Linux 4.19-rc7

[linux-2.6/btrfs-unstable.git] / drivers / block / zram / zram_drv.c

/*
 * 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 KMSG_COMPONENT "zram"
#define pr_fmt(fmt) KMSG_COMPONENT ": " 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/genhd.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 "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 = "lzo";

/* 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 void zram_free_page(struct zram *zram, size_t index);

static void zram_slot_lock(struct zram *zram, u32 index)
{
        bit_spin_lock(ZRAM_LOCK, &zram->table[index].value);
}

static void zram_slot_unlock(struct zram *zram, u32 index)
{
        bit_spin_unlock(ZRAM_LOCK, &zram->table[index].value);
}

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

static inline bool zram_allocated(struct zram *zram, u32 index)
{

        return (zram->table[index].value >> (ZRAM_FLAG_SHIFT + 1)) ||
                                        zram->table[index].handle;
}

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

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

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

/* flag operations require table entry bit_spin_lock() being held */
static bool zram_test_flag(struct zram *zram, u32 index,
                        enum zram_pageflags flag)
{
        return zram->table[index].value & BIT(flag);
}

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

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

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

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

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

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

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

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

/*
 * Check if request is within bounds and aligned on zram logical blocks.
 */
static inline bool valid_io_request(struct zram *zram,
                sector_t start, unsigned int size)
{
        u64 end, bound;

        /* unaligned request */
        if (unlikely(start & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)))
                return false;
        if (unlikely(size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))
                return false;

        end = start + (size >> SECTOR_SHIFT);
        bound = zram->disksize >> SECTOR_SHIFT;
        /* out of range range */
        if (unlikely(start >= bound || end > bound || start > end))
                return false;

        /* I/O request is valid */
        return true;
}

static void update_position(u32 *index, int *offset, struct bio_vec *bvec)
{
        *index  += (*offset + bvec->bv_len) / PAGE_SIZE;
        *offset = (*offset + bvec->bv_len) % PAGE_SIZE;
}

static inline void update_used_max(struct zram *zram,
                                        const unsigned long pages)
{
        unsigned long old_max, cur_max;

        old_max = atomic_long_read(&zram->stats.max_used_pages);

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

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 int pos;
        unsigned long *page;
        unsigned long val;

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

        for (pos = 1; pos < PAGE_SIZE / sizeof(*page); 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);

        down_read(&zram->init_lock);
        val = init_done(zram);
        up_read(&zram->init_lock);

        return scnprintf(buf, PAGE_SIZE, "%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 scnprintf(buf, PAGE_SIZE, "%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;

        down_write(&zram->init_lock);
        zram->limit_pages = PAGE_ALIGN(limit) >> PAGE_SHIFT;
        up_write(&zram->init_lock);

        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;

        down_read(&zram->init_lock);
        if (init_done(zram)) {
                atomic_long_set(&zram->stats.max_used_pages,
                                zs_get_total_pages(zram->mem_pool));
        }
        up_read(&zram->init_lock);

        return len;
}

#ifdef CONFIG_ZRAM_WRITEBACK
static bool zram_wb_enabled(struct zram *zram)
{
        return zram->backing_dev;
}

static void reset_bdev(struct zram *zram)
{
        struct block_device *bdev;

        if (!zram_wb_enabled(zram))
                return;

        bdev = zram->bdev;
        if (zram->old_block_size)
                set_blocksize(bdev, zram->old_block_size);
        blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
        /* hope filp_close flush all of IO */
        filp_close(zram->backing_dev, NULL);
        zram->backing_dev = NULL;
        zram->old_block_size = 0;
        zram->bdev = NULL;
        zram->disk->queue->backing_dev_info->capabilities |=
                                BDI_CAP_SYNCHRONOUS_IO;
        kvfree(zram->bitmap);
        zram->bitmap = NULL;
}

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

        down_read(&zram->init_lock);
        if (!zram_wb_enabled(zram)) {
                memcpy(buf, "none\n", 5);
                up_read(&zram->init_lock);
                return 5;
        }

        p = file_path(file, buf, PAGE_SIZE - 1);
        if (IS_ERR(p)) {
                ret = PTR_ERR(p);
                goto out;
        }

        ret = strlen(p);
        memmove(buf, p, ret);
        buf[ret++] = '\n';
out:
        up_read(&zram->init_lock);
        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;
        struct address_space *mapping;
        unsigned int bitmap_sz, old_block_size = 0;
        unsigned long nr_pages, *bitmap = NULL;
        struct block_device *bdev = NULL;
        int err;
        struct zram *zram = dev_to_zram(dev);

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

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

        strlcpy(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, 0);
        if (IS_ERR(backing_dev)) {
                err = PTR_ERR(backing_dev);
                backing_dev = NULL;
                goto out;
        }

        mapping = backing_dev->f_mapping;
        inode = mapping->host;

