/*
 * Compressed RAM block device
 *
 * Copyright (C) 2008, 2009, 2010  Nitin Gupta
 *               2012, 2013 Minchan Kim
 *
 * This code is released using a dual license strategy: BSD/GPL
 * You can choose the licence 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) "zram: " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bio.h>
#include <linux/bitops.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/device.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/string.h>
#include <linux/vmalloc.h>
#include <linux/err.h>
#include <linux/idr.h>
#include <linux/sysfs.h>
#include <linux/debugfs.h>
#include <linux/cpuhotplug.h>
#include <linux/part_stat.h>
#include <linux/kernel_read_file.h>

#include "zram_drv.h"

static DEFINE_IDR(zram_index_idr);
/* idr index must be protected */
static DEFINE_MUTEX(zram_index_mutex);

static int zram_major;
static const char *default_compressor = CONFIG_ZRAM_DEF_COMP;

#define ZRAM_MAX_ALGO_NAME_SZ   128

/* Module params (documentation at end) */
static unsigned int num_devices = 1;
/*
 * Pages that compress to sizes equals or greater than this are stored
 * uncompressed in memory.
 */
static size_t huge_class_size;

static const struct block_device_operations zram_devops;

static void slot_free(struct zram *zram, u32 index);
#define slot_dep_map(zram, index) (&(zram)->table[(index)].dep_map)

static void slot_lock_init(struct zram *zram, u32 index)
{
        static struct lock_class_key __key;

        lockdep_init_map(slot_dep_map(zram, index), "zram->table[index].lock",
                         &__key, 0);
}

/*
 * entry locking rules:
 *
 * 1) Lock is exclusive
 *
 * 2) lock() function can sleep waiting for the lock
 *
 * 3) Lock owner can sleep
 *
 * 4) Use TRY lock variant when in atomic context
 *    - must check return value and handle locking failers
 */
static __must_check bool slot_trylock(struct zram *zram, u32 index)
{
        unsigned long *lock = &zram->table[index].__lock;

        if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) {
                mutex_acquire(slot_dep_map(zram, index), 0, 1, _RET_IP_);
                lock_acquired(slot_dep_map(zram, index), _RET_IP_);
                return true;
        }

        return false;
}

static void slot_lock(struct zram *zram, u32 index)
{
        unsigned long *lock = &zram->table[index].__lock;

        mutex_acquire(slot_dep_map(zram, index), 0, 0, _RET_IP_);
        wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE);
        lock_acquired(slot_dep_map(zram, index), _RET_IP_);
}

static void slot_unlock(struct zram *zram, u32 index)
{
        unsigned long *lock = &zram->table[index].__lock;

        mutex_release(slot_dep_map(zram, index), _RET_IP_);
        clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock);
}

static inline bool init_done(struct zram *zram)
{
        return zram->disksize;
}

static inline struct zram *dev_to_zram(struct device *dev)
{
        return (struct zram *)dev_to_disk(dev)->private_data;
}

static unsigned long get_slot_handle(struct zram *zram, u32 index)
{
        return zram->table[index].handle;
}

static void set_slot_handle(struct zram *zram, u32 index, unsigned long handle)
{
        zram->table[index].handle = handle;
}

static bool test_slot_flag(struct zram *zram, u32 index,
                           enum zram_pageflags flag)
{
        return zram->table[index].attr.flags & BIT(flag);
}

static void set_slot_flag(struct zram *zram, u32 index,
                          enum zram_pageflags flag)
{
        zram->table[index].attr.flags |= BIT(flag);
}

static void clear_slot_flag(struct zram *zram, u32 index,
                            enum zram_pageflags flag)
{
        zram->table[index].attr.flags &= ~BIT(flag);
}

static size_t get_slot_size(struct zram *zram, u32 index)
{
        return zram->table[index].attr.flags & (BIT(ZRAM_FLAG_SHIFT) - 1);
}

static void set_slot_size(struct zram *zram, u32 index, size_t size)
{
        unsigned long flags = zram->table[index].attr.flags >> ZRAM_FLAG_SHIFT;

        zram->table[index].attr.flags = (flags << ZRAM_FLAG_SHIFT) | size;
}

static inline bool slot_allocated(struct zram *zram, u32 index)
{
        return get_slot_size(zram, index) ||
                test_slot_flag(zram, index, ZRAM_SAME) ||
                test_slot_flag(zram, index, ZRAM_WB);
}

static inline void set_slot_comp_priority(struct zram *zram, u32 index,
                                          u32 prio)
{
        prio &= ZRAM_COMP_PRIORITY_MASK;
        /*
         * Clear previous priority value first, in case if we recompress
         * further an already recompressed page
         */
        zram->table[index].attr.flags &= ~(ZRAM_COMP_PRIORITY_MASK <<
                                           ZRAM_COMP_PRIORITY_BIT1);
        zram->table[index].attr.flags |= (prio << ZRAM_COMP_PRIORITY_BIT1);
}

static inline u32 get_slot_comp_priority(struct zram *zram, u32 index)
{
        u32 prio = zram->table[index].attr.flags >> ZRAM_COMP_PRIORITY_BIT1;

        return prio & ZRAM_COMP_PRIORITY_MASK;
}

static void mark_slot_accessed(struct zram *zram, u32 index)
{
        clear_slot_flag(zram, index, ZRAM_IDLE);
        clear_slot_flag(zram, index, ZRAM_PP_SLOT);
#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
        zram->table[index].attr.ac_time = (u32)ktime_get_boottime_seconds();
#endif
}

static inline void update_used_max(struct zram *zram, const unsigned long pages)
{
        unsigned long cur_max = atomic_long_read(&zram->stats.max_used_pages);

        do {
                if (cur_max >= pages)
                        return;
        } while (!atomic_long_try_cmpxchg(&zram->stats.max_used_pages,
                                          &cur_max, pages));
}

static bool zram_can_store_page(struct zram *zram)
{
        unsigned long alloced_pages;

        alloced_pages = zs_get_total_pages(zram->mem_pool);
        update_used_max(zram, alloced_pages);

        return !zram->limit_pages || alloced_pages <= zram->limit_pages;
}

#if PAGE_SIZE != 4096
static inline bool is_partial_io(struct bio_vec *bvec)
{
        return bvec->bv_len != PAGE_SIZE;
}
#define ZRAM_PARTIAL_IO         1
#else
static inline bool is_partial_io(struct bio_vec *bvec)
{
        return false;
}
#endif

#if defined CONFIG_ZRAM_WRITEBACK || defined CONFIG_ZRAM_MULTI_COMP
struct zram_pp_slot {
        unsigned long           index;
        struct list_head        entry;
};

/*
 * A post-processing bucket is, essentially, a size class, this defines
 * the range (in bytes) of pp-slots sizes in particular bucket.
 */
#define PP_BUCKET_SIZE_RANGE    64
#define NUM_PP_BUCKETS          ((PAGE_SIZE / PP_BUCKET_SIZE_RANGE) + 1)

struct zram_pp_ctl {
        struct list_head        pp_buckets[NUM_PP_BUCKETS];
};

static struct zram_pp_ctl *init_pp_ctl(void)
{
        struct zram_pp_ctl *ctl;
        u32 idx;

        ctl = kmalloc_obj(*ctl);
        if (!ctl)
                return NULL;

        for (idx = 0; idx < NUM_PP_BUCKETS; idx++)
                INIT_LIST_HEAD(&ctl->pp_buckets[idx]);
        return ctl;
}

static void release_pp_slot(struct zram *zram, struct zram_pp_slot *pps)
{
        list_del_init(&pps->entry);

        slot_lock(zram, pps->index);
        clear_slot_flag(zram, pps->index, ZRAM_PP_SLOT);
        slot_unlock(zram, pps->index);

        kfree(pps);
}

static void release_pp_ctl(struct zram *zram, struct zram_pp_ctl *ctl)
{
        u32 idx;

        if (!ctl)
                return;

        for (idx = 0; idx < NUM_PP_BUCKETS; idx++) {
                while (!list_empty(&ctl->pp_buckets[idx])) {
                        struct zram_pp_slot *pps;

                        pps = list_first_entry(&ctl->pp_buckets[idx],
                                               struct zram_pp_slot,
                                               entry);
                        release_pp_slot(zram, pps);
                }
        }

        kfree(ctl);
}

static bool place_pp_slot(struct zram *zram, struct zram_pp_ctl *ctl,
                          u32 index)
{
        struct zram_pp_slot *pps;
        u32 bid;

        pps = kmalloc_obj(*pps, GFP_NOIO | __GFP_NOWARN);
        if (!pps)
                return false;

        INIT_LIST_HEAD(&pps->entry);
        pps->index = index;

        bid = get_slot_size(zram, pps->index) / PP_BUCKET_SIZE_RANGE;
        list_add(&pps->entry, &ctl->pp_buckets[bid]);

        set_slot_flag(zram, pps->index, ZRAM_PP_SLOT);
        return true;
}

static struct zram_pp_slot *select_pp_slot(struct zram_pp_ctl *ctl)
{
        struct zram_pp_slot *pps = NULL;
        s32 idx = NUM_PP_BUCKETS - 1;

        /* The higher the bucket id the more optimal slot post-processing is */
        while (idx >= 0) {
                pps = list_first_entry_or_null(&ctl->pp_buckets[idx],
                                               struct zram_pp_slot,
                                               entry);
                if (pps)
                        break;

                idx--;
        }
        return pps;
}
#endif

static inline void zram_fill_page(void *ptr, unsigned long len,
                                        unsigned long value)
{
        WARN_ON_ONCE(!IS_ALIGNED(len, sizeof(unsigned long)));
        memset_l(ptr, value, len / sizeof(unsigned long));
}

static bool page_same_filled(void *ptr, unsigned long *element)
{
        unsigned long *page;
        unsigned long val;
        unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1;

        page = (unsigned long *)ptr;
        val = page[0];

        if (val != page[last_pos])
                return false;

        for (pos = 1; pos < last_pos; pos++) {
                if (val != page[pos])
                        return false;
        }

        *element = val;

        return true;
}

static ssize_t initstate_show(struct device *dev, struct device_attribute *attr,
                              char *buf)
{
        u32 val;
        struct zram *zram = dev_to_zram(dev);

        guard(rwsem_read)(&zram->dev_lock);
        val = init_done(zram);

        return sysfs_emit(buf, "%u\n", val);
}

static ssize_t disksize_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        struct zram *zram = dev_to_zram(dev);

        return sysfs_emit(buf, "%llu\n", zram->disksize);
}

static ssize_t mem_limit_store(struct device *dev,
                               struct device_attribute *attr, const char *buf,
                               size_t len)
{
        u64 limit;
        char *tmp;
        struct zram *zram = dev_to_zram(dev);

        limit = memparse(buf, &tmp);
        if (buf == tmp) /* no chars parsed, invalid input */
                return -EINVAL;

        guard(rwsem_write)(&zram->dev_lock);
        zram->limit_pages = PAGE_ALIGN(limit) >> PAGE_SHIFT;

        return len;
}

static ssize_t mem_used_max_store(struct device *dev,
                                  struct device_attribute *attr,
                                  const char *buf, size_t len)
{
        int err;
        unsigned long val;
        struct zram *zram = dev_to_zram(dev);

        err = kstrtoul(buf, 10, &val);
        if (err || val != 0)
                return -EINVAL;

        guard(rwsem_read)(&zram->dev_lock);
        if (init_done(zram)) {
                atomic_long_set(&zram->stats.max_used_pages,
                                zs_get_total_pages(zram->mem_pool));
        }

        return len;
}

/*
 * Mark all pages which are older than or equal to cutoff as IDLE.
 * Callers should hold the zram init lock in read mode
 */
static void mark_idle(struct zram *zram, ktime_t cutoff)
{
        int is_idle = 1;
        unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
        int index;

        for (index = 0; index < nr_pages; index++) {
                /*
                 * Do not mark ZRAM_SAME slots as ZRAM_IDLE, because no
                 * post-processing (recompress, writeback) happens to the
                 * ZRAM_SAME slot.
                 *
                 * And ZRAM_WB slots simply cannot be ZRAM_IDLE.
                 */
                slot_lock(zram, index);
                if (!slot_allocated(zram, index) ||
                    test_slot_flag(zram, index, ZRAM_WB) ||
                    test_slot_flag(zram, index, ZRAM_SAME)) {
                        slot_unlock(zram, index);
                        continue;
                }

