[safe/jmp/linux-2.6] / drivers / staging / ramzswap / ramzswap_drv.c

/*
 * Compressed RAM based swap device
 *
 * Copyright (C) 2008, 2009  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 "ramzswap"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/module.h>
#include <linux/kernel.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/lzo.h>
#include <linux/string.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/vmalloc.h>

#include "ramzswap_drv.h"

/* Globals */
static int ramzswap_major;
static struct ramzswap *devices;

/*
 * Pages that compress to larger than this size are
 * forwarded to backing swap, if present or stored
 * uncompressed in memory otherwise.
 */
static unsigned int max_zpage_size;

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

static int rzs_test_flag(struct ramzswap *rzs, u32 index,
                        enum rzs_pageflags flag)
{
        return rzs->table[index].flags & BIT(flag);
}

static void rzs_set_flag(struct ramzswap *rzs, u32 index,
                        enum rzs_pageflags flag)
{
        rzs->table[index].flags |= BIT(flag);
}

static void rzs_clear_flag(struct ramzswap *rzs, u32 index,
                        enum rzs_pageflags flag)
{
        rzs->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;
}

/*
 * memlimit cannot be greater than backing disk size.
 */
static void ramzswap_set_memlimit(struct ramzswap *rzs, size_t totalram_bytes)
{
        int memlimit_valid = 1;

        if (!rzs->memlimit) {
                pr_info("Memory limit not set.\n");
                memlimit_valid = 0;
        }

        if (rzs->memlimit > rzs->disksize) {
                pr_info("Memory limit cannot be greater than "
                        "disksize: limit=%zu, disksize=%zu\n",
                        rzs->memlimit, rzs->disksize);
                memlimit_valid = 0;
        }

        if (!memlimit_valid) {
                size_t mempart, disksize;
                pr_info("Using default: smaller of (%u%% of RAM) and "
                        "(backing disk size).\n",
                        default_memlimit_perc_ram);
                mempart = default_memlimit_perc_ram * (totalram_bytes / 100);
                disksize = rzs->disksize;
                rzs->memlimit = mempart > disksize ? disksize : mempart;
        }

        if (rzs->memlimit > totalram_bytes / 2) {
                pr_info(
                "Its not advisable setting limit more than half of "
                "size of memory since we expect a 2:1 compression ratio. "
                "Limit represents amount of *compressed* data we can keep "
                "in memory!\n"
                "\tMemory Size: %zu kB\n"
                "\tLimit you selected: %zu kB\n"
                "Continuing anyway ...\n",
                totalram_bytes >> 10, rzs->memlimit >> 10
                );
        }

        rzs->memlimit &= PAGE_MASK;
        BUG_ON(!rzs->memlimit);
}

static void ramzswap_set_disksize(struct ramzswap *rzs, size_t totalram_bytes)
{
        if (!rzs->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
                );
                rzs->disksize = default_disksize_perc_ram *
                                        (totalram_bytes / 100);
        }

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

        rzs->disksize &= PAGE_MASK;
}

/*
 * Swap header (1st page of swap device) contains information
 * to indentify it as a swap partition. Prepare such a header
 * for ramzswap device (ramzswap0) so that swapon can identify
 * it as swap partition. In case backing swap device is provided,
 * copy its swap header.
 */
static int setup_swap_header(struct ramzswap *rzs, union swap_header *s)
{
        int ret = 0;
        struct page *page;
        struct address_space *mapping;
        union swap_header *backing_swap_header;

        /*
         * There is no backing swap device. Create a swap header
         * that is acceptable by swapon.
         */
        if (!rzs->backing_swap) {
                s->info.version = 1;
                s->info.last_page = (rzs->disksize >> PAGE_SHIFT) - 1;
                s->info.nr_badpages = 0;
                memcpy(s->magic.magic, "SWAPSPACE2", 10);
                return 0;
        }

        /*
         * We have a backing swap device. Copy its swap header
         * to ramzswap device header. If this header contains
         * invalid information (backing device not a swap
         * partition, etc.), swapon will fail for ramzswap
         * which is correct behavior - we don't want to swap
         * over filesystem partition!
         */