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

        bdev = bdgrab(I_BDEV(inode));
        err = blkdev_get(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL, zram);
        if (err < 0)
                goto out;

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

        old_block_size = block_size(bdev);
        err = set_blocksize(bdev, PAGE_SIZE);
        if (err)
                goto out;

        reset_bdev(zram);
        spin_lock_init(&zram->bitmap_lock);

        zram->old_block_size = old_block_size;
        zram->bdev = bdev;
        zram->backing_dev = backing_dev;
        zram->bitmap = bitmap;
        zram->nr_pages = nr_pages;
        /*
         * With writeback feature, zram does asynchronous IO so it's no longer
         * synchronous device so let's remove synchronous io flag. Othewise,
         * upper layer(e.g., swap) could wait IO completion rather than
         * (submit and return), which will cause system sluggish.
         * Furthermore, when the IO function returns(e.g., swap_readpage),
         * upper layer expects IO was done so it could deallocate the page
         * freely but in fact, IO is going on so finally could cause
         * use-after-free when the IO is really done.
         */
        zram->disk->queue->backing_dev_info->capabilities &=
                        ~BDI_CAP_SYNCHRONOUS_IO;
        up_write(&zram->init_lock);

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

        return len;
out:
        if (bitmap)
                kvfree(bitmap);

        if (bdev)
                blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);

        if (backing_dev)
                filp_close(backing_dev, NULL);

        up_write(&zram->init_lock);

        kfree(file_name);

        return err;
}

static unsigned long get_entry_bdev(struct zram *zram)
{
        unsigned long entry;

        spin_lock(&zram->bitmap_lock);
        /* skip 0 bit to confuse zram.handle = 0 */
        entry = find_next_zero_bit(zram->bitmap, zram->nr_pages, 1);
        if (entry == zram->nr_pages) {
                spin_unlock(&zram->bitmap_lock);
                return 0;
        }

        set_bit(entry, zram->bitmap);
        spin_unlock(&zram->bitmap_lock);

        return entry;
}

static void put_entry_bdev(struct zram *zram, unsigned long entry)
{
        int was_set;

        spin_lock(&zram->bitmap_lock);
        was_set = test_and_clear_bit(entry, zram->bitmap);
        spin_unlock(&zram->bitmap_lock);
        WARN_ON_ONCE(!was_set);
}

static void zram_page_end_io(struct bio *bio)
{
        struct page *page = bio_first_page_all(bio);

        page_endio(page, op_is_write(bio_op(bio)),
                        blk_status_to_errno(bio->bi_status));
        bio_put(bio);
}

/*
 * Returns 1 if the submission is successful.
 */
static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
                        unsigned long entry, struct bio *parent)
{
        struct bio *bio;

        bio = bio_alloc(GFP_ATOMIC, 1);
        if (!bio)
                return -ENOMEM;

        bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
        bio_set_dev(bio, zram->bdev);
        if (!bio_add_page(bio, bvec->bv_page, bvec->bv_len, bvec->bv_offset)) {
                bio_put(bio);
                return -EIO;
        }

        if (!parent) {
                bio->bi_opf = REQ_OP_READ;
                bio->bi_end_io = zram_page_end_io;
        } else {
                bio->bi_opf = parent->bi_opf;
                bio_chain(bio, parent);
        }

        submit_bio(bio);
        return 1;
}

struct zram_work {
        struct work_struct work;
        struct zram *zram;
        unsigned long entry;
        struct bio *bio;
};

#if PAGE_SIZE != 4096
static void zram_sync_read(struct work_struct *work)
{
        struct bio_vec bvec;
        struct zram_work *zw = container_of(work, struct zram_work, work);
        struct zram *zram = zw->zram;
        unsigned long entry = zw->entry;
        struct bio *bio = zw->bio;

        read_from_bdev_async(zram, &bvec, entry, bio);
}

/*
 * Block layer want one ->make_request_fn to be active at a time
 * so if we use chained IO with parent IO in same context,
 * it's a deadlock. To avoid, it, it uses worker thread context.
 */
static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
                                unsigned long entry, struct bio *bio)
{
        struct zram_work work;

        work.zram = zram;
        work.entry = entry;
        work.bio = bio;

