZBH);
    zh->size = size;
    zh->index = index;
    zh->oid = *oid;
    zh->pool_id = pool_id;
    zh->client_id = client_id;
    to = zbud_data(zh, size);
    memcpy(to, cdata, size);
    spin_unlock(&zbpg->lock);
    spin_unlock(&zbud_budlists_spinlock);

    zbud_cumul_chunk_counts[nchunks]++;
    atomic_inc(&zcache_zbud_curr_zpages);
    zcache_zbud_cumul_zpages++;
    zcache_zbud_curr_zbytes += size;
    zcache_zbud_cumul_zbytes += size;
out:
    return zh;
}

static int zbud_decompress(struct page *page, struct zbud_hdr *zh)
{
    struct zbud_page *zbpg;
    unsigned budnum = zbud_budnum(zh);
    unsigned int out_len = PAGE_SIZE;
    char *to_va, *from_va;
    unsigned size;
    int ret = 0;

    zbpg = container_of(zh, struct zbud_page, buddy[budnum]);
    spin_lock(&zbpg->lock);
    if (list_empty(&zbpg->bud_list)) {
        /* ignore zombie page... see zbud_evict_pages() */
        ret = -EINVAL;
        goto out;
    }
    ASSERT_SENTINEL(zh, ZBH);
    BUG_ON(zh->size == 0 || zh->size > zbud_max_buddy_size());
    to_va = kmap_atomic(page);
    size = zh->size;
    from_va = zbud_data(zh, size);
    ret = zcache_comp_op(ZCACHE_COMPOP_DECOMPRESS, from_va, size,
                to_va, &out_len);
    BUG_ON(ret);
    BUG_ON(out_len != PAGE_SIZE);
    kunmap_atomic(to_va);
out:
    spin_unlock(&zbpg->lock);
    return ret;
}

/*
 * The following routines handle shrinking of ephemeral pages by evicting
 * pages "least valuable" first.
 */

static unsigned long zcache_evicted_raw_pages;
static unsigned long zcache_evicted_buddied_pages;
static unsigned long zcache_evicted_unbuddied_pages;

static struct tmem_pool *zcache_get_pool_by_id(uint16_t cli_id,
                        uint16_t poolid);
static void zcache_put_pool(struct tmem_pool *pool);

/*
 * Flush and free all zbuds in a zbpg, then free the pageframe
 */
static void zbud_evict_zbpg(struct zbud_page *zbpg)
{
    struct zbud_hdr *zh;
    int i, j;
    uint32_t pool_id[ZBUD_MAX_BUDS], client_id[ZBUD_MAX_BUDS];
    uint32_t index[ZBUD_MAX_BUDS];
    struct tmem_oid oid[ZBUD_MAX_BUDS];
    struct tmem_pool *pool;

    ASSERT_SPINLOCK(&zbpg->lock);
    BUG_ON(!list_empty(&zbpg->bud_list));
    for (i = 0, j = 0; i < ZBUD_MAX_BUDS; i++) {
        zh = &zbpg->buddy[i];
        if (zh->size) {
            client_id[j] = zh->client_id;
            pool_id[j] = zh->pool_id;
            oid[j] = zh->oid;
            index[j] = zh->index;
            j++;
            zbud_free(zh);
        }
    }
    spin_unlock(&zbpg->lock);
    for (i = 0; i < j; i++) {
        pool = zcache_get_pool_by_id(client_id[i], pool_id[i]);
        if (pool != NULL) {
            tmem_flush_page(pool, &oid[i], index[i]);
            zcache_put_pool(pool);
        }
    }
    ASSERT_SENTINEL(zbpg, ZBPG);
    spin_lock(&zbpg->lock);
    zbud_free_raw_page(zbpg);
}

/*
 * Free nr pages.  This code is funky because we want to hold the locks
 * protecting various lists for as short a time as possible, and in some
 * circumstances the list may change asynchronously when the list lock is
 * not held.  In some cases we also trylock not only to avoid waiting on a
 * page in use by another cpu, but also to avoid potential deadlock due to
 * lock inversion.
 */
static void zbud_evict_pages(int nr)
{
    struct zbud_page *zbpg;
    int i;

    /* first try freeing any pages on unused list */
retry_unused_list:
    spin_lock_bh(&zbpg_unused_list_spinlock);
    if (!list_empty(&zbpg_unused_list)) {
        /* can't walk list here, since it may change when unlocked */
        zbpg = list_first_entry(&zbpg_unused_list,
                struct zbud_page, bud_list);
        list_del_init(&zbpg->bud_list);
        zcache_zbpg_unused_list_count--;
        atomic_dec(&zcache_zbud_curr_raw_pages);
        spin_unlock_bh(&zbpg_unused_list_spinlock);
        zcache_free_page(zbpg);
        zcache_evicted_raw_pages++;
        if (--nr <= 0)
            goto out;
        goto retry_unused_list;
    }
    spin_unlock_bh(&zbpg_unused_list_spinlock);

    /* now try freeing unbuddied pages, starting with least space avail */
    for (i = 0; i < MAX_CHUNK; i++) {
retry_unbud_list_i:
        spin_lock_bh(&zbud_budlists_spinlock);
        if (list_empty(&zbud_unbuddied[i].list)) {
            spin_unlock_bh(&zbud_budlists_spinlock);
            continue;
        }
        list_for_each_entry(zbpg, &zbud_unbuddied[i].list, bud_list) {
            if (unlikely(!spin_trylock(&zbpg->lock)))
                continue;
            list_del_init(&zbpg->bud_list);
            zbud_unbuddied[i].count--;
            spin_unlock(&zbud_budlists_spinlock);
            zcache_evicted_unbuddied_pages++;
            /* want budlists unlocked when doing zbpg eviction */
            zbud_evict_zbpg(zbpg);
            local_bh_enable();
            if (--nr <= 0)
                goto out;
            goto retry_unbud_list_i;
        }
        spin_unlock_bh(&zbud_budlists_spinlock);
    }

    /* as a last resort, free buddied pages */
retry_bud_list:
    spin_lock_bh(&zbud_budlists_spinlock);
    if (list_empty(&zbud_buddied_list)) {
        spin_unlock_bh(&zbud_budlists_spinlock);
        goto out;
    }
    list_for_each_entry(zbpg, &zbud_buddied_list, bud_list) {
        if (unlikely(!spin_trylock(&zbpg->lock)))
            continue;
        list_del_init(&zbpg->bud_list);
        zcache_zbud_buddied_count--;
        spin_unlock(&zbud_budlists_spinlock);
        zcache_evicted_buddied_pages++;
        /* want budlists unlocked when doing zbpg eviction */
        zbud_evict_zbpg(zbpg);
        local_bh_enable();
        if (--nr <= 0)
            goto out;
        goto retry_bud_list;
    }
    spin_unlock_bh(&zbud_budlists_spinlock);
out:
    return;
}

static void __init zbud_init(void)
{
    int i;