#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
                is_idle = !cutoff ||
                        ktime_after(cutoff, zram->table[index].attr.ac_time);
#endif
                if (is_idle)
                        set_slot_flag(zram, index, ZRAM_IDLE);
                else
                        clear_slot_flag(zram, index, ZRAM_IDLE);
                slot_unlock(zram, index);
        }
}

static ssize_t idle_store(struct device *dev, struct device_attribute *attr,
                          const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        ktime_t cutoff = 0;

        if (!sysfs_streq(buf, "all")) {
                /*
                 * If it did not parse as 'all' try to treat it as an integer
                 * when we have memory tracking enabled.
                 */
                u32 age_sec;

                if (IS_ENABLED(CONFIG_ZRAM_TRACK_ENTRY_ACTIME) &&
                    !kstrtouint(buf, 0, &age_sec))
                        cutoff = ktime_sub((u32)ktime_get_boottime_seconds(),
                                           age_sec);
                else
                        return -EINVAL;
        }

        guard(rwsem_read)(&zram->dev_lock);
        if (!init_done(zram))
                return -EINVAL;

        /*
         * A cutoff of 0 marks everything as idle, this is the
         * "all" behavior.
         */
        mark_idle(zram, cutoff);
        return len;
}

#ifdef CONFIG_ZRAM_WRITEBACK
#define INVALID_BDEV_BLOCK              (~0UL)

static int read_from_zspool_raw(struct zram *zram, struct page *page,
                                u32 index);
static int read_from_zspool(struct zram *zram, struct page *page, u32 index);

struct zram_wb_ctl {
        /* idle list is accessed only by the writeback task, no concurency */
        struct list_head idle_reqs;
        /* done list is accessed concurrently, protect by done_lock */
        struct list_head done_reqs;
        wait_queue_head_t done_wait;
        spinlock_t done_lock;
        atomic_t num_inflight;
};

struct zram_wb_req {
        unsigned long blk_idx;
        struct page *page;
        struct zram_pp_slot *pps;
        struct bio_vec bio_vec;
        struct bio bio;

        struct list_head entry;
};

struct zram_rb_req {
        struct work_struct work;
        struct zram *zram;
        struct page *page;
        /* The read bio for backing device */
        struct bio *bio;
        unsigned long blk_idx;
        union {
                /* The original bio to complete (async read) */
                struct bio *parent;
                /* error status (sync read) */
                int error;
        };
        u32 index;
};

#define FOUR_K(x) ((x) * (1 << (PAGE_SHIFT - 12)))
static ssize_t bd_stat_show(struct device *dev, struct device_attribute *attr,
                            char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        ssize_t ret;

        guard(rwsem_read)(&zram->dev_lock);
        ret = sysfs_emit(buf,
                         "%8llu %8llu %8llu\n",
                         FOUR_K((u64)atomic64_read(&zram->stats.bd_count)),
                         FOUR_K((u64)atomic64_read(&zram->stats.bd_reads)),
                         FOUR_K((u64)atomic64_read(&zram->stats.bd_writes)));

        return ret;
}

static ssize_t compressed_writeback_store(struct device *dev,
                                          struct device_attribute *attr,
                                          const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        bool val;

        if (kstrtobool(buf, &val))
                return -EINVAL;

        guard(rwsem_write)(&zram->dev_lock);
        if (init_done(zram)) {
                return -EBUSY;
        }

        zram->compressed_wb = val;

        return len;
}

static ssize_t compressed_writeback_show(struct device *dev,
                                         struct device_attribute *attr,
                                         char *buf)
{
        bool val;
        struct zram *zram = dev_to_zram(dev);

        guard(rwsem_read)(&zram->dev_lock);
        val = zram->compressed_wb;

        return sysfs_emit(buf, "%d\n", val);
}

static ssize_t writeback_limit_enable_store(struct device *dev,
                                            struct device_attribute *attr,
                                            const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        u64 val;

        if (kstrtoull(buf, 10, &val))
                return -EINVAL;

        guard(rwsem_write)(&zram->dev_lock);
        zram->wb_limit_enable = val;

        return len;
}

static ssize_t writeback_limit_enable_show(struct device *dev,
                                           struct device_attribute *attr,
                                           char *buf)
{
        bool val;
        struct zram *zram = dev_to_zram(dev);

        guard(rwsem_read)(&zram->dev_lock);
        val = zram->wb_limit_enable;

        return sysfs_emit(buf, "%d\n", val);
}

static ssize_t writeback_limit_store(struct device *dev,
                                     struct device_attribute *attr,
                                     const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        u64 val;

        if (kstrtoull(buf, 10, &val))
                return -EINVAL;

        /*
         * When the page size is greater than 4KB, if bd_wb_limit is set to
         * a value that is not page - size aligned, it will cause value
         * wrapping. For example, when the page size is set to 16KB and
         * bd_wb_limit is set to 3, a single write - back operation will
         * cause bd_wb_limit to become -1. Even more terrifying is that
         * bd_wb_limit is an unsigned number.
         */
        val = rounddown(val, PAGE_SIZE / 4096);

        guard(rwsem_write)(&zram->dev_lock);
        zram->bd_wb_limit = val;

        return len;
}

static ssize_t writeback_limit_show(struct device *dev,
                                    struct device_attribute *attr, char *buf)
{
        u64 val;
        struct zram *zram = dev_to_zram(dev);

        guard(rwsem_read)(&zram->dev_lock);
        val = zram->bd_wb_limit;

        return sysfs_emit(buf, "%llu\n", val);
}

static ssize_t writeback_batch_size_store(struct device *dev,
                                          struct device_attribute *attr,
                                          const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        u32 val;

        if (kstrtouint(buf, 10, &val))
                return -EINVAL;

        if (!val)
                return -EINVAL;

        guard(rwsem_write)(&zram->dev_lock);
        zram->wb_batch_size = val;

        return len;
}

static ssize_t writeback_batch_size_show(struct device *dev,
                                         struct device_attribute *attr,
                                         char *buf)
{
        u32 val;
        struct zram *zram = dev_to_zram(dev);

        guard(rwsem_read)(&zram->dev_lock);
        val = zram->wb_batch_size;

        return sysfs_emit(buf, "%u\n", val);
}

static void reset_bdev(struct zram *zram)
{
        if (!zram->backing_dev)
                return;

        /* hope filp_close flush all of IO */
        filp_close(zram->backing_dev, NULL);
        zram->backing_dev = NULL;
        zram->bdev = NULL;
        zram->disk->fops = &zram_devops;
        kvfree(zram->bitmap);
        zram->bitmap = NULL;
}

static ssize_t backing_dev_show(struct device *dev,
                                struct device_attribute *attr, char *buf)
{
        struct file *file;
        struct zram *zram = dev_to_zram(dev);
        char *p;
        ssize_t ret;

        guard(rwsem_read)(&zram->dev_lock);
        file = zram->backing_dev;
        if (!file) {
                memcpy(buf, "none\n", 5);
                return 5;
        }

        p = file_path(file, buf, PAGE_SIZE - 1);
        if (IS_ERR(p))
                return PTR_ERR(p);

        ret = strlen(p);
        memmove(buf, p, ret);
        buf[ret++] = '\n';
        return ret;
}

static ssize_t backing_dev_store(struct device *dev,
                                 struct device_attribute *attr, const char *buf,
                                 size_t len)
{
        char *file_name;
        size_t sz;
        struct file *backing_dev = NULL;
        struct inode *inode;
        unsigned int bitmap_sz;
        unsigned long nr_pages, *bitmap = NULL;
        int err;
        struct zram *zram = dev_to_zram(dev);

        file_name = kmalloc(PATH_MAX, GFP_KERNEL);
        if (!file_name)
                return -ENOMEM;

        guard(rwsem_write)(&zram->dev_lock);
        if (init_done(zram)) {
                pr_info("Can't setup backing device for initialized device\n");
                err = -EBUSY;
                goto out;
        }

        strscpy(file_name, buf, PATH_MAX);
        /* ignore trailing newline */
        sz = strlen(file_name);
        if (sz > 0 && file_name[sz - 1] == '\n')
                file_name[sz - 1] = 0x00;

        backing_dev = filp_open(file_name, O_RDWR | O_LARGEFILE | O_EXCL, 0);
        if (IS_ERR(backing_dev)) {
                err = PTR_ERR(backing_dev);
                backing_dev = NULL;
                goto out;
        }

        inode = backing_dev->f_mapping->host;

        /* Support only block device in this moment */
        if (!S_ISBLK(inode->i_mode)) {
                err = -ENOTBLK;
                goto out;
        }

        nr_pages = i_size_read(inode) >> PAGE_SHIFT;
        /* Refuse to use zero sized device (also prevents self reference) */
        if (!nr_pages) {
                err = -EINVAL;
                goto out;
        }

        bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);
        bitmap = kvzalloc(bitmap_sz, GFP_KERNEL);
        if (!bitmap) {
                err = -ENOMEM;
                goto out;
        }

        reset_bdev(zram);

        zram->bdev = I_BDEV(inode);
        zram->backing_dev = backing_dev;
        zram->bitmap = bitmap;
        zram->nr_pages = nr_pages;

        pr_info("setup backing device %s\n", file_name);
        kfree(file_name);

        return len;
out:
        kvfree(bitmap);

        if (backing_dev)
                filp_close(backing_dev, NULL);

        kfree(file_name);

        return err;
}

static unsigned long zram_reserve_bdev_block(struct zram *zram)
{
        unsigned long blk_idx;

        blk_idx = find_next_zero_bit(zram->bitmap, zram->nr_pages, 0);
        if (blk_idx == zram->nr_pages)
                return INVALID_BDEV_BLOCK;

        set_bit(blk_idx, zram->bitmap);
        atomic64_inc(&zram->stats.bd_count);
        return blk_idx;
}

static void zram_release_bdev_block(struct zram *zram, unsigned long blk_idx)
{
        int was_set;

        was_set = test_and_clear_bit(blk_idx, zram->bitmap);
        WARN_ON_ONCE(!was_set);
        atomic64_dec(&zram->stats.bd_count);
}

static void release_wb_req(struct zram_wb_req *req)
{
        __free_page(req->page);
        kfree(req);
}

static void release_wb_ctl(struct zram_wb_ctl *wb_ctl)
{
        if (!wb_ctl)
                return;

        /* We should never have inflight requests at this point */
        WARN_ON(atomic_read(&wb_ctl->num_inflight));
        WARN_ON(!list_empty(&wb_ctl->done_reqs));

        while (!list_empty(&wb_ctl->idle_reqs)) {
                struct zram_wb_req *req;

                req = list_first_entry(&wb_ctl->idle_reqs,
                                       struct zram_wb_req, entry);
                list_del(&req->entry);
                release_wb_req(req);
        }

        kfree(wb_ctl);
}

static struct zram_wb_ctl *init_wb_ctl(struct zram *zram)
{
        struct zram_wb_ctl *wb_ctl;
        int i;

        wb_ctl = kmalloc_obj(*wb_ctl);
        if (!wb_ctl)
                return NULL;