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

        return 1;
}
#else
static int read_from_bdev_sync(struct zram *zram, struct bio_vec *bvec,
                                unsigned long entry, struct bio *bio)
{
        WARN_ON(1);
        return -EIO;
}
#endif

static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
                        unsigned long entry, struct bio *parent, bool sync)
{
        if (sync)
                return read_from_bdev_sync(zram, bvec, entry, parent);
        else
                return read_from_bdev_async(zram, bvec, entry, parent);
}

static int write_to_bdev(struct zram *zram, struct bio_vec *bvec,
                                        u32 index, struct bio *parent,
                                        unsigned long *pentry)
{
        struct bio *bio;
        unsigned long entry;

        bio = bio_alloc(GFP_ATOMIC, 1);
        if (!bio)
                return -ENOMEM;

        entry = get_entry_bdev(zram);
        if (!entry) {
                bio_put(bio);
                return -ENOSPC;
        }

        bio->bi_iter.bi_sector = entry * (PAGE_SIZE >> 9);
        bio_set_dev(bio, zram->bdev);
        if (!bio_add_page(bio, bvec->bv_page, bvec->bv_len,
                                        bvec->bv_offset)) {
                bio_put(bio);
                put_entry_bdev(zram, entry);
                return -EIO;
        }

        if (!parent) {
                bio->bi_opf = REQ_OP_WRITE | REQ_SYNC;
                bio->bi_end_io = zram_page_end_io;
        } else {
                bio->bi_opf = parent->bi_opf;
                bio_chain(bio, parent);
        }

        submit_bio(bio);
        *pentry = entry;

        return 0;
}

static void zram_wb_clear(struct zram *zram, u32 index)
{
        unsigned long entry;

        zram_clear_flag(zram, index, ZRAM_WB);
        entry = zram_get_element(zram, index);
        zram_set_element(zram, index, 0);
        put_entry_bdev(zram, entry);
}

#else
static bool zram_wb_enabled(struct zram *zram) { return false; }
static inline void reset_bdev(struct zram *zram) {};
static int write_to_bdev(struct zram *zram, struct bio_vec *bvec,
                                        u32 index, struct bio *parent,
                                        unsigned long *pentry)

{
        return -EIO;
}

static int read_from_bdev(struct zram *zram, struct bio_vec *bvec,
                        unsigned long entry, struct bio *parent, bool sync)
{
        return -EIO;
}
static void zram_wb_clear(struct zram *zram, u32 index) {}
#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 void zram_accessed(struct zram *zram, u32 index)
{
        zram->table[index].ac_time = ktime_get_boottime();
}

static void zram_reset_access(struct zram *zram, u32 index)
{
        zram->table[index].ac_time = 0;
}

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;
        struct timespec64 ts;

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

        down_read(&zram->init_lock);
        if (!init_done(zram)) {
                up_read(&zram->init_lock);
                kvfree(kbuf);
                return -EINVAL;
        }

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

                zram_slot_lock(zram, index);
                if (!zram_allocated(zram, index))
                        goto next;

                ts = ktime_to_timespec64(zram->table[index].ac_time);
                copied = snprintf(kbuf + written, count,
                        "%12zd %12lld.%06lu %c%c%c\n",
                        index, (s64)ts.tv_sec,
                        ts.tv_nsec / NSEC_PER_USEC,
                        zram_test_flag(zram, index, ZRAM_SAME) ? 's' : '.',
                        zram_test_flag(zram, index, ZRAM_WB) ? 'w' : '.',
                        zram_test_flag(zram, index, ZRAM_HUGE) ? 'h' : '.');

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

        up_read(&zram->init_lock);
        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_accessed(struct zram *zram, u32 index) {};
static void zram_reset_access(struct zram *zram, u32 index) {};
static void zram_debugfs_register(struct zram *zram) {};
static void zram_debugfs_unregister(struct zram *zram) {};
#endif

/*
 * We switched to per-cpu streams and this attr is not needed anymore.
 * However, we will keep it around for some time, because:
 * a) we may revert per-cpu streams in the future
 * b) it's visible to user space and we need to follow our 2 years
 *    retirement rule; but we already have a number of 'soon to be
 *    altered' attrs, so max_comp_streams need to wait for the next
 *    layoff cycle.
 */
static ssize_t max_comp_streams_show(struct device *dev,
                struct device_attribute *attr, char *buf)
{
        return scnprintf(buf, PAGE_SIZE, "%d\n", num_online_cpus());
}

static ssize_t max_comp_streams_store(struct device *dev,
                struct device_attribute *attr, const char *buf, size_t len)
{
        return len;
}

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

        down_read(&zram->init_lock);
        sz = zcomp_available_show(zram->compressor, buf);
        up_read(&zram->init_lock);

        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);
        char compressor[ARRAY_SIZE(zram->compressor)];
        size_t sz;

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

        if (!zcomp_available_algorithm(compressor))
                return -EINVAL;

        down_write(&zram->init_lock);
        if (init_done(zram)) {
                up_write(&zram->init_lock);
                pr_info("Can't change algorithm for initialized device\n");
                return -EBUSY;
        }

        strcpy(zram->compressor, compressor);
        up_write(&zram->init_lock);
        return len;
}

