zram_drv.c

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/*
 * Compressed RAM block device
 *
 * Copyright (C) 2008, 2009, 2010  Nitin Gupta
 *
 * 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
 *
 * Project home: http://compcache.googlecode.com
 */

#define KMSG_COMPONENT "zram"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#ifdef CONFIG_ZRAM_DEBUG
#define DEBUG
#endif

#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/lzo.h>
#include <linux/string.h>
#include <linux/vmalloc.h>

#include "zram_drv.h"

/* Globals */
static int zram_major;
struct zram *zram_devices;

/* Module params (documentation at end) */
static unsigned int num_devices;

static void zram_stat_inc(u32 *v)
{
    *v = *v + 1;
}

static void zram_stat_dec(u32 *v)
{
    *v = *v - 1;
}

static void zram_stat64_add(struct zram *zram, u64 *v, u64 inc)
{
    spin_lock(&zram->stat64_lock);
    *v = *v + inc;
    spin_unlock(&zram->stat64_lock);
}

static void zram_stat64_sub(struct zram *zram, u64 *v, u64 dec)
{
    spin_lock(&zram->stat64_lock);
    *v = *v - dec;
    spin_unlock(&zram->stat64_lock);
}

static void zram_stat64_inc(struct zram *zram, u64 *v)
{
    zram_stat64_add(zram, v, 1);
}

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

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

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

static int page_zero_filled(void *ptr)
{
    unsigned int pos;
    unsigned long *page;

    page = (unsigned long *)ptr;

    for (pos = 0; pos != PAGE_SIZE / sizeof(*page); pos++) {
        if (page[pos])
            return 0;
    }

    return 1;
}

static void zram_set_disksize(struct zram *zram, size_t totalram_bytes)
{
    if (!zram->disksize) {
        pr_info(
        "disk size not provided. You can use disksize_kb module "
        "param to specify size.\nUsing default: (%u%% of RAM).\n",
        default_disksize_perc_ram
        );
        zram->disksize = default_disksize_perc_ram *
                    (totalram_bytes / 100);
    }

    if (zram->disksize > 2 * (totalram_bytes)) {
        pr_info(
        "There is little point creating a zram of greater than "
        "twice the size of memory since we expect a 2:1 compression "
        "ratio. Note that zram uses about 0.1%% of the size of "
        "the disk when not in use so a huge zram is "
        "wasteful.\n"
        "\tMemory Size: %zu kB\n"
        "\tSize you selected: %llu kB\n"
        "Continuing anyway ...\n",
        totalram_bytes >> 10, zram->disksize
        );
    }

    zram->disksize &= PAGE_MASK;
}

static void zram_free_page(struct zram *zram, size_t index)
{
    unsigned long handle = zram->table[index].handle;
    u16 size = zram->table[index].size;

    if (unlikely(!handle)) {
        /*
         * No memory is allocated for zero filled pages.
         * Simply clear zero page flag.
         */
        if (zram_test_flag(zram, index, ZRAM_ZERO)) {
            zram_clear_flag(zram, index, ZRAM_ZERO);
            zram_stat_dec(&zram->stats.pages_zero);
        }
        return;
    }

    if (unlikely(size > max_zpage_size))
        zram_stat_dec(&zram->stats.bad_compress);

    zs_free(zram->mem_pool, handle);

    if (size <= PAGE_SIZE / 2)
        zram_stat_dec(&zram->stats.good_compress);

    zram_stat64_sub(zram, &zram->stats.compr_size,
            zram->table[index].size);
    zram_stat_dec(&zram->stats.pages_stored);

    zram->table[index].handle = 0;
    zram->table[index].size = 0;
}

static void handle_zero_page(struct bio_vec *bvec)
{
    struct page *page = bvec->bv_page;
    void *user_mem;

    user_mem = kmap_atomic(page);
    memset(user_mem + bvec->bv_offset, 0, bvec->bv_len);
    kunmap_atomic(user_mem);

    flush_dcache_page(page);
}

static inline int is_partial_io(struct bio_vec *bvec)
{
    return bvec->bv_len != PAGE_SIZE;
}

static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
              u32 index, int offset, struct bio *bio)
{
    int ret;
    size_t clen;
    struct page *page;
    unsigned char *user_mem, *cmem, *uncmem = NULL;

    page = bvec->bv_page;

    if (zram_test_flag(zram, index, ZRAM_ZERO)) {
        handle_zero_page(bvec);
        return 0;
    }

