zsmalloc-main.c

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/*
 * zsmalloc memory allocator
 *
 * Copyright (C) 2011  Nitin Gupta
 *
 * This code is released using a dual license strategy: BSD/GPL
 * You can choose the license that better fits your requirements.
 *
 * Released under the terms of 3-clause BSD License
 * Released under the terms of GNU General Public License Version 2.0
 */


/*
 * This allocator is designed for use with zcache and zram. Thus, the
 * allocator is supposed to work well under low memory conditions. In
 * particular, it never attempts higher order page allocation which is
 * very likely to fail under memory pressure. On the other hand, if we
 * just use single (0-order) pages, it would suffer from very high
 * fragmentation -- any object of size PAGE_SIZE/2 or larger would occupy
 * an entire page. This was one of the major issues with its predecessor
 * (xvmalloc).
 *
 * To overcome these issues, zsmalloc allocates a bunch of 0-order pages
 * and links them together using various 'struct page' fields. These linked
 * pages act as a single higher-order page i.e. an object can span 0-order
 * page boundaries. The code refers to these linked pages as a single entity
 * called zspage.
 *
 * Following is how we use various fields and flags of underlying
 * struct page(s) to form a zspage.
 *
 * Usage of struct page fields:
 *  page->first_page: points to the first component (0-order) page
 *  page->index (union with page->freelist): offset of the first object
 *      starting in this page. For the first page, this is
 *      always 0, so we use this field (aka freelist) to point
 *      to the first free object in zspage.
 *  page->lru: links together all component pages (except the first page)
 *      of a zspage
 *
 *  For _first_ page only:
 *
 *  page->private (union with page->first_page): refers to the
 *      component page after the first page
 *  page->freelist: points to the first free object in zspage.
 *      Free objects are linked together using in-place
 *      metadata.
 *  page->objects: maximum number of objects we can store in this
 *      zspage (class->zspage_order * PAGE_SIZE / class->size)
 *  page->lru: links together first pages of various zspages.
 *      Basically forming list of zspages in a fullness group.
 *  page->mapping: class index and fullness group of the zspage
 *
 * Usage of struct page flags:
 *  PG_private: identifies the first component page
 *  PG_private2: identifies the last component page
 *
 */

#ifdef CONFIG_ZSMALLOC_DEBUG
#define DEBUG
#endif

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <asm/tlbflush.h>
#include <asm/pgtable.h>
#include <linux/cpumask.h>
#include <linux/cpu.h>
#include <linux/vmalloc.h>
#include <linux/hardirq.h>
#include <linux/spinlock.h>
#include <linux/types.h>

#include "zsmalloc.h"

/*
 * This must be power of 2 and greater than of equal to sizeof(link_free).
 * These two conditions ensure that any 'struct link_free' itself doesn't
 * span more than 1 page which avoids complex case of mapping 2 pages simply
 * to restore link_free pointer values.
 */
#define ZS_ALIGN        8

/*
 * A single 'zspage' is composed of up to 2^N discontiguous 0-order (single)
 * pages. ZS_MAX_ZSPAGE_ORDER defines upper limit on N.
 */
#define ZS_MAX_ZSPAGE_ORDER 2
#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)

/*
 * Object location (<PFN>, <obj_idx>) is encoded as
 * as single (void *) handle value.
 *
 * Note that object index <obj_idx> is relative to system
 * page <PFN> it is stored in, so for each sub-page belonging
 * to a zspage, obj_idx starts with 0.
 *
 * This is made more complicated by various memory models and PAE.
 */

#ifndef MAX_PHYSMEM_BITS
#ifdef CONFIG_HIGHMEM64G
#define MAX_PHYSMEM_BITS 36
#else /* !CONFIG_HIGHMEM64G */
/*
 * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
 * be PAGE_SHIFT
 */
#define MAX_PHYSMEM_BITS BITS_PER_LONG
#endif
#endif
#define _PFN_BITS       (MAX_PHYSMEM_BITS - PAGE_SHIFT)
#define OBJ_INDEX_BITS  (BITS_PER_LONG - _PFN_BITS)
#define OBJ_INDEX_MASK  ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)