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);

        down_read(&zram->init_lock);
        if (!init_done(zram)) {
                up_read(&zram->init_lock);
                return -EINVAL;
        }

        zs_compact(zram->mem_pool);
        up_read(&zram->init_lock);

        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;

        down_read(&zram->init_lock);
        ret = scnprintf(buf, PAGE_SIZE,
                        "%8llu %8llu %8llu %8llu\n",
                        (u64)atomic64_read(&zram->stats.failed_reads),
                        (u64)atomic64_read(&zram->stats.failed_writes),
                        (u64)atomic64_read(&zram->stats.invalid_io),
                        (u64)atomic64_read(&zram->stats.notify_free));
        up_read(&zram->init_lock);

        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));

        down_read(&zram->init_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 = scnprintf(buf, PAGE_SIZE,
                        "%8llu %8llu %8llu %8lu %8ld %8llu %8lu %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),
                        pool_stats.pages_compacted,
                        (u64)atomic64_read(&zram->stats.huge_pages));
        up_read(&zram->init_lock);

        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;

        down_read(&zram->init_lock);
        ret = scnprintf(buf, PAGE_SIZE,
                        "version: %d\n%8llu\n",
                        version,
                        (u64)atomic64_read(&zram->stats.writestall));
        up_read(&zram->init_lock);

        return ret;
}

static DEVICE_ATTR_RO(io_stat);
static DEVICE_ATTR_RO(mm_stat);
static DEVICE_ATTR_RO(debug_stat);

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

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

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

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

        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);
                return false;
        }

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

/*
 * To protect concurrent access to the same index entry,
 * caller should hold this table index entry's bit_spinlock to
 * indicate this index entry is accessing.
 */
static void zram_free_page(struct zram *zram, size_t index)
{
        unsigned long handle;

        zram_reset_access(zram, index);

        if (zram_test_flag(zram, index, ZRAM_HUGE)) {
                zram_clear_flag(zram, index, ZRAM_HUGE);
                atomic64_dec(&zram->stats.huge_pages);
        }

        if (zram_wb_enabled(zram) && zram_test_flag(zram, index, ZRAM_WB)) {
                zram_wb_clear(zram, index);
                atomic64_dec(&zram->stats.pages_stored);
                return;
        }

        /*
         * No memory is allocated for same element filled pages.
         * Simply clear same page flag.
         */
        if (zram_test_flag(zram, index, ZRAM_SAME)) {
                zram_clear_flag(zram, index, ZRAM_SAME);
                zram_set_element(zram, index, 0);
                atomic64_dec(&zram->stats.same_pages);
                atomic64_dec(&zram->stats.pages_stored);
                return;
        }

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

        zs_free(zram->mem_pool, handle);

        atomic64_sub(zram_get_obj_size(zram, index),
                        &zram->stats.compr_data_size);
        atomic64_dec(&zram->stats.pages_stored);

        zram_set_handle(zram, index, 0);
        zram_set_obj_size(zram, index, 0);
}

static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
                                struct bio *bio, bool partial_io)
{
        int ret;
        unsigned long handle;
        unsigned int size;
        void *src, *dst;

        if (zram_wb_enabled(zram)) {
                zram_slot_lock(zram, index);
                if (zram_test_flag(zram, index, ZRAM_WB)) {
                        struct bio_vec bvec;

                        zram_slot_unlock(zram, index);

                        bvec.bv_page = page;
                        bvec.bv_len = PAGE_SIZE;
                        bvec.bv_offset = 0;
                        return read_from_bdev(zram, &bvec,
                                        zram_get_element(zram, index),
                                        bio, partial_io);
                }
                zram_slot_unlock(zram, index);
        }

        zram_slot_lock(zram, index);
        handle = zram_get_handle(zram, index);
        if (!handle || zram_test_flag(zram, index, ZRAM_SAME)) {
                unsigned long value;
                void *mem;

                value = handle ? zram_get_element(zram, index) : 0;
                mem = kmap_atomic(page);
                zram_fill_page(mem, PAGE_SIZE, value);
                kunmap_atomic(mem);
                zram_slot_unlock(zram, index);
                return 0;
        }

        size = zram_get_obj_size(zram, index);

        src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
        if (size == PAGE_SIZE) {
                dst = kmap_atomic(page);
                memcpy(dst, src, PAGE_SIZE);
                kunmap_atomic(dst);
                ret = 0;
        } else {
                struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);

                dst = kmap_atomic(page);
                ret = zcomp_decompress(zstrm, src, size, dst);
                kunmap_atomic(dst);
                zcomp_stream_put(zram->comp);
        }
        zs_unmap_object(zram->mem_pool, handle);
        zram_slot_unlock(zram, index);

