Merge tag 'hardening-v6.14-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-stable.git] / mm / zsmalloc.c

// SPDX-License-Identifier: GPL-2.0-or-later

/*
 * zsmalloc memory allocator
 *
 * Copyright (C) 2011  Nitin Gupta
 * Copyright (C) 2012, 2013 Minchan Kim
 *
 * 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
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

/*
 * lock ordering:
 *      page_lock
 *      pool->migrate_lock
 *      class->lock
 *      zspage->lock
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/highmem.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/pgtable.h>
#include <asm/tlbflush.h>
#include <linux/cpumask.h>
#include <linux/cpu.h>
#include <linux/vmalloc.h>
#include <linux/preempt.h>
#include <linux/spinlock.h>
#include <linux/sprintf.h>
#include <linux/shrinker.h>
#include <linux/types.h>
#include <linux/debugfs.h>
#include <linux/zsmalloc.h>
#include <linux/zpool.h>
#include <linux/migrate.h>
#include <linux/wait.h>
#include <linux/pagemap.h>
#include <linux/fs.h>
#include <linux/local_lock.h>
#include "zpdesc.h"

#define ZSPAGE_MAGIC    0x58

/*
 * This must be power of 2 and greater than or 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

#define ZS_HANDLE_SIZE (sizeof(unsigned long))

/*
 * Object location (<PFN>, <obj_idx>) is encoded as
 * a single (unsigned long) handle value.
 *
 * Note that object index <obj_idx> starts from 0.
 *
 * This is made more complicated by various memory models and PAE.
 */

#ifndef MAX_POSSIBLE_PHYSMEM_BITS
#ifdef MAX_PHYSMEM_BITS
#define MAX_POSSIBLE_PHYSMEM_BITS MAX_PHYSMEM_BITS
#else
/*
 * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
 * be PAGE_SHIFT
 */
#define MAX_POSSIBLE_PHYSMEM_BITS BITS_PER_LONG
#endif
#endif

#define _PFN_BITS               (MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)

/*
 * Head in allocated object should have OBJ_ALLOCATED_TAG
 * to identify the object was allocated or not.
 * It's okay to add the status bit in the least bit because
 * header keeps handle which is 4byte-aligned address so we
 * have room for two bit at least.
 */
#define OBJ_ALLOCATED_TAG 1

#define OBJ_TAG_BITS    1
#define OBJ_TAG_MASK    OBJ_ALLOCATED_TAG

#define OBJ_INDEX_BITS  (BITS_PER_LONG - _PFN_BITS)
#define OBJ_INDEX_MASK  ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)

#define HUGE_BITS       1
#define FULLNESS_BITS   4
#define CLASS_BITS      8
#define MAGIC_VAL_BITS  8

#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(CONFIG_ZSMALLOC_CHAIN_SIZE, UL))

/* 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))
/* each chunk includes extra space to keep handle */
#define ZS_MAX_ALLOC_SIZE       PAGE_SIZE

/*
 * On systems with 4K page size, this gives 255 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     (PAGE_SIZE >> CLASS_BITS)
#define ZS_SIZE_CLASSES (DIV_ROUND_UP(ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE, \
                                      ZS_SIZE_CLASS_DELTA) + 1)

/*
 * Pages are distinguished by the ratio of used memory (that is the ratio
 * of ->inuse objects to all objects that page can store). For example,
 * INUSE_RATIO_10 means that the ratio of used objects is > 0% and <= 10%.
 *
 * The number of fullness groups is not random. It allows us to keep
 * difference between the least busy page in the group (minimum permitted
 * number of ->inuse objects) and the most busy page (maximum permitted
 * number of ->inuse objects) at a reasonable value.
 */
enum fullness_group {
        ZS_INUSE_RATIO_0,
        ZS_INUSE_RATIO_10,
        /* NOTE: 8 more fullness groups here */
        ZS_INUSE_RATIO_99       = 10,
        ZS_INUSE_RATIO_100,
        NR_FULLNESS_GROUPS,
};

enum class_stat_type {
        /* NOTE: stats for 12 fullness groups here: from inuse 0 to 100 */
        ZS_OBJS_ALLOCATED       = NR_FULLNESS_GROUPS,
        ZS_OBJS_INUSE,
        NR_CLASS_STAT_TYPES,
};

struct zs_size_stat {
        unsigned long objs[NR_CLASS_STAT_TYPES];
};

#ifdef CONFIG_ZSMALLOC_STAT
static struct dentry *zs_stat_root;
#endif

static size_t huge_class_size;

struct size_class {
        spinlock_t lock;
        struct list_head fullness_list[NR_FULLNESS_GROUPS];
        /*
         * Size of objects stored in this class. Must be multiple
         * of ZS_ALIGN.
         */
        int size;
        int objs_per_zspage;
        /* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
        int pages_per_zspage;

        unsigned int index;
        struct zs_size_stat stats;
};

/*
 * Placed within free objects to form a singly linked list.
 * For every zspage, zspage->freeobj gives head of this list.
 *
 * This must be power of 2 and less than or equal to ZS_ALIGN
 */
struct link_free {
        union {
                /*
                 * Free object index;
                 * It's valid for non-allocated object
                 */
                unsigned long next;
                /*
                 * Handle of allocated object.
                 */
                unsigned long handle;
        };
};

struct zs_pool {
        const char *name;

        struct size_class *size_class[ZS_SIZE_CLASSES];
        struct kmem_cache *handle_cachep;
        struct kmem_cache *zspage_cachep;

        atomic_long_t pages_allocated;

        struct zs_pool_stats stats;

        /* Compact classes */
        struct shrinker *shrinker;

#ifdef CONFIG_ZSMALLOC_STAT
        struct dentry *stat_dentry;
#endif
#ifdef CONFIG_COMPACTION
        struct work_struct free_work;
#endif
        /* protect page/zspage migration */
        rwlock_t migrate_lock;
        atomic_t compaction_in_progress;
};

static inline void zpdesc_set_first(struct zpdesc *zpdesc)
{
        SetPagePrivate(zpdesc_page(zpdesc));
}

static inline void zpdesc_inc_zone_page_state(struct zpdesc *zpdesc)
{
        inc_zone_page_state(zpdesc_page(zpdesc), NR_ZSPAGES);
}

static inline void zpdesc_dec_zone_page_state(struct zpdesc *zpdesc)
{
        dec_zone_page_state(zpdesc_page(zpdesc), NR_ZSPAGES);
}

static inline struct zpdesc *alloc_zpdesc(gfp_t gfp)
{
        struct page *page = alloc_page(gfp);

        return page_zpdesc(page);
}

static inline void free_zpdesc(struct zpdesc *zpdesc)
{
        struct page *page = zpdesc_page(zpdesc);

        __free_page(page);
}

struct zspage {
        struct {
                unsigned int huge:HUGE_BITS;
                unsigned int fullness:FULLNESS_BITS;
                unsigned int class:CLASS_BITS + 1;
                unsigned int magic:MAGIC_VAL_BITS;
        };
        unsigned int inuse;
        unsigned int freeobj;
        struct zpdesc *first_zpdesc;
        struct list_head list; /* fullness list */
        struct zs_pool *pool;
        rwlock_t lock;
};

struct mapping_area {
        local_lock_t lock;
        char *vm_buf; /* copy buffer for objects that span pages */
        char *vm_addr; /* address of kmap_local_page()'ed pages */
        enum zs_mapmode vm_mm; /* mapping mode */
};

/* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
static void SetZsHugePage(struct zspage *zspage)
{
        zspage->huge = 1;
}

static bool ZsHugePage(struct zspage *zspage)
{
        return zspage->huge;
}

static void migrate_lock_init(struct zspage *zspage);
static void migrate_read_lock(struct zspage *zspage);
static void migrate_read_unlock(struct zspage *zspage);
static void migrate_write_lock(struct zspage *zspage);
static void migrate_write_unlock(struct zspage *zspage);