    INIT_LIST_HEAD(&zbud_buddied_list);

    for (i = 0; i < NCHUNKS; i++)
        INIT_LIST_HEAD(&zbud_unbuddied[i].list);
}

#ifdef CONFIG_SYSFS
/*
 * These sysfs routines show a nice distribution of how many zbpg's are
 * currently (and have ever been placed) in each unbuddied list.  It's fun
 * to watch but can probably go away before final merge.
 */
static int zbud_show_unbuddied_list_counts(char *buf)
{
    int i;
    char *p = buf;

    for (i = 0; i < NCHUNKS; i++)
        p += sprintf(p, "%u ", zbud_unbuddied[i].count);
    return p - buf;
}

static int zbud_show_cumul_chunk_counts(char *buf)
{
    unsigned long i, chunks = 0, total_chunks = 0, sum_total_chunks = 0;
    unsigned long total_chunks_lte_21 = 0, total_chunks_lte_32 = 0;
    unsigned long total_chunks_lte_42 = 0;
    char *p = buf;

    for (i = 0; i < NCHUNKS; i++) {
        p += sprintf(p, "%lu ", zbud_cumul_chunk_counts[i]);
        chunks += zbud_cumul_chunk_counts[i];
        total_chunks += zbud_cumul_chunk_counts[i];
        sum_total_chunks += i * zbud_cumul_chunk_counts[i];
        if (i == 21)
            total_chunks_lte_21 = total_chunks;
        if (i == 32)
            total_chunks_lte_32 = total_chunks;
        if (i == 42)
            total_chunks_lte_42 = total_chunks;
    }
    p += sprintf(p, "<=21:%lu <=32:%lu <=42:%lu, mean:%lu\n",
        total_chunks_lte_21, total_chunks_lte_32, total_chunks_lte_42,
        chunks == 0 ? 0 : sum_total_chunks / chunks);
    return p - buf;
}
#endif

/**********
 * This "zv" PAM implementation combines the slab-based zsmalloc
 * with the crypto compression API to maximize the amount of data that can
 * be packed into a physical page.
 *
 * Zv represents a PAM page with the index and object (plus a "size" value
 * necessary for decompression) immediately preceding the compressed data.
 */

#define ZVH_SENTINEL  0x43214321

struct zv_hdr {
    uint32_t pool_id;
    struct tmem_oid oid;
    uint32_t index;
    size_t size;
    DECL_SENTINEL
};

/* rudimentary policy limits */
/* total number of persistent pages may not exceed this percentage */
static unsigned int zv_page_count_policy_percent = 75;
/*
 * byte count defining poor compression; pages with greater zsize will be
 * rejected
 */
static unsigned int zv_max_zsize = (PAGE_SIZE / 8) * 7;
/*
 * byte count defining poor *mean* compression; pages with greater zsize
 * will be rejected until sufficient better-compressed pages are accepted
 * driving the mean below this threshold
 */
static unsigned int zv_max_mean_zsize = (PAGE_SIZE / 8) * 5;

static atomic_t zv_curr_dist_counts[NCHUNKS];
static atomic_t zv_cumul_dist_counts[NCHUNKS];

static unsigned long zv_create(struct zs_pool *pool, uint32_t pool_id,
                struct tmem_oid *oid, uint32_t index,
                void *cdata, unsigned clen)
{
    struct zv_hdr *zv;
    u32 size = clen + sizeof(struct zv_hdr);
    int chunks = (size + (CHUNK_SIZE - 1)) >> CHUNK_SHIFT;
    unsigned long handle = 0;

    BUG_ON(!irqs_disabled());
    BUG_ON(chunks >= NCHUNKS);
    handle = zs_malloc(pool, size);
    if (!handle)
        goto out;
    atomic_inc(&zv_curr_dist_counts[chunks]);
    atomic_inc(&zv_cumul_dist_counts[chunks]);
    zv = zs_map_object(pool, handle, ZS_MM_WO);
    zv->index = index;
    zv->oid = *oid;
    zv->pool_id = pool_id;
    zv->size = clen;
    SET_SENTINEL(zv, ZVH);
    memcpy((char *)zv + sizeof(struct zv_hdr), cdata, clen);
    zs_unmap_object(pool, handle);
out:
    return handle;
}

static void zv_free(struct zs_pool *pool, unsigned long handle)
{
    unsigned long flags;
    struct zv_hdr *zv;
    uint16_t size;
    int chunks;

    zv = zs_map_object(pool, handle, ZS_MM_RW);
    ASSERT_SENTINEL(zv, ZVH);
    size = zv->size + sizeof(struct zv_hdr);
    INVERT_SENTINEL(zv, ZVH);
    zs_unmap_object(pool, handle);

    chunks = (size + (CHUNK_SIZE - 1)) >> CHUNK_SHIFT;
    BUG_ON(chunks >= NCHUNKS);
    atomic_dec(&zv_curr_dist_counts[chunks]);

    local_irq_save(flags);
    zs_free(pool, handle);
    local_irq_restore(flags);
}

static void zv_decompress(struct page *page, unsigned long handle)
{
    unsigned int clen = PAGE_SIZE;
    char *to_va;
    int ret;
    struct zv_hdr *zv;

    zv = zs_map_object(zcache_host.zspool, handle, ZS_MM_RO);
    BUG_ON(zv->size == 0);
    ASSERT_SENTINEL(zv, ZVH);
    to_va = kmap_atomic(page);
    ret = zcache_comp_op(ZCACHE_COMPOP_DECOMPRESS, (char *)zv + sizeof(*zv),
                zv->size, to_va, &clen);
    kunmap_atomic(to_va);
    zs_unmap_object(zcache_host.zspool, handle);
    BUG_ON(ret);
    BUG_ON(clen != PAGE_SIZE);
}

#ifdef CONFIG_SYSFS
/*
 * show a distribution of compression stats for zv pages.
 */

static int zv_curr_dist_counts_show(char *buf)
{
    unsigned long i, n, chunks = 0, sum_total_chunks = 0;
    char *p = buf;

    for (i = 0; i < NCHUNKS; i++) {
        n = atomic_read(&zv_curr_dist_counts[i]);
        p += sprintf(p, "%lu ", n);
        chunks += n;
        sum_total_chunks += i * n;
    }
    p += sprintf(p, "mean:%lu\n",
        chunks == 0 ? 0 : sum_total_chunks / chunks);
    return p - buf;
}

static int zv_cumul_dist_counts_show(char *buf)
{
    unsigned long i, n, chunks = 0, sum_total_chunks = 0;
    char *p = buf;

    for (i = 0; i < NCHUNKS; i++) {
        n = atomic_read(&zv_cumul_dist_counts[i]);
        p += sprintf(p, "%lu ", n);
        chunks += n;
        sum_total_chunks += i * n;
    }
    p += sprintf(p, "mean:%lu\n",
        chunks == 0 ? 0 : sum_total_chunks / chunks);
    return p - buf;
}

/*
 * setting zv_max_zsize via sysfs causes all persistent (e.g. swap)
 * pages that don't compress to less than this value (including metadata
 * overhead) to be rejected.  We don't allow the value to get too close
 * to PAGE_SIZE.
 */
static ssize_t zv_max_zsize_show(struct kobject *kobj,
                    struct kobj_attribute *attr,
                    char *buf)
{
    return sprintf(buf, "%u\n", zv_max_zsize);
}

static ssize_t zv_max_zsize_store(struct kobject *kobj,
                    struct kobj_attribute *attr,
                    const char *buf, size_t count)
{
    unsigned long val;
    int err;