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

        return ret;
}

static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
                                u32 index, int offset, struct bio *bio)
{
        int ret;
        struct page *page;

        page = bvec->bv_page;
        if (is_partial_io(bvec)) {
                /* Use a temporary buffer to decompress the page */
                page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
                if (!page)
                        return -ENOMEM;
        }

        ret = __zram_bvec_read(zram, page, index, bio, is_partial_io(bvec));
        if (unlikely(ret))
                goto out;

        if (is_partial_io(bvec)) {
                void *dst = kmap_atomic(bvec->bv_page);
                void *src = kmap_atomic(page);

                memcpy(dst + bvec->bv_offset, src + offset, bvec->bv_len);
                kunmap_atomic(src);
                kunmap_atomic(dst);
        }
out:
        if (is_partial_io(bvec))
                __free_page(page);

        return ret;
}

static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
                                u32 index, struct bio *bio)
{
        int ret = 0;
        unsigned long alloced_pages;
        unsigned long handle = 0;
        unsigned int comp_len = 0;
        void *src, *dst, *mem;
        struct zcomp_strm *zstrm;
        struct page *page = bvec->bv_page;
        unsigned long element = 0;
        enum zram_pageflags flags = 0;
        bool allow_wb = true;

        mem = kmap_atomic(page);
        if (page_same_filled(mem, &element)) {
                kunmap_atomic(mem);
                /* Free memory associated with this sector now. */
                flags = ZRAM_SAME;
                atomic64_inc(&zram->stats.same_pages);
                goto out;
        }
        kunmap_atomic(mem);

compress_again:
        zstrm = zcomp_stream_get(zram->comp);
        src = kmap_atomic(page);
        ret = zcomp_compress(zstrm, src, &comp_len);
        kunmap_atomic(src);

        if (unlikely(ret)) {
                zcomp_stream_put(zram->comp);
                pr_err("Compression failed! err=%d\n", ret);
                zs_free(zram->mem_pool, handle);
                return ret;
        }

        if (unlikely(comp_len >= huge_class_size)) {
                comp_len = PAGE_SIZE;
                if (zram_wb_enabled(zram) && allow_wb) {
                        zcomp_stream_put(zram->comp);
                        ret = write_to_bdev(zram, bvec, index, bio, &element);
                        if (!ret) {
                                flags = ZRAM_WB;
                                ret = 1;
                                goto out;
                        }
                        allow_wb = false;
                        goto compress_again;
                }
        }

        /*
         * handle allocation has 2 paths:
         * a) fast path is executed with preemption disabled (for
         *  per-cpu streams) and has __GFP_DIRECT_RECLAIM bit clear,
         *  since we can't sleep;
         * b) slow path enables preemption and attempts to allocate
         *  the page with __GFP_DIRECT_RECLAIM bit set. we have to
         *  put per-cpu compression stream and, thus, to re-do
         *  the compression once handle is allocated.
         *
         * if we have a 'non-null' handle here then we are coming
         * from the slow path and handle has already been allocated.
         */
        if (!handle)
                handle = zs_malloc(zram->mem_pool, comp_len,
                                __GFP_KSWAPD_RECLAIM |
                                __GFP_NOWARN |
                                __GFP_HIGHMEM |
                                __GFP_MOVABLE);
        if (!handle) {
                zcomp_stream_put(zram->comp);
                atomic64_inc(&zram->stats.writestall);
                handle = zs_malloc(zram->mem_pool, comp_len,
                                GFP_NOIO | __GFP_HIGHMEM |
                                __GFP_MOVABLE);
                if (handle)
                        goto compress_again;
                return -ENOMEM;
        }

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

        if (zram->limit_pages && alloced_pages > zram->limit_pages) {
                zcomp_stream_put(zram->comp);
                zs_free(zram->mem_pool, handle);
                return -ENOMEM;
        }

        dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);

        src = zstrm->buffer;
        if (comp_len == PAGE_SIZE)
                src = kmap_atomic(page);
        memcpy(dst, src, comp_len);
        if (comp_len == PAGE_SIZE)
                kunmap_atomic(src);

        zcomp_stream_put(zram->comp);
        zs_unmap_object(zram->mem_pool, handle);
        atomic64_add(comp_len, &zram->stats.compr_data_size);
out:
        /*
         * Free memory associated with this sector
         * before overwriting unused sectors.
         */
        zram_slot_lock(zram, index);
        zram_free_page(zram, index);

        if (comp_len == PAGE_SIZE) {
                zram_set_flag(zram, index, ZRAM_HUGE);
                atomic64_inc(&zram->stats.huge_pages);
        }

        if (flags) {
                zram_set_flag(zram, index, flags);
                zram_set_element(zram, index, element);
        }  else {
                zram_set_handle(zram, index, handle);
                zram_set_obj_size(zram, index, comp_len);
        }
        zram_slot_unlock(zram, index);