#define MAX(a, b) ((a) >= (b) ? (a) : (b))
/* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
#define ZS_MIN_ALLOC_SIZE \
    MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
#define ZS_MAX_ALLOC_SIZE   PAGE_SIZE

/*
 * On systems with 4K page size, this gives 254 size classes! There is a
 * trader-off here:
 *  - Large number of size classes is potentially wasteful as free page are
 *    spread across these classes
 *  - Small number of size classes causes large internal fragmentation
 *  - Probably its better to use specific size classes (empirically
 *    determined). NOTE: all those class sizes must be set as multiple of
 *    ZS_ALIGN to make sure link_free itself never has to span 2 pages.
 *
 *  ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
 *  (reason above)
 */
#define ZS_SIZE_CLASS_DELTA 16
#define ZS_SIZE_CLASSES     ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / \
                    ZS_SIZE_CLASS_DELTA + 1)

/*
 * We do not maintain any list for completely empty or full pages
 */
enum fullness_group {
    ZS_ALMOST_FULL,
    ZS_ALMOST_EMPTY,
    _ZS_NR_FULLNESS_GROUPS,

    ZS_EMPTY,
    ZS_FULL
};

/*
 * We assign a page to ZS_ALMOST_EMPTY fullness group when:
 *  n <= N / f, where
 * n = number of allocated objects
 * N = total number of objects zspage can store
 * f = 1/fullness_threshold_frac
 *
 * Similarly, we assign zspage to:
 *  ZS_ALMOST_FULL  when n > N / f
 *  ZS_EMPTY    when n == 0
 *  ZS_FULL     when n == N
 *
 * (see: fix_fullness_group())
 */
static const int fullness_threshold_frac = 4;

struct size_class {
    /*
     * Size of objects stored in this class. Must be multiple
     * of ZS_ALIGN.
     */
    int size;
    unsigned int index;

    /* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
    int pages_per_zspage;

    spinlock_t lock;

    /* stats */
    u64 pages_allocated;

    struct page *fullness_list[_ZS_NR_FULLNESS_GROUPS];
};

/*
 * Placed within free objects to form a singly linked list.
 * For every zspage, first_page->freelist gives head of this list.
 *
 * This must be power of 2 and less than or equal to ZS_ALIGN
 */
struct link_free {
    /* Handle of next free chunk (encodes <PFN, obj_idx>) */
    void *next;
};

struct zs_pool {
    struct size_class size_class[ZS_SIZE_CLASSES];

    gfp_t flags;    /* allocation flags used when growing pool */
    const char *name;
};

/*
 * A zspage's class index and fullness group
 * are encoded in its (first)page->mapping
 */
#define CLASS_IDX_BITS  28
#define FULLNESS_BITS   4
#define CLASS_IDX_MASK  ((1 << CLASS_IDX_BITS) - 1)
#define FULLNESS_MASK   ((1 << FULLNESS_BITS) - 1)

/*
 * By default, zsmalloc uses a copy-based object mapping method to access
 * allocations that span two pages. However, if a particular architecture
 * 1) Implements local_flush_tlb_kernel_range() and 2) Performs VM mapping
 * faster than copying, then it should be added here so that
 * USE_PGTABLE_MAPPING is defined. This causes zsmalloc to use page table
 * mapping rather than copying
 * for object mapping.
*/
#if defined(CONFIG_ARM)
#define USE_PGTABLE_MAPPING
#endif

struct mapping_area {
#ifdef USE_PGTABLE_MAPPING
    struct vm_struct *vm; /* vm area for mapping object that span pages */
#else
    char *vm_buf; /* copy buffer for objects that span pages */
#endif
    char *vm_addr; /* address of kmap_atomic()'ed pages */
    enum zs_mapmode vm_mm; /* mapping mode */
};