#ifdef CONFIG_COMPACTION
static void kick_deferred_free(struct zs_pool *pool);
static void init_deferred_free(struct zs_pool *pool);
static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage);
#else
static void kick_deferred_free(struct zs_pool *pool) {}
static void init_deferred_free(struct zs_pool *pool) {}
static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage) {}
#endif

static int create_cache(struct zs_pool *pool)
{
        char *name;

        name = kasprintf(GFP_KERNEL, "zs_handle-%s", pool->name);
        if (!name)
                return -ENOMEM;
        pool->handle_cachep = kmem_cache_create(name, ZS_HANDLE_SIZE,
                                                0, 0, NULL);
        kfree(name);
        if (!pool->handle_cachep)
                return -EINVAL;

        name = kasprintf(GFP_KERNEL, "zspage-%s", pool->name);
        if (!name)
                return -ENOMEM;
        pool->zspage_cachep = kmem_cache_create(name, sizeof(struct zspage),
                                                0, 0, NULL);
        kfree(name);
        if (!pool->zspage_cachep) {
                kmem_cache_destroy(pool->handle_cachep);
                pool->handle_cachep = NULL;
                return -EINVAL;
        }

        return 0;
}

static void destroy_cache(struct zs_pool *pool)
{
        kmem_cache_destroy(pool->handle_cachep);
        kmem_cache_destroy(pool->zspage_cachep);
}

static unsigned long cache_alloc_handle(struct zs_pool *pool, gfp_t gfp)
{
        return (unsigned long)kmem_cache_alloc(pool->handle_cachep,
                        gfp & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
}

static void cache_free_handle(struct zs_pool *pool, unsigned long handle)
{
        kmem_cache_free(pool->handle_cachep, (void *)handle);
}

static struct zspage *cache_alloc_zspage(struct zs_pool *pool, gfp_t flags)
{
        return kmem_cache_zalloc(pool->zspage_cachep,
                        flags & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
}

static void cache_free_zspage(struct zs_pool *pool, struct zspage *zspage)
{
        kmem_cache_free(pool->zspage_cachep, zspage);
}

/* class->lock(which owns the handle) synchronizes races */
static void record_obj(unsigned long handle, unsigned long obj)
{
        *(unsigned long *)handle = obj;
}

/* zpool driver */

#ifdef CONFIG_ZPOOL

static void *zs_zpool_create(const char *name, gfp_t gfp)
{
        /*
         * Ignore global gfp flags: zs_malloc() may be invoked from
         * different contexts and its caller must provide a valid
         * gfp mask.
         */
        return zs_create_pool(name);
}

static void zs_zpool_destroy(void *pool)
{
        zs_destroy_pool(pool);
}

static int zs_zpool_malloc(void *pool, size_t size, gfp_t gfp,
                        unsigned long *handle)
{
        *handle = zs_malloc(pool, size, gfp);

        if (IS_ERR_VALUE(*handle))
                return PTR_ERR((void *)*handle);
        return 0;
}
static void zs_zpool_free(void *pool, unsigned long handle)
{
        zs_free(pool, handle);
}

static void *zs_zpool_map(void *pool, unsigned long handle,
                        enum zpool_mapmode mm)
{
        enum zs_mapmode zs_mm;

        switch (mm) {
        case ZPOOL_MM_RO:
                zs_mm = ZS_MM_RO;
                break;
        case ZPOOL_MM_WO:
                zs_mm = ZS_MM_WO;
                break;
        case ZPOOL_MM_RW:
        default:
                zs_mm = ZS_MM_RW;
                break;
        }

        return zs_map_object(pool, handle, zs_mm);
}
static void zs_zpool_unmap(void *pool, unsigned long handle)
{
        zs_unmap_object(pool, handle);
}

static u64 zs_zpool_total_pages(void *pool)
{
        return zs_get_total_pages(pool);
}

static struct zpool_driver zs_zpool_driver = {
        .type =                   "zsmalloc",
        .owner =                  THIS_MODULE,
        .create =                 zs_zpool_create,
        .destroy =                zs_zpool_destroy,
        .malloc_support_movable = true,
        .malloc =                 zs_zpool_malloc,
        .free =                   zs_zpool_free,
        .map =                    zs_zpool_map,
        .unmap =                  zs_zpool_unmap,
        .total_pages =            zs_zpool_total_pages,
};

MODULE_ALIAS("zpool-zsmalloc");
#endif /* CONFIG_ZPOOL */

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

static inline bool __maybe_unused is_first_zpdesc(struct zpdesc *zpdesc)
{
        return PagePrivate(zpdesc_page(zpdesc));
}

/* Protected by class->lock */
static inline int get_zspage_inuse(struct zspage *zspage)
{
        return zspage->inuse;
}

static inline void mod_zspage_inuse(struct zspage *zspage, int val)
{
        zspage->inuse += val;
}

static struct zpdesc *get_first_zpdesc(struct zspage *zspage)
{
        struct zpdesc *first_zpdesc = zspage->first_zpdesc;

        VM_BUG_ON_PAGE(!is_first_zpdesc(first_zpdesc), zpdesc_page(first_zpdesc));
        return first_zpdesc;
}

#define FIRST_OBJ_PAGE_TYPE_MASK        0xffffff

static inline unsigned int get_first_obj_offset(struct zpdesc *zpdesc)
{
        VM_WARN_ON_ONCE(!PageZsmalloc(zpdesc_page(zpdesc)));
        return zpdesc->first_obj_offset & FIRST_OBJ_PAGE_TYPE_MASK;
}

static inline void set_first_obj_offset(struct zpdesc *zpdesc, unsigned int offset)
{
        /* With 24 bits available, we can support offsets into 16 MiB pages. */
        BUILD_BUG_ON(PAGE_SIZE > SZ_16M);
        VM_WARN_ON_ONCE(!PageZsmalloc(zpdesc_page(zpdesc)));
        VM_WARN_ON_ONCE(offset & ~FIRST_OBJ_PAGE_TYPE_MASK);
        zpdesc->first_obj_offset &= ~FIRST_OBJ_PAGE_TYPE_MASK;
        zpdesc->first_obj_offset |= offset & FIRST_OBJ_PAGE_TYPE_MASK;
}

static inline unsigned int get_freeobj(struct zspage *zspage)
{
        return zspage->freeobj;
}

static inline void set_freeobj(struct zspage *zspage, unsigned int obj)
{
        zspage->freeobj = obj;
}

static struct size_class *zspage_class(struct zs_pool *pool,
                                       struct zspage *zspage)
{
        return pool->size_class[zspage->class];
}

/*
 * zsmalloc divides the pool into various size classes where each
 * class maintains a list of zspages where each zspage is divided
 * into equal sized chunks. Each allocation falls into one of these
 * classes depending on its size. This function returns index of the
 * size class which has chunk size big enough to hold the given size.
 */
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 min_t(int, ZS_SIZE_CLASSES - 1, idx);
}

static inline void class_stat_add(struct size_class *class, int type,
                                  unsigned long cnt)
{
        class->stats.objs[type] += cnt;
}

static inline void class_stat_sub(struct size_class *class, int type,
                                  unsigned long cnt)
{
        class->stats.objs[type] -= cnt;
}

static inline unsigned long class_stat_read(struct size_class *class, int type)
{
        return class->stats.objs[type];
}

#ifdef CONFIG_ZSMALLOC_STAT

static void __init zs_stat_init(void)
{
        if (!debugfs_initialized()) {
                pr_warn("debugfs not available, stat dir not created\n");
                return;
        }

        zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
}

static void __exit zs_stat_exit(void)
{
        debugfs_remove_recursive(zs_stat_root);
}

static unsigned long zs_can_compact(struct size_class *class);

static int zs_stats_size_show(struct seq_file *s, void *v)
{
        int i, fg;
        struct zs_pool *pool = s->private;
        struct size_class *class;
        int objs_per_zspage;
        unsigned long obj_allocated, obj_used, pages_used, freeable;
        unsigned long total_objs = 0, total_used_objs = 0, total_pages = 0;
        unsigned long total_freeable = 0;
        unsigned long inuse_totals[NR_FULLNESS_GROUPS] = {0, };

        seq_printf(s, " %5s %5s %9s %9s %9s %9s %9s %9s %9s %9s %9s %9s %9s %13s %10s %10s %16s %8s\n",
                        "class", "size", "10%", "20%", "30%", "40%",
                        "50%", "60%", "70%", "80%", "90%", "99%", "100%",
                        "obj_allocated", "obj_used", "pages_used",
                        "pages_per_zspage", "freeable");

        for (i = 0; i < ZS_SIZE_CLASSES; i++) {

                class = pool->size_class[i];

                if (class->index != i)
                        continue;

                spin_lock(&class->lock);