    /* Requested page is not present in compressed area */
    if (unlikely(!zram->table[index].handle)) {
        pr_debug("Read before write: sector=%lu, size=%u",
             (ulong)(bio->bi_sector), bio->bi_size);
        handle_zero_page(bvec);
        return 0;
    }

    if (is_partial_io(bvec)) {
        /* Use  a temporary buffer to decompress the page */
        uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!uncmem) {
            pr_info("Error allocating temp memory!\n");
            return -ENOMEM;
        }
    }

    user_mem = kmap_atomic(page);
    if (!is_partial_io(bvec))
        uncmem = user_mem;
    clen = PAGE_SIZE;

    cmem = zs_map_object(zram->mem_pool, zram->table[index].handle,
                ZS_MM_RO);

    if (zram->table[index].size == PAGE_SIZE) {
        memcpy(uncmem, cmem, PAGE_SIZE);
        ret = LZO_E_OK;
    } else {
        ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
                    uncmem, &clen);
    }

    if (is_partial_io(bvec)) {
        memcpy(user_mem + bvec->bv_offset, uncmem + offset,
               bvec->bv_len);
        kfree(uncmem);
    }

    zs_unmap_object(zram->mem_pool, zram->table[index].handle);
    kunmap_atomic(user_mem);

    /* Should NEVER happen. Return bio error if it does. */
    if (unlikely(ret != LZO_E_OK)) {
        pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
        zram_stat64_inc(zram, &zram->stats.failed_reads);
        return ret;
    }

    flush_dcache_page(page);

    return 0;
}

static int zram_read_before_write(struct zram *zram, char *mem, u32 index)
{
    int ret;
    size_t clen = PAGE_SIZE;
    unsigned char *cmem;
    unsigned long handle = zram->table[index].handle;

    if (zram_test_flag(zram, index, ZRAM_ZERO) || !handle) {
        memset(mem, 0, PAGE_SIZE);
        return 0;
    }

    cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
    ret = lzo1x_decompress_safe(cmem, zram->table[index].size,
                    mem, &clen);
    zs_unmap_object(zram->mem_pool, handle);

    /* Should NEVER happen. Return bio error if it does. */
    if (unlikely(ret != LZO_E_OK)) {
        pr_err("Decompression failed! err=%d, page=%u\n", ret, index);
        zram_stat64_inc(zram, &zram->stats.failed_reads);
        return ret;
    }

    return 0;
}

static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
               int offset)
{
    int ret;
    size_t clen;
    unsigned long handle;
    struct page *page;
    unsigned char *user_mem, *cmem, *src, *uncmem = NULL;

    page = bvec->bv_page;
    src = zram->compress_buffer;

    if (is_partial_io(bvec)) {
        /*
         * This is a partial IO. We need to read the full page
         * before to write the changes.
         */
        uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!uncmem) {
            pr_info("Error allocating temp memory!\n");
            ret = -ENOMEM;
            goto out;
        }
        ret = zram_read_before_write(zram, uncmem, index);
        if (ret) {
            kfree(uncmem);
            goto out;
        }
    }

    /*
     * System overwrites unused sectors. Free memory associated
     * with this sector now.
     */
    if (zram->table[index].handle ||
        zram_test_flag(zram, index, ZRAM_ZERO))
        zram_free_page(zram, index);

    user_mem = kmap_atomic(page);

    if (is_partial_io(bvec))
        memcpy(uncmem + offset, user_mem + bvec->bv_offset,
               bvec->bv_len);
    else
        uncmem = user_mem;

    if (page_zero_filled(uncmem)) {
        kunmap_atomic(user_mem);
        if (is_partial_io(bvec))
            kfree(uncmem);
        zram_stat_inc(&zram->stats.pages_zero);
        zram_set_flag(zram, index, ZRAM_ZERO);
        ret = 0;
        goto out;
    }

    ret = lzo1x_1_compress(uncmem, PAGE_SIZE, src, &clen,
                   zram->compress_workmem);

    kunmap_atomic(user_mem);
    if (is_partial_io(bvec))
            kfree(uncmem);

    if (unlikely(ret != LZO_E_OK)) {
        pr_err("Compression failed! err=%d\n", ret);
        goto out;
    }

    if (unlikely(clen > max_zpage_size)) {
        zram_stat_inc(&zram->stats.bad_compress);
        src = uncmem;
        clen = PAGE_SIZE;
    }

    handle = zs_malloc(zram->mem_pool, clen);
    if (!handle) {
        pr_info("Error allocating memory for compressed "
            "page: %u, size=%zu\n", index, clen);
        ret = -ENOMEM;
        goto out;
    }
    cmem = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);

    memcpy(cmem, src, clen);

    zs_unmap_object(zram->mem_pool, handle);

    zram->table[index].handle = handle;
    zram->table[index].size = clen;