/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
static DEFINE_PER_CPU(struct mapping_area, zs_map_area);

static int is_first_page(struct page *page)
{
    return PagePrivate(page);
}

static int is_last_page(struct page *page)
{
    return PagePrivate2(page);
}

static void get_zspage_mapping(struct page *page, unsigned int *class_idx,
                enum fullness_group *fullness)
{
    unsigned long m;
    BUG_ON(!is_first_page(page));

    m = (unsigned long)page->mapping;
    *fullness = m & FULLNESS_MASK;
    *class_idx = (m >> FULLNESS_BITS) & CLASS_IDX_MASK;
}

static void set_zspage_mapping(struct page *page, unsigned int class_idx,
                enum fullness_group fullness)
{
    unsigned long m;
    BUG_ON(!is_first_page(page));

    m = ((class_idx & CLASS_IDX_MASK) << FULLNESS_BITS) |
            (fullness & FULLNESS_MASK);
    page->mapping = (struct address_space *)m;
}

static int get_size_class_index(int size)
{
    int idx = 0;

    if (likely(size > ZS_MIN_ALLOC_SIZE))
        idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
                ZS_SIZE_CLASS_DELTA);

    return idx;
}

static enum fullness_group get_fullness_group(struct page *page)
{
    int inuse, max_objects;
    enum fullness_group fg;
    BUG_ON(!is_first_page(page));

    inuse = page->inuse;
    max_objects = page->objects;

    if (inuse == 0)
        fg = ZS_EMPTY;
    else if (inuse == max_objects)
        fg = ZS_FULL;
    else if (inuse <= max_objects / fullness_threshold_frac)
        fg = ZS_ALMOST_EMPTY;
    else
        fg = ZS_ALMOST_FULL;

    return fg;
}

static void insert_zspage(struct page *page, struct size_class *class,
                enum fullness_group fullness)
{
    struct page **head;

    BUG_ON(!is_first_page(page));

    if (fullness >= _ZS_NR_FULLNESS_GROUPS)
        return;

    head = &class->fullness_list[fullness];
    if (*head)
        list_add_tail(&page->lru, &(*head)->lru);

    *head = page;
}

static void remove_zspage(struct page *page, struct size_class *class,
                enum fullness_group fullness)
{
    struct page **head;

    BUG_ON(!is_first_page(page));

    if (fullness >= _ZS_NR_FULLNESS_GROUPS)
        return;

    head = &class->fullness_list[fullness];
    BUG_ON(!*head);
    if (list_empty(&(*head)->lru))
        *head = NULL;
    else if (*head == page)
        *head = (struct page *)list_entry((*head)->lru.next,
                    struct page, lru);

    list_del_init(&page->lru);
}

static enum fullness_group fix_fullness_group(struct zs_pool *pool,
                        struct page *page)
{
    int class_idx;
    struct size_class *class;
    enum fullness_group currfg, newfg;

    BUG_ON(!is_first_page(page));

    get_zspage_mapping(page, &class_idx, &currfg);
    newfg = get_fullness_group(page);
    if (newfg == currfg)
        goto out;

    class = &pool->size_class[class_idx];
    remove_zspage(page, class, currfg);
    insert_zspage(page, class, newfg);
    set_zspage_mapping(page, class_idx, newfg);

out:
    return newfg;
}

/*
 * We have to decide on how many pages to link together
 * to form a zspage for each size class. This is important
 * to reduce wastage due to unusable space left at end of
 * each zspage which is given as:
 *  wastage = Zp - Zp % size_class
 * where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
 *
 * For example, for size class of 3/8 * PAGE_SIZE, we should
 * link together 3 PAGE_SIZE sized pages to form a zspage
 * since then we can perfectly fit in 8 such objects.
 */
static int get_pages_per_zspage(int class_size)
{
    int i, max_usedpc = 0;
    /* zspage order which gives maximum used size per KB */
    int max_usedpc_order = 1;

    for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
        int zspage_size;
        int waste, usedpc;

        zspage_size = i * PAGE_SIZE;
        waste = zspage_size % class_size;
        usedpc = (zspage_size - waste) * 100 / zspage_size;

        if (usedpc > max_usedpc) {
            max_usedpc = usedpc;
            max_usedpc_order = i;
        }
    }

    return max_usedpc_order;
}

/*
 * A single 'zspage' is composed of many system pages which are
 * linked together using fields in struct page. This function finds
 * the first/head page, given any component page of a zspage.
 */
static struct page *get_first_page(struct page *page)
{
    if (is_first_page(page))
        return page;
    else
        return page->first_page;
}

static struct page *get_next_page(struct page *page)
{
    struct page *next;