        INIT_LIST_HEAD(&wb_ctl->idle_reqs);
        INIT_LIST_HEAD(&wb_ctl->done_reqs);
        atomic_set(&wb_ctl->num_inflight, 0);
        init_waitqueue_head(&wb_ctl->done_wait);
        spin_lock_init(&wb_ctl->done_lock);

        for (i = 0; i < zram->wb_batch_size; i++) {
                struct zram_wb_req *req;

                /*
                 * This is fatal condition only if we couldn't allocate
                 * any requests at all.  Otherwise we just work with the
                 * requests that we have successfully allocated, so that
                 * writeback can still proceed, even if there is only one
                 * request on the idle list.
                 */
                req = kzalloc_obj(*req, GFP_KERNEL | __GFP_NOWARN);
                if (!req)
                        break;

                req->page = alloc_page(GFP_KERNEL | __GFP_NOWARN);
                if (!req->page) {
                        kfree(req);
                        break;
                }

                list_add(&req->entry, &wb_ctl->idle_reqs);
        }

        /* We couldn't allocate any requests, so writeabck is not possible */
        if (list_empty(&wb_ctl->idle_reqs))
                goto release_wb_ctl;

        return wb_ctl;

release_wb_ctl:
        release_wb_ctl(wb_ctl);
        return NULL;
}

static void zram_account_writeback_rollback(struct zram *zram)
{
        lockdep_assert_held_write(&zram->dev_lock);

        if (zram->wb_limit_enable)
                zram->bd_wb_limit +=  1UL << (PAGE_SHIFT - 12);
}

static void zram_account_writeback_submit(struct zram *zram)
{
        lockdep_assert_held_write(&zram->dev_lock);

        if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
                zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
}

static int zram_writeback_complete(struct zram *zram, struct zram_wb_req *req)
{
        u32 index = req->pps->index;
        int err;

        err = blk_status_to_errno(req->bio.bi_status);
        if (err) {
                /*
                 * Failed wb requests should not be accounted in wb_limit
                 * (if enabled).
                 */
                zram_account_writeback_rollback(zram);
                zram_release_bdev_block(zram, req->blk_idx);
                return err;
        }

        atomic64_inc(&zram->stats.bd_writes);
        slot_lock(zram, index);
        /*
         * We release slot lock during writeback so slot can change under us:
         * slot_free() or slot_free() and zram_write_page(). In both cases
         * slot loses ZRAM_PP_SLOT flag. No concurrent post-processing can
         * set ZRAM_PP_SLOT on such slots until current post-processing
         * finishes.
         */
        if (!test_slot_flag(zram, index, ZRAM_PP_SLOT)) {
                zram_release_bdev_block(zram, req->blk_idx);
                goto out;
        }

        clear_slot_flag(zram, index, ZRAM_IDLE);
        if (test_slot_flag(zram, index, ZRAM_HUGE))
                atomic64_dec(&zram->stats.huge_pages);
        atomic64_sub(get_slot_size(zram, index), &zram->stats.compr_data_size);
        zs_free(zram->mem_pool, get_slot_handle(zram, index));
        set_slot_handle(zram, index, req->blk_idx);
        set_slot_flag(zram, index, ZRAM_WB);

out:
        slot_unlock(zram, index);
        return 0;
}

static void zram_writeback_endio(struct bio *bio)
{
        struct zram_wb_req *req = container_of(bio, struct zram_wb_req, bio);
        struct zram_wb_ctl *wb_ctl = bio->bi_private;
        unsigned long flags;

        spin_lock_irqsave(&wb_ctl->done_lock, flags);
        list_add(&req->entry, &wb_ctl->done_reqs);
        spin_unlock_irqrestore(&wb_ctl->done_lock, flags);

        wake_up(&wb_ctl->done_wait);
}

static void zram_submit_wb_request(struct zram *zram,
                                   struct zram_wb_ctl *wb_ctl,
                                   struct zram_wb_req *req)
{
        /*
         * wb_limit (if enabled) should be adjusted before submission,
         * so that we don't over-submit.
         */
        zram_account_writeback_submit(zram);
        atomic_inc(&wb_ctl->num_inflight);
        req->bio.bi_private = wb_ctl;
        submit_bio(&req->bio);
}

static int zram_complete_done_reqs(struct zram *zram,
                                   struct zram_wb_ctl *wb_ctl)
{
        struct zram_wb_req *req;
        unsigned long flags;
        int ret = 0, err;

        while (atomic_read(&wb_ctl->num_inflight) > 0) {
                spin_lock_irqsave(&wb_ctl->done_lock, flags);
                req = list_first_entry_or_null(&wb_ctl->done_reqs,
                                               struct zram_wb_req, entry);
                if (req)
                        list_del(&req->entry);
                spin_unlock_irqrestore(&wb_ctl->done_lock, flags);

                /* ->num_inflight > 0 doesn't mean we have done requests */
                if (!req)
                        break;

                err = zram_writeback_complete(zram, req);
                if (err)
                        ret = err;

                atomic_dec(&wb_ctl->num_inflight);
                release_pp_slot(zram, req->pps);
                req->pps = NULL;

                list_add(&req->entry, &wb_ctl->idle_reqs);
        }

        return ret;
}

static struct zram_wb_req *zram_select_idle_req(struct zram_wb_ctl *wb_ctl)
{
        struct zram_wb_req *req;

        req = list_first_entry_or_null(&wb_ctl->idle_reqs,
                                       struct zram_wb_req, entry);
        if (req)
                list_del(&req->entry);
        return req;
}

static int zram_writeback_slots(struct zram *zram,
                                struct zram_pp_ctl *ctl,
                                struct zram_wb_ctl *wb_ctl)
{
        unsigned long blk_idx = INVALID_BDEV_BLOCK;
        struct zram_wb_req *req = NULL;
        struct zram_pp_slot *pps;
        int ret = 0, err = 0;
        u32 index = 0;

        while ((pps = select_pp_slot(ctl))) {
                if (zram->wb_limit_enable && !zram->bd_wb_limit) {
                        ret = -EIO;
                        break;
                }

                while (!req) {
                        req = zram_select_idle_req(wb_ctl);
                        if (req)
                                break;

                        wait_event(wb_ctl->done_wait,
                                   !list_empty(&wb_ctl->done_reqs));

                        err = zram_complete_done_reqs(zram, wb_ctl);
                        /*
                         * BIO errors are not fatal, we continue and simply
                         * attempt to writeback the remaining objects (pages).
                         * At the same time we need to signal user-space that
                         * some writes (at least one, but also could be all of
                         * them) were not successful and we do so by returning
                         * the most recent BIO error.
                         */
                        if (err)
                                ret = err;
                }

                if (blk_idx == INVALID_BDEV_BLOCK) {
                        blk_idx = zram_reserve_bdev_block(zram);
                        if (blk_idx == INVALID_BDEV_BLOCK) {
                                ret = -ENOSPC;
                                break;
                        }
                }

                index = pps->index;
                slot_lock(zram, index);
                /*
                 * scan_slots() sets ZRAM_PP_SLOT and releases slot lock, so
                 * slots can change in the meantime. If slots are accessed or
                 * freed they lose ZRAM_PP_SLOT flag and hence we don't
                 * post-process them.
                 */
                if (!test_slot_flag(zram, index, ZRAM_PP_SLOT))
                        goto next;
                if (zram->compressed_wb)
                        err = read_from_zspool_raw(zram, req->page, index);
                else
                        err = read_from_zspool(zram, req->page, index);
                if (err)
                        goto next;
                slot_unlock(zram, index);

                /*
                 * From now on pp-slot is owned by the req, remove it from
                 * its pp bucket.
                 */
                list_del_init(&pps->entry);

                req->blk_idx = blk_idx;
                req->pps = pps;
                bio_init(&req->bio, zram->bdev, &req->bio_vec, 1, REQ_OP_WRITE);
                req->bio.bi_iter.bi_sector = req->blk_idx * (PAGE_SIZE >> 9);
                req->bio.bi_end_io = zram_writeback_endio;
                __bio_add_page(&req->bio, req->page, PAGE_SIZE, 0);

                zram_submit_wb_request(zram, wb_ctl, req);
                blk_idx = INVALID_BDEV_BLOCK;
                req = NULL;
                cond_resched();
                continue;

next:
                slot_unlock(zram, index);
                release_pp_slot(zram, pps);
        }

        /*
         * Selected idle req, but never submitted it due to some error or
         * wb limit.
         */
        if (req)
                release_wb_req(req);

        while (atomic_read(&wb_ctl->num_inflight) > 0) {
                wait_event(wb_ctl->done_wait, !list_empty(&wb_ctl->done_reqs));
                err = zram_complete_done_reqs(zram, wb_ctl);
                if (err)
                        ret = err;
        }

        return ret;
}

#define PAGE_WRITEBACK                  0
#define HUGE_WRITEBACK                  (1 << 0)
#define IDLE_WRITEBACK                  (1 << 1)
#define INCOMPRESSIBLE_WRITEBACK        (1 << 2)

static int parse_page_index(char *val, unsigned long nr_pages,
                            unsigned long *lo, unsigned long *hi)
{
        int ret;

        ret = kstrtoul(val, 10, lo);
        if (ret)
                return ret;
        if (*lo >= nr_pages)
                return -ERANGE;
        *hi = *lo + 1;
        return 0;
}

static int parse_page_indexes(char *val, unsigned long nr_pages,
                              unsigned long *lo, unsigned long *hi)
{
        char *delim;
        int ret;

        delim = strchr(val, '-');
        if (!delim)
                return -EINVAL;

        *delim = 0x00;
        ret = kstrtoul(val, 10, lo);
        if (ret)
                return ret;
        if (*lo >= nr_pages)
                return -ERANGE;

        ret = kstrtoul(delim + 1, 10, hi);
        if (ret)
                return ret;
        if (*hi >= nr_pages || *lo > *hi)
                return -ERANGE;
        *hi += 1;
        return 0;
}

static int parse_mode(char *val, u32 *mode)
{
        *mode = 0;

        if (!strcmp(val, "idle"))
                *mode = IDLE_WRITEBACK;
        if (!strcmp(val, "huge"))
                *mode = HUGE_WRITEBACK;
        if (!strcmp(val, "huge_idle"))
                *mode = IDLE_WRITEBACK | HUGE_WRITEBACK;
        if (!strcmp(val, "incompressible"))
                *mode = INCOMPRESSIBLE_WRITEBACK;

        if (*mode == 0)
                return -EINVAL;
        return 0;
}

static int scan_slots_for_writeback(struct zram *zram, u32 mode,
                                    unsigned long lo, unsigned long hi,
                                    struct zram_pp_ctl *ctl)
{
        u32 index = lo;

        while (index < hi) {
                bool ok = true;

                slot_lock(zram, index);
                if (!slot_allocated(zram, index))
                        goto next;

                if (test_slot_flag(zram, index, ZRAM_WB) ||
                    test_slot_flag(zram, index, ZRAM_SAME))
                        goto next;

                if (mode & IDLE_WRITEBACK &&
                    !test_slot_flag(zram, index, ZRAM_IDLE))
                        goto next;
                if (mode & HUGE_WRITEBACK &&
                    !test_slot_flag(zram, index, ZRAM_HUGE))
                        goto next;
                if (mode & INCOMPRESSIBLE_WRITEBACK &&
                    !test_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE))
                        goto next;

                ok = place_pp_slot(zram, ctl, index);
next:
                slot_unlock(zram, index);
                if (!ok)
                        break;
                index++;
        }

        return 0;
}

static ssize_t writeback_store(struct device *dev,
                               struct device_attribute *attr,
                               const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        u64 nr_pages = zram->disksize >> PAGE_SHIFT;
        unsigned long lo = 0, hi = nr_pages;
        struct zram_pp_ctl *pp_ctl = NULL;
        struct zram_wb_ctl *wb_ctl = NULL;
        char *args, *param, *val;
        ssize_t ret = len;
        int err, mode = 0;

        guard(rwsem_write)(&zram->dev_lock);
        if (!init_done(zram))
                return -EINVAL;

        if (!zram->backing_dev)
                return -ENODEV;

        pp_ctl = init_pp_ctl();
        if (!pp_ctl)
                return -ENOMEM;

        wb_ctl = init_wb_ctl(zram);
        if (!wb_ctl) {
                ret = -ENOMEM;
                goto out;
        }

        args = skip_spaces(buf);
        while (*args) {
                args = next_arg(args, &param, &val);