    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;

    err = kstrtoul(buf, 10, &val);
    if (err || (val == 0) || (val > (PAGE_SIZE / 8) * 7))
        return -EINVAL;
    zv_max_zsize = val;
    return count;
}

/*
 * setting zv_max_mean_zsize via sysfs causes all persistent (e.g. swap)
 * pages that don't compress to less than this value (including metadata
 * overhead) to be rejected UNLESS the mean compression is also smaller
 * than this value.  In other words, we are load-balancing-by-zsize the
 * accepted pages.  Again, we don't allow the value to get too close
 * to PAGE_SIZE.
 */
static ssize_t zv_max_mean_zsize_show(struct kobject *kobj,
                    struct kobj_attribute *attr,
                    char *buf)
{
    return sprintf(buf, "%u\n", zv_max_mean_zsize);
}

static ssize_t zv_max_mean_zsize_store(struct kobject *kobj,
                    struct kobj_attribute *attr,
                    const char *buf, size_t count)
{
    unsigned long val;
    int err;

    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;

    err = kstrtoul(buf, 10, &val);
    if (err || (val == 0) || (val > (PAGE_SIZE / 8) * 7))
        return -EINVAL;
    zv_max_mean_zsize = val;
    return count;
}

/*
 * setting zv_page_count_policy_percent via sysfs sets an upper bound of
 * persistent (e.g. swap) pages that will be retained according to:
 *     (zv_page_count_policy_percent * totalram_pages) / 100)
 * when that limit is reached, further puts will be rejected (until
 * some pages have been flushed).  Note that, due to compression,
 * this number may exceed 100; it defaults to 75 and we set an
 * arbitary limit of 150.  A poor choice will almost certainly result
 * in OOM's, so this value should only be changed prudently.
 */
static ssize_t zv_page_count_policy_percent_show(struct kobject *kobj,
                         struct kobj_attribute *attr,
                         char *buf)
{
    return sprintf(buf, "%u\n", zv_page_count_policy_percent);
}

static ssize_t zv_page_count_policy_percent_store(struct kobject *kobj,
                          struct kobj_attribute *attr,
                          const char *buf, size_t count)
{
    unsigned long val;
    int err;

    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;

    err = kstrtoul(buf, 10, &val);
    if (err || (val == 0) || (val > 150))
        return -EINVAL;
    zv_page_count_policy_percent = val;
    return count;
}

static struct kobj_attribute zcache_zv_max_zsize_attr = {
        .attr = { .name = "zv_max_zsize", .mode = 0644 },
        .show = zv_max_zsize_show,
        .store = zv_max_zsize_store,
};

static struct kobj_attribute zcache_zv_max_mean_zsize_attr = {
        .attr = { .name = "zv_max_mean_zsize", .mode = 0644 },
        .show = zv_max_mean_zsize_show,
        .store = zv_max_mean_zsize_store,
};

static struct kobj_attribute zcache_zv_page_count_policy_percent_attr = {
        .attr = { .name = "zv_page_count_policy_percent",
              .mode = 0644 },
        .show = zv_page_count_policy_percent_show,
        .store = zv_page_count_policy_percent_store,
};
#endif

/*
 * zcache core code starts here
 */

/* useful stats not collected by cleancache or frontswap */
static unsigned long zcache_flush_total;
static unsigned long zcache_flush_found;
static unsigned long zcache_flobj_total;
static unsigned long zcache_flobj_found;
static unsigned long zcache_failed_eph_puts;
static unsigned long zcache_failed_pers_puts;

/*
 * Tmem operations assume the poolid implies the invoking client.
 * Zcache only has one client (the kernel itself): LOCAL_CLIENT.
 * RAMster has each client numbered by cluster node, and a KVM version
 * of zcache would have one client per guest and each client might
 * have a poolid==N.
 */
static struct tmem_pool *zcache_get_pool_by_id(uint16_t cli_id, uint16_t poolid)
{
    struct tmem_pool *pool = NULL;
    struct zcache_client *cli = NULL;

    cli = get_zcache_client(cli_id);
    if (!cli)
        goto out;

    atomic_inc(&cli->refcount);
    pool = idr_find(&cli->tmem_pools, poolid);
    if (pool != NULL)
        atomic_inc(&pool->refcount);
out:
    return pool;
}

static void zcache_put_pool(struct tmem_pool *pool)
{
    struct zcache_client *cli = NULL;

    if (pool == NULL)
        BUG();
    cli = pool->client;
    atomic_dec(&pool->refcount);
    atomic_dec(&cli->refcount);
}

int zcache_new_client(uint16_t cli_id)
{
    struct zcache_client *cli;
    int ret = -1;

    cli = get_zcache_client(cli_id);

    if (cli == NULL)
        goto out;
    if (cli->allocated)
        goto out;
    cli->allocated = 1;
#ifdef CONFIG_FRONTSWAP
    cli->zspool = zs_create_pool("zcache", ZCACHE_GFP_MASK);
    if (cli->zspool == NULL)
        goto out;
    idr_init(&cli->tmem_pools);
#endif
    ret = 0;
out:
    return ret;
}

/* counters for debugging */
static unsigned long zcache_failed_get_free_pages;
static unsigned long zcache_failed_alloc;
static unsigned long zcache_put_to_flush;

/*
 * for now, used named slabs so can easily track usage; later can
 * either just use kmalloc, or perhaps add a slab-like allocator
 * to more carefully manage total memory utilization
 */
static struct kmem_cache *zcache_objnode_cache;
static struct kmem_cache *zcache_obj_cache;
static atomic_t zcache_curr_obj_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_obj_count_max;
static atomic_t zcache_curr_objnode_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_objnode_count_max;

/*
 * to avoid memory allocation recursion (e.g. due to direct reclaim), we
 * preload all necessary data structures so the hostops callbacks never
 * actually do a malloc
 */
struct zcache_preload {
    void *page;
    struct tmem_obj *obj;
    int nr;
    struct tmem_objnode *objnodes[OBJNODE_TREE_MAX_PATH];
};
static DEFINE_PER_CPU(struct zcache_preload, zcache_preloads) = { 0, };

static int zcache_do_preload(struct tmem_pool *pool)
{
    struct zcache_preload *kp;
    struct tmem_objnode *objnode;
    struct tmem_obj *obj;
    void *page;
    int ret = -ENOMEM;

    if (unlikely(zcache_objnode_cache == NULL))
        goto out;
    if (unlikely(zcache_obj_cache == NULL))
        goto out;