        /* Read the backing swap header (code from sys_swapon) */
        mapping = rzs->swap_file->f_mapping;
        if (!mapping->a_ops->readpage) {
                ret = -EINVAL;
                goto out;
        }

        page = read_mapping_page(mapping, 0, rzs->swap_file);
        if (IS_ERR(page)) {
                ret = PTR_ERR(page);
                goto out;
        }

        backing_swap_header = kmap(page);
        memcpy(s, backing_swap_header, sizeof(*s));
        if (s->info.nr_badpages) {
                pr_info("Cannot use backing swap with bad pages (%u)\n",
                        s->info.nr_badpages);
                ret = -EINVAL;
        }
        /*
         * ramzswap disksize equals number of usable pages in backing
         * swap. Set last_page in swap header to match this disksize
         * ('last_page' means 0-based index of last usable swap page).
         */
        s->info.last_page = (rzs->disksize >> PAGE_SHIFT) - 1;
        kunmap(page);

out:
        return ret;
}

void ramzswap_ioctl_get_stats(struct ramzswap *rzs,
                        struct ramzswap_ioctl_stats *s)
{
        strncpy(s->backing_swap_name, rzs->backing_swap_name,
                MAX_SWAP_NAME_LEN - 1);
        s->backing_swap_name[MAX_SWAP_NAME_LEN - 1] = '\0';

        s->disksize = rzs->disksize;
        s->memlimit = rzs->memlimit;

#if defined(CONFIG_RAMZSWAP_STATS)
        {
        struct ramzswap_stats *rs = &rzs->stats;
        size_t succ_writes, mem_used;
        unsigned int good_compress_perc = 0, no_compress_perc = 0;

        mem_used = xv_get_total_size_bytes(rzs->mem_pool)
                        + (rs->pages_expand << PAGE_SHIFT);
        succ_writes = rzs_stat64_read(rzs, &rs->num_writes) -
                        rzs_stat64_read(rzs, &rs->failed_writes);

        if (succ_writes && rs->pages_stored) {
                good_compress_perc = rs->good_compress * 100
                                        / rs->pages_stored;
                no_compress_perc = rs->pages_expand * 100
                                        / rs->pages_stored;
        }

        s->num_reads = rzs_stat64_read(rzs, &rs->num_reads);
        s->num_writes = rzs_stat64_read(rzs, &rs->num_writes);
        s->failed_reads = rzs_stat64_read(rzs, &rs->failed_reads);
        s->failed_writes = rzs_stat64_read(rzs, &rs->failed_writes);
        s->invalid_io = rzs_stat64_read(rzs, &rs->invalid_io);
        s->notify_free = rzs_stat64_read(rzs, &rs->notify_free);
        s->pages_zero = rs->pages_zero;

        s->good_compress_pct = good_compress_perc;
        s->pages_expand_pct = no_compress_perc;

        s->pages_stored = rs->pages_stored;
        s->pages_used = mem_used >> PAGE_SHIFT;
        s->orig_data_size = rs->pages_stored << PAGE_SHIFT;
        s->compr_data_size = rs->compr_size;
        s->mem_used_total = mem_used;

        s->bdev_num_reads = rzs_stat64_read(rzs, &rs->bdev_num_reads);
        s->bdev_num_writes = rzs_stat64_read(rzs, &rs->bdev_num_writes);
        }
#endif /* CONFIG_RAMZSWAP_STATS */
}

static int add_backing_swap_extent(struct ramzswap *rzs,
                                pgoff_t phy_pagenum,
                                pgoff_t num_pages)
{
        unsigned int idx;
        struct list_head *head;
        struct page *curr_page, *new_page;
        unsigned int extents_per_page = PAGE_SIZE /
                                sizeof(struct ramzswap_backing_extent);

        idx = rzs->num_extents % extents_per_page;
        if (!idx) {
                new_page = alloc_page(__GFP_ZERO);
                if (!new_page)
                        return -ENOMEM;

                if (rzs->num_extents) {
                        curr_page = virt_to_page(rzs->curr_extent);
                        head = &curr_page->lru;
                } else {
                        head = &rzs->backing_swap_extent_list;
                }

                list_add(&new_page->lru, head);
                rzs->curr_extent = page_address(new_page);
        }

        rzs->curr_extent->phy_pagenum = phy_pagenum;
        rzs->curr_extent->num_pages = num_pages;

        pr_debug("add_extent: idx=%u, phy_pgnum=%lu, num_pgs=%lu, "
                "pg_last=%lu, curr_ext=%p\n", idx, phy_pagenum, num_pages,
                phy_pagenum + num_pages - 1, rzs->curr_extent);

        if (idx != extents_per_page - 1)
                rzs->curr_extent++;

        return 0;
}

static int setup_backing_swap_extents(struct ramzswap *rzs,
                                struct inode *inode, unsigned long *num_pages)
{
        int ret = 0;
        unsigned blkbits;
        unsigned blocks_per_page;
        pgoff_t contig_pages = 0, total_pages = 0;
        pgoff_t pagenum = 0, prev_pagenum = 0;
        sector_t probe_block = 0;
        sector_t last_block;

        blkbits = inode->i_blkbits;
        blocks_per_page = PAGE_SIZE >> blkbits;

        last_block = i_size_read(inode) >> blkbits;
        while (probe_block + blocks_per_page <= last_block) {
                unsigned block_in_page;
                sector_t first_block;

                first_block = bmap(inode, probe_block);
                if (first_block == 0)
                        goto bad_bmap;