                seq_printf(s, " %5u %5u ", i, class->size);
                for (fg = ZS_INUSE_RATIO_10; fg < NR_FULLNESS_GROUPS; fg++) {
                        inuse_totals[fg] += class_stat_read(class, fg);
                        seq_printf(s, "%9lu ", class_stat_read(class, fg));
                }

                obj_allocated = class_stat_read(class, ZS_OBJS_ALLOCATED);
                obj_used = class_stat_read(class, ZS_OBJS_INUSE);
                freeable = zs_can_compact(class);
                spin_unlock(&class->lock);

                objs_per_zspage = class->objs_per_zspage;
                pages_used = obj_allocated / objs_per_zspage *
                                class->pages_per_zspage;

                seq_printf(s, "%13lu %10lu %10lu %16d %8lu\n",
                           obj_allocated, obj_used, pages_used,
                           class->pages_per_zspage, freeable);

                total_objs += obj_allocated;
                total_used_objs += obj_used;
                total_pages += pages_used;
                total_freeable += freeable;
        }

        seq_puts(s, "\n");
        seq_printf(s, " %5s %5s ", "Total", "");

        for (fg = ZS_INUSE_RATIO_10; fg < NR_FULLNESS_GROUPS; fg++)
                seq_printf(s, "%9lu ", inuse_totals[fg]);

        seq_printf(s, "%13lu %10lu %10lu %16s %8lu\n",
                   total_objs, total_used_objs, total_pages, "",
                   total_freeable);

        return 0;
}
DEFINE_SHOW_ATTRIBUTE(zs_stats_size);

static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
{
        if (!zs_stat_root) {
                pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
                return;
        }

        pool->stat_dentry = debugfs_create_dir(name, zs_stat_root);

        debugfs_create_file("classes", S_IFREG | 0444, pool->stat_dentry, pool,
                            &zs_stats_size_fops);
}

static void zs_pool_stat_destroy(struct zs_pool *pool)
{
        debugfs_remove_recursive(pool->stat_dentry);
}

#else /* CONFIG_ZSMALLOC_STAT */
static void __init zs_stat_init(void)
{
}

static void __exit zs_stat_exit(void)
{
}

static inline void zs_pool_stat_create(struct zs_pool *pool, const char *name)
{
}

static inline void zs_pool_stat_destroy(struct zs_pool *pool)
{
}
#endif


/*
 * For each size class, zspages are divided into different groups
 * depending on their usage ratio. This function returns fullness
 * status of the given page.
 */
static int get_fullness_group(struct size_class *class, struct zspage *zspage)
{
        int inuse, objs_per_zspage, ratio;

        inuse = get_zspage_inuse(zspage);
        objs_per_zspage = class->objs_per_zspage;

        if (inuse == 0)
                return ZS_INUSE_RATIO_0;
        if (inuse == objs_per_zspage)
                return ZS_INUSE_RATIO_100;

        ratio = 100 * inuse / objs_per_zspage;
        /*
         * Take integer division into consideration: a page with one inuse
         * object out of 127 possible, will end up having 0 usage ratio,
         * which is wrong as it belongs in ZS_INUSE_RATIO_10 fullness group.
         */
        return ratio / 10 + 1;
}

/*
 * Each size class maintains various freelists and zspages are assigned
 * to one of these freelists based on the number of live objects they
 * have. This functions inserts the given zspage into the freelist
 * identified by <class, fullness_group>.
 */
static void insert_zspage(struct size_class *class,
                                struct zspage *zspage,
                                int fullness)
{
        class_stat_add(class, fullness, 1);
        list_add(&zspage->list, &class->fullness_list[fullness]);
        zspage->fullness = fullness;
}

/*
 * This function removes the given zspage from the freelist identified
 * by <class, fullness_group>.
 */
static void remove_zspage(struct size_class *class, struct zspage *zspage)
{
        int fullness = zspage->fullness;

        VM_BUG_ON(list_empty(&class->fullness_list[fullness]));

        list_del_init(&zspage->list);
        class_stat_sub(class, fullness, 1);
}

/*
 * Each size class maintains zspages in different fullness groups depending
 * on the number of live objects they contain. When allocating or freeing
 * objects, the fullness status of the page can change, for instance, from
 * INUSE_RATIO_80 to INUSE_RATIO_70 when freeing an object. This function
 * checks if such a status change has occurred for the given page and
 * accordingly moves the page from the list of the old fullness group to that
 * of the new fullness group.
 */
static int fix_fullness_group(struct size_class *class, struct zspage *zspage)
{
        int newfg;

        newfg = get_fullness_group(class, zspage);
        if (newfg == zspage->fullness)
                goto out;

        remove_zspage(class, zspage);
        insert_zspage(class, zspage, newfg);
out:
        return newfg;
}

static struct zspage *get_zspage(struct zpdesc *zpdesc)
{
        struct zspage *zspage = zpdesc->zspage;

        BUG_ON(zspage->magic != ZSPAGE_MAGIC);
        return zspage;
}

static struct zpdesc *get_next_zpdesc(struct zpdesc *zpdesc)
{
        struct zspage *zspage = get_zspage(zpdesc);

        if (unlikely(ZsHugePage(zspage)))
                return NULL;

        return zpdesc->next;
}

/**
 * obj_to_location - get (<zpdesc>, <obj_idx>) from encoded object value
 * @obj: the encoded object value
 * @zpdesc: zpdesc object resides in zspage
 * @obj_idx: object index
 */
static void obj_to_location(unsigned long obj, struct zpdesc **zpdesc,
                                unsigned int *obj_idx)
{
        *zpdesc = pfn_zpdesc(obj >> OBJ_INDEX_BITS);
        *obj_idx = (obj & OBJ_INDEX_MASK);
}

static void obj_to_zpdesc(unsigned long obj, struct zpdesc **zpdesc)
{
        *zpdesc = pfn_zpdesc(obj >> OBJ_INDEX_BITS);
}

/**
 * location_to_obj - get obj value encoded from (<zpdesc>, <obj_idx>)
 * @zpdesc: zpdesc object resides in zspage
 * @obj_idx: object index
 */
static unsigned long location_to_obj(struct zpdesc *zpdesc, unsigned int obj_idx)
{
        unsigned long obj;

        obj = zpdesc_pfn(zpdesc) << OBJ_INDEX_BITS;
        obj |= obj_idx & OBJ_INDEX_MASK;

        return obj;
}

static unsigned long handle_to_obj(unsigned long handle)
{
        return *(unsigned long *)handle;
}

static inline bool obj_allocated(struct zpdesc *zpdesc, void *obj,
                                 unsigned long *phandle)
{
        unsigned long handle;
        struct zspage *zspage = get_zspage(zpdesc);

        if (unlikely(ZsHugePage(zspage))) {
                VM_BUG_ON_PAGE(!is_first_zpdesc(zpdesc), zpdesc_page(zpdesc));
                handle = zpdesc->handle;
        } else
                handle = *(unsigned long *)obj;

        if (!(handle & OBJ_ALLOCATED_TAG))
                return false;

        /* Clear all tags before returning the handle */
        *phandle = handle & ~OBJ_TAG_MASK;
        return true;
}

static void reset_zpdesc(struct zpdesc *zpdesc)
{
        struct page *page = zpdesc_page(zpdesc);

        __ClearPageMovable(page);
        ClearPagePrivate(page);
        zpdesc->zspage = NULL;
        zpdesc->next = NULL;
        __ClearPageZsmalloc(page);
}

static int trylock_zspage(struct zspage *zspage)
{
        struct zpdesc *cursor, *fail;

        for (cursor = get_first_zpdesc(zspage); cursor != NULL; cursor =
                                        get_next_zpdesc(cursor)) {
                if (!zpdesc_trylock(cursor)) {
                        fail = cursor;
                        goto unlock;
                }
        }

        return 1;
unlock:
        for (cursor = get_first_zpdesc(zspage); cursor != fail; cursor =
                                        get_next_zpdesc(cursor))
                zpdesc_unlock(cursor);

        return 0;
}

static void __free_zspage(struct zs_pool *pool, struct size_class *class,
                                struct zspage *zspage)
{
        struct zpdesc *zpdesc, *next;

        assert_spin_locked(&class->lock);