    /* IRQ has already been disabled. */
    kp = &__get_cpu_var(zcache_preloads);
    while (kp->nr < ARRAY_SIZE(kp->objnodes)) {
        objnode = kmem_cache_alloc(zcache_objnode_cache,
                ZCACHE_GFP_MASK);
        if (unlikely(objnode == NULL)) {
            zcache_failed_alloc++;
            goto out;
        }

        kp->objnodes[kp->nr++] = objnode;
    }

    if (!kp->obj) {
        obj = kmem_cache_alloc(zcache_obj_cache, ZCACHE_GFP_MASK);
        if (unlikely(obj == NULL)) {
            zcache_failed_alloc++;
            goto out;
        }
        kp->obj = obj;
    }

    if (!kp->page) {
        page = (void *)__get_free_page(ZCACHE_GFP_MASK);
        if (unlikely(page == NULL)) {
            zcache_failed_get_free_pages++;
            goto out;
        }
        kp->page =  page;
    }

    ret = 0;
out:
    return ret;
}

static void *zcache_get_free_page(void)
{
    struct zcache_preload *kp;
    void *page;

    kp = &__get_cpu_var(zcache_preloads);
    page = kp->page;
    BUG_ON(page == NULL);
    kp->page = NULL;
    return page;
}

static void zcache_free_page(void *p)
{
    free_page((unsigned long)p);
}

/*
 * zcache implementation for tmem host ops
 */

static struct tmem_objnode *zcache_objnode_alloc(struct tmem_pool *pool)
{
    struct tmem_objnode *objnode = NULL;
    unsigned long count;
    struct zcache_preload *kp;

    kp = &__get_cpu_var(zcache_preloads);
    if (kp->nr <= 0)
        goto out;
    objnode = kp->objnodes[kp->nr - 1];
    BUG_ON(objnode == NULL);
    kp->objnodes[kp->nr - 1] = NULL;
    kp->nr--;
    count = atomic_inc_return(&zcache_curr_objnode_count);
    if (count > zcache_curr_objnode_count_max)
        zcache_curr_objnode_count_max = count;
out:
    return objnode;
}

static void zcache_objnode_free(struct tmem_objnode *objnode,
                    struct tmem_pool *pool)
{
    atomic_dec(&zcache_curr_objnode_count);
    BUG_ON(atomic_read(&zcache_curr_objnode_count) < 0);
    kmem_cache_free(zcache_objnode_cache, objnode);
}

static struct tmem_obj *zcache_obj_alloc(struct tmem_pool *pool)
{
    struct tmem_obj *obj = NULL;
    unsigned long count;
    struct zcache_preload *kp;

    kp = &__get_cpu_var(zcache_preloads);
    obj = kp->obj;
    BUG_ON(obj == NULL);
    kp->obj = NULL;
    count = atomic_inc_return(&zcache_curr_obj_count);
    if (count > zcache_curr_obj_count_max)
        zcache_curr_obj_count_max = count;
    return obj;
}

static void zcache_obj_free(struct tmem_obj *obj, struct tmem_pool *pool)
{
    atomic_dec(&zcache_curr_obj_count);
    BUG_ON(atomic_read(&zcache_curr_obj_count) < 0);
    kmem_cache_free(zcache_obj_cache, obj);
}

static struct tmem_hostops zcache_hostops = {
    .obj_alloc = zcache_obj_alloc,
    .obj_free = zcache_obj_free,
    .objnode_alloc = zcache_objnode_alloc,
    .objnode_free = zcache_objnode_free,
};

/*
 * zcache implementations for PAM page descriptor ops
 */

static atomic_t zcache_curr_eph_pampd_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_eph_pampd_count_max;
static atomic_t zcache_curr_pers_pampd_count = ATOMIC_INIT(0);
static unsigned long zcache_curr_pers_pampd_count_max;

/* forward reference */
static int zcache_compress(struct page *from, void **out_va, unsigned *out_len);

static void *zcache_pampd_create(char *data, size_t size, bool raw, int eph,
                struct tmem_pool *pool, struct tmem_oid *oid,
                 uint32_t index)
{
    void *pampd = NULL, *cdata;
    unsigned clen;
    int ret;
    unsigned long count;
    struct page *page = (struct page *)(data);
    struct zcache_client *cli = pool->client;
    uint16_t client_id = get_client_id_from_client(cli);
    unsigned long zv_mean_zsize;
    unsigned long curr_pers_pampd_count;
    u64 total_zsize;

    if (eph) {
        ret = zcache_compress(page, &cdata, &clen);
        if (ret == 0)
            goto out;
        if (clen == 0 || clen > zbud_max_buddy_size()) {
            zcache_compress_poor++;
            goto out;
        }
        pampd = (void *)zbud_create(client_id, pool->pool_id, oid,
                        index, page, cdata, clen);
        if (pampd != NULL) {
            count = atomic_inc_return(&zcache_curr_eph_pampd_count);
            if (count > zcache_curr_eph_pampd_count_max)
                zcache_curr_eph_pampd_count_max = count;
        }
    } else {
        curr_pers_pampd_count =
            atomic_read(&zcache_curr_pers_pampd_count);
        if (curr_pers_pampd_count >
            (zv_page_count_policy_percent * totalram_pages) / 100)
            goto out;
        ret = zcache_compress(page, &cdata, &clen);
        if (ret == 0)
            goto out;
        /* reject if compression is too poor */
        if (clen > zv_max_zsize) {
            zcache_compress_poor++;
            goto out;
        }
        /* reject if mean compression is too poor */
        if ((clen > zv_max_mean_zsize) && (curr_pers_pampd_count > 0)) {
            total_zsize = zs_get_total_size_bytes(cli->zspool);
            zv_mean_zsize = div_u64(total_zsize,
                        curr_pers_pampd_count);
            if (zv_mean_zsize > zv_max_mean_zsize) {
                zcache_mean_compress_poor++;
                goto out;
            }
        }
        pampd = (void *)zv_create(cli->zspool, pool->pool_id,
                        oid, index, cdata, clen);
        if (pampd == NULL)
            goto out;
        count = atomic_inc_return(&zcache_curr_pers_pampd_count);
        if (count > zcache_curr_pers_pampd_count_max)
            zcache_curr_pers_pampd_count_max = count;
    }
out:
    return pampd;
}

/*
 * fill the pageframe corresponding to the struct page with the data
 * from the passed pampd
 */
static int zcache_pampd_get_data(char *data, size_t *bufsize, bool raw,
                    void *pampd, struct tmem_pool *pool,
                    struct tmem_oid *oid, uint32_t index)
{
    int ret = 0;

    BUG_ON(is_ephemeral(pool));
    zv_decompress((struct page *)(data), (unsigned long)pampd);
    return ret;
}

/*
 * fill the pageframe corresponding to the struct page with the data
 * from the passed pampd
 */
static int zcache_pampd_get_data_and_free(char *data, size_t *bufsize, bool raw,
                    void *pampd, struct tmem_pool *pool,
                    struct tmem_oid *oid, uint32_t index)
{
    BUG_ON(!is_ephemeral(pool));
    if (zbud_decompress((struct page *)(data), pampd) < 0)
        return -EINVAL;
    zbud_free_and_delist((struct zbud_hdr *)pampd);
    atomic_dec(&zcache_curr_eph_pampd_count);
    return 0;
}