    /* Update stats */
    zram_stat64_add(zram, &zram->stats.compr_size, clen);
    zram_stat_inc(&zram->stats.pages_stored);
    if (clen <= PAGE_SIZE / 2)
        zram_stat_inc(&zram->stats.good_compress);

    return 0;

out:
    if (ret)
        zram_stat64_inc(zram, &zram->stats.failed_writes);
    return ret;
}

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

    if (rw == READ) {
        down_read(&zram->lock);
        ret = zram_bvec_read(zram, bvec, index, offset, bio);
        up_read(&zram->lock);
    } else {
        down_write(&zram->lock);
        ret = zram_bvec_write(zram, bvec, index, offset);
        up_write(&zram->lock);
    }

    return ret;
}

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

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

    switch (rw) {
    case READ:
        zram_stat64_inc(zram, &zram->stats.num_reads);
        break;
    case WRITE:
        zram_stat64_inc(zram, &zram->stats.num_writes);
        break;
    }

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

    bio_for_each_segment(bvec, bio, i) {
        int max_transfer_size = PAGE_SIZE - offset;

        if (bvec->bv_len > max_transfer_size) {
            /*
             * zram_bvec_rw() can only make operation on a single
             * zram page. Split the bio vector.
             */
            struct bio_vec bv;

            bv.bv_page = bvec->bv_page;
            bv.bv_len = max_transfer_size;
            bv.bv_offset = bvec->bv_offset;

            if (zram_bvec_rw(zram, &bv, index, offset, bio, rw) < 0)
                goto out;

            bv.bv_len = bvec->bv_len - max_transfer_size;
            bv.bv_offset += max_transfer_size;
            if (zram_bvec_rw(zram, &bv, index+1, 0, bio, rw) < 0)
                goto out;
        } else
            if (zram_bvec_rw(zram, bvec, index, offset, bio, rw)
                < 0)
                goto out;

        update_position(&index, &offset, bvec);
    }

    set_bit(BIO_UPTODATE, &bio->bi_flags);
    bio_endio(bio, 0);
    return;

out:
    bio_io_error(bio);
}

/*
 * Check if request is within bounds and aligned on zram logical blocks.
 */
static inline int valid_io_request(struct zram *zram, struct bio *bio)
{
    if (unlikely(
        (bio->bi_sector >= (zram->disksize >> SECTOR_SHIFT)) ||
        (bio->bi_sector & (ZRAM_SECTOR_PER_LOGICAL_BLOCK - 1)) ||
        (bio->bi_size & (ZRAM_LOGICAL_BLOCK_SIZE - 1)))) {

        return 0;
    }

    /* I/O request is valid */
    return 1;
}

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

    if (unlikely(!zram->init_done) && zram_init_device(zram))
        goto error;

    down_read(&zram->init_lock);
    if (unlikely(!zram->init_done))
        goto error_unlock;

    if (!valid_io_request(zram, bio)) {
        zram_stat64_inc(zram, &zram->stats.invalid_io);
        goto error_unlock;
    }

    __zram_make_request(zram, bio, bio_data_dir(bio));
    up_read(&zram->init_lock);

    return;

error_unlock:
    up_read(&zram->init_lock);
error:
    bio_io_error(bio);
}

void __zram_reset_device(struct zram *zram)
{
    size_t index;

    zram->init_done = 0;

    /* Free various per-device buffers */
    kfree(zram->compress_workmem);
    free_pages((unsigned long)zram->compress_buffer, 1);

    zram->compress_workmem = NULL;
    zram->compress_buffer = NULL;

    /* Free all pages that are still in this zram device */
    for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
        unsigned long handle = zram->table[index].handle;
        if (!handle)
            continue;

        zs_free(zram->mem_pool, handle);
    }

    vfree(zram->table);
    zram->table = NULL;

    zs_destroy_pool(zram->mem_pool);
    zram->mem_pool = NULL;

    /* Reset stats */
    memset(&zram->stats, 0, sizeof(zram->stats));

    zram->disksize = 0;
}

void zram_reset_device(struct zram *zram)
{
    down_write(&zram->init_lock);
    __zram_reset_device(zram);
    up_write(&zram->init_lock);
}

int zram_init_device(struct zram *zram)
{
    int ret;
    size_t num_pages;

    down_write(&zram->init_lock);

    if (zram->init_done) {
        up_write(&zram->init_lock);
        return 0;
    }

    zram_set_disksize(zram, totalram_pages << PAGE_SHIFT);

    zram->compress_workmem = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
    if (!zram->compress_workmem) {
        pr_err("Error allocating compressor working memory!\n");
        ret = -ENOMEM;
        goto fail_no_table;
    }

    zram->compress_buffer =
        (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
    if (!zram->compress_buffer) {
        pr_err("Error allocating compressor buffer space\n");
        ret = -ENOMEM;
        goto fail_no_table;
    }

    num_pages = zram->disksize >> PAGE_SHIFT;
    zram->table = vzalloc(num_pages * sizeof(*zram->table));
    if (!zram->table) {
        pr_err("Error allocating zram address table\n");
        ret = -ENOMEM;
        goto fail_no_table;
    }