                /*
                 * Workaround to support the old writeback interface.
                 *
                 * The old writeback interface has a minor inconsistency and
                 * requires key=value only for page_index parameter, while the
                 * writeback mode is a valueless parameter.
                 *
                 * This is not the case anymore and now all parameters are
                 * required to have values, however, we need to support the
                 * legacy writeback interface format so we check if we can
                 * recognize a valueless parameter as the (legacy) writeback
                 * mode.
                 */
                if (!val || !*val) {
                        err = parse_mode(param, &mode);
                        if (err) {
                                ret = err;
                                goto out;
                        }

                        scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
                        break;
                }

                if (!strcmp(param, "type")) {
                        err = parse_mode(val, &mode);
                        if (err) {
                                ret = err;
                                goto out;
                        }

                        scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
                        break;
                }

                if (!strcmp(param, "page_index")) {
                        err = parse_page_index(val, nr_pages, &lo, &hi);
                        if (err) {
                                ret = err;
                                goto out;
                        }

                        scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
                        continue;
                }

                if (!strcmp(param, "page_indexes")) {
                        err = parse_page_indexes(val, nr_pages, &lo, &hi);
                        if (err) {
                                ret = err;
                                goto out;
                        }

                        scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
                        continue;
                }
        }

        err = zram_writeback_slots(zram, pp_ctl, wb_ctl);
        if (err)
                ret = err;

out:
        release_pp_ctl(zram, pp_ctl);
        release_wb_ctl(wb_ctl);

        return ret;
}

static int decompress_bdev_page(struct zram *zram, struct page *page, u32 index)
{
        struct zcomp_strm *zstrm;
        unsigned int size;
        int ret, prio;
        void *src;

        slot_lock(zram, index);
        /* Since slot was unlocked we need to make sure it's still ZRAM_WB */
        if (!test_slot_flag(zram, index, ZRAM_WB)) {
                slot_unlock(zram, index);
                /* We read some stale data, zero it out */
                memset_page(page, 0, 0, PAGE_SIZE);
                return -EIO;
        }

        if (test_slot_flag(zram, index, ZRAM_HUGE)) {
                slot_unlock(zram, index);
                return 0;
        }

        size = get_slot_size(zram, index);
        prio = get_slot_comp_priority(zram, index);

        zstrm = zcomp_stream_get(zram->comps[prio]);
        src = kmap_local_page(page);
        ret = zcomp_decompress(zram->comps[prio], zstrm, src, size,
                               zstrm->local_copy);
        if (!ret)
                copy_page(src, zstrm->local_copy);
        kunmap_local(src);
        zcomp_stream_put(zstrm);
        slot_unlock(zram, index);

        return ret;
}

static void zram_deferred_decompress(struct work_struct *w)
{
        struct zram_rb_req *req = container_of(w, struct zram_rb_req, work);
        struct page *page = bio_first_page_all(req->bio);
        struct zram *zram = req->zram;
        u32 index = req->index;
        int ret;

        ret = decompress_bdev_page(zram, page, index);
        if (ret)
                req->parent->bi_status = BLK_STS_IOERR;

        /* Decrement parent's ->remaining */
        bio_endio(req->parent);
        bio_put(req->bio);
        kfree(req);
}

static void zram_async_read_endio(struct bio *bio)
{
        struct zram_rb_req *req = bio->bi_private;
        struct zram *zram = req->zram;

        if (bio->bi_status) {
                req->parent->bi_status = bio->bi_status;
                bio_endio(req->parent);
                bio_put(bio);
                kfree(req);
                return;
        }

        /*
         * NOTE: zram_async_read_endio() is not exactly right place for this.
         * Ideally, we need to do it after ZRAM_WB check, but this requires
         * us to use wq path even on systems that don't enable compressed
         * writeback, because we cannot take slot-lock in the current context.
         *
         * Keep the existing behavior for now.
         */
        if (zram->compressed_wb == false) {
                /* No decompression needed, complete the parent IO */
                bio_endio(req->parent);
                bio_put(bio);
                kfree(req);
                return;
        }

        /*
         * zram decompression is sleepable, so we need to deffer it to
         * a preemptible context.
         */
        INIT_WORK(&req->work, zram_deferred_decompress);
        queue_work(system_highpri_wq, &req->work);
}

static void read_from_bdev_async(struct zram *zram, struct page *page,
                                 u32 index, unsigned long blk_idx,
                                 struct bio *parent)
{
        struct zram_rb_req *req;
        struct bio *bio;

        req = kmalloc_obj(*req, GFP_NOIO);
        if (!req)
                return;

        bio = bio_alloc(zram->bdev, 1, parent->bi_opf, GFP_NOIO);
        if (!bio) {
                kfree(req);
                return;
        }

        req->zram = zram;
        req->index = index;
        req->blk_idx = blk_idx;
        req->bio = bio;
        req->parent = parent;

        bio->bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
        bio->bi_private = req;
        bio->bi_end_io = zram_async_read_endio;

        __bio_add_page(bio, page, PAGE_SIZE, 0);
        bio_inc_remaining(parent);
        submit_bio(bio);
}

static void zram_sync_read(struct work_struct *w)
{
        struct zram_rb_req *req = container_of(w, struct zram_rb_req, work);
        struct bio_vec bv;
        struct bio bio;

        bio_init(&bio, req->zram->bdev, &bv, 1, REQ_OP_READ);
        bio.bi_iter.bi_sector = req->blk_idx * (PAGE_SIZE >> 9);
        __bio_add_page(&bio, req->page, PAGE_SIZE, 0);
        req->error = submit_bio_wait(&bio);
}

/*
 * Block layer want one ->submit_bio to be active at a time, so if we use
 * chained IO with parent IO in same context, it's a deadlock. To avoid that,
 * use a worker thread context.
 */
static int read_from_bdev_sync(struct zram *zram, struct page *page, u32 index,
                               unsigned long blk_idx)
{
        struct zram_rb_req req;

        req.page = page;
        req.zram = zram;
        req.blk_idx = blk_idx;

        INIT_WORK_ONSTACK(&req.work, zram_sync_read);
        queue_work(system_dfl_wq, &req.work);
        flush_work(&req.work);
        destroy_work_on_stack(&req.work);

        if (req.error || zram->compressed_wb == false)
                return req.error;

        return decompress_bdev_page(zram, page, index);
}

static int read_from_bdev(struct zram *zram, struct page *page, u32 index,
                          unsigned long blk_idx, struct bio *parent)
{
        atomic64_inc(&zram->stats.bd_reads);
        if (!parent) {
                if (WARN_ON_ONCE(!IS_ENABLED(ZRAM_PARTIAL_IO)))
                        return -EIO;
                return read_from_bdev_sync(zram, page, index, blk_idx);
        }
        read_from_bdev_async(zram, page, index, blk_idx, parent);
        return 0;
}
#else
static inline void reset_bdev(struct zram *zram) {};
static int read_from_bdev(struct zram *zram, struct page *page, u32 index,
                          unsigned long blk_idx, struct bio *parent)
{
        return -EIO;
}

static void zram_release_bdev_block(struct zram *zram, unsigned long blk_idx)
{
}
#endif

#ifdef CONFIG_ZRAM_MEMORY_TRACKING

static struct dentry *zram_debugfs_root;

static void zram_debugfs_create(void)
{
        zram_debugfs_root = debugfs_create_dir("zram", NULL);
}

static void zram_debugfs_destroy(void)
{
        debugfs_remove_recursive(zram_debugfs_root);
}

static ssize_t read_block_state(struct file *file, char __user *buf,
                                size_t count, loff_t *ppos)
{
        char *kbuf;
        ssize_t index, written = 0;
        struct zram *zram = file->private_data;
        unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;

        kbuf = kvmalloc(count, GFP_KERNEL);
        if (!kbuf)
                return -ENOMEM;

        guard(rwsem_read)(&zram->dev_lock);
        if (!init_done(zram)) {
                kvfree(kbuf);
                return -EINVAL;
        }

        for (index = *ppos; index < nr_pages; index++) {
                int copied;

                slot_lock(zram, index);
                if (!slot_allocated(zram, index))
                        goto next;

                copied = snprintf(kbuf + written, count,
                        "%12zd %12u.%06d %c%c%c%c%c%c\n",
                        index, zram->table[index].attr.ac_time, 0,
                        test_slot_flag(zram, index, ZRAM_SAME) ? 's' : '.',
                        test_slot_flag(zram, index, ZRAM_WB) ? 'w' : '.',
                        test_slot_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
                        test_slot_flag(zram, index, ZRAM_IDLE) ? 'i' : '.',
                        get_slot_comp_priority(zram, index) ? 'r' : '.',
                        test_slot_flag(zram, index,
                                       ZRAM_INCOMPRESSIBLE) ? 'n' : '.');

                if (count <= copied) {
                        slot_unlock(zram, index);
                        break;
                }
                written += copied;
                count -= copied;
next:
                slot_unlock(zram, index);
                *ppos += 1;
        }

        if (copy_to_user(buf, kbuf, written))
                written = -EFAULT;
        kvfree(kbuf);

        return written;
}

static const struct file_operations proc_zram_block_state_op = {
        .open = simple_open,
        .read = read_block_state,
        .llseek = default_llseek,
};

static void zram_debugfs_register(struct zram *zram)
{
        if (!zram_debugfs_root)
                return;

        zram->debugfs_dir = debugfs_create_dir(zram->disk->disk_name,
                                                zram_debugfs_root);
        debugfs_create_file("block_state", 0400, zram->debugfs_dir,
                                zram, &proc_zram_block_state_op);
}

static void zram_debugfs_unregister(struct zram *zram)
{
        debugfs_remove_recursive(zram->debugfs_dir);
}
#else
static void zram_debugfs_create(void) {};
static void zram_debugfs_destroy(void) {};
static void zram_debugfs_register(struct zram *zram) {};
static void zram_debugfs_unregister(struct zram *zram) {};
#endif

static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg)
{
        /* Do not free statically defined compression algorithms */
        if (zram->comp_algs[prio] != default_compressor)
                kfree(zram->comp_algs[prio]);

        zram->comp_algs[prio] = alg;
}

static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)
{
        char *compressor;
        size_t sz;

        sz = strlen(buf);
        if (sz >= ZRAM_MAX_ALGO_NAME_SZ)
                return -E2BIG;

        compressor = kstrdup(buf, GFP_KERNEL);
        if (!compressor)
                return -ENOMEM;