        /* Update stats */
        atomic64_inc(&zram->stats.pages_stored);
        return ret;
}

static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
                                u32 index, int offset, struct bio *bio)
{
        int ret;
        struct page *page = NULL;
        void *src;
        struct bio_vec vec;

        vec = *bvec;
        if (is_partial_io(bvec)) {
                void *dst;
                /*
                 * This is a partial IO. We need to read the full page
                 * before to write the changes.
                 */
                page = alloc_page(GFP_NOIO|__GFP_HIGHMEM);
                if (!page)
                        return -ENOMEM;

                ret = __zram_bvec_read(zram, page, index, bio, true);
                if (ret)
                        goto out;

                src = kmap_atomic(bvec->bv_page);
                dst = kmap_atomic(page);
                memcpy(dst + offset, src + bvec->bv_offset, bvec->bv_len);
                kunmap_atomic(dst);
                kunmap_atomic(src);

                vec.bv_page = page;
                vec.bv_len = PAGE_SIZE;
                vec.bv_offset = 0;
        }

        ret = __zram_bvec_write(zram, &vec, index, bio);
out:
        if (is_partial_io(bvec))
                __free_page(page);
        return ret;
}

/*
 * zram_bio_discard - handler on discard request
 * @index: physical block index in PAGE_SIZE units
 * @offset: byte offset within physical block
 */
static void zram_bio_discard(struct zram *zram, u32 index,
                             int offset, struct bio *bio)
{
        size_t n = bio->bi_iter.bi_size;

        /*
         * 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) {
                zram_slot_lock(zram, index);
                zram_free_page(zram, index);
                zram_slot_unlock(zram, index);
                atomic64_inc(&zram->stats.notify_free);
                index++;
                n -= PAGE_SIZE;
        }
}

/*
 * Returns errno if it has some problem. Otherwise return 0 or 1.
 * Returns 0 if IO request was done synchronously
 * Returns 1 if IO request was successfully submitted.
 */
static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
                        int offset, unsigned int op, struct bio *bio)
{
        unsigned long start_time = jiffies;
        struct request_queue *q = zram->disk->queue;
        int ret;

        generic_start_io_acct(q, op, bvec->bv_len >> SECTOR_SHIFT,
                        &zram->disk->part0);

        if (!op_is_write(op)) {
                atomic64_inc(&zram->stats.num_reads);
                ret = zram_bvec_read(zram, bvec, index, offset, bio);
                flush_dcache_page(bvec->bv_page);
        } else {
                atomic64_inc(&zram->stats.num_writes);
                ret = zram_bvec_write(zram, bvec, index, offset, bio);
        }

        generic_end_io_acct(q, op, &zram->disk->part0, start_time);

        zram_slot_lock(zram, index);
        zram_accessed(zram, index);
        zram_slot_unlock(zram, index);

        if (unlikely(ret < 0)) {
                if (!op_is_write(op))
                        atomic64_inc(&zram->stats.failed_reads);
                else
                        atomic64_inc(&zram->stats.failed_writes);
        }

        return ret;
}

static void __zram_make_request(struct zram *zram, struct bio *bio)
{
        int offset;
        u32 index;
        struct bio_vec bvec;
        struct bvec_iter iter;

        index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
        offset = (bio->bi_iter.bi_sector &
                  (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;

        switch (bio_op(bio)) {
        case REQ_OP_DISCARD:
        case REQ_OP_WRITE_ZEROES:
                zram_bio_discard(zram, index, offset, bio);
                bio_endio(bio);
                return;
        default:
                break;
        }

        bio_for_each_segment(bvec, bio, iter) {
                struct bio_vec bv = bvec;
                unsigned int unwritten = bvec.bv_len;

                do {
                        bv.bv_len = min_t(unsigned int, PAGE_SIZE - offset,
                                                        unwritten);
                        if (zram_bvec_rw(zram, &bv, index, offset,
                                         bio_op(bio), bio) < 0)
                                goto out;

                        bv.bv_offset += bv.bv_len;
                        unwritten -= bv.bv_len;

                        update_position(&index, &offset, &bv);
                } while (unwritten);
        }

        bio_endio(bio);
        return;

out:
        bio_io_error(bio);
}

/*
 * Handler function for all zram I/O requests.
 */
static blk_qc_t zram_make_request(struct request_queue *queue, struct bio *bio)
{
        struct zram *zram = queue->queuedata;

        if (!valid_io_request(zram, bio->bi_iter.bi_sector,
                                        bio->bi_iter.bi_size)) {
                atomic64_inc(&zram->stats.invalid_io);
                goto error;
        }