    if (is_last_page(page))
        next = NULL;
    else if (is_first_page(page))
        next = (struct page *)page->private;
    else
        next = list_entry(page->lru.next, struct page, lru);

    return next;
}

/* Encode <page, obj_idx> as a single handle value */
static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
{
    unsigned long handle;

    if (!page) {
        BUG_ON(obj_idx);
        return NULL;
    }

    handle = page_to_pfn(page) << OBJ_INDEX_BITS;
    handle |= (obj_idx & OBJ_INDEX_MASK);

    return (void *)handle;
}

/* Decode <page, obj_idx> pair from the given object handle */
static void obj_handle_to_location(unsigned long handle, struct page **page,
                unsigned long *obj_idx)
{
    *page = pfn_to_page(handle >> OBJ_INDEX_BITS);
    *obj_idx = handle & OBJ_INDEX_MASK;
}

static unsigned long obj_idx_to_offset(struct page *page,
                unsigned long obj_idx, int class_size)
{
    unsigned long off = 0;

    if (!is_first_page(page))
        off = page->index;

    return off + obj_idx * class_size;
}

static void reset_page(struct page *page)
{
    clear_bit(PG_private, &page->flags);
    clear_bit(PG_private_2, &page->flags);
    set_page_private(page, 0);
    page->mapping = NULL;
    page->freelist = NULL;
    reset_page_mapcount(page);
}

static void free_zspage(struct page *first_page)
{
    struct page *nextp, *tmp, *head_extra;

    BUG_ON(!is_first_page(first_page));
    BUG_ON(first_page->inuse);

    head_extra = (struct page *)page_private(first_page);

    reset_page(first_page);
    __free_page(first_page);

    /* zspage with only 1 system page */
    if (!head_extra)
        return;

    list_for_each_entry_safe(nextp, tmp, &head_extra->lru, lru) {
        list_del(&nextp->lru);
        reset_page(nextp);
        __free_page(nextp);
    }
    reset_page(head_extra);
    __free_page(head_extra);
}

/* Initialize a newly allocated zspage */
static void init_zspage(struct page *first_page, struct size_class *class)
{
    unsigned long off = 0;
    struct page *page = first_page;

    BUG_ON(!is_first_page(first_page));
    while (page) {
        struct page *next_page;
        struct link_free *link;
        unsigned int i, objs_on_page;

        /*
         * page->index stores offset of first object starting
         * in the page. For the first page, this is always 0,
         * so we use first_page->index (aka ->freelist) to store
         * head of corresponding zspage's freelist.
         */
        if (page != first_page)
            page->index = off;

        link = (struct link_free *)kmap_atomic(page) +
                        off / sizeof(*link);
        objs_on_page = (PAGE_SIZE - off) / class->size;

        for (i = 1; i <= objs_on_page; i++) {
            off += class->size;
            if (off < PAGE_SIZE) {
                link->next = obj_location_to_handle(page, i);
                link += class->size / sizeof(*link);
            }
        }

        /*
         * We now come to the last (full or partial) object on this
         * page, which must point to the first object on the next
         * page (if present)
         */
        next_page = get_next_page(page);
        link->next = obj_location_to_handle(next_page, 0);
        kunmap_atomic(link);
        page = next_page;
        off = (off + class->size) % PAGE_SIZE;
    }
}

/*
 * Allocate a zspage for the given size class
 */
static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
{
    int i, error;
    struct page *first_page = NULL, *uninitialized_var(prev_page);

    /*
     * Allocate individual pages and link them together as:
     * 1. first page->private = first sub-page
     * 2. all sub-pages are linked together using page->lru
     * 3. each sub-page is linked to the first page using page->first_page
     *
     * For each size class, First/Head pages are linked together using
     * page->lru. Also, we set PG_private to identify the first page
     * (i.e. no other sub-page has this flag set) and PG_private_2 to
     * identify the last page.
     */
    error = -ENOMEM;
    for (i = 0; i < class->pages_per_zspage; i++) {
        struct page *page;

        page = alloc_page(flags);
        if (!page)
            goto cleanup;