        VM_BUG_ON(get_zspage_inuse(zspage));
        VM_BUG_ON(zspage->fullness != ZS_INUSE_RATIO_0);

        next = zpdesc = get_first_zpdesc(zspage);
        do {
                VM_BUG_ON_PAGE(!zpdesc_is_locked(zpdesc), zpdesc_page(zpdesc));
                next = get_next_zpdesc(zpdesc);
                reset_zpdesc(zpdesc);
                zpdesc_unlock(zpdesc);
                zpdesc_dec_zone_page_state(zpdesc);
                zpdesc_put(zpdesc);
                zpdesc = next;
        } while (zpdesc != NULL);

        cache_free_zspage(pool, zspage);

        class_stat_sub(class, ZS_OBJS_ALLOCATED, class->objs_per_zspage);
        atomic_long_sub(class->pages_per_zspage, &pool->pages_allocated);
}

static void free_zspage(struct zs_pool *pool, struct size_class *class,
                                struct zspage *zspage)
{
        VM_BUG_ON(get_zspage_inuse(zspage));
        VM_BUG_ON(list_empty(&zspage->list));

        /*
         * Since zs_free couldn't be sleepable, this function cannot call
         * lock_page. The page locks trylock_zspage got will be released
         * by __free_zspage.
         */
        if (!trylock_zspage(zspage)) {
                kick_deferred_free(pool);
                return;
        }

        remove_zspage(class, zspage);
        __free_zspage(pool, class, zspage);
}

/* Initialize a newly allocated zspage */
static void init_zspage(struct size_class *class, struct zspage *zspage)
{
        unsigned int freeobj = 1;
        unsigned long off = 0;
        struct zpdesc *zpdesc = get_first_zpdesc(zspage);

        while (zpdesc) {
                struct zpdesc *next_zpdesc;
                struct link_free *link;
                void *vaddr;

                set_first_obj_offset(zpdesc, off);

                vaddr = kmap_local_zpdesc(zpdesc);
                link = (struct link_free *)vaddr + off / sizeof(*link);

                while ((off += class->size) < PAGE_SIZE) {
                        link->next = freeobj++ << OBJ_TAG_BITS;
                        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_zpdesc = get_next_zpdesc(zpdesc);
                if (next_zpdesc) {
                        link->next = freeobj++ << OBJ_TAG_BITS;
                } else {
                        /*
                         * Reset OBJ_TAG_BITS bit to last link to tell
                         * whether it's allocated object or not.
                         */
                        link->next = -1UL << OBJ_TAG_BITS;
                }
                kunmap_local(vaddr);
                zpdesc = next_zpdesc;
                off %= PAGE_SIZE;
        }

        set_freeobj(zspage, 0);
}

static void create_page_chain(struct size_class *class, struct zspage *zspage,
                                struct zpdesc *zpdescs[])
{
        int i;
        struct zpdesc *zpdesc;
        struct zpdesc *prev_zpdesc = NULL;
        int nr_zpdescs = class->pages_per_zspage;

        /*
         * Allocate individual pages and link them together as:
         * 1. all pages are linked together using zpdesc->next
         * 2. each sub-page point to zspage using zpdesc->zspage
         *
         * we set PG_private to identify the first zpdesc (i.e. no other zpdesc
         * has this flag set).
         */
        for (i = 0; i < nr_zpdescs; i++) {
                zpdesc = zpdescs[i];
                zpdesc->zspage = zspage;
                zpdesc->next = NULL;
                if (i == 0) {
                        zspage->first_zpdesc = zpdesc;
                        zpdesc_set_first(zpdesc);
                        if (unlikely(class->objs_per_zspage == 1 &&
                                        class->pages_per_zspage == 1))
                                SetZsHugePage(zspage);
                } else {
                        prev_zpdesc->next = zpdesc;
                }
                prev_zpdesc = zpdesc;
        }
}

/*
 * Allocate a zspage for the given size class
 */
static struct zspage *alloc_zspage(struct zs_pool *pool,
                                        struct size_class *class,
                                        gfp_t gfp)
{
        int i;
        struct zpdesc *zpdescs[ZS_MAX_PAGES_PER_ZSPAGE];
        struct zspage *zspage = cache_alloc_zspage(pool, gfp);

        if (!zspage)
                return NULL;

        zspage->magic = ZSPAGE_MAGIC;
        migrate_lock_init(zspage);

        for (i = 0; i < class->pages_per_zspage; i++) {
                struct zpdesc *zpdesc;

                zpdesc = alloc_zpdesc(gfp);
                if (!zpdesc) {
                        while (--i >= 0) {
                                zpdesc_dec_zone_page_state(zpdescs[i]);
                                __zpdesc_clear_zsmalloc(zpdescs[i]);
                                free_zpdesc(zpdescs[i]);
                        }
                        cache_free_zspage(pool, zspage);
                        return NULL;
                }
                __zpdesc_set_zsmalloc(zpdesc);

                zpdesc_inc_zone_page_state(zpdesc);
                zpdescs[i] = zpdesc;
        }

        create_page_chain(class, zspage, zpdescs);
        init_zspage(class, zspage);
        zspage->pool = pool;
        zspage->class = class->index;

        return zspage;
}

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

        for (i = ZS_INUSE_RATIO_99; i >= ZS_INUSE_RATIO_0; i--) {
                zspage = list_first_entry_or_null(&class->fullness_list[i],
                                                  struct zspage, list);
                if (zspage)
                        break;
        }

        return zspage;
}

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 = kmalloc(ZS_MAX_ALLOC_SIZE, GFP_KERNEL);
        if (!area->vm_buf)
                return -ENOMEM;
        return 0;
}

static inline void __zs_cpu_down(struct mapping_area *area)
{
        kfree(area->vm_buf);
        area->vm_buf = NULL;
}

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

        /* disable page faults to match kmap_local_page() 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 */
        memcpy_from_page(buf, zpdesc_page(zpdescs[0]), off, sizes[0]);
        memcpy_from_page(buf + sizes[0], zpdesc_page(zpdescs[1]), 0, sizes[1]);
out:
        return area->vm_buf;
}

static void __zs_unmap_object(struct mapping_area *area,
                        struct zpdesc *zpdescs[2], int off, int size)
{
        size_t sizes[2];
        char *buf;

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

        buf = area->vm_buf;
        buf = buf + ZS_HANDLE_SIZE;
        size -= ZS_HANDLE_SIZE;
        off += ZS_HANDLE_SIZE;

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

        /* copy per-cpu buffer to object */
        memcpy_to_page(zpdesc_page(zpdescs[0]), off, buf, sizes[0]);
        memcpy_to_page(zpdesc_page(zpdescs[1]), 0, buf + sizes[0], sizes[1]);

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

static int zs_cpu_prepare(unsigned int cpu)
{
        struct mapping_area *area;

        area = &per_cpu(zs_map_area, cpu);
        return __zs_cpu_up(area);
}

static int zs_cpu_dead(unsigned int cpu)
{
        struct mapping_area *area;

        area = &per_cpu(zs_map_area, cpu);
        __zs_cpu_down(area);
        return 0;
}

static bool can_merge(struct size_class *prev, int pages_per_zspage,
                                        int objs_per_zspage)
{
        if (prev->pages_per_zspage == pages_per_zspage &&
                prev->objs_per_zspage == objs_per_zspage)
                return true;

        return false;
}

static bool zspage_full(struct size_class *class, struct zspage *zspage)
{
        return get_zspage_inuse(zspage) == class->objs_per_zspage;
}

static bool zspage_empty(struct zspage *zspage)
{
        return get_zspage_inuse(zspage) == 0;
}

/**
 * zs_lookup_class_index() - Returns index of the zsmalloc &size_class
 * that hold objects of the provided size.
 * @pool: zsmalloc pool to use
 * @size: object size
 *
 * Context: Any context.
 *
 * Return: the index of the zsmalloc &size_class that hold objects of the
 * provided size.
 */
unsigned int zs_lookup_class_index(struct zs_pool *pool, unsigned int size)
{
        struct size_class *class;

        class = pool->size_class[get_size_class_index(size)];

        return class->index;
}
EXPORT_SYMBOL_GPL(zs_lookup_class_index);

unsigned long zs_get_total_pages(struct zs_pool *pool)
{
        return atomic_long_read(&pool->pages_allocated);
}
EXPORT_SYMBOL_GPL(zs_get_total_pages);