                /* It must be PAGE_SIZE aligned on-disk */
                if (first_block & (blocks_per_page - 1)) {
                        probe_block++;
                        goto probe_next;
                }

                /* All blocks within this page must be contiguous on disk */
                for (block_in_page = 1; block_in_page < blocks_per_page;
                                        block_in_page++) {
                        sector_t block;

                        block = bmap(inode, probe_block + block_in_page);
                        if (block == 0)
                                goto bad_bmap;
                        if (block != first_block + block_in_page) {
                                /* Discontiguity */
                                probe_block++;
                                goto probe_next;
                        }
                }

                /*
                 * We found a PAGE_SIZE length, PAGE_SIZE aligned
                 * run of blocks.
                 */
                pagenum = first_block >> (PAGE_SHIFT - blkbits);

                if (total_pages && (pagenum != prev_pagenum + 1)) {
                        ret = add_backing_swap_extent(rzs, prev_pagenum -
                                        (contig_pages - 1), contig_pages);
                        if (ret < 0)
                                goto out;
                        rzs->num_extents++;
                        contig_pages = 0;
                }
                total_pages++;
                contig_pages++;
                prev_pagenum = pagenum;
                probe_block += blocks_per_page;

probe_next:
                continue;
        }

        if (contig_pages) {
                pr_debug("adding last extent: pagenum=%lu, "
                        "contig_pages=%lu\n", pagenum, contig_pages);
                ret = add_backing_swap_extent(rzs,
                        prev_pagenum - (contig_pages - 1), contig_pages);
                if (ret < 0)
                        goto out;
                rzs->num_extents++;
        }
        if (!rzs->num_extents) {
                pr_err("No swap extents found!\n");
                ret = -EINVAL;
        }

        if (!ret) {
                *num_pages = total_pages;
                pr_info("Found %lu extents containing %luk\n",
                        rzs->num_extents, *num_pages << (PAGE_SHIFT - 10));
        }
        goto out;

bad_bmap:
        pr_err("Backing swapfile has holes\n");
        ret = -EINVAL;
out:
        while (ret && !list_empty(&rzs->backing_swap_extent_list)) {
                struct page *page;
                struct list_head *entry = rzs->backing_swap_extent_list.next;
                page = list_entry(entry, struct page, lru);
                list_del(entry);
                __free_page(page);
        }
        return ret;
}

static void map_backing_swap_extents(struct ramzswap *rzs)
{
        struct ramzswap_backing_extent *se;
        struct page *table_page, *se_page;
        unsigned long num_pages, num_table_pages, entry;
        unsigned long se_idx, span;
        unsigned entries_per_page = PAGE_SIZE / sizeof(*rzs->table);
        unsigned extents_per_page = PAGE_SIZE / sizeof(*se);

        /* True for block device */
        if (!rzs->num_extents)
                return;

        se_page = list_entry(rzs->backing_swap_extent_list.next,
                                        struct page, lru);
        se = page_address(se_page);
        span = se->num_pages;
        num_pages = rzs->disksize >> PAGE_SHIFT;
        num_table_pages = DIV_ROUND_UP(num_pages * sizeof(*rzs->table),
                                                        PAGE_SIZE);

        entry = 0;
        se_idx = 0;
        while (num_table_pages--) {
                table_page = vmalloc_to_page(&rzs->table[entry]);
                while (span <= entry) {
                        se_idx++;
                        if (se_idx == rzs->num_extents)
                                BUG();

                        if (!(se_idx % extents_per_page)) {
                                se_page = list_entry(se_page->lru.next,
                                                struct page, lru);
                                se = page_address(se_page);
                        } else
                                se++;

                        span += se->num_pages;
                }
                table_page->mapping = (struct address_space *)se;
                table_page->private = se->num_pages - (span - entry);
                pr_debug("map_table: entry=%lu, span=%lu, map=%p, priv=%lu\n",
                        entry, span, table_page->mapping, table_page->private);
                entry += entries_per_page;
        }
}