        __zram_make_request(zram, bio);
        return BLK_QC_T_NONE;

error:
        bio_io_error(bio);
        return BLK_QC_T_NONE;
}

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

        zram = bdev->bd_disk->private_data;

        zram_slot_lock(zram, index);
        zram_free_page(zram, index);
        zram_slot_unlock(zram, index);
        atomic64_inc(&zram->stats.notify_free);
}

static int zram_rw_page(struct block_device *bdev, sector_t sector,
                       struct page *page, unsigned int op)
{
        int offset, ret;
        u32 index;
        struct zram *zram;
        struct bio_vec bv;

        if (PageTransHuge(page))
                return -ENOTSUPP;
        zram = bdev->bd_disk->private_data;

        if (!valid_io_request(zram, sector, PAGE_SIZE)) {
                atomic64_inc(&zram->stats.invalid_io);
                ret = -EINVAL;
                goto out;
        }

        index = sector >> SECTORS_PER_PAGE_SHIFT;
        offset = (sector & (SECTORS_PER_PAGE - 1)) << SECTOR_SHIFT;

        bv.bv_page = page;
        bv.bv_len = PAGE_SIZE;
        bv.bv_offset = 0;

        ret = zram_bvec_rw(zram, &bv, index, offset, op, NULL);
out:
        /*
         * If I/O fails, just return error(ie, non-zero) without
         * calling page_endio.
         * It causes resubmit the I/O with bio request by upper functions
         * of rw_page(e.g., swap_readpage, __swap_writepage) and
         * bio->bi_end_io does things to handle the error
         * (e.g., SetPageError, set_page_dirty and extra works).
         */
        if (unlikely(ret < 0))
                return ret;

        switch (ret) {
        case 0:
                page_endio(page, op_is_write(op), 0);
                break;
        case 1:
                ret = 0;
                break;
        default:
                WARN_ON(1);
        }
        return ret;
}

static void zram_reset_device(struct zram *zram)
{
        struct zcomp *comp;
        u64 disksize;

        down_write(&zram->init_lock);

        zram->limit_pages = 0;

        if (!init_done(zram)) {
                up_write(&zram->init_lock);
                return;
        }

        comp = zram->comp;
        disksize = zram->disksize;
        zram->disksize = 0;

        set_capacity(zram->disk, 0);
        part_stat_set_all(&zram->disk->part0, 0);

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

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;

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

        down_write(&zram->init_lock);
        if (init_done(zram)) {
                pr_info("Cannot change disksize for initialized device\n");
                err = -EBUSY;
                goto out_unlock;
        }

        disksize = PAGE_ALIGN(disksize);
        if (!zram_meta_alloc(zram, disksize)) {
                err = -ENOMEM;
                goto out_unlock;
        }

        comp = zcomp_create(zram->compressor);
        if (IS_ERR(comp)) {
                pr_err("Cannot initialise %s compressing backend\n",
                                zram->compressor);
                err = PTR_ERR(comp);
                goto out_free_meta;
        }

        zram->comp = comp;
        zram->disksize = disksize;
        set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);

        revalidate_disk(zram->disk);
        up_write(&zram->init_lock);

        return len;

out_free_meta:
        zram_meta_free(zram, disksize);
out_unlock:
        up_write(&zram->init_lock);
        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 block_device *bdev;

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

        if (!do_reset)
                return -EINVAL;

        zram = dev_to_zram(dev);
        bdev = bdget_disk(zram->disk, 0);
        if (!bdev)
                return -ENOMEM;

        mutex_lock(&bdev->bd_mutex);
        /* Do not reset an active device or claimed device */
        if (bdev->bd_openers || zram->claim) {
                mutex_unlock(&bdev->bd_mutex);
                bdput(bdev);
                return -EBUSY;
        }

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

        /* Make sure all the pending I/O are finished */
        fsync_bdev(bdev);
        zram_reset_device(zram);
        revalidate_disk(zram->disk);
        bdput(bdev);

        mutex_lock(&bdev->bd_mutex);
        zram->claim = false;
        mutex_unlock(&bdev->bd_mutex);

        return len;
}

static int zram_open(struct block_device *bdev, fmode_t mode)
{
        int ret = 0;
        struct zram *zram;

        WARN_ON(!mutex_is_locked(&bdev->bd_mutex));

        zram = bdev->bd_disk->private_data;
        /* zram was claimed to reset so open request fails */
        if (zram->claim)
                ret = -EBUSY;

        return ret;
}

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

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_RW(max_comp_streams);
static DEVICE_ATTR_RW(comp_algorithm);
#ifdef CONFIG_ZRAM_WRITEBACK
static DEVICE_ATTR_RW(backing_dev);
#endif