        INIT_LIST_HEAD(&page->lru);
        if (i == 0) {   /* first page */
            SetPagePrivate(page);
            set_page_private(page, 0);
            first_page = page;
            first_page->inuse = 0;
        }
        if (i == 1)
            first_page->private = (unsigned long)page;
        if (i >= 1)
            page->first_page = first_page;
        if (i >= 2)
            list_add(&page->lru, &prev_page->lru);
        if (i == class->pages_per_zspage - 1)   /* last page */
            SetPagePrivate2(page);
        prev_page = page;
    }

    init_zspage(first_page, class);

    first_page->freelist = obj_location_to_handle(first_page, 0);
    /* Maximum number of objects we can store in this zspage */
    first_page->objects = class->pages_per_zspage * PAGE_SIZE / class->size;

    error = 0; /* Success */

cleanup:
    if (unlikely(error) && first_page) {
        free_zspage(first_page);
        first_page = NULL;
    }

    return first_page;
}

static struct page *find_get_zspage(struct size_class *class)
{
    int i;
    struct page *page;

    for (i = 0; i < _ZS_NR_FULLNESS_GROUPS; i++) {
        page = class->fullness_list[i];
        if (page)
            break;
    }

    return page;
}

#ifdef USE_PGTABLE_MAPPING
static inline int __zs_cpu_up(struct mapping_area *area)
{
    /*
     * Make sure we don't leak memory if a cpu UP notification
     * and zs_init() race and both call zs_cpu_up() on the same cpu
     */
    if (area->vm)
        return 0;
    area->vm = alloc_vm_area(PAGE_SIZE * 2, NULL);
    if (!area->vm)
        return -ENOMEM;
    return 0;
}

static inline void __zs_cpu_down(struct mapping_area *area)
{
    if (area->vm)
        free_vm_area(area->vm);
    area->vm = NULL;
}

static inline void *__zs_map_object(struct mapping_area *area,
                struct page *pages[2], int off, int size)
{
    BUG_ON(map_vm_area(area->vm, PAGE_KERNEL, &pages));
    area->vm_addr = area->vm->addr;
    return area->vm_addr + off;
}

static inline void __zs_unmap_object(struct mapping_area *area,
                struct page *pages[2], int off, int size)
{
    unsigned long addr = (unsigned long)area->vm_addr;
    unsigned long end = addr + (PAGE_SIZE * 2);

    flush_cache_vunmap(addr, end);
    unmap_kernel_range_noflush(addr, PAGE_SIZE * 2);
    local_flush_tlb_kernel_range(addr, end);
}

#else /* USE_PGTABLE_MAPPING */

static inline int __zs_cpu_up(struct mapping_area *area)
{
    /*
     * Make sure we don't leak memory if a cpu UP notification
     * and zs_init() race and both call zs_cpu_up() on the same cpu
     */
    if (area->vm_buf)
        return 0;
    area->vm_buf = (char *)__get_free_page(GFP_KERNEL);
    if (!area->vm_buf)
        return -ENOMEM;
    return 0;
}

static inline void __zs_cpu_down(struct mapping_area *area)
{
    if (area->vm_buf)
        free_page((unsigned long)area->vm_buf);
    area->vm_buf = NULL;
}

static void *__zs_map_object(struct mapping_area *area,
            struct page *pages[2], int off, int size)
{
    int sizes[2];
    void *addr;
    char *buf = area->vm_buf;

    /* disable page faults to match kmap_atomic() return conditions */
    pagefault_disable();

    /* no read fastpath */
    if (area->vm_mm == ZS_MM_WO)
        goto out;

    sizes[0] = PAGE_SIZE - off;
    sizes[1] = size - sizes[0];

    /* copy object to per-cpu buffer */
    addr = kmap_atomic(pages[0]);
    memcpy(buf, addr + off, sizes[0]);
    kunmap_atomic(addr);
    addr = kmap_atomic(pages[1]);
    memcpy(buf + sizes[0], addr, sizes[1]);
    kunmap_atomic(addr);
out:
    return area->vm_buf;
}

static void __zs_unmap_object(struct mapping_area *area,
            struct page *pages[2], int off, int size)
{
    int sizes[2];
    void *addr;
    char *buf = area->vm_buf;

    /* no write fastpath */
    if (area->vm_mm == ZS_MM_RO)
        goto out;

    sizes[0] = PAGE_SIZE - off;
    sizes[1] = size - sizes[0];