/*
 * Check if value of backing_swap module param is sane.
 * Claim this device and set ramzswap size equal to
 * size of this block device.
 */
static int setup_backing_swap(struct ramzswap *rzs)
{
        int ret = 0;
        size_t disksize;
        unsigned long num_pages = 0;
        struct inode *inode;
        struct file *swap_file;
        struct address_space *mapping;
        struct block_device *bdev = NULL;

        if (!rzs->backing_swap_name[0]) {
                pr_debug("backing_swap param not given\n");
                goto out;
        }

        pr_info("Using backing swap device: %s\n", rzs->backing_swap_name);

        swap_file = filp_open(rzs->backing_swap_name,
                                O_RDWR | O_LARGEFILE, 0);
        if (IS_ERR(swap_file)) {
                pr_err("Error opening backing device: %s\n",
                        rzs->backing_swap_name);
                ret = -EINVAL;
                goto out;
        }

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

        if (S_ISBLK(inode->i_mode)) {
                bdev = I_BDEV(inode);
                ret = bd_claim(bdev, setup_backing_swap);
                if (ret < 0) {
                        bdev = NULL;
                        goto bad_param;
                }
                disksize = i_size_read(inode);
        } else if (S_ISREG(inode->i_mode)) {
                bdev = inode->i_sb->s_bdev;
                if (IS_SWAPFILE(inode)) {
                        ret = -EBUSY;
                        goto bad_param;
                }
                ret = setup_backing_swap_extents(rzs, inode, &num_pages);
                if (ret < 0)
                        goto bad_param;
                disksize = num_pages << PAGE_SHIFT;
        } else {
                goto bad_param;
        }

        rzs->swap_file = swap_file;
        rzs->backing_swap = bdev;
        rzs->disksize = disksize;
        BUG_ON(!rzs->disksize);

        return 0;

bad_param:
        if (bdev)
                bd_release(bdev);
        filp_close(swap_file, NULL);

out:
        rzs->backing_swap = NULL;
        return ret;
}

/*
 * Map logical page number 'pagenum' to physical page number
 * on backing swap device. For block device, this is a nop.
 */
u32 map_backing_swap_page(struct ramzswap *rzs, u32 pagenum)
{
        u32 skip_pages, entries_per_page;
        size_t delta, se_offset, skipped;
        struct page *table_page, *se_page;
        struct ramzswap_backing_extent *se;

        if (!rzs->num_extents)
                return pagenum;

        entries_per_page = PAGE_SIZE / sizeof(*rzs->table);

        table_page = vmalloc_to_page(&rzs->table[pagenum]);
        se = (struct ramzswap_backing_extent *)table_page->mapping;
        se_page = virt_to_page(se);

        skip_pages = pagenum - (pagenum / entries_per_page * entries_per_page);
        se_offset = table_page->private + skip_pages;

        if (se_offset < se->num_pages)
                return se->phy_pagenum + se_offset;

        skipped = se->num_pages - table_page->private;
        do {
                struct ramzswap_backing_extent *se_base;
                u32 se_entries_per_page = PAGE_SIZE / sizeof(*se);

                /* Get next swap extent */
                se_base = (struct ramzswap_backing_extent *)
                                                page_address(se_page);
                if (se - se_base == se_entries_per_page - 1) {
                        se_page = list_entry(se_page->lru.next,
                                                struct page, lru);
                        se = page_address(se_page);
                } else {
                        se++;
                }

                skipped += se->num_pages;
        } while (skipped < skip_pages);

        delta = skipped - skip_pages;
        se_offset = se->num_pages - delta;

        return se->phy_pagenum + se_offset;
}

static void ramzswap_free_page(struct ramzswap *rzs, size_t index)
{
        u32 clen;
        void *obj;

        struct page *page = rzs->table[index].page;
        u32 offset = rzs->table[index].offset;

        if (unlikely(!page)) {
                /*
                 * No memory is allocated for zero filled pages.
                 * Simply clear zero page flag.
                 */
                if (rzs_test_flag(rzs, index, RZS_ZERO)) {
                        rzs_clear_flag(rzs, index, RZS_ZERO);
                        rzs_stat_dec(&rzs->stats.pages_zero);
                }
                return;
        }

        if (unlikely(rzs_test_flag(rzs, index, RZS_UNCOMPRESSED))) {
                clen = PAGE_SIZE;
                __free_page(page);
                rzs_clear_flag(rzs, index, RZS_UNCOMPRESSED);
                rzs_stat_dec(&rzs->stats.pages_expand);
                goto out;
        }

        obj = kmap_atomic(page, KM_USER0) + offset;
        clen = xv_get_object_size(obj) - sizeof(struct zobj_header);
        kunmap_atomic(obj, KM_USER0);