/*
 * free the pampd and remove it from any zcache lists
 * pampd must no longer be pointed to from any tmem data structures!
 */
static void zcache_pampd_free(void *pampd, struct tmem_pool *pool,
                struct tmem_oid *oid, uint32_t index)
{
    struct zcache_client *cli = pool->client;

    if (is_ephemeral(pool)) {
        zbud_free_and_delist((struct zbud_hdr *)pampd);
        atomic_dec(&zcache_curr_eph_pampd_count);
        BUG_ON(atomic_read(&zcache_curr_eph_pampd_count) < 0);
    } else {
        zv_free(cli->zspool, (unsigned long)pampd);
        atomic_dec(&zcache_curr_pers_pampd_count);
        BUG_ON(atomic_read(&zcache_curr_pers_pampd_count) < 0);
    }
}

static void zcache_pampd_free_obj(struct tmem_pool *pool, struct tmem_obj *obj)
{
}

static void zcache_pampd_new_obj(struct tmem_obj *obj)
{
}

static int zcache_pampd_replace_in_obj(void *pampd, struct tmem_obj *obj)
{
    return -1;
}

static bool zcache_pampd_is_remote(void *pampd)
{
    return 0;
}

static struct tmem_pamops zcache_pamops = {
    .create = zcache_pampd_create,
    .get_data = zcache_pampd_get_data,
    .get_data_and_free = zcache_pampd_get_data_and_free,
    .free = zcache_pampd_free,
    .free_obj = zcache_pampd_free_obj,
    .new_obj = zcache_pampd_new_obj,
    .replace_in_obj = zcache_pampd_replace_in_obj,
    .is_remote = zcache_pampd_is_remote,
};

/*
 * zcache compression/decompression and related per-cpu stuff
 */

static DEFINE_PER_CPU(unsigned char *, zcache_dstmem);
#define ZCACHE_DSTMEM_ORDER 1

static int zcache_compress(struct page *from, void **out_va, unsigned *out_len)
{
    int ret = 0;
    unsigned char *dmem = __get_cpu_var(zcache_dstmem);
    char *from_va;

    BUG_ON(!irqs_disabled());
    if (unlikely(dmem == NULL))
        goto out;  /* no buffer or no compressor so can't compress */
    *out_len = PAGE_SIZE << ZCACHE_DSTMEM_ORDER;
    from_va = kmap_atomic(from);
    mb();
    ret = zcache_comp_op(ZCACHE_COMPOP_COMPRESS, from_va, PAGE_SIZE, dmem,
                out_len);
    BUG_ON(ret);
    *out_va = dmem;
    kunmap_atomic(from_va);
    ret = 1;
out:
    return ret;
}

static int zcache_comp_cpu_up(int cpu)
{
    struct crypto_comp *tfm;

    tfm = crypto_alloc_comp(zcache_comp_name, 0, 0);
    if (IS_ERR(tfm))
        return NOTIFY_BAD;
    *per_cpu_ptr(zcache_comp_pcpu_tfms, cpu) = tfm;
    return NOTIFY_OK;
}

static void zcache_comp_cpu_down(int cpu)
{
    struct crypto_comp *tfm;

    tfm = *per_cpu_ptr(zcache_comp_pcpu_tfms, cpu);
    crypto_free_comp(tfm);
    *per_cpu_ptr(zcache_comp_pcpu_tfms, cpu) = NULL;
}

static int zcache_cpu_notifier(struct notifier_block *nb,
                unsigned long action, void *pcpu)
{
    int ret, cpu = (long)pcpu;
    struct zcache_preload *kp;

    switch (action) {
    case CPU_UP_PREPARE:
        ret = zcache_comp_cpu_up(cpu);
        if (ret != NOTIFY_OK) {
            pr_err("zcache: can't allocate compressor transform\n");
            return ret;
        }
        per_cpu(zcache_dstmem, cpu) = (void *)__get_free_pages(
            GFP_KERNEL | __GFP_REPEAT, ZCACHE_DSTMEM_ORDER);
        break;
    case CPU_DEAD:
    case CPU_UP_CANCELED:
        zcache_comp_cpu_down(cpu);
        free_pages((unsigned long)per_cpu(zcache_dstmem, cpu),
            ZCACHE_DSTMEM_ORDER);
        per_cpu(zcache_dstmem, cpu) = NULL;
        kp = &per_cpu(zcache_preloads, cpu);
        while (kp->nr) {
            kmem_cache_free(zcache_objnode_cache,
                    kp->objnodes[kp->nr - 1]);
            kp->objnodes[kp->nr - 1] = NULL;
            kp->nr--;
        }
        if (kp->obj) {
            kmem_cache_free(zcache_obj_cache, kp->obj);
            kp->obj = NULL;
        }
        if (kp->page) {
            free_page((unsigned long)kp->page);
            kp->page = NULL;
        }
        break;
    default:
        break;
    }
    return NOTIFY_OK;
}

static struct notifier_block zcache_cpu_notifier_block = {
    .notifier_call = zcache_cpu_notifier
};

#ifdef CONFIG_SYSFS
#define ZCACHE_SYSFS_RO(_name) \
    static ssize_t zcache_##_name##_show(struct kobject *kobj, \
                struct kobj_attribute *attr, char *buf) \
    { \
        return sprintf(buf, "%lu\n", zcache_##_name); \
    } \
    static struct kobj_attribute zcache_##_name##_attr = { \
        .attr = { .name = __stringify(_name), .mode = 0444 }, \
        .show = zcache_##_name##_show, \
    }

#define ZCACHE_SYSFS_RO_ATOMIC(_name) \
    static ssize_t zcache_##_name##_show(struct kobject *kobj, \
                struct kobj_attribute *attr, char *buf) \
    { \
        return sprintf(buf, "%d\n", atomic_read(&zcache_##_name)); \
    } \
    static struct kobj_attribute zcache_##_name##_attr = { \
        .attr = { .name = __stringify(_name), .mode = 0444 }, \
        .show = zcache_##_name##_show, \
    }

#define ZCACHE_SYSFS_RO_CUSTOM(_name, _func) \
    static ssize_t zcache_##_name##_show(struct kobject *kobj, \
                struct kobj_attribute *attr, char *buf) \
    { \
        return _func(buf); \
    } \
    static struct kobj_attribute zcache_##_name##_attr = { \
        .attr = { .name = __stringify(_name), .mode = 0444 }, \
        .show = zcache_##_name##_show, \
    }