    /* copy per-cpu buffer to object */
    addr = kmap_atomic(pages[0]);
    memcpy(addr + off, buf, sizes[0]);
    kunmap_atomic(addr);
    addr = kmap_atomic(pages[1]);
    memcpy(addr, buf + sizes[0], sizes[1]);
    kunmap_atomic(addr);

out:
    /* enable page faults to match kunmap_atomic() return conditions */
    pagefault_enable();
}

#endif /* USE_PGTABLE_MAPPING */

static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
                void *pcpu)
{
    int ret, cpu = (long)pcpu;
    struct mapping_area *area;

    switch (action) {
    case CPU_UP_PREPARE:
        area = &per_cpu(zs_map_area, cpu);
        ret = __zs_cpu_up(area);
        if (ret)
            return notifier_from_errno(ret);
        break;
    case CPU_DEAD:
    case CPU_UP_CANCELED:
        area = &per_cpu(zs_map_area, cpu);
        __zs_cpu_down(area);
        break;
    }

    return NOTIFY_OK;
}

static struct notifier_block zs_cpu_nb = {
    .notifier_call = zs_cpu_notifier
};

static void zs_exit(void)
{
    int cpu;

    for_each_online_cpu(cpu)
        zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
    unregister_cpu_notifier(&zs_cpu_nb);
}

static int zs_init(void)
{
    int cpu, ret;

    register_cpu_notifier(&zs_cpu_nb);
    for_each_online_cpu(cpu) {
        ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
        if (notifier_to_errno(ret))
            goto fail;
    }
    return 0;
fail:
    zs_exit();
    return notifier_to_errno(ret);
}

struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
{
    int i, ovhd_size;
    struct zs_pool *pool;

    if (!name)
        return NULL;

    ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
    pool = kzalloc(ovhd_size, GFP_KERNEL);
    if (!pool)
        return NULL;

    for (i = 0; i < ZS_SIZE_CLASSES; i++) {
        int size;
        struct size_class *class;

        size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
        if (size > ZS_MAX_ALLOC_SIZE)
            size = ZS_MAX_ALLOC_SIZE;

        class = &pool->size_class[i];
        class->size = size;
        class->index = i;
        spin_lock_init(&class->lock);
        class->pages_per_zspage = get_pages_per_zspage(size);

    }

    pool->flags = flags;
    pool->name = name;

    return pool;
}
EXPORT_SYMBOL_GPL(zs_create_pool);

void zs_destroy_pool(struct zs_pool *pool)
{
    int i;

    for (i = 0; i < ZS_SIZE_CLASSES; i++) {
        int fg;
        struct size_class *class = &pool->size_class[i];

        for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
            if (class->fullness_list[fg]) {
                pr_info("Freeing non-empty class with size "
                    "%db, fullness group %d\n",
                    class->size, fg);
            }
        }
    }
    kfree(pool);
}
EXPORT_SYMBOL_GPL(zs_destroy_pool);

unsigned long zs_malloc(struct zs_pool *pool, size_t size)
{
    unsigned long obj;
    struct link_free *link;
    int class_idx;
    struct size_class *class;

    struct page *first_page, *m_page;
    unsigned long m_objidx, m_offset;

    if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
        return 0;

    class_idx = get_size_class_index(size);
    class = &pool->size_class[class_idx];
    BUG_ON(class_idx != class->index);

    spin_lock(&class->lock);
    first_page = find_get_zspage(class);

    if (!first_page) {
        spin_unlock(&class->lock);
        first_page = alloc_zspage(class, pool->flags);
        if (unlikely(!first_page))
            return 0;

        set_zspage_mapping(first_page, class->index, ZS_EMPTY);
        spin_lock(&class->lock);
        class->pages_allocated += class->pages_per_zspage;
    }

    obj = (unsigned long)first_page->freelist;
    obj_handle_to_location(obj, &m_page, &m_objidx);
    m_offset = obj_idx_to_offset(m_page, m_objidx, class->size);

    link = (struct link_free *)kmap_atomic(m_page) +
                    m_offset / sizeof(*link);
    first_page->freelist = link->next;
    memset(link, POISON_INUSE, sizeof(*link));
    kunmap_atomic(link);