        /* ignore trailing newline */
        if (sz > 0 && compressor[sz - 1] == '\n')
                compressor[sz - 1] = 0x00;

        if (!zcomp_available_algorithm(compressor)) {
                kfree(compressor);
                return -EINVAL;
        }

        guard(rwsem_write)(&zram->dev_lock);
        if (init_done(zram)) {
                kfree(compressor);
                pr_info("Can't change algorithm for initialized device\n");
                return -EBUSY;
        }

        comp_algorithm_set(zram, prio, compressor);
        return 0;
}

static void comp_params_reset(struct zram *zram, u32 prio)
{
        struct zcomp_params *params = &zram->params[prio];

        vfree(params->dict);
        params->level = ZCOMP_PARAM_NOT_SET;
        params->deflate.winbits = ZCOMP_PARAM_NOT_SET;
        params->dict_sz = 0;
        params->dict = NULL;
}

static int comp_params_store(struct zram *zram, u32 prio, s32 level,
                             const char *dict_path,
                             struct deflate_params *deflate_params)
{
        ssize_t sz = 0;

        comp_params_reset(zram, prio);

        if (dict_path) {
                sz = kernel_read_file_from_path(dict_path, 0,
                                                &zram->params[prio].dict,
                                                INT_MAX,
                                                NULL,
                                                READING_POLICY);
                if (sz < 0)
                        return -EINVAL;
        }

        zram->params[prio].dict_sz = sz;
        zram->params[prio].level = level;
        zram->params[prio].deflate.winbits = deflate_params->winbits;
        return 0;
}

static ssize_t algorithm_params_store(struct device *dev,
                                      struct device_attribute *attr,
                                      const char *buf,
                                      size_t len)
{
        s32 prio = ZRAM_PRIMARY_COMP, level = ZCOMP_PARAM_NOT_SET;
        char *args, *param, *val, *algo = NULL, *dict_path = NULL;
        struct deflate_params deflate_params;
        struct zram *zram = dev_to_zram(dev);
        int ret;

        deflate_params.winbits = ZCOMP_PARAM_NOT_SET;

        args = skip_spaces(buf);
        while (*args) {
                args = next_arg(args, &param, &val);

                if (!val || !*val)
                        return -EINVAL;

                if (!strcmp(param, "priority")) {
                        ret = kstrtoint(val, 10, &prio);
                        if (ret)
                                return ret;
                        continue;
                }

                if (!strcmp(param, "level")) {
                        ret = kstrtoint(val, 10, &level);
                        if (ret)
                                return ret;
                        continue;
                }

                if (!strcmp(param, "algo")) {
                        algo = val;
                        continue;
                }

                if (!strcmp(param, "dict")) {
                        dict_path = val;
                        continue;
                }

                if (!strcmp(param, "deflate.winbits")) {
                        ret = kstrtoint(val, 10, &deflate_params.winbits);
                        if (ret)
                                return ret;
                        continue;
                }
        }

        /* Lookup priority by algorithm name */
        if (algo) {
                s32 p;

                prio = -EINVAL;
                for (p = ZRAM_PRIMARY_COMP; p < ZRAM_MAX_COMPS; p++) {
                        if (!zram->comp_algs[p])
                                continue;

                        if (!strcmp(zram->comp_algs[p], algo)) {
                                prio = p;
                                break;
                        }
                }
        }

        if (prio < ZRAM_PRIMARY_COMP || prio >= ZRAM_MAX_COMPS)
                return -EINVAL;

        ret = comp_params_store(zram, prio, level, dict_path, &deflate_params);
        return ret ? ret : len;
}

static ssize_t comp_algorithm_show(struct device *dev,
                                   struct device_attribute *attr,
                                   char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        ssize_t sz;

        guard(rwsem_read)(&zram->dev_lock);
        sz = zcomp_available_show(zram->comp_algs[ZRAM_PRIMARY_COMP], buf, 0);
        return sz;
}

static ssize_t comp_algorithm_store(struct device *dev,
                                    struct device_attribute *attr,
                                    const char *buf,
                                    size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        int ret;

        ret = __comp_algorithm_store(zram, ZRAM_PRIMARY_COMP, buf);
        return ret ? ret : len;
}

#ifdef CONFIG_ZRAM_MULTI_COMP
static ssize_t recomp_algorithm_show(struct device *dev,
                                     struct device_attribute *attr,
                                     char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        ssize_t sz = 0;
        u32 prio;

        guard(rwsem_read)(&zram->dev_lock);
        for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
                if (!zram->comp_algs[prio])
                        continue;

                sz += sysfs_emit_at(buf, sz, "#%d: ", prio);
                sz += zcomp_available_show(zram->comp_algs[prio], buf, sz);
        }
        return sz;
}

static ssize_t recomp_algorithm_store(struct device *dev,
                                      struct device_attribute *attr,
                                      const char *buf,
                                      size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        int prio = ZRAM_SECONDARY_COMP;
        char *args, *param, *val;
        char *alg = NULL;
        int ret;

        args = skip_spaces(buf);
        while (*args) {
                args = next_arg(args, &param, &val);

                if (!val || !*val)
                        return -EINVAL;

                if (!strcmp(param, "algo")) {
                        alg = val;
                        continue;
                }

                if (!strcmp(param, "priority")) {
                        ret = kstrtoint(val, 10, &prio);
                        if (ret)
                                return ret;
                        continue;
                }
        }

        if (!alg)
                return -EINVAL;

        if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS)
                return -EINVAL;

        ret = __comp_algorithm_store(zram, prio, alg);
        return ret ? ret : len;
}
#endif

static ssize_t compact_store(struct device *dev, struct device_attribute *attr,
                             const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);

        guard(rwsem_read)(&zram->dev_lock);
        if (!init_done(zram))
                return -EINVAL;

        zs_compact(zram->mem_pool);

        return len;
}

static ssize_t io_stat_show(struct device *dev, struct device_attribute *attr,
                            char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        ssize_t ret;

        guard(rwsem_read)(&zram->dev_lock);
        ret = sysfs_emit(buf,
                        "%8llu %8llu 0 %8llu\n",
                        (u64)atomic64_read(&zram->stats.failed_reads),
                        (u64)atomic64_read(&zram->stats.failed_writes),
                        (u64)atomic64_read(&zram->stats.notify_free));

        return ret;
}

static ssize_t mm_stat_show(struct device *dev, struct device_attribute *attr,
                            char *buf)
{
        struct zram *zram = dev_to_zram(dev);
        struct zs_pool_stats pool_stats;
        u64 orig_size, mem_used = 0;
        long max_used;
        ssize_t ret;

        memset(&pool_stats, 0x00, sizeof(struct zs_pool_stats));

        guard(rwsem_read)(&zram->dev_lock);
        if (init_done(zram)) {
                mem_used = zs_get_total_pages(zram->mem_pool);
                zs_pool_stats(zram->mem_pool, &pool_stats);
        }

        orig_size = atomic64_read(&zram->stats.pages_stored);
        max_used = atomic_long_read(&zram->stats.max_used_pages);

        ret = sysfs_emit(buf,
                        "%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu %8llu\n",
                        orig_size << PAGE_SHIFT,
                        (u64)atomic64_read(&zram->stats.compr_data_size),
                        mem_used << PAGE_SHIFT,
                        zram->limit_pages << PAGE_SHIFT,
                        max_used << PAGE_SHIFT,
                        (u64)atomic64_read(&zram->stats.same_pages),
                        atomic_long_read(&pool_stats.pages_compacted),
                        (u64)atomic64_read(&zram->stats.huge_pages),
                        (u64)atomic64_read(&zram->stats.huge_pages_since));

        return ret;
}

static ssize_t debug_stat_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
{
        int version = 1;
        struct zram *zram = dev_to_zram(dev);
        ssize_t ret;

        guard(rwsem_read)(&zram->dev_lock);
        ret = sysfs_emit(buf,
                        "version: %d\n0 %8llu\n",
                        version,
                        (u64)atomic64_read(&zram->stats.miss_free));

        return ret;
}

static void zram_meta_free(struct zram *zram, u64 disksize)
{
        size_t num_pages = disksize >> PAGE_SHIFT;
        size_t index;

        if (!zram->table)
                return;

        /* Free all pages that are still in this zram device */
        for (index = 0; index < num_pages; index++)
                slot_free(zram, index);

        zs_destroy_pool(zram->mem_pool);
        vfree(zram->table);
        zram->table = NULL;
}

static bool zram_meta_alloc(struct zram *zram, u64 disksize)
{
        size_t num_pages, index;

        num_pages = disksize >> PAGE_SHIFT;
        zram->table = vzalloc(array_size(num_pages, sizeof(*zram->table)));
        if (!zram->table)
                return false;

        zram->mem_pool = zs_create_pool(zram->disk->disk_name);
        if (!zram->mem_pool) {
                vfree(zram->table);
                zram->table = NULL;
                return false;
        }

        if (!huge_class_size)
                huge_class_size = zs_huge_class_size(zram->mem_pool);

        for (index = 0; index < num_pages; index++)
                slot_lock_init(zram, index);

        return true;
}

static void slot_free(struct zram *zram, u32 index)
{
        unsigned long handle;

#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
        zram->table[index].attr.ac_time = 0;
#endif

        clear_slot_flag(zram, index, ZRAM_IDLE);
        clear_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE);
        clear_slot_flag(zram, index, ZRAM_PP_SLOT);
        set_slot_comp_priority(zram, index, 0);

        if (test_slot_flag(zram, index, ZRAM_HUGE)) {
                /*
                 * Writeback completion decrements ->huge_pages but keeps
                 * ZRAM_HUGE flag for deferred decompression path.
                 */
                if (!test_slot_flag(zram, index, ZRAM_WB))
                        atomic64_dec(&zram->stats.huge_pages);
                clear_slot_flag(zram, index, ZRAM_HUGE);
        }

        if (test_slot_flag(zram, index, ZRAM_WB)) {
                clear_slot_flag(zram, index, ZRAM_WB);
                zram_release_bdev_block(zram, get_slot_handle(zram, index));
                goto out;
        }

        /*
         * No memory is allocated for same element filled pages.
         * Simply clear same page flag.
         */
        if (test_slot_flag(zram, index, ZRAM_SAME)) {
                clear_slot_flag(zram, index, ZRAM_SAME);
                atomic64_dec(&zram->stats.same_pages);
                goto out;
        }

        handle = get_slot_handle(zram, index);
        if (!handle)
                return;

        zs_free(zram->mem_pool, handle);

        atomic64_sub(get_slot_size(zram, index),
                     &zram->stats.compr_data_size);
out:
        atomic64_dec(&zram->stats.pages_stored);
        set_slot_handle(zram, index, 0);
        set_slot_size(zram, index, 0);
}

static int read_same_filled_page(struct zram *zram, struct page *page,
                                 u32 index)
{
        void *mem;

        mem = kmap_local_page(page);
        zram_fill_page(mem, PAGE_SIZE, get_slot_handle(zram, index));
        kunmap_local(mem);
        return 0;
}

static int read_incompressible_page(struct zram *zram, struct page *page,
                                    u32 index)
{
        unsigned long handle;
        void *src, *dst;

        handle = get_slot_handle(zram, index);
        src = zs_obj_read_begin(zram->mem_pool, handle, PAGE_SIZE, NULL);
        dst = kmap_local_page(page);
        copy_page(dst, src);
        kunmap_local(dst);
        zs_obj_read_end(zram->mem_pool, handle, PAGE_SIZE, src);

        return 0;
}

static int read_compressed_page(struct zram *zram, struct page *page, u32 index)
{
        struct zcomp_strm *zstrm;
        unsigned long handle;
        unsigned int size;
        void *src, *dst;
        int ret, prio;

        handle = get_slot_handle(zram, index);
        size = get_slot_size(zram, index);
        prio = get_slot_comp_priority(zram, index);

        zstrm = zcomp_stream_get(zram->comps[prio]);
        src = zs_obj_read_begin(zram->mem_pool, handle, size,
                                zstrm->local_copy);
        dst = kmap_local_page(page);
        ret = zcomp_decompress(zram->comps[prio], zstrm, src, size, dst);
        kunmap_local(dst);
        zs_obj_read_end(zram->mem_pool, handle, size, src);
        zcomp_stream_put(zstrm);

        return ret;
}

#if defined CONFIG_ZRAM_WRITEBACK
static int read_from_zspool_raw(struct zram *zram, struct page *page, u32 index)
{
        struct zcomp_strm *zstrm;
        unsigned long handle;
        unsigned int size;
        void *src;

        handle = get_slot_handle(zram, index);
        size = get_slot_size(zram, index);