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

    /* zram devices sort of resembles non-rotational disks */
    queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);

    zram->mem_pool = zs_create_pool("zram", GFP_NOIO | __GFP_HIGHMEM);
    if (!zram->mem_pool) {
        pr_err("Error creating memory pool\n");
        ret = -ENOMEM;
        goto fail;
    }

    zram->init_done = 1;
    up_write(&zram->init_lock);

    pr_debug("Initialization done!\n");
    return 0;

fail_no_table:
    /* To prevent accessing table entries during cleanup */
    zram->disksize = 0;
fail:
    __zram_reset_device(zram);
    up_write(&zram->init_lock);
    pr_err("Initialization failed: err=%d\n", ret);
    return ret;
}

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

    zram = bdev->bd_disk->private_data;
    zram_free_page(zram, index);
    zram_stat64_inc(zram, &zram->stats.notify_free);
}

static const struct block_device_operations zram_devops = {
    .swap_slot_free_notify = zram_slot_free_notify,
    .owner = THIS_MODULE
};

static int create_device(struct zram *zram, int device_id)
{
    int ret = 0;

    init_rwsem(&zram->lock);
    init_rwsem(&zram->init_lock);
    spin_lock_init(&zram->stat64_lock);

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

    blk_queue_make_request(zram->queue, zram_make_request);
    zram->queue->queuedata = zram;

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

    zram->disk->major = zram_major;
    zram->disk->first_minor = device_id;
    zram->disk->fops = &zram_devops;
    zram->disk->queue = zram->queue;
    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);

    /*
     * 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);

    add_disk(zram->disk);

    ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,
                &zram_disk_attr_group);
    if (ret < 0) {
        pr_warn("Error creating sysfs group");
        goto out;
    }

    zram->init_done = 0;

out:
    return ret;
}

static void destroy_device(struct zram *zram)
{
    sysfs_remove_group(&disk_to_dev(zram->disk)->kobj,
            &zram_disk_attr_group);

    if (zram->disk) {
        del_gendisk(zram->disk);
        put_disk(zram->disk);
    }

    if (zram->queue)
        blk_cleanup_queue(zram->queue);
}

unsigned int zram_get_num_devices(void)
{
    return num_devices;
}

static int __init zram_init(void)
{
    int ret, dev_id;

    if (num_devices > max_num_devices) {
        pr_warn("Invalid value for num_devices: %u\n",
                num_devices);
        ret = -EINVAL;
        goto out;
    }

    zram_major = register_blkdev(0, "zram");
    if (zram_major <= 0) {
        pr_warn("Unable to get major number\n");
        ret = -EBUSY;
        goto out;
    }

    if (!num_devices) {
        pr_info("num_devices not specified. Using default: 1\n");
        num_devices = 1;
    }

    /* Allocate the device array and initialize each one */
    pr_info("Creating %u devices ...\n", num_devices);
    zram_devices = kzalloc(num_devices * sizeof(struct zram), GFP_KERNEL);
    if (!zram_devices) {
        ret = -ENOMEM;
        goto unregister;
    }

    for (dev_id = 0; dev_id < num_devices; dev_id++) {
        ret = create_device(&zram_devices[dev_id], dev_id);
        if (ret)
            goto free_devices;
    }

    return 0;

free_devices:
    while (dev_id)
        destroy_device(&zram_devices[--dev_id]);
    kfree(zram_devices);
unregister:
    unregister_blkdev(zram_major, "zram");
out:
    return ret;
}

static void __exit zram_exit(void)
{
    int i;
    struct zram *zram;

    for (i = 0; i < num_devices; i++) {
        zram = &zram_devices[i];

        destroy_device(zram);
        if (zram->init_done)
            zram_reset_device(zram);
    }

    unregister_blkdev(zram_major, "zram");

    kfree(zram_devices);
    pr_debug("Cleanup done!\n");
}

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

module_init(zram_init);
module_exit(zram_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("Nitin Gupta <[email protected]>");
MODULE_DESCRIPTION("Compressed RAM Block Device");