    first_page->inuse++;
    /* Now move the zspage to another fullness group, if required */
    fix_fullness_group(pool, first_page);
    spin_unlock(&class->lock);

    return obj;
}
EXPORT_SYMBOL_GPL(zs_malloc);

void zs_free(struct zs_pool *pool, unsigned long obj)
{
    struct link_free *link;
    struct page *first_page, *f_page;
    unsigned long f_objidx, f_offset;

    int class_idx;
    struct size_class *class;
    enum fullness_group fullness;

    if (unlikely(!obj))
        return;

    obj_handle_to_location(obj, &f_page, &f_objidx);
    first_page = get_first_page(f_page);

    get_zspage_mapping(first_page, &class_idx, &fullness);
    class = &pool->size_class[class_idx];
    f_offset = obj_idx_to_offset(f_page, f_objidx, class->size);

    spin_lock(&class->lock);

    /* Insert this object in containing zspage's freelist */
    link = (struct link_free *)((unsigned char *)kmap_atomic(f_page)
                            + f_offset);
    link->next = first_page->freelist;
    kunmap_atomic(link);
    first_page->freelist = (void *)obj;

    first_page->inuse--;
    fullness = fix_fullness_group(pool, first_page);

    if (fullness == ZS_EMPTY)
        class->pages_allocated -= class->pages_per_zspage;

    spin_unlock(&class->lock);

    if (fullness == ZS_EMPTY)
        free_zspage(first_page);
}
EXPORT_SYMBOL_GPL(zs_free);

void *zs_map_object(struct zs_pool *pool, unsigned long handle,
            enum zs_mapmode mm)
{
    struct page *page;
    unsigned long obj_idx, off;

    unsigned int class_idx;
    enum fullness_group fg;
    struct size_class *class;
    struct mapping_area *area;
    struct page *pages[2];

    BUG_ON(!handle);

    /*
     * Because we use per-cpu mapping areas shared among the
     * pools/users, we can't allow mapping in interrupt context
     * because it can corrupt another users mappings.
     */
    BUG_ON(in_interrupt());

    obj_handle_to_location(handle, &page, &obj_idx);
    get_zspage_mapping(get_first_page(page), &class_idx, &fg);
    class = &pool->size_class[class_idx];
    off = obj_idx_to_offset(page, obj_idx, class->size);

    area = &get_cpu_var(zs_map_area);
    area->vm_mm = mm;
    if (off + class->size <= PAGE_SIZE) {
        /* this object is contained entirely within a page */
        area->vm_addr = kmap_atomic(page);
        return area->vm_addr + off;
    }

    /* this object spans two pages */
    pages[0] = page;
    pages[1] = get_next_page(page);
    BUG_ON(!pages[1]);

    return __zs_map_object(area, pages, off, class->size);
}
EXPORT_SYMBOL_GPL(zs_map_object);

void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
{
    struct page *page;
    unsigned long obj_idx, off;

    unsigned int class_idx;
    enum fullness_group fg;
    struct size_class *class;
    struct mapping_area *area;

    BUG_ON(!handle);

    obj_handle_to_location(handle, &page, &obj_idx);
    get_zspage_mapping(get_first_page(page), &class_idx, &fg);
    class = &pool->size_class[class_idx];
    off = obj_idx_to_offset(page, obj_idx, class->size);

    area = &__get_cpu_var(zs_map_area);
    if (off + class->size <= PAGE_SIZE)
        kunmap_atomic(area->vm_addr);
    else {
        struct page *pages[2];

        pages[0] = page;
        pages[1] = get_next_page(page);
        BUG_ON(!pages[1]);

        __zs_unmap_object(area, pages, off, class->size);
    }
    put_cpu_var(zs_map_area);
}
EXPORT_SYMBOL_GPL(zs_unmap_object);

u64 zs_get_total_size_bytes(struct zs_pool *pool)
{
    int i;
    u64 npages = 0;

    for (i = 0; i < ZS_SIZE_CLASSES; i++)
        npages += pool->size_class[i].pages_allocated;

    return npages << PAGE_SHIFT;
}
EXPORT_SYMBOL_GPL(zs_get_total_size_bytes);

module_init(zs_init);
module_exit(zs_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Nitin Gupta <[email protected]>");