/**
 * zs_map_object - get address of allocated object from handle.
 * @pool: pool from which the object was allocated
 * @handle: handle returned from zs_malloc
 * @mm: mapping mode to use
 *
 * Before using an object allocated from zs_malloc, it must be mapped using
 * this function. When done with the object, it must be unmapped using
 * zs_unmap_object.
 *
 * Only one object can be mapped per cpu at a time. There is no protection
 * against nested mappings.
 *
 * This function returns with preemption and page faults disabled.
 */
void *zs_map_object(struct zs_pool *pool, unsigned long handle,
                        enum zs_mapmode mm)
{
        struct zspage *zspage;
        struct zpdesc *zpdesc;
        unsigned long obj, off;
        unsigned int obj_idx;

        struct size_class *class;
        struct mapping_area *area;
        struct zpdesc *zpdescs[2];
        void *ret;

        /*
         * 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());

        /* It guarantees it can get zspage from handle safely */
        read_lock(&pool->migrate_lock);
        obj = handle_to_obj(handle);
        obj_to_location(obj, &zpdesc, &obj_idx);
        zspage = get_zspage(zpdesc);

        /*
         * migration cannot move any zpages in this zspage. Here, class->lock
         * is too heavy since callers would take some time until they calls
         * zs_unmap_object API so delegate the locking from class to zspage
         * which is smaller granularity.
         */
        migrate_read_lock(zspage);
        read_unlock(&pool->migrate_lock);

        class = zspage_class(pool, zspage);
        off = offset_in_page(class->size * obj_idx);

        local_lock(&zs_map_area.lock);
        area = this_cpu_ptr(&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_local_zpdesc(zpdesc);
                ret = area->vm_addr + off;
                goto out;
        }

        /* this object spans two pages */
        zpdescs[0] = zpdesc;
        zpdescs[1] = get_next_zpdesc(zpdesc);
        BUG_ON(!zpdescs[1]);

        ret = __zs_map_object(area, zpdescs, off, class->size);
out:
        if (likely(!ZsHugePage(zspage)))
                ret += ZS_HANDLE_SIZE;

        return ret;
}
EXPORT_SYMBOL_GPL(zs_map_object);

void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
{
        struct zspage *zspage;
        struct zpdesc *zpdesc;
        unsigned long obj, off;
        unsigned int obj_idx;

        struct size_class *class;
        struct mapping_area *area;

        obj = handle_to_obj(handle);
        obj_to_location(obj, &zpdesc, &obj_idx);
        zspage = get_zspage(zpdesc);
        class = zspage_class(pool, zspage);
        off = offset_in_page(class->size * obj_idx);

        area = this_cpu_ptr(&zs_map_area);
        if (off + class->size <= PAGE_SIZE)
                kunmap_local(area->vm_addr);
        else {
                struct zpdesc *zpdescs[2];

                zpdescs[0] = zpdesc;
                zpdescs[1] = get_next_zpdesc(zpdesc);
                BUG_ON(!zpdescs[1]);

                __zs_unmap_object(area, zpdescs, off, class->size);
        }
        local_unlock(&zs_map_area.lock);

        migrate_read_unlock(zspage);
}
EXPORT_SYMBOL_GPL(zs_unmap_object);

/**
 * zs_huge_class_size() - Returns the size (in bytes) of the first huge
 *                        zsmalloc &size_class.
 * @pool: zsmalloc pool to use
 *
 * The function returns the size of the first huge class - any object of equal
 * or bigger size will be stored in zspage consisting of a single physical
 * page.
 *
 * Context: Any context.
 *
 * Return: the size (in bytes) of the first huge zsmalloc &size_class.
 */
size_t zs_huge_class_size(struct zs_pool *pool)
{
        return huge_class_size;
}
EXPORT_SYMBOL_GPL(zs_huge_class_size);

static unsigned long obj_malloc(struct zs_pool *pool,
                                struct zspage *zspage, unsigned long handle)
{
        int i, nr_zpdesc, offset;
        unsigned long obj;
        struct link_free *link;
        struct size_class *class;

        struct zpdesc *m_zpdesc;
        unsigned long m_offset;
        void *vaddr;

        class = pool->size_class[zspage->class];
        obj = get_freeobj(zspage);

        offset = obj * class->size;
        nr_zpdesc = offset >> PAGE_SHIFT;
        m_offset = offset_in_page(offset);
        m_zpdesc = get_first_zpdesc(zspage);

        for (i = 0; i < nr_zpdesc; i++)
                m_zpdesc = get_next_zpdesc(m_zpdesc);

        vaddr = kmap_local_zpdesc(m_zpdesc);
        link = (struct link_free *)vaddr + m_offset / sizeof(*link);
        set_freeobj(zspage, link->next >> OBJ_TAG_BITS);
        if (likely(!ZsHugePage(zspage)))
                /* record handle in the header of allocated chunk */
                link->handle = handle | OBJ_ALLOCATED_TAG;
        else
                zspage->first_zpdesc->handle = handle | OBJ_ALLOCATED_TAG;

        kunmap_local(vaddr);
        mod_zspage_inuse(zspage, 1);

        obj = location_to_obj(m_zpdesc, obj);
        record_obj(handle, obj);

        return obj;
}


/**
 * zs_malloc - Allocate block of given size from pool.
 * @pool: pool to allocate from
 * @size: size of block to allocate
 * @gfp: gfp flags when allocating object
 *
 * On success, handle to the allocated object is returned,
 * otherwise an ERR_PTR().
 * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
 */
unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
{
        unsigned long handle;
        struct size_class *class;
        int newfg;
        struct zspage *zspage;

        if (unlikely(!size))
                return (unsigned long)ERR_PTR(-EINVAL);

        if (unlikely(size > ZS_MAX_ALLOC_SIZE))
                return (unsigned long)ERR_PTR(-ENOSPC);

        handle = cache_alloc_handle(pool, gfp);
        if (!handle)
                return (unsigned long)ERR_PTR(-ENOMEM);

        /* extra space in chunk to keep the handle */
        size += ZS_HANDLE_SIZE;
        class = pool->size_class[get_size_class_index(size)];

        /* class->lock effectively protects the zpage migration */
        spin_lock(&class->lock);
        zspage = find_get_zspage(class);
        if (likely(zspage)) {
                obj_malloc(pool, zspage, handle);
                /* Now move the zspage to another fullness group, if required */
                fix_fullness_group(class, zspage);
                class_stat_add(class, ZS_OBJS_INUSE, 1);

                goto out;
        }

        spin_unlock(&class->lock);

        zspage = alloc_zspage(pool, class, gfp);
        if (!zspage) {
                cache_free_handle(pool, handle);
                return (unsigned long)ERR_PTR(-ENOMEM);
        }

        spin_lock(&class->lock);
        obj_malloc(pool, zspage, handle);
        newfg = get_fullness_group(class, zspage);
        insert_zspage(class, zspage, newfg);
        atomic_long_add(class->pages_per_zspage, &pool->pages_allocated);
        class_stat_add(class, ZS_OBJS_ALLOCATED, class->objs_per_zspage);
        class_stat_add(class, ZS_OBJS_INUSE, 1);

        /* We completely set up zspage so mark them as movable */
        SetZsPageMovable(pool, zspage);
out:
        spin_unlock(&class->lock);

        return handle;
}
EXPORT_SYMBOL_GPL(zs_malloc);

static void obj_free(int class_size, unsigned long obj)
{
        struct link_free *link;
        struct zspage *zspage;
        struct zpdesc *f_zpdesc;
        unsigned long f_offset;
        unsigned int f_objidx;
        void *vaddr;


        obj_to_location(obj, &f_zpdesc, &f_objidx);
        f_offset = offset_in_page(class_size * f_objidx);
        zspage = get_zspage(f_zpdesc);

        vaddr = kmap_local_zpdesc(f_zpdesc);
        link = (struct link_free *)(vaddr + f_offset);

        /* Insert this object in containing zspage's freelist */
        if (likely(!ZsHugePage(zspage)))
                link->next = get_freeobj(zspage) << OBJ_TAG_BITS;
        else
                f_zpdesc->handle = 0;
        set_freeobj(zspage, f_objidx);

        kunmap_local(vaddr);
        mod_zspage_inuse(zspage, -1);
}

void zs_free(struct zs_pool *pool, unsigned long handle)
{
        struct zspage *zspage;
        struct zpdesc *f_zpdesc;
        unsigned long obj;
        struct size_class *class;
        int fullness;

        if (IS_ERR_OR_NULL((void *)handle))
                return;