        /*
         * We need to get stream just for ->local_copy buffer, in
         * case if object spans two physical pages. No decompression
         * takes place here, as we read raw compressed data.
         */
        zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
        src = zs_obj_read_begin(zram->mem_pool, handle, size,
                                zstrm->local_copy);
        memcpy_to_page(page, 0, src, size);
        zs_obj_read_end(zram->mem_pool, handle, size, src);
        zcomp_stream_put(zstrm);

        return 0;
}
#endif

/*
 * Reads (decompresses if needed) a page from zspool (zsmalloc).
 * Corresponding ZRAM slot should be locked.
 */
static int read_from_zspool(struct zram *zram, struct page *page, u32 index)
{
        if (test_slot_flag(zram, index, ZRAM_SAME) ||
            !get_slot_handle(zram, index))
                return read_same_filled_page(zram, page, index);

        if (!test_slot_flag(zram, index, ZRAM_HUGE))
                return read_compressed_page(zram, page, index);
        else
                return read_incompressible_page(zram, page, index);
}

static int zram_read_page(struct zram *zram, struct page *page, u32 index,
                          struct bio *parent)
{
        int ret;

        slot_lock(zram, index);
        if (!test_slot_flag(zram, index, ZRAM_WB)) {
                /* Slot should be locked through out the function call */
                ret = read_from_zspool(zram, page, index);
                slot_unlock(zram, index);
        } else {
                unsigned long blk_idx = get_slot_handle(zram, index);

                /*
                 * The slot should be unlocked before reading from the backing
                 * device.
                 */
                slot_unlock(zram, index);
                ret = read_from_bdev(zram, page, index, blk_idx, parent);
        }

        /* Should NEVER happen. Return bio error if it does. */
        if (WARN_ON(ret < 0))
                pr_err("Decompression failed! err=%d, page=%u\n", ret, index);

        return ret;
}

/*
 * Use a temporary buffer to decompress the page, as the decompressor
 * always expects a full page for the output.
 */
static int zram_bvec_read_partial(struct zram *zram, struct bio_vec *bvec,
                                  u32 index, int offset)
{
        struct page *page = alloc_page(GFP_NOIO);
        int ret;

        if (!page)
                return -ENOMEM;
        ret = zram_read_page(zram, page, index, NULL);
        if (likely(!ret))
                memcpy_to_bvec(bvec, page_address(page) + offset);
        __free_page(page);
        return ret;
}

static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
                          u32 index, int offset, struct bio *bio)
{
        if (is_partial_io(bvec))
                return zram_bvec_read_partial(zram, bvec, index, offset);
        return zram_read_page(zram, bvec->bv_page, index, bio);
}

static int write_same_filled_page(struct zram *zram, unsigned long fill,
                                  u32 index)
{
        slot_lock(zram, index);
        slot_free(zram, index);
        set_slot_flag(zram, index, ZRAM_SAME);
        set_slot_handle(zram, index, fill);
        slot_unlock(zram, index);

        atomic64_inc(&zram->stats.same_pages);
        atomic64_inc(&zram->stats.pages_stored);

        return 0;
}

static int write_incompressible_page(struct zram *zram, struct page *page,
                                     u32 index)
{
        unsigned long handle;
        void *src;

        /*
         * This function is called from preemptible context so we don't need
         * to do optimistic and fallback to pessimistic handle allocation,
         * like we do for compressible pages.
         */
        handle = zs_malloc(zram->mem_pool, PAGE_SIZE,
                           GFP_NOIO | __GFP_NOWARN |
                           __GFP_HIGHMEM | __GFP_MOVABLE, page_to_nid(page));
        if (IS_ERR_VALUE(handle))
                return PTR_ERR((void *)handle);

        if (!zram_can_store_page(zram)) {
                zs_free(zram->mem_pool, handle);
                return -ENOMEM;
        }

        src = kmap_local_page(page);
        zs_obj_write(zram->mem_pool, handle, src, PAGE_SIZE);
        kunmap_local(src);

        slot_lock(zram, index);
        slot_free(zram, index);
        set_slot_flag(zram, index, ZRAM_HUGE);
        set_slot_handle(zram, index, handle);
        set_slot_size(zram, index, PAGE_SIZE);
        slot_unlock(zram, index);

        atomic64_add(PAGE_SIZE, &zram->stats.compr_data_size);
        atomic64_inc(&zram->stats.huge_pages);
        atomic64_inc(&zram->stats.huge_pages_since);
        atomic64_inc(&zram->stats.pages_stored);

        return 0;
}

static int zram_write_page(struct zram *zram, struct page *page, u32 index)
{
        int ret = 0;
        unsigned long handle;
        unsigned int comp_len;
        void *mem;
        struct zcomp_strm *zstrm;
        unsigned long element;
        bool same_filled;

        mem = kmap_local_page(page);
        same_filled = page_same_filled(mem, &element);
        kunmap_local(mem);
        if (same_filled)
                return write_same_filled_page(zram, element, index);

        zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
        mem = kmap_local_page(page);
        ret = zcomp_compress(zram->comps[ZRAM_PRIMARY_COMP], zstrm,
                             mem, &comp_len);
        kunmap_local(mem);

        if (unlikely(ret)) {
                zcomp_stream_put(zstrm);
                pr_err("Compression failed! err=%d\n", ret);
                return ret;
        }

        if (comp_len >= huge_class_size) {
                zcomp_stream_put(zstrm);
                return write_incompressible_page(zram, page, index);
        }

        handle = zs_malloc(zram->mem_pool, comp_len,
                           GFP_NOIO | __GFP_NOWARN |
                           __GFP_HIGHMEM | __GFP_MOVABLE, page_to_nid(page));
        if (IS_ERR_VALUE(handle)) {
                zcomp_stream_put(zstrm);
                return PTR_ERR((void *)handle);
        }

        if (!zram_can_store_page(zram)) {
                zcomp_stream_put(zstrm);
                zs_free(zram->mem_pool, handle);
                return -ENOMEM;
        }

        zs_obj_write(zram->mem_pool, handle, zstrm->buffer, comp_len);
        zcomp_stream_put(zstrm);

        slot_lock(zram, index);
        slot_free(zram, index);
        set_slot_handle(zram, index, handle);
        set_slot_size(zram, index, comp_len);
        slot_unlock(zram, index);

        /* Update stats */
        atomic64_inc(&zram->stats.pages_stored);
        atomic64_add(comp_len, &zram->stats.compr_data_size);

        return ret;
}

/*
 * This is a partial IO. Read the full page before writing the changes.
 */
static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
                                   u32 index, int offset, struct bio *bio)
{
        struct page *page = alloc_page(GFP_NOIO);
        int ret;

        if (!page)
                return -ENOMEM;

        ret = zram_read_page(zram, page, index, bio);
        if (!ret) {
                memcpy_from_bvec(page_address(page) + offset, bvec);
                ret = zram_write_page(zram, page, index);
        }
        __free_page(page);
        return ret;
}

static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
                           u32 index, int offset, struct bio *bio)
{
        if (is_partial_io(bvec))
                return zram_bvec_write_partial(zram, bvec, index, offset, bio);
        return zram_write_page(zram, bvec->bv_page, index);
}

#ifdef CONFIG_ZRAM_MULTI_COMP
#define RECOMPRESS_IDLE         (1 << 0)
#define RECOMPRESS_HUGE         (1 << 1)

static int scan_slots_for_recompress(struct zram *zram, u32 mode, u32 prio_max,
                                     struct zram_pp_ctl *ctl)
{
        unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
        unsigned long index;

        for (index = 0; index < nr_pages; index++) {
                bool ok = true;

                slot_lock(zram, index);
                if (!slot_allocated(zram, index))
                        goto next;

                if (mode & RECOMPRESS_IDLE &&
                    !test_slot_flag(zram, index, ZRAM_IDLE))
                        goto next;

                if (mode & RECOMPRESS_HUGE &&
                    !test_slot_flag(zram, index, ZRAM_HUGE))
                        goto next;

                if (test_slot_flag(zram, index, ZRAM_WB) ||
                    test_slot_flag(zram, index, ZRAM_SAME) ||
                    test_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE))
                        goto next;

                /* Already compressed with same of higher priority */
                if (get_slot_comp_priority(zram, index) + 1 >= prio_max)
                        goto next;

                ok = place_pp_slot(zram, ctl, index);
next:
                slot_unlock(zram, index);
                if (!ok)
                        break;
        }

        return 0;
}

/*
 * This function will decompress (unless it's ZRAM_HUGE) the page and then
 * attempt to compress it using provided compression algorithm priority
 * (which is potentially more effective).
 *
 * Corresponding ZRAM slot should be locked.
 */
static int recompress_slot(struct zram *zram, u32 index, struct page *page,
                           u64 *num_recomp_pages, u32 threshold, u32 prio,
                           u32 prio_max)
{
        struct zcomp_strm *zstrm = NULL;
        unsigned long handle_old;
        unsigned long handle_new;
        unsigned int comp_len_old;
        unsigned int comp_len_new;
        unsigned int class_index_old;
        unsigned int class_index_new;
        void *src;
        int ret = 0;

        handle_old = get_slot_handle(zram, index);
        if (!handle_old)
                return -EINVAL;

        comp_len_old = get_slot_size(zram, index);
        /*
         * Do not recompress objects that are already "small enough".
         */
        if (comp_len_old < threshold)
                return 0;

        ret = read_from_zspool(zram, page, index);
        if (ret)
                return ret;

        /*
         * We touched this entry so mark it as non-IDLE. This makes sure that
         * we don't preserve IDLE flag and don't incorrectly pick this entry
         * for different post-processing type (e.g. writeback).
         */
        clear_slot_flag(zram, index, ZRAM_IDLE);

        class_index_old = zs_lookup_class_index(zram->mem_pool, comp_len_old);

        prio = max(prio, get_slot_comp_priority(zram, index) + 1);
        /*
         * Recompression slots scan should not select slots that are
         * already compressed with a higher priority algorithm, but
         * just in case
         */
        if (prio >= prio_max)
                return 0;

        /*
         * Iterate the secondary comp algorithms list (in order of priority)
         * and try to recompress the page.
         */
        for (; prio < prio_max; prio++) {
                if (!zram->comps[prio])
                        continue;

                zstrm = zcomp_stream_get(zram->comps[prio]);
                src = kmap_local_page(page);
                ret = zcomp_compress(zram->comps[prio], zstrm,
                                     src, &comp_len_new);
                kunmap_local(src);

                if (ret) {
                        zcomp_stream_put(zstrm);
                        zstrm = NULL;
                        break;
                }

                class_index_new = zs_lookup_class_index(zram->mem_pool,
                                                        comp_len_new);

                /* Continue until we make progress */
                if (class_index_new >= class_index_old ||
                    (threshold && comp_len_new >= threshold)) {
                        zcomp_stream_put(zstrm);
                        zstrm = NULL;
                        continue;
                }

                /* Recompression was successful so break out */
                break;
        }

        /*
         * Decrement the limit (if set) on pages we can recompress, even
         * when current recompression was unsuccessful or did not compress
         * the page below the threshold, because we still spent resources
         * on it.
         */
        if (*num_recomp_pages)
                *num_recomp_pages -= 1;