ZCACHE_SYSFS_RO(curr_obj_count_max);
ZCACHE_SYSFS_RO(curr_objnode_count_max);
ZCACHE_SYSFS_RO(flush_total);
ZCACHE_SYSFS_RO(flush_found);
ZCACHE_SYSFS_RO(flobj_total);
ZCACHE_SYSFS_RO(flobj_found);
ZCACHE_SYSFS_RO(failed_eph_puts);
ZCACHE_SYSFS_RO(failed_pers_puts);
ZCACHE_SYSFS_RO(zbud_curr_zbytes);
ZCACHE_SYSFS_RO(zbud_cumul_zpages);
ZCACHE_SYSFS_RO(zbud_cumul_zbytes);
ZCACHE_SYSFS_RO(zbud_buddied_count);
ZCACHE_SYSFS_RO(zbpg_unused_list_count);
ZCACHE_SYSFS_RO(evicted_raw_pages);
ZCACHE_SYSFS_RO(evicted_unbuddied_pages);
ZCACHE_SYSFS_RO(evicted_buddied_pages);
ZCACHE_SYSFS_RO(failed_get_free_pages);
ZCACHE_SYSFS_RO(failed_alloc);
ZCACHE_SYSFS_RO(put_to_flush);
ZCACHE_SYSFS_RO(compress_poor);
ZCACHE_SYSFS_RO(mean_compress_poor);
ZCACHE_SYSFS_RO_ATOMIC(zbud_curr_raw_pages);
ZCACHE_SYSFS_RO_ATOMIC(zbud_curr_zpages);
ZCACHE_SYSFS_RO_ATOMIC(curr_obj_count);
ZCACHE_SYSFS_RO_ATOMIC(curr_objnode_count);
ZCACHE_SYSFS_RO_CUSTOM(zbud_unbuddied_list_counts,
            zbud_show_unbuddied_list_counts);
ZCACHE_SYSFS_RO_CUSTOM(zbud_cumul_chunk_counts,
            zbud_show_cumul_chunk_counts);
ZCACHE_SYSFS_RO_CUSTOM(zv_curr_dist_counts,
            zv_curr_dist_counts_show);
ZCACHE_SYSFS_RO_CUSTOM(zv_cumul_dist_counts,
            zv_cumul_dist_counts_show);

static struct attribute *zcache_attrs[] = {
    &zcache_curr_obj_count_attr.attr,
    &zcache_curr_obj_count_max_attr.attr,
    &zcache_curr_objnode_count_attr.attr,
    &zcache_curr_objnode_count_max_attr.attr,
    &zcache_flush_total_attr.attr,
    &zcache_flobj_total_attr.attr,
    &zcache_flush_found_attr.attr,
    &zcache_flobj_found_attr.attr,
    &zcache_failed_eph_puts_attr.attr,
    &zcache_failed_pers_puts_attr.attr,
    &zcache_compress_poor_attr.attr,
    &zcache_mean_compress_poor_attr.attr,
    &zcache_zbud_curr_raw_pages_attr.attr,
    &zcache_zbud_curr_zpages_attr.attr,
    &zcache_zbud_curr_zbytes_attr.attr,
    &zcache_zbud_cumul_zpages_attr.attr,
    &zcache_zbud_cumul_zbytes_attr.attr,
    &zcache_zbud_buddied_count_attr.attr,
    &zcache_zbpg_unused_list_count_attr.attr,
    &zcache_evicted_raw_pages_attr.attr,
    &zcache_evicted_unbuddied_pages_attr.attr,
    &zcache_evicted_buddied_pages_attr.attr,
    &zcache_failed_get_free_pages_attr.attr,
    &zcache_failed_alloc_attr.attr,
    &zcache_put_to_flush_attr.attr,
    &zcache_zbud_unbuddied_list_counts_attr.attr,
    &zcache_zbud_cumul_chunk_counts_attr.attr,
    &zcache_zv_curr_dist_counts_attr.attr,
    &zcache_zv_cumul_dist_counts_attr.attr,
    &zcache_zv_max_zsize_attr.attr,
    &zcache_zv_max_mean_zsize_attr.attr,
    &zcache_zv_page_count_policy_percent_attr.attr,
    NULL,
};

static struct attribute_group zcache_attr_group = {
    .attrs = zcache_attrs,
    .name = "zcache",
};

#endif /* CONFIG_SYSFS */
/*
 * When zcache is disabled ("frozen"), pools can be created and destroyed,
 * but all puts (and thus all other operations that require memory allocation)
 * must fail.  If zcache is unfrozen, accepts puts, then frozen again,
 * data consistency requires all puts while frozen to be converted into
 * flushes.
 */
static bool zcache_freeze;

/*
 * zcache shrinker interface (only useful for ephemeral pages, so zbud only)
 */
static int shrink_zcache_memory(struct shrinker *shrink,
                struct shrink_control *sc)
{
    int ret = -1;
    int nr = sc->nr_to_scan;
    gfp_t gfp_mask = sc->gfp_mask;

    if (nr >= 0) {
        if (!(gfp_mask & __GFP_FS))
            /* does this case really need to be skipped? */
            goto out;
        zbud_evict_pages(nr);
    }
    ret = (int)atomic_read(&zcache_zbud_curr_raw_pages);
out:
    return ret;
}

static struct shrinker zcache_shrinker = {
    .shrink = shrink_zcache_memory,
    .seeks = DEFAULT_SEEKS,
};

/*
 * zcache shims between cleancache/frontswap ops and tmem
 */

static int zcache_put_page(int cli_id, int pool_id, struct tmem_oid *oidp,
                uint32_t index, struct page *page)
{
    struct tmem_pool *pool;
    int ret = -1;

    BUG_ON(!irqs_disabled());
    pool = zcache_get_pool_by_id(cli_id, pool_id);
    if (unlikely(pool == NULL))
        goto out;
    if (!zcache_freeze && zcache_do_preload(pool) == 0) {
        /* preload does preempt_disable on success */
        ret = tmem_put(pool, oidp, index, (char *)(page),
                PAGE_SIZE, 0, is_ephemeral(pool));
        if (ret < 0) {
            if (is_ephemeral(pool))
                zcache_failed_eph_puts++;
            else
                zcache_failed_pers_puts++;
        }
    } else {
        zcache_put_to_flush++;
        if (atomic_read(&pool->obj_count) > 0)
            /* the put fails whether the flush succeeds or not */
            (void)tmem_flush_page(pool, oidp, index);
    }

    zcache_put_pool(pool);
out:
    return ret;
}

static int zcache_get_page(int cli_id, int pool_id, struct tmem_oid *oidp,
                uint32_t index, struct page *page)
{
    struct tmem_pool *pool;
    int ret = -1;
    unsigned long flags;
    size_t size = PAGE_SIZE;

    local_irq_save(flags);
    pool = zcache_get_pool_by_id(cli_id, pool_id);
    if (likely(pool != NULL)) {
        if (atomic_read(&pool->obj_count) > 0)
            ret = tmem_get(pool, oidp, index, (char *)(page),
                    &size, 0, is_ephemeral(pool));
        zcache_put_pool(pool);
    }
    local_irq_restore(flags);
    return ret;
}

static int zcache_flush_page(int cli_id, int pool_id,
                struct tmem_oid *oidp, uint32_t index)
{
    struct tmem_pool *pool;
    int ret = -1;
    unsigned long flags;

    local_irq_save(flags);
    zcache_flush_total++;
    pool = zcache_get_pool_by_id(cli_id, pool_id);
    if (likely(pool != NULL)) {
        if (atomic_read(&pool->obj_count) > 0)
            ret = tmem_flush_page(pool, oidp, index);
        zcache_put_pool(pool);
    }
    if (ret >= 0)
        zcache_flush_found++;
    local_irq_restore(flags);
    return ret;
}

static int zcache_flush_object(int cli_id, int pool_id,
                struct tmem_oid *oidp)
{
    struct tmem_pool *pool;
    int ret = -1;
    unsigned long flags;