        /*
         * The pool->migrate_lock protects the race with zpage's migration
         * so it's safe to get the page from handle.
         */
        read_lock(&pool->migrate_lock);
        obj = handle_to_obj(handle);
        obj_to_zpdesc(obj, &f_zpdesc);
        zspage = get_zspage(f_zpdesc);
        class = zspage_class(pool, zspage);
        spin_lock(&class->lock);
        read_unlock(&pool->migrate_lock);

        class_stat_sub(class, ZS_OBJS_INUSE, 1);
        obj_free(class->size, obj);

        fullness = fix_fullness_group(class, zspage);
        if (fullness == ZS_INUSE_RATIO_0)
                free_zspage(pool, class, zspage);

        spin_unlock(&class->lock);
        cache_free_handle(pool, handle);
}
EXPORT_SYMBOL_GPL(zs_free);

static void zs_object_copy(struct size_class *class, unsigned long dst,
                                unsigned long src)
{
        struct zpdesc *s_zpdesc, *d_zpdesc;
        unsigned int s_objidx, d_objidx;
        unsigned long s_off, d_off;
        void *s_addr, *d_addr;
        int s_size, d_size, size;
        int written = 0;

        s_size = d_size = class->size;

        obj_to_location(src, &s_zpdesc, &s_objidx);
        obj_to_location(dst, &d_zpdesc, &d_objidx);

        s_off = offset_in_page(class->size * s_objidx);
        d_off = offset_in_page(class->size * d_objidx);

        if (s_off + class->size > PAGE_SIZE)
                s_size = PAGE_SIZE - s_off;

        if (d_off + class->size > PAGE_SIZE)
                d_size = PAGE_SIZE - d_off;

        s_addr = kmap_local_zpdesc(s_zpdesc);
        d_addr = kmap_local_zpdesc(d_zpdesc);

        while (1) {
                size = min(s_size, d_size);
                memcpy(d_addr + d_off, s_addr + s_off, size);
                written += size;

                if (written == class->size)
                        break;

                s_off += size;
                s_size -= size;
                d_off += size;
                d_size -= size;

                /*
                 * Calling kunmap_local(d_addr) is necessary. kunmap_local()
                 * calls must occurs in reverse order of calls to kmap_local_page().
                 * So, to call kunmap_local(s_addr) we should first call
                 * kunmap_local(d_addr). For more details see
                 * Documentation/mm/highmem.rst.
                 */
                if (s_off >= PAGE_SIZE) {
                        kunmap_local(d_addr);
                        kunmap_local(s_addr);
                        s_zpdesc = get_next_zpdesc(s_zpdesc);
                        s_addr = kmap_local_zpdesc(s_zpdesc);
                        d_addr = kmap_local_zpdesc(d_zpdesc);
                        s_size = class->size - written;
                        s_off = 0;
                }

                if (d_off >= PAGE_SIZE) {
                        kunmap_local(d_addr);
                        d_zpdesc = get_next_zpdesc(d_zpdesc);
                        d_addr = kmap_local_zpdesc(d_zpdesc);
                        d_size = class->size - written;
                        d_off = 0;
                }
        }

        kunmap_local(d_addr);
        kunmap_local(s_addr);
}

/*
 * Find alloced object in zspage from index object and
 * return handle.
 */
static unsigned long find_alloced_obj(struct size_class *class,
                                      struct zpdesc *zpdesc, int *obj_idx)
{
        unsigned int offset;
        int index = *obj_idx;
        unsigned long handle = 0;
        void *addr = kmap_local_zpdesc(zpdesc);

        offset = get_first_obj_offset(zpdesc);
        offset += class->size * index;

        while (offset < PAGE_SIZE) {
                if (obj_allocated(zpdesc, addr + offset, &handle))
                        break;

                offset += class->size;
                index++;
        }

        kunmap_local(addr);

        *obj_idx = index;

        return handle;
}

static void migrate_zspage(struct zs_pool *pool, struct zspage *src_zspage,
                           struct zspage *dst_zspage)
{
        unsigned long used_obj, free_obj;
        unsigned long handle;
        int obj_idx = 0;
        struct zpdesc *s_zpdesc = get_first_zpdesc(src_zspage);
        struct size_class *class = pool->size_class[src_zspage->class];

        while (1) {
                handle = find_alloced_obj(class, s_zpdesc, &obj_idx);
                if (!handle) {
                        s_zpdesc = get_next_zpdesc(s_zpdesc);
                        if (!s_zpdesc)
                                break;
                        obj_idx = 0;
                        continue;
                }

                used_obj = handle_to_obj(handle);
                free_obj = obj_malloc(pool, dst_zspage, handle);
                zs_object_copy(class, free_obj, used_obj);
                obj_idx++;
                obj_free(class->size, used_obj);

                /* Stop if there is no more space */
                if (zspage_full(class, dst_zspage))
                        break;

                /* Stop if there are no more objects to migrate */
                if (zspage_empty(src_zspage))
                        break;
        }
}

static struct zspage *isolate_src_zspage(struct size_class *class)
{
        struct zspage *zspage;
        int fg;

        for (fg = ZS_INUSE_RATIO_10; fg <= ZS_INUSE_RATIO_99; fg++) {
                zspage = list_first_entry_or_null(&class->fullness_list[fg],
                                                  struct zspage, list);
                if (zspage) {
                        remove_zspage(class, zspage);
                        return zspage;
                }
        }

        return zspage;
}

static struct zspage *isolate_dst_zspage(struct size_class *class)
{
        struct zspage *zspage;
        int fg;

        for (fg = ZS_INUSE_RATIO_99; fg >= ZS_INUSE_RATIO_10; fg--) {
                zspage = list_first_entry_or_null(&class->fullness_list[fg],
                                                  struct zspage, list);
                if (zspage) {
                        remove_zspage(class, zspage);
                        return zspage;
                }
        }

        return zspage;
}

/*
 * putback_zspage - add @zspage into right class's fullness list
 * @class: destination class
 * @zspage: target page
 *
 * Return @zspage's fullness status
 */
static int putback_zspage(struct size_class *class, struct zspage *zspage)
{
        int fullness;

        fullness = get_fullness_group(class, zspage);
        insert_zspage(class, zspage, fullness);

        return fullness;
}

#ifdef CONFIG_COMPACTION
/*
 * To prevent zspage destroy during migration, zspage freeing should
 * hold locks of all pages in the zspage.
 */
static void lock_zspage(struct zspage *zspage)
{
        struct zpdesc *curr_zpdesc, *zpdesc;

        /*
         * Pages we haven't locked yet can be migrated off the list while we're
         * trying to lock them, so we need to be careful and only attempt to
         * lock each page under migrate_read_lock(). Otherwise, the page we lock
         * may no longer belong to the zspage. This means that we may wait for
         * the wrong page to unlock, so we must take a reference to the page
         * prior to waiting for it to unlock outside migrate_read_lock().
         */
        while (1) {
                migrate_read_lock(zspage);
                zpdesc = get_first_zpdesc(zspage);
                if (zpdesc_trylock(zpdesc))
                        break;
                zpdesc_get(zpdesc);
                migrate_read_unlock(zspage);
                zpdesc_wait_locked(zpdesc);
                zpdesc_put(zpdesc);
        }

        curr_zpdesc = zpdesc;
        while ((zpdesc = get_next_zpdesc(curr_zpdesc))) {
                if (zpdesc_trylock(zpdesc)) {
                        curr_zpdesc = zpdesc;
                } else {
                        zpdesc_get(zpdesc);
                        migrate_read_unlock(zspage);
                        zpdesc_wait_locked(zpdesc);
                        zpdesc_put(zpdesc);
                        migrate_read_lock(zspage);
                }
        }
        migrate_read_unlock(zspage);
}
#endif /* CONFIG_COMPACTION */

static void migrate_lock_init(struct zspage *zspage)
{
        rwlock_init(&zspage->lock);
}

static void migrate_read_lock(struct zspage *zspage) __acquires(&zspage->lock)
{
        read_lock(&zspage->lock);
}

static void migrate_read_unlock(struct zspage *zspage) __releases(&zspage->lock)
{
        read_unlock(&zspage->lock);
}

static void migrate_write_lock(struct zspage *zspage)
{
        write_lock(&zspage->lock);
}

static void migrate_write_unlock(struct zspage *zspage)
{
        write_unlock(&zspage->lock);
}