        /* Compression error */
        if (ret)
                return ret;

        if (!zstrm) {
                /*
                 * Secondary algorithms failed to re-compress the page
                 * in a way that would save memory.
                 *
                 * Mark the object incompressible if the max-priority
                 * algorithm couldn't re-compress it.
                 */
                if (prio < zram->num_active_comps)
                        return 0;
                set_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE);
                return 0;
        }

        /*
         * We are holding per-CPU stream mutex and entry lock so better
         * avoid direct reclaim.  Allocation error is not fatal since
         * we still have the old object in the mem_pool.
         *
         * XXX: technically, the node we really want here is the node that
         * holds the original compressed data. But that would require us to
         * modify zsmalloc API to return this information. For now, we will
         * make do with the node of the page allocated for recompression.
         */
        handle_new = zs_malloc(zram->mem_pool, comp_len_new,
                               GFP_NOIO | __GFP_NOWARN |
                               __GFP_HIGHMEM | __GFP_MOVABLE,
                               page_to_nid(page));
        if (IS_ERR_VALUE(handle_new)) {
                zcomp_stream_put(zstrm);
                return PTR_ERR((void *)handle_new);
        }

        zs_obj_write(zram->mem_pool, handle_new, zstrm->buffer, comp_len_new);
        zcomp_stream_put(zstrm);

        slot_free(zram, index);
        set_slot_handle(zram, index, handle_new);
        set_slot_size(zram, index, comp_len_new);
        set_slot_comp_priority(zram, index, prio);

        atomic64_add(comp_len_new, &zram->stats.compr_data_size);
        atomic64_inc(&zram->stats.pages_stored);

        return 0;
}

static ssize_t recompress_store(struct device *dev,
                                struct device_attribute *attr,
                                const char *buf, size_t len)
{
        struct zram *zram = dev_to_zram(dev);
        char *args, *param, *val, *algo = NULL;
        u64 num_recomp_pages = ULLONG_MAX;
        struct zram_pp_ctl *ctl = NULL;
        struct zram_pp_slot *pps;
        u32 mode = 0, threshold = 0;
        u32 prio, prio_max;
        struct page *page = NULL;
        ssize_t ret;

        prio = ZRAM_SECONDARY_COMP;
        prio_max = zram->num_active_comps;

        args = skip_spaces(buf);
        while (*args) {
                args = next_arg(args, &param, &val);

                if (!val || !*val)
                        return -EINVAL;

                if (!strcmp(param, "type")) {
                        if (!strcmp(val, "idle"))
                                mode = RECOMPRESS_IDLE;
                        if (!strcmp(val, "huge"))
                                mode = RECOMPRESS_HUGE;
                        if (!strcmp(val, "huge_idle"))
                                mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
                        continue;
                }

                if (!strcmp(param, "max_pages")) {
                        /*
                         * Limit the number of entries (pages) we attempt to
                         * recompress.
                         */
                        ret = kstrtoull(val, 10, &num_recomp_pages);
                        if (ret)
                                return ret;
                        continue;
                }

                if (!strcmp(param, "threshold")) {
                        /*
                         * We will re-compress only idle objects equal or
                         * greater in size than watermark.
                         */
                        ret = kstrtouint(val, 10, &threshold);
                        if (ret)
                                return ret;
                        continue;
                }

                if (!strcmp(param, "algo")) {
                        algo = val;
                        continue;
                }

                if (!strcmp(param, "priority")) {
                        ret = kstrtouint(val, 10, &prio);
                        if (ret)
                                return ret;

                        if (prio == ZRAM_PRIMARY_COMP)
                                prio = ZRAM_SECONDARY_COMP;

                        prio_max = prio + 1;
                        continue;
                }
        }

        if (threshold >= huge_class_size)
                return -EINVAL;

        guard(rwsem_write)(&zram->dev_lock);
        if (!init_done(zram))
                return -EINVAL;

        if (algo) {
                bool found = false;

                for (; prio < ZRAM_MAX_COMPS; prio++) {
                        if (!zram->comp_algs[prio])
                                continue;

                        if (!strcmp(zram->comp_algs[prio], algo)) {
                                prio_max = prio + 1;
                                found = true;
                                break;
                        }
                }

                if (!found) {
                        ret = -EINVAL;
                        goto out;
                }
        }

        prio_max = min(prio_max, (u32)zram->num_active_comps);
        if (prio >= prio_max) {
                ret = -EINVAL;
                goto out;
        }

        page = alloc_page(GFP_KERNEL);
        if (!page) {
                ret = -ENOMEM;
                goto out;
        }

        ctl = init_pp_ctl();
        if (!ctl) {
                ret = -ENOMEM;
                goto out;
        }

        scan_slots_for_recompress(zram, mode, prio_max, ctl);

        ret = len;
        while ((pps = select_pp_slot(ctl))) {
                int err = 0;

                if (!num_recomp_pages)
                        break;

                slot_lock(zram, pps->index);
                if (!test_slot_flag(zram, pps->index, ZRAM_PP_SLOT))
                        goto next;

                err = recompress_slot(zram, pps->index, page,
                                      &num_recomp_pages, threshold,
                                      prio, prio_max);
next:
                slot_unlock(zram, pps->index);
                release_pp_slot(zram, pps);

                if (err) {
                        ret = err;
                        break;
                }

                cond_resched();
        }

out:
        if (page)
                __free_page(page);
        release_pp_ctl(zram, ctl);
        return ret;
}
#endif

static void zram_bio_discard(struct zram *zram, struct bio *bio)
{
        size_t n = bio->bi_iter.bi_size;
        u32 index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
        u32 offset = (bio->bi_iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
                        SECTOR_SHIFT;

        /*
         * zram manages data in physical block size units. Because logical block
         * size isn't identical with physical block size on some arch, we
         * could get a discard request pointing to a specific offset within a
         * certain physical block.  Although we can handle this request by
         * reading that physiclal block and decompressing and partially zeroing
         * and re-compressing and then re-storing it, this isn't reasonable
         * because our intent with a discard request is to save memory.  So
         * skipping this logical block is appropriate here.
         */
        if (offset) {
                if (n <= (PAGE_SIZE - offset))
                        return;

                n -= (PAGE_SIZE - offset);
                index++;
        }

        while (n >= PAGE_SIZE) {
                slot_lock(zram, index);
                slot_free(zram, index);
                slot_unlock(zram, index);
                atomic64_inc(&zram->stats.notify_free);
                index++;
                n -= PAGE_SIZE;
        }

        bio_endio(bio);
}

static void zram_bio_read(struct zram *zram, struct bio *bio)
{
        unsigned long start_time = bio_start_io_acct(bio);
        struct bvec_iter iter = bio->bi_iter;

        do {
                u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
                u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
                                SECTOR_SHIFT;
                struct bio_vec bv = bio_iter_iovec(bio, iter);

                bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);

                if (zram_bvec_read(zram, &bv, index, offset, bio) < 0) {
                        atomic64_inc(&zram->stats.failed_reads);
                        bio->bi_status = BLK_STS_IOERR;
                        break;
                }
                flush_dcache_page(bv.bv_page);

                slot_lock(zram, index);
                mark_slot_accessed(zram, index);
                slot_unlock(zram, index);

                bio_advance_iter_single(bio, &iter, bv.bv_len);
        } while (iter.bi_size);

        bio_end_io_acct(bio, start_time);
        bio_endio(bio);
}

static void zram_bio_write(struct zram *zram, struct bio *bio)
{
        unsigned long start_time = bio_start_io_acct(bio);
        struct bvec_iter iter = bio->bi_iter;

        do {
                u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
                u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
                                SECTOR_SHIFT;
                struct bio_vec bv = bio_iter_iovec(bio, iter);

                bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);

                if (zram_bvec_write(zram, &bv, index, offset, bio) < 0) {
                        atomic64_inc(&zram->stats.failed_writes);
                        bio->bi_status = BLK_STS_IOERR;
                        break;
                }

                slot_lock(zram, index);
                mark_slot_accessed(zram, index);
                slot_unlock(zram, index);

                bio_advance_iter_single(bio, &iter, bv.bv_len);
        } while (iter.bi_size);

        bio_end_io_acct(bio, start_time);
        bio_endio(bio);
}

/*
 * Handler function for all zram I/O requests.
 */
static void zram_submit_bio(struct bio *bio)
{
        struct zram *zram = bio->bi_bdev->bd_disk->private_data;

        switch (bio_op(bio)) {
        case REQ_OP_READ:
                zram_bio_read(zram, bio);
                break;
        case REQ_OP_WRITE:
                zram_bio_write(zram, bio);
                break;
        case REQ_OP_DISCARD:
        case REQ_OP_WRITE_ZEROES:
                zram_bio_discard(zram, bio);
                break;
        default:
                WARN_ON_ONCE(1);
                bio_endio(bio);
        }
}

static void zram_slot_free_notify(struct block_device *bdev,
                                unsigned long index)
{
        struct zram *zram;

        zram = bdev->bd_disk->private_data;

        atomic64_inc(&zram->stats.notify_free);
        if (!slot_trylock(zram, index)) {
                atomic64_inc(&zram->stats.miss_free);
                return;
        }

        slot_free(zram, index);
        slot_unlock(zram, index);
}

static void zram_comp_params_reset(struct zram *zram)
{
        u32 prio;

        for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
                comp_params_reset(zram, prio);
        }
}

static void zram_destroy_comps(struct zram *zram)
{
        u32 prio;

        for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
                struct zcomp *comp = zram->comps[prio];

                zram->comps[prio] = NULL;
                if (!comp)
                        continue;
                zcomp_destroy(comp);
                zram->num_active_comps--;
        }

        for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
                /* Do not free statically defined compression algorithms */
                if (zram->comp_algs[prio] != default_compressor)
                        kfree(zram->comp_algs[prio]);
                zram->comp_algs[prio] = NULL;
        }

        zram_comp_params_reset(zram);
}

static void zram_reset_device(struct zram *zram)
{
        guard(rwsem_write)(&zram->dev_lock);

        zram->limit_pages = 0;

        set_capacity_and_notify(zram->disk, 0);
        part_stat_set_all(zram->disk->part0, 0);

        /* I/O operation under all of CPU are done so let's free */
        zram_meta_free(zram, zram->disksize);
        zram->disksize = 0;
        zram_destroy_comps(zram);
        memset(&zram->stats, 0, sizeof(zram->stats));
        reset_bdev(zram);

        comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
}

static ssize_t disksize_store(struct device *dev, struct device_attribute *attr,
                              const char *buf, size_t len)
{
        u64 disksize;
        struct zcomp *comp;
        struct zram *zram = dev_to_zram(dev);
        int err;
        u32 prio;

        disksize = memparse(buf, NULL);
        if (!disksize)
                return -EINVAL;

        guard(rwsem_write)(&zram->dev_lock);
        if (init_done(zram)) {
                pr_info("Cannot change disksize for initialized device\n");
                return -EBUSY;
        }

        disksize = PAGE_ALIGN(disksize);
        if (!zram_meta_alloc(zram, disksize))
                return -ENOMEM;

        for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
                if (!zram->comp_algs[prio])
                        continue;

                comp = zcomp_create(zram->comp_algs[prio],
                                    &zram->params[prio]);
                if (IS_ERR(comp)) {
                        pr_err("Cannot initialise %s compressing backend\n",
                               zram->comp_algs[prio]);
                        err = PTR_ERR(comp);
                        goto out_free_comps;
                }

                zram->comps[prio] = comp;
                zram->num_active_comps++;
        }
        zram->disksize = disksize;
        set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);

        return len;

out_free_comps:
        zram_destroy_comps(zram);
        zram_meta_free(zram, disksize);
        return err;
}

static ssize_t reset_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        int ret;
        unsigned short do_reset;
        struct zram *zram;
        struct gendisk *disk;

        ret = kstrtou16(buf, 10, &do_reset);
        if (ret)
                return ret;

        if (!do_reset)
                return -EINVAL;

        zram = dev_to_zram(dev);
        disk = zram->disk;

        mutex_lock(&disk->open_mutex);
        /* Do not reset an active device or claimed device */
        if (disk_openers(disk) || zram->claim) {
                mutex_unlock(&disk->open_mutex);
                return -EBUSY;
        }