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_max_comp_streams.attr,
        &dev_attr_comp_algorithm.attr,
#ifdef CONFIG_ZRAM_WRITEBACK
        &dev_attr_backing_dev.attr,
#endif
        &dev_attr_io_stat.attr,
        &dev_attr_mm_stat.attr,
        &dev_attr_debug_stat.attr,
        NULL,
};

static const struct attribute_group zram_disk_attr_group = {
        .attrs = zram_disk_attrs,
};

/*
 * Allocate and initialize new zram device. the function returns
 * '>= 0' device_id upon success, and negative value otherwise.
 */
static int zram_add(void)
{
        struct zram *zram;
        struct request_queue *queue;
        int ret, device_id;

        zram = kzalloc(sizeof(struct zram), GFP_KERNEL);
        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->init_lock);

        queue = blk_alloc_queue(GFP_KERNEL);
        if (!queue) {
                pr_err("Error allocating disk queue for device %d\n",
                        device_id);
                ret = -ENOMEM;
                goto out_free_idr;
        }

        blk_queue_make_request(queue, zram_make_request);

        /* gendisk structure */
        zram->disk = alloc_disk(1);
        if (!zram->disk) {
                pr_err("Error allocating disk structure for device %d\n",
                        device_id);
                ret = -ENOMEM;
                goto out_free_queue;
        }

        zram->disk->major = zram_major;
        zram->disk->first_minor = device_id;
        zram->disk->fops = &zram_devops;
        zram->disk->queue = queue;
        zram->disk->queue->queuedata = zram;
        zram->disk->private_data = zram;
        snprintf(zram->disk->disk_name, 16, "zram%d", device_id);

        /* Actual capacity set using syfs (/sys/block/zram<id>/disksize */
        set_capacity(zram->disk, 0);
        /* zram devices sort of resembles non-rotational disks */
        blk_queue_flag_set(QUEUE_FLAG_NONROT, zram->disk->queue);
        blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, zram->disk->queue);

        /*
         * To ensure that we always get PAGE_SIZE aligned
         * and n*PAGE_SIZED sized I/O requests.
         */
        blk_queue_physical_block_size(zram->disk->queue, PAGE_SIZE);
        blk_queue_logical_block_size(zram->disk->queue,
                                        ZRAM_LOGICAL_BLOCK_SIZE);
        blk_queue_io_min(zram->disk->queue, PAGE_SIZE);
        blk_queue_io_opt(zram->disk->queue, PAGE_SIZE);
        zram->disk->queue->limits.discard_granularity = PAGE_SIZE;
        blk_queue_max_discard_sectors(zram->disk->queue, UINT_MAX);
        blk_queue_flag_set(QUEUE_FLAG_DISCARD, zram->disk->queue);

        /*
         * 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)
                blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);

        zram->disk->queue->backing_dev_info->capabilities |=
                        (BDI_CAP_STABLE_WRITES | BDI_CAP_SYNCHRONOUS_IO);
        add_disk(zram->disk);

        ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
                                &zram_disk_attr_group);
        if (ret < 0) {
                pr_err("Error creating sysfs group for device %d\n",
                                device_id);
                goto out_free_disk;
        }
        strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));

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

out_free_disk:
        del_gendisk(zram->disk);
        put_disk(zram->disk);
out_free_queue:
        blk_cleanup_queue(queue);
out_free_idr:
        idr_remove(&zram_index_idr, device_id);
out_free_dev:
        kfree(zram);
        return ret;
}

static int zram_remove(struct zram *zram)
{
        struct block_device *bdev;

        bdev = bdget_disk(zram->disk, 0);
        if (!bdev)
                return -ENOMEM;

        mutex_lock(&bdev->bd_mutex);
        if (bdev->bd_openers || zram->claim) {
                mutex_unlock(&bdev->bd_mutex);
                bdput(bdev);
                return -EBUSY;
        }

        zram->claim = true;
        mutex_unlock(&bdev->bd_mutex);

        zram_debugfs_unregister(zram);
        /*
         * Remove sysfs first, so no one will perform a disksize
         * store while we destroy the devices. This also helps during
         * hot_remove -- zram_reset_device() is the last holder of
         * ->init_lock, no later/concurrent disksize_store() or any
         * other sysfs handlers are possible.
         */
        sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
                        &zram_disk_attr_group);

        /* Make sure all the pending I/O are finished */
        fsync_bdev(bdev);
        zram_reset_device(zram);
        bdput(bdev);

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

        del_gendisk(zram->disk);
        blk_cleanup_queue(zram->disk->queue);
        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(struct class *class,
                        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 scnprintf(buf, PAGE_SIZE, "%d\n", ret);
}
static CLASS_ATTR_RO(hot_add);

static ssize_t hot_remove_store(struct class *class,
                        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",
        .owner          = THIS_MODULE,
        .class_groups   = zram_control_class_groups,
};

static int zram_remove_cb(int id, void *ptr, void *data)
{
        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)
{
        int ret;

        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");