#ifdef CONFIG_COMPACTION

static const struct movable_operations zsmalloc_mops;

static void replace_sub_page(struct size_class *class, struct zspage *zspage,
                                struct zpdesc *newzpdesc, struct zpdesc *oldzpdesc)
{
        struct zpdesc *zpdesc;
        struct zpdesc *zpdescs[ZS_MAX_PAGES_PER_ZSPAGE] = {NULL, };
        unsigned int first_obj_offset;
        int idx = 0;

        zpdesc = get_first_zpdesc(zspage);
        do {
                if (zpdesc == oldzpdesc)
                        zpdescs[idx] = newzpdesc;
                else
                        zpdescs[idx] = zpdesc;
                idx++;
        } while ((zpdesc = get_next_zpdesc(zpdesc)) != NULL);

        create_page_chain(class, zspage, zpdescs);
        first_obj_offset = get_first_obj_offset(oldzpdesc);
        set_first_obj_offset(newzpdesc, first_obj_offset);
        if (unlikely(ZsHugePage(zspage)))
                newzpdesc->handle = oldzpdesc->handle;
        __zpdesc_set_movable(newzpdesc, &zsmalloc_mops);
}

static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
{
        /*
         * Page is locked so zspage couldn't be destroyed. For detail, look at
         * lock_zspage in free_zspage.
         */
        VM_BUG_ON_PAGE(PageIsolated(page), page);

        return true;
}

static int zs_page_migrate(struct page *newpage, struct page *page,
                enum migrate_mode mode)
{
        struct zs_pool *pool;
        struct size_class *class;
        struct zspage *zspage;
        struct zpdesc *dummy;
        struct zpdesc *newzpdesc = page_zpdesc(newpage);
        struct zpdesc *zpdesc = page_zpdesc(page);
        void *s_addr, *d_addr, *addr;
        unsigned int offset;
        unsigned long handle;
        unsigned long old_obj, new_obj;
        unsigned int obj_idx;

        VM_BUG_ON_PAGE(!zpdesc_is_isolated(zpdesc), zpdesc_page(zpdesc));

        /* We're committed, tell the world that this is a Zsmalloc page. */
        __zpdesc_set_zsmalloc(newzpdesc);

        /* The page is locked, so this pointer must remain valid */
        zspage = get_zspage(zpdesc);
        pool = zspage->pool;

        /*
         * The pool migrate_lock protects the race between zpage migration
         * and zs_free.
         */
        write_lock(&pool->migrate_lock);
        class = zspage_class(pool, zspage);

        /*
         * the class lock protects zpage alloc/free in the zspage.
         */
        spin_lock(&class->lock);
        /* the migrate_write_lock protects zpage access via zs_map_object */
        migrate_write_lock(zspage);

        offset = get_first_obj_offset(zpdesc);
        s_addr = kmap_local_zpdesc(zpdesc);

        /*
         * Here, any user cannot access all objects in the zspage so let's move.
         */
        d_addr = kmap_local_zpdesc(newzpdesc);
        copy_page(d_addr, s_addr);
        kunmap_local(d_addr);

        for (addr = s_addr + offset; addr < s_addr + PAGE_SIZE;
                                        addr += class->size) {
                if (obj_allocated(zpdesc, addr, &handle)) {

                        old_obj = handle_to_obj(handle);
                        obj_to_location(old_obj, &dummy, &obj_idx);
                        new_obj = (unsigned long)location_to_obj(newzpdesc, obj_idx);
                        record_obj(handle, new_obj);
                }
        }
        kunmap_local(s_addr);

        replace_sub_page(class, zspage, newzpdesc, zpdesc);
        /*
         * Since we complete the data copy and set up new zspage structure,
         * it's okay to release migration_lock.
         */
        write_unlock(&pool->migrate_lock);
        spin_unlock(&class->lock);
        migrate_write_unlock(zspage);

        zpdesc_get(newzpdesc);
        if (zpdesc_zone(newzpdesc) != zpdesc_zone(zpdesc)) {
                zpdesc_dec_zone_page_state(zpdesc);
                zpdesc_inc_zone_page_state(newzpdesc);
        }

        reset_zpdesc(zpdesc);
        zpdesc_put(zpdesc);

        return MIGRATEPAGE_SUCCESS;
}

static void zs_page_putback(struct page *page)
{
        VM_BUG_ON_PAGE(!PageIsolated(page), page);
}

static const struct movable_operations zsmalloc_mops = {
        .isolate_page = zs_page_isolate,
        .migrate_page = zs_page_migrate,
        .putback_page = zs_page_putback,
};

/*
 * Caller should hold page_lock of all pages in the zspage
 * In here, we cannot use zspage meta data.
 */
static void async_free_zspage(struct work_struct *work)
{
        int i;
        struct size_class *class;
        struct zspage *zspage, *tmp;
        LIST_HEAD(free_pages);
        struct zs_pool *pool = container_of(work, struct zs_pool,
                                        free_work);

        for (i = 0; i < ZS_SIZE_CLASSES; i++) {
                class = pool->size_class[i];
                if (class->index != i)
                        continue;

                spin_lock(&class->lock);
                list_splice_init(&class->fullness_list[ZS_INUSE_RATIO_0],
                                 &free_pages);
                spin_unlock(&class->lock);
        }

        list_for_each_entry_safe(zspage, tmp, &free_pages, list) {
                list_del(&zspage->list);
                lock_zspage(zspage);

                class = zspage_class(pool, zspage);
                spin_lock(&class->lock);
                class_stat_sub(class, ZS_INUSE_RATIO_0, 1);
                __free_zspage(pool, class, zspage);
                spin_unlock(&class->lock);
        }
};

static void kick_deferred_free(struct zs_pool *pool)
{
        schedule_work(&pool->free_work);
}

static void zs_flush_migration(struct zs_pool *pool)
{
        flush_work(&pool->free_work);
}

static void init_deferred_free(struct zs_pool *pool)
{
        INIT_WORK(&pool->free_work, async_free_zspage);
}

static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage)
{
        struct zpdesc *zpdesc = get_first_zpdesc(zspage);

        do {
                WARN_ON(!zpdesc_trylock(zpdesc));
                __zpdesc_set_movable(zpdesc, &zsmalloc_mops);
                zpdesc_unlock(zpdesc);
        } while ((zpdesc = get_next_zpdesc(zpdesc)) != NULL);
}
#else
static inline void zs_flush_migration(struct zs_pool *pool) { }
#endif

/*
 *
 * Based on the number of unused allocated objects calculate
 * and return the number of pages that we can free.
 */
static unsigned long zs_can_compact(struct size_class *class)
{
        unsigned long obj_wasted;
        unsigned long obj_allocated = class_stat_read(class, ZS_OBJS_ALLOCATED);
        unsigned long obj_used = class_stat_read(class, ZS_OBJS_INUSE);

        if (obj_allocated <= obj_used)
                return 0;

        obj_wasted = obj_allocated - obj_used;
        obj_wasted /= class->objs_per_zspage;

        return obj_wasted * class->pages_per_zspage;
}

static unsigned long __zs_compact(struct zs_pool *pool,
                                  struct size_class *class)
{
        struct zspage *src_zspage = NULL;
        struct zspage *dst_zspage = NULL;
        unsigned long pages_freed = 0;

        /*
         * protect the race between zpage migration and zs_free
         * as well as zpage allocation/free
         */
        write_lock(&pool->migrate_lock);
        spin_lock(&class->lock);
        while (zs_can_compact(class)) {
                int fg;

                if (!dst_zspage) {
                        dst_zspage = isolate_dst_zspage(class);
                        if (!dst_zspage)
                                break;
                }

                src_zspage = isolate_src_zspage(class);
                if (!src_zspage)
                        break;

                migrate_write_lock(src_zspage);
                migrate_zspage(pool, src_zspage, dst_zspage);
                migrate_write_unlock(src_zspage);

                fg = putback_zspage(class, src_zspage);
                if (fg == ZS_INUSE_RATIO_0) {
                        free_zspage(pool, class, src_zspage);
                        pages_freed += class->pages_per_zspage;
                }
                src_zspage = NULL;

                if (get_fullness_group(class, dst_zspage) == ZS_INUSE_RATIO_100
                    || rwlock_is_contended(&pool->migrate_lock)) {
                        putback_zspage(class, dst_zspage);
                        dst_zspage = NULL;