        /* From now on, anyone can't open /dev/zram[0-9] */
        zram->claim = true;
        mutex_unlock(&disk->open_mutex);

        /* Make sure all the pending I/O are finished */
        sync_blockdev(disk->part0);
        zram_reset_device(zram);

        mutex_lock(&disk->open_mutex);
        zram->claim = false;
        mutex_unlock(&disk->open_mutex);

        return len;
}

static int zram_open(struct gendisk *disk, blk_mode_t mode)
{
        struct zram *zram = disk->private_data;

        WARN_ON(!mutex_is_locked(&disk->open_mutex));

        /* zram was claimed to reset so open request fails */
        if (zram->claim)
                return -EBUSY;
        return 0;
}

static const struct block_device_operations zram_devops = {
        .open = zram_open,
        .submit_bio = zram_submit_bio,
        .swap_slot_free_notify = zram_slot_free_notify,
        .owner = THIS_MODULE
};

static DEVICE_ATTR_RO(io_stat);
static DEVICE_ATTR_RO(mm_stat);
static DEVICE_ATTR_RO(debug_stat);
static DEVICE_ATTR_WO(compact);
static DEVICE_ATTR_RW(disksize);
static DEVICE_ATTR_RO(initstate);
static DEVICE_ATTR_WO(reset);
static DEVICE_ATTR_WO(mem_limit);
static DEVICE_ATTR_WO(mem_used_max);
static DEVICE_ATTR_WO(idle);
static DEVICE_ATTR_RW(comp_algorithm);
#ifdef CONFIG_ZRAM_WRITEBACK
static DEVICE_ATTR_RO(bd_stat);
static DEVICE_ATTR_RW(backing_dev);
static DEVICE_ATTR_WO(writeback);
static DEVICE_ATTR_RW(writeback_limit);
static DEVICE_ATTR_RW(writeback_limit_enable);
static DEVICE_ATTR_RW(writeback_batch_size);
static DEVICE_ATTR_RW(compressed_writeback);
#endif
#ifdef CONFIG_ZRAM_MULTI_COMP
static DEVICE_ATTR_RW(recomp_algorithm);
static DEVICE_ATTR_WO(recompress);
#endif
static DEVICE_ATTR_WO(algorithm_params);

static struct attribute *zram_disk_attrs[] = {
        &dev_attr_disksize.attr,
        &dev_attr_initstate.attr,
        &dev_attr_reset.attr,
        &dev_attr_compact.attr,
        &dev_attr_mem_limit.attr,
        &dev_attr_mem_used_max.attr,
        &dev_attr_idle.attr,
        &dev_attr_comp_algorithm.attr,
#ifdef CONFIG_ZRAM_WRITEBACK
        &dev_attr_bd_stat.attr,
        &dev_attr_backing_dev.attr,
        &dev_attr_writeback.attr,
        &dev_attr_writeback_limit.attr,
        &dev_attr_writeback_limit_enable.attr,
        &dev_attr_writeback_batch_size.attr,
        &dev_attr_compressed_writeback.attr,
#endif
        &dev_attr_io_stat.attr,
        &dev_attr_mm_stat.attr,
        &dev_attr_debug_stat.attr,
#ifdef CONFIG_ZRAM_MULTI_COMP
        &dev_attr_recomp_algorithm.attr,
        &dev_attr_recompress.attr,
#endif
        &dev_attr_algorithm_params.attr,
        NULL,
};

ATTRIBUTE_GROUPS(zram_disk);

/*
 * Allocate and initialize new zram device. the function returns
 * '>= 0' device_id upon success, and negative value otherwise.
 */
static int zram_add(void)
{
        struct queue_limits lim = {
                .logical_block_size             = ZRAM_LOGICAL_BLOCK_SIZE,
                /*
                 * To ensure that we always get PAGE_SIZE aligned and
                 * n*PAGE_SIZED sized I/O requests.
                 */
                .physical_block_size            = PAGE_SIZE,
                .io_min                         = PAGE_SIZE,
                .io_opt                         = PAGE_SIZE,
                .max_hw_discard_sectors         = UINT_MAX,
                /*
                 * zram_bio_discard() will clear all logical blocks if logical
                 * block size is identical with physical block size(PAGE_SIZE).
                 * But if it is different, we will skip discarding some parts of
                 * logical blocks in the part of the request range which isn't
                 * aligned to physical block size.  So we can't ensure that all
                 * discarded logical blocks are zeroed.
                 */
#if ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE
                .max_write_zeroes_sectors       = UINT_MAX,
#endif
                .features                       = BLK_FEAT_STABLE_WRITES |
                                                  BLK_FEAT_SYNCHRONOUS,
        };
        struct zram *zram;
        int ret, device_id;

        zram = kzalloc_obj(struct zram);
        if (!zram)
                return -ENOMEM;

        ret = idr_alloc(&zram_index_idr, zram, 0, 0, GFP_KERNEL);
        if (ret < 0)
                goto out_free_dev;
        device_id = ret;

        init_rwsem(&zram->dev_lock);
#ifdef CONFIG_ZRAM_WRITEBACK
        zram->wb_batch_size = 32;
        zram->compressed_wb = false;
#endif

        /* gendisk structure */
        zram->disk = blk_alloc_disk(&lim, NUMA_NO_NODE);
        if (IS_ERR(zram->disk)) {
                pr_err("Error allocating disk structure for device %d\n",
                        device_id);
                ret = PTR_ERR(zram->disk);
                goto out_free_idr;
        }

        zram->disk->major = zram_major;
        zram->disk->first_minor = device_id;
        zram->disk->minors = 1;
        zram->disk->flags |= GENHD_FL_NO_PART;
        zram->disk->fops = &zram_devops;
        zram->disk->private_data = zram;
        snprintf(zram->disk->disk_name, 16, "zram%d", device_id);
        zram_comp_params_reset(zram);
        comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);

        /* Actual capacity set using sysfs (/sys/block/zram<id>/disksize */
        set_capacity(zram->disk, 0);
        ret = device_add_disk(NULL, zram->disk, zram_disk_groups);
        if (ret)
                goto out_cleanup_disk;

        zram_debugfs_register(zram);
        pr_info("Added device: %s\n", zram->disk->disk_name);
        return device_id;

out_cleanup_disk:
        put_disk(zram->disk);
out_free_idr:
        idr_remove(&zram_index_idr, device_id);
out_free_dev:
        kfree(zram);
        return ret;
}

static int zram_remove(struct zram *zram)
{
        bool claimed;

        mutex_lock(&zram->disk->open_mutex);
        if (disk_openers(zram->disk)) {
                mutex_unlock(&zram->disk->open_mutex);
                return -EBUSY;
        }

        claimed = zram->claim;
        if (!claimed)
                zram->claim = true;
        mutex_unlock(&zram->disk->open_mutex);

        zram_debugfs_unregister(zram);

        if (claimed) {
                /*
                 * If we were claimed by reset_store(), del_gendisk() will
                 * wait until reset_store() is done, so nothing need to do.
                 */
                ;
        } else {
                /* Make sure all the pending I/O are finished */
                sync_blockdev(zram->disk->part0);
                zram_reset_device(zram);
        }

        pr_info("Removed device: %s\n", zram->disk->disk_name);

        del_gendisk(zram->disk);

        /* del_gendisk drains pending reset_store */
        WARN_ON_ONCE(claimed && zram->claim);

        /*
         * disksize_store() may be called in between zram_reset_device()
         * and del_gendisk(), so run the last reset to avoid leaking
         * anything allocated with disksize_store()
         */
        zram_reset_device(zram);

        put_disk(zram->disk);
        kfree(zram);
        return 0;
}

/* zram-control sysfs attributes */

/*
 * NOTE: hot_add attribute is not the usual read-only sysfs attribute. In a
 * sense that reading from this file does alter the state of your system -- it
 * creates a new un-initialized zram device and returns back this device's
 * device_id (or an error code if it fails to create a new device).
 */
static ssize_t hot_add_show(const struct class *class,
                        const struct class_attribute *attr,
                        char *buf)
{
        int ret;

        mutex_lock(&zram_index_mutex);
        ret = zram_add();
        mutex_unlock(&zram_index_mutex);

        if (ret < 0)
                return ret;
        return sysfs_emit(buf, "%d\n", ret);
}
/* This attribute must be set to 0400, so CLASS_ATTR_RO() can not be used */
static struct class_attribute class_attr_hot_add =
        __ATTR(hot_add, 0400, hot_add_show, NULL);

static ssize_t hot_remove_store(const struct class *class,
                        const struct class_attribute *attr,
                        const char *buf,
                        size_t count)
{
        struct zram *zram;
        int ret, dev_id;

        /* dev_id is gendisk->first_minor, which is `int' */
        ret = kstrtoint(buf, 10, &dev_id);
        if (ret)
                return ret;
        if (dev_id < 0)
                return -EINVAL;

        mutex_lock(&zram_index_mutex);

        zram = idr_find(&zram_index_idr, dev_id);
        if (zram) {
                ret = zram_remove(zram);
                if (!ret)
                        idr_remove(&zram_index_idr, dev_id);
        } else {
                ret = -ENODEV;
        }

        mutex_unlock(&zram_index_mutex);
        return ret ? ret : count;
}
static CLASS_ATTR_WO(hot_remove);

static struct attribute *zram_control_class_attrs[] = {
        &class_attr_hot_add.attr,
        &class_attr_hot_remove.attr,
        NULL,
};
ATTRIBUTE_GROUPS(zram_control_class);

static struct class zram_control_class = {
        .name           = "zram-control",
        .class_groups   = zram_control_class_groups,
};

static int zram_remove_cb(int id, void *ptr, void *data)
{
        WARN_ON_ONCE(zram_remove(ptr));
        return 0;
}

static void destroy_devices(void)
{
        class_unregister(&zram_control_class);
        idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);
        zram_debugfs_destroy();
        idr_destroy(&zram_index_idr);
        unregister_blkdev(zram_major, "zram");
        cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
}

static int __init zram_init(void)
{
        struct zram_table_entry zram_te;
        int ret;

        BUILD_BUG_ON(__NR_ZRAM_PAGEFLAGS > sizeof(zram_te.attr.flags) * 8);

        ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare",
                                      zcomp_cpu_up_prepare, zcomp_cpu_dead);
        if (ret < 0)
                return ret;

        ret = class_register(&zram_control_class);
        if (ret) {
                pr_err("Unable to register zram-control class\n");
                cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
                return ret;
        }

        zram_debugfs_create();
        zram_major = register_blkdev(0, "zram");
        if (zram_major <= 0) {
                pr_err("Unable to get major number\n");
                class_unregister(&zram_control_class);
                cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
                return -EBUSY;
        }

        while (num_devices != 0) {
                mutex_lock(&zram_index_mutex);
                ret = zram_add();
                mutex_unlock(&zram_index_mutex);
                if (ret < 0)
                        goto out_error;
                num_devices--;
        }

        return 0;

out_error:
        destroy_devices();
        return ret;
}

static void __exit zram_exit(void)
{
        destroy_devices();
}

module_init(zram_init);
module_exit(zram_exit);

module_param(num_devices, uint, 0);
MODULE_PARM_DESC(num_devices, "Number of pre-created zram devices");

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
MODULE_DESCRIPTION("Compressed RAM Block Device");