    local_irq_save(flags);
    zcache_flobj_total++;
    pool = zcache_get_pool_by_id(cli_id, pool_id);
    if (likely(pool != NULL)) {
        if (atomic_read(&pool->obj_count) > 0)
            ret = tmem_flush_object(pool, oidp);
        zcache_put_pool(pool);
    }
    if (ret >= 0)
        zcache_flobj_found++;
    local_irq_restore(flags);
    return ret;
}

static int zcache_destroy_pool(int cli_id, int pool_id)
{
    struct tmem_pool *pool = NULL;
    struct zcache_client *cli;
    int ret = -1;

    if (pool_id < 0)
        goto out;

    cli = get_zcache_client(cli_id);
    if (cli == NULL)
        goto out;

    atomic_inc(&cli->refcount);
    pool = idr_find(&cli->tmem_pools, pool_id);
    if (pool == NULL)
        goto out;
    idr_remove(&cli->tmem_pools, pool_id);
    /* wait for pool activity on other cpus to quiesce */
    while (atomic_read(&pool->refcount) != 0)
        ;
    atomic_dec(&cli->refcount);
    local_bh_disable();
    ret = tmem_destroy_pool(pool);
    local_bh_enable();
    kfree(pool);
    pr_info("zcache: destroyed pool id=%d, cli_id=%d\n",
            pool_id, cli_id);
out:
    return ret;
}

static int zcache_new_pool(uint16_t cli_id, uint32_t flags)
{
    int poolid = -1;
    struct tmem_pool *pool;
    struct zcache_client *cli = NULL;
    int r;

    cli = get_zcache_client(cli_id);
    if (cli == NULL)
        goto out;

    atomic_inc(&cli->refcount);
    pool = kmalloc(sizeof(struct tmem_pool), GFP_ATOMIC);
    if (pool == NULL) {
        pr_info("zcache: pool creation failed: out of memory\n");
        goto out;
    }

    do {
        r = idr_pre_get(&cli->tmem_pools, GFP_ATOMIC);
        if (r != 1) {
            kfree(pool);
            pr_info("zcache: pool creation failed: out of memory\n");
            goto out;
        }
        r = idr_get_new(&cli->tmem_pools, pool, &poolid);
    } while (r == -EAGAIN);
    if (r) {
        pr_info("zcache: pool creation failed: error %d\n", r);
        kfree(pool);
        goto out;
    }

    atomic_set(&pool->refcount, 0);
    pool->client = cli;
    pool->pool_id = poolid;
    tmem_new_pool(pool, flags);
    pr_info("zcache: created %s tmem pool, id=%d, client=%d\n",
        flags & TMEM_POOL_PERSIST ? "persistent" : "ephemeral",
        poolid, cli_id);
out:
    if (cli != NULL)
        atomic_dec(&cli->refcount);
    return poolid;
}

/**********
 * Two kernel functionalities currently can be layered on top of tmem.
 * These are "cleancache" which is used as a second-chance cache for clean
 * page cache pages; and "frontswap" which is used for swap pages
 * to avoid writes to disk.  A generic "shim" is provided here for each
 * to translate in-kernel semantics to zcache semantics.
 */

#ifdef CONFIG_CLEANCACHE
static void zcache_cleancache_put_page(int pool_id,
                    struct cleancache_filekey key,
                    pgoff_t index, struct page *page)
{
    u32 ind = (u32) index;
    struct tmem_oid oid = *(struct tmem_oid *)&key;

    if (likely(ind == index))
        (void)zcache_put_page(LOCAL_CLIENT, pool_id, &oid, index, page);
}

static int zcache_cleancache_get_page(int pool_id,
                    struct cleancache_filekey key,
                    pgoff_t index, struct page *page)
{
    u32 ind = (u32) index;
    struct tmem_oid oid = *(struct tmem_oid *)&key;
    int ret = -1;

    if (likely(ind == index))
        ret = zcache_get_page(LOCAL_CLIENT, pool_id, &oid, index, page);
    return ret;
}

static void zcache_cleancache_flush_page(int pool_id,
                    struct cleancache_filekey key,
                    pgoff_t index)
{
    u32 ind = (u32) index;
    struct tmem_oid oid = *(struct tmem_oid *)&key;

    if (likely(ind == index))
        (void)zcache_flush_page(LOCAL_CLIENT, pool_id, &oid, ind);
}

static void zcache_cleancache_flush_inode(int pool_id,
                    struct cleancache_filekey key)
{
    struct tmem_oid oid = *(struct tmem_oid *)&key;

    (void)zcache_flush_object(LOCAL_CLIENT, pool_id, &oid);
}

static void zcache_cleancache_flush_fs(int pool_id)
{
    if (pool_id >= 0)
        (void)zcache_destroy_pool(LOCAL_CLIENT, pool_id);
}

static int zcache_cleancache_init_fs(size_t pagesize)
{
    BUG_ON(sizeof(struct cleancache_filekey) !=
                sizeof(struct tmem_oid));
    BUG_ON(pagesize != PAGE_SIZE);
    return zcache_new_pool(LOCAL_CLIENT, 0);
}

static int zcache_cleancache_init_shared_fs(char *uuid, size_t pagesize)
{
    /* shared pools are unsupported and map to private */
    BUG_ON(sizeof(struct cleancache_filekey) !=
                sizeof(struct tmem_oid));
    BUG_ON(pagesize != PAGE_SIZE);
    return zcache_new_pool(LOCAL_CLIENT, 0);
}

static struct cleancache_ops zcache_cleancache_ops = {
    .put_page = zcache_cleancache_put_page,
    .get_page = zcache_cleancache_get_page,
    .invalidate_page = zcache_cleancache_flush_page,
    .invalidate_inode = zcache_cleancache_flush_inode,
    .invalidate_fs = zcache_cleancache_flush_fs,
    .init_shared_fs = zcache_cleancache_init_shared_fs,
    .init_fs = zcache_cleancache_init_fs
};

struct cleancache_ops zcache_cleancache_register_ops(void)
{
    struct cleancache_ops old_ops =
        cleancache_register_ops(&zcache_cleancache_ops);

    return old_ops;
}
#endif

#ifdef CONFIG_FRONTSWAP
/* a single tmem poolid is used for all frontswap "types" (swapfiles) */
static int zcache_frontswap_poolid = -1;

/*
 * Swizzling increases objects per swaptype, increasing tmem concurrency
 * for heavy swaploads.  Later, larger nr_cpus -> larger SWIZ_BITS
 * Setting SWIZ_BITS to 27 basically reconstructs the swap entry from
 * frontswap_load(), but has side-effects. Hence using 8.
 */
#define SWIZ_BITS       8
#define SWIZ_MASK       ((1 << SWIZ_BITS) - 1)
#define _oswiz(_type, _ind) ((_type << SWIZ_BITS) | (_ind & SWIZ_MASK))
#define iswiz(_ind)     (_ind >> SWIZ_BITS)

static inline struct tmem_oid oswiz(unsigned type, u32 ind)
{
    struct tmem_oid oid = { .oid = { 0 } };
    oid.oid[0] = _oswiz(type, ind);
    return oid;
}

static int zcache_frontswap_store(unsigned type, pgoff_t offset,
                   struct page *page)
{
    u64 ind64 = (u64)offset;
    u32 ind = (u32)offset;
    struct tmem_oid oid = oswiz(type, ind);
    int ret = -1;
    unsigned long flags;