                        spin_unlock(&class->lock);
                        write_unlock(&pool->migrate_lock);
                        cond_resched();
                        write_lock(&pool->migrate_lock);
                        spin_lock(&class->lock);
                }
        }

        if (src_zspage)
                putback_zspage(class, src_zspage);

        if (dst_zspage)
                putback_zspage(class, dst_zspage);

        spin_unlock(&class->lock);
        write_unlock(&pool->migrate_lock);

        return pages_freed;
}

unsigned long zs_compact(struct zs_pool *pool)
{
        int i;
        struct size_class *class;
        unsigned long pages_freed = 0;

        /*
         * Pool compaction is performed under pool->migrate_lock so it is basically
         * single-threaded. Having more than one thread in __zs_compact()
         * will increase pool->migrate_lock contention, which will impact other
         * zsmalloc operations that need pool->migrate_lock.
         */
        if (atomic_xchg(&pool->compaction_in_progress, 1))
                return 0;

        for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
                class = pool->size_class[i];
                if (class->index != i)
                        continue;
                pages_freed += __zs_compact(pool, class);
        }
        atomic_long_add(pages_freed, &pool->stats.pages_compacted);
        atomic_set(&pool->compaction_in_progress, 0);

        return pages_freed;
}
EXPORT_SYMBOL_GPL(zs_compact);

void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats)
{
        memcpy(stats, &pool->stats, sizeof(struct zs_pool_stats));
}
EXPORT_SYMBOL_GPL(zs_pool_stats);

static unsigned long zs_shrinker_scan(struct shrinker *shrinker,
                struct shrink_control *sc)
{
        unsigned long pages_freed;
        struct zs_pool *pool = shrinker->private_data;

        /*
         * Compact classes and calculate compaction delta.
         * Can run concurrently with a manually triggered
         * (by user) compaction.
         */
        pages_freed = zs_compact(pool);

        return pages_freed ? pages_freed : SHRINK_STOP;
}

static unsigned long zs_shrinker_count(struct shrinker *shrinker,
                struct shrink_control *sc)
{
        int i;
        struct size_class *class;
        unsigned long pages_to_free = 0;
        struct zs_pool *pool = shrinker->private_data;

        for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
                class = pool->size_class[i];
                if (class->index != i)
                        continue;

                pages_to_free += zs_can_compact(class);
        }

        return pages_to_free;
}

static void zs_unregister_shrinker(struct zs_pool *pool)
{
        shrinker_free(pool->shrinker);
}

static int zs_register_shrinker(struct zs_pool *pool)
{
        pool->shrinker = shrinker_alloc(0, "mm-zspool:%s", pool->name);
        if (!pool->shrinker)
                return -ENOMEM;

        pool->shrinker->scan_objects = zs_shrinker_scan;
        pool->shrinker->count_objects = zs_shrinker_count;
        pool->shrinker->batch = 0;
        pool->shrinker->private_data = pool;

        shrinker_register(pool->shrinker);

        return 0;
}

static int calculate_zspage_chain_size(int class_size)
{
        int i, min_waste = INT_MAX;
        int chain_size = 1;

        if (is_power_of_2(class_size))
                return chain_size;

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

                waste = (i * PAGE_SIZE) % class_size;
                if (waste < min_waste) {
                        min_waste = waste;
                        chain_size = i;
                }
        }

        return chain_size;
}

/**
 * zs_create_pool - Creates an allocation pool to work from.
 * @name: pool name to be created
 *
 * This function must be called before anything when using
 * the zsmalloc allocator.
 *
 * On success, a pointer to the newly created pool is returned,
 * otherwise NULL.
 */
struct zs_pool *zs_create_pool(const char *name)
{
        int i;
        struct zs_pool *pool;
        struct size_class *prev_class = NULL;

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

        init_deferred_free(pool);
        rwlock_init(&pool->migrate_lock);
        atomic_set(&pool->compaction_in_progress, 0);

        pool->name = kstrdup(name, GFP_KERNEL);
        if (!pool->name)
                goto err;

        if (create_cache(pool))
                goto err;

        /*
         * Iterate reversely, because, size of size_class that we want to use
         * for merging should be larger or equal to current size.
         */
        for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
                int size;
                int pages_per_zspage;
                int objs_per_zspage;
                struct size_class *class;
                int fullness;

                size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
                if (size > ZS_MAX_ALLOC_SIZE)
                        size = ZS_MAX_ALLOC_SIZE;
                pages_per_zspage = calculate_zspage_chain_size(size);
                objs_per_zspage = pages_per_zspage * PAGE_SIZE / size;

                /*
                 * We iterate from biggest down to smallest classes,
                 * so huge_class_size holds the size of the first huge
                 * class. Any object bigger than or equal to that will
                 * endup in the huge class.
                 */
                if (pages_per_zspage != 1 && objs_per_zspage != 1 &&
                                !huge_class_size) {
                        huge_class_size = size;
                        /*
                         * The object uses ZS_HANDLE_SIZE bytes to store the
                         * handle. We need to subtract it, because zs_malloc()
                         * unconditionally adds handle size before it performs
                         * size class search - so object may be smaller than
                         * huge class size, yet it still can end up in the huge
                         * class because it grows by ZS_HANDLE_SIZE extra bytes
                         * right before class lookup.
                         */
                        huge_class_size -= (ZS_HANDLE_SIZE - 1);
                }

                /*
                 * size_class is used for normal zsmalloc operation such
                 * as alloc/free for that size. Although it is natural that we
                 * have one size_class for each size, there is a chance that we
                 * can get more memory utilization if we use one size_class for
                 * many different sizes whose size_class have same
                 * characteristics. So, we makes size_class point to
                 * previous size_class if possible.
                 */
                if (prev_class) {
                        if (can_merge(prev_class, pages_per_zspage, objs_per_zspage)) {
                                pool->size_class[i] = prev_class;
                                continue;
                        }
                }

                class = kzalloc(sizeof(struct size_class), GFP_KERNEL);
                if (!class)
                        goto err;

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

                fullness = ZS_INUSE_RATIO_0;
                while (fullness < NR_FULLNESS_GROUPS) {
                        INIT_LIST_HEAD(&class->fullness_list[fullness]);
                        fullness++;
                }

                prev_class = class;
        }

        /* debug only, don't abort if it fails */
        zs_pool_stat_create(pool, name);

        /*
         * Not critical since shrinker is only used to trigger internal
         * defragmentation of the pool which is pretty optional thing.  If
         * registration fails we still can use the pool normally and user can
         * trigger compaction manually. Thus, ignore return code.
         */
        zs_register_shrinker(pool);

        return pool;

err:
        zs_destroy_pool(pool);
        return NULL;
}
EXPORT_SYMBOL_GPL(zs_create_pool);

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

        zs_unregister_shrinker(pool);
        zs_flush_migration(pool);
        zs_pool_stat_destroy(pool);

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

                if (!class)
                        continue;

                if (class->index != i)
                        continue;

                for (fg = ZS_INUSE_RATIO_0; fg < NR_FULLNESS_GROUPS; fg++) {
                        if (list_empty(&class->fullness_list[fg]))
                                continue;

                        pr_err("Class-%d fullness group %d is not empty\n",
                               class->size, fg);
                }
                kfree(class);
        }

        destroy_cache(pool);
        kfree(pool->name);
        kfree(pool);
}
EXPORT_SYMBOL_GPL(zs_destroy_pool);

static int __init zs_init(void)
{
        int ret;

        ret = cpuhp_setup_state(CPUHP_MM_ZS_PREPARE, "mm/zsmalloc:prepare",
                                zs_cpu_prepare, zs_cpu_dead);
        if (ret)
                goto out;

#ifdef CONFIG_ZPOOL
        zpool_register_driver(&zs_zpool_driver);
#endif

        zs_stat_init();

        return 0;

out:
        return ret;
}

static void __exit zs_exit(void)
{
#ifdef CONFIG_ZPOOL
        zpool_unregister_driver(&zs_zpool_driver);
#endif
        cpuhp_remove_state(CPUHP_MM_ZS_PREPARE);

        zs_stat_exit();
}

module_init(zs_init);
module_exit(zs_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
MODULE_DESCRIPTION("zsmalloc memory allocator");