    BUG_ON(!PageLocked(page));
    if (likely(ind64 == ind)) {
        local_irq_save(flags);
        ret = zcache_put_page(LOCAL_CLIENT, zcache_frontswap_poolid,
                    &oid, iswiz(ind), page);
        local_irq_restore(flags);
    }
    return ret;
}

/* returns 0 if the page was successfully gotten from frontswap, -1 if
 * was not present (should never happen!) */
static int zcache_frontswap_load(unsigned type, pgoff_t offset,
                   struct page *page)
{
    u64 ind64 = (u64)offset;
    u32 ind = (u32)offset;
    struct tmem_oid oid = oswiz(type, ind);
    int ret = -1;

    BUG_ON(!PageLocked(page));
    if (likely(ind64 == ind))
        ret = zcache_get_page(LOCAL_CLIENT, zcache_frontswap_poolid,
                    &oid, iswiz(ind), page);
    return ret;
}

/* flush a single page from frontswap */
static void zcache_frontswap_flush_page(unsigned type, pgoff_t offset)
{
    u64 ind64 = (u64)offset;
    u32 ind = (u32)offset;
    struct tmem_oid oid = oswiz(type, ind);

    if (likely(ind64 == ind))
        (void)zcache_flush_page(LOCAL_CLIENT, zcache_frontswap_poolid,
                    &oid, iswiz(ind));
}

/* flush all pages from the passed swaptype */
static void zcache_frontswap_flush_area(unsigned type)
{
    struct tmem_oid oid;
    int ind;

    for (ind = SWIZ_MASK; ind >= 0; ind--) {
        oid = oswiz(type, ind);
        (void)zcache_flush_object(LOCAL_CLIENT,
                        zcache_frontswap_poolid, &oid);
    }
}

static void zcache_frontswap_init(unsigned ignored)
{
    /* a single tmem poolid is used for all frontswap "types" (swapfiles) */
    if (zcache_frontswap_poolid < 0)
        zcache_frontswap_poolid =
            zcache_new_pool(LOCAL_CLIENT, TMEM_POOL_PERSIST);
}

static struct frontswap_ops zcache_frontswap_ops = {
    .store = zcache_frontswap_store,
    .load = zcache_frontswap_load,
    .invalidate_page = zcache_frontswap_flush_page,
    .invalidate_area = zcache_frontswap_flush_area,
    .init = zcache_frontswap_init
};

struct frontswap_ops zcache_frontswap_register_ops(void)
{
    struct frontswap_ops old_ops =
        frontswap_register_ops(&zcache_frontswap_ops);

    return old_ops;
}
#endif

/*
 * zcache initialization
 * NOTE FOR NOW zcache MUST BE PROVIDED AS A KERNEL BOOT PARAMETER OR
 * NOTHING HAPPENS!
 */

static int zcache_enabled;

static int __init enable_zcache(char *s)
{
    zcache_enabled = 1;
    return 1;
}
__setup("zcache", enable_zcache);

/* allow independent dynamic disabling of cleancache and frontswap */

static int use_cleancache = 1;

static int __init no_cleancache(char *s)
{
    use_cleancache = 0;
    return 1;
}

__setup("nocleancache", no_cleancache);

static int use_frontswap = 1;

static int __init no_frontswap(char *s)
{
    use_frontswap = 0;
    return 1;
}

__setup("nofrontswap", no_frontswap);

static int __init enable_zcache_compressor(char *s)
{
    strncpy(zcache_comp_name, s, ZCACHE_COMP_NAME_SZ);
    zcache_enabled = 1;
    return 1;
}
__setup("zcache=", enable_zcache_compressor);


static int __init zcache_comp_init(void)
{
    int ret = 0;

    /* check crypto algorithm */
    if (*zcache_comp_name != '\0') {
        ret = crypto_has_comp(zcache_comp_name, 0, 0);
        if (!ret)
            pr_info("zcache: %s not supported\n",
                    zcache_comp_name);
    }
    if (!ret)
        strcpy(zcache_comp_name, "lzo");
    ret = crypto_has_comp(zcache_comp_name, 0, 0);
    if (!ret) {
        ret = 1;
        goto out;
    }
    pr_info("zcache: using %s compressor\n", zcache_comp_name);

    /* alloc percpu transforms */
    ret = 0;
    zcache_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
    if (!zcache_comp_pcpu_tfms)
        ret = 1;
out:
    return ret;
}

static int __init zcache_init(void)
{
    int ret = 0;

#ifdef CONFIG_SYSFS
    ret = sysfs_create_group(mm_kobj, &zcache_attr_group);
    if (ret) {
        pr_err("zcache: can't create sysfs\n");
        goto out;
    }
#endif /* CONFIG_SYSFS */

    if (zcache_enabled) {
        unsigned int cpu;

        tmem_register_hostops(&zcache_hostops);
        tmem_register_pamops(&zcache_pamops);
        ret = register_cpu_notifier(&zcache_cpu_notifier_block);
        if (ret) {
            pr_err("zcache: can't register cpu notifier\n");
            goto out;
        }
        ret = zcache_comp_init();
        if (ret) {
            pr_err("zcache: compressor initialization failed\n");
            goto out;
        }
        for_each_online_cpu(cpu) {
            void *pcpu = (void *)(long)cpu;
            zcache_cpu_notifier(&zcache_cpu_notifier_block,
                CPU_UP_PREPARE, pcpu);
        }
    }
    zcache_objnode_cache = kmem_cache_create("zcache_objnode",
                sizeof(struct tmem_objnode), 0, 0, NULL);
    zcache_obj_cache = kmem_cache_create("zcache_obj",
                sizeof(struct tmem_obj), 0, 0, NULL);
    ret = zcache_new_client(LOCAL_CLIENT);
    if (ret) {
        pr_err("zcache: can't create client\n");
        goto out;
    }

#ifdef CONFIG_CLEANCACHE
    if (zcache_enabled && use_cleancache) {
        struct cleancache_ops old_ops;

        zbud_init();
        register_shrinker(&zcache_shrinker);
        old_ops = zcache_cleancache_register_ops();
        pr_info("zcache: cleancache enabled using kernel "
            "transcendent memory and compression buddies\n");
        if (old_ops.init_fs != NULL)
            pr_warning("zcache: cleancache_ops overridden");
    }
#endif
#ifdef CONFIG_FRONTSWAP
    if (zcache_enabled && use_frontswap) {
        struct frontswap_ops old_ops;

        old_ops = zcache_frontswap_register_ops();
        pr_info("zcache: frontswap enabled using kernel "
            "transcendent memory and zsmalloc\n");
        if (old_ops.init != NULL)
            pr_warning("zcache: frontswap_ops overridden");
    }
#endif
out:
    return ret;
}

module_init(zcache_init)