        xv_free(rzs->mem_pool, page, offset);
        if (clen <= PAGE_SIZE / 2)
                rzs_stat_dec(&rzs->stats.good_compress);

out:
        rzs->stats.compr_size -= clen;
        rzs_stat_dec(&rzs->stats.pages_stored);

        rzs->table[index].page = NULL;
        rzs->table[index].offset = 0;
}

static int handle_zero_page(struct bio *bio)
{
        void *user_mem;
        struct page *page = bio->bi_io_vec[0].bv_page;

        user_mem = kmap_atomic(page, KM_USER0);
        memset(user_mem, 0, PAGE_SIZE);
        kunmap_atomic(user_mem, KM_USER0);

        flush_dcache_page(page);

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

static int handle_uncompressed_page(struct ramzswap *rzs, struct bio *bio)
{
        u32 index;
        struct page *page;
        unsigned char *user_mem, *cmem;

        page = bio->bi_io_vec[0].bv_page;
        index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;

        user_mem = kmap_atomic(page, KM_USER0);
        cmem = kmap_atomic(rzs->table[index].page, KM_USER1) +
                        rzs->table[index].offset;

        memcpy(user_mem, cmem, PAGE_SIZE);
        kunmap_atomic(user_mem, KM_USER0);
        kunmap_atomic(cmem, KM_USER1);

        flush_dcache_page(page);

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


/*
 * Called when request page is not present in ramzswap.
 * Its either in backing swap device (if present) or
 * this is an attempt to read before any previous write
 * to this location - this happens due to readahead when
 * swap device is read from user-space (e.g. during swapon)
 */
static int handle_ramzswap_fault(struct ramzswap *rzs, struct bio *bio)
{
        /*
         * Always forward such requests to backing swap
         * device (if present)
         */
        if (rzs->backing_swap) {
                u32 pagenum;
                rzs_stat64_dec(rzs, &rzs->stats.num_reads);
                rzs_stat64_inc(rzs, &rzs->stats.bdev_num_reads);
                bio->bi_bdev = rzs->backing_swap;

                /*
                 * In case backing swap is a file, find the right offset within
                 * the file corresponding to logical position 'index'. For block
                 * device, this is a nop.
                 */
                pagenum = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;
                bio->bi_sector = map_backing_swap_page(rzs, pagenum)
                                        << SECTORS_PER_PAGE_SHIFT;
                return 1;
        }

        /*
         * Its unlikely event in case backing dev is
         * not present
         */
        pr_debug("Read before write on swap device: "
                "sector=%lu, size=%u, offset=%u\n",
                (ulong)(bio->bi_sector), bio->bi_size,
                bio->bi_io_vec[0].bv_offset);

        /* Do nothing. Just return success */
        set_bit(BIO_UPTODATE, &bio->bi_flags);
        bio_endio(bio, 0);
        return 0;
}

static int ramzswap_read(struct ramzswap *rzs, struct bio *bio)
{
        int ret;
        u32 index;
        size_t clen;
        struct page *page;
        struct zobj_header *zheader;
        unsigned char *user_mem, *cmem;

        rzs_stat64_inc(rzs, &rzs->stats.num_reads);

        page = bio->bi_io_vec[0].bv_page;
        index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;

        if (rzs_test_flag(rzs, index, RZS_ZERO))
                return handle_zero_page(bio);

        /* Requested page is not present in compressed area */
        if (!rzs->table[index].page)
                return handle_ramzswap_fault(rzs, bio);

        /* Page is stored uncompressed since it's incompressible */
        if (unlikely(rzs_test_flag(rzs, index, RZS_UNCOMPRESSED)))
                return handle_uncompressed_page(rzs, bio);

        user_mem = kmap_atomic(page, KM_USER0);
        clen = PAGE_SIZE;

        cmem = kmap_atomic(rzs->table[index].page, KM_USER1) +
                        rzs->table[index].offset;

        ret = lzo1x_decompress_safe(
                cmem + sizeof(*zheader),
                xv_get_object_size(cmem) - sizeof(*zheader),
                user_mem, &clen);

        kunmap_atomic(user_mem, KM_USER0);
        kunmap_atomic(cmem, KM_USER1);

        /* should NEVER happen */
        if (unlikely(ret != LZO_E_OK)) {
                pr_err("Decompression failed! err=%d, page=%u\n",
                        ret, index);
                rzs_stat64_inc(rzs, &rzs->stats.failed_reads);
                goto out;
        }

        flush_dcache_page(page);

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

out:
        bio_io_error(bio);
        return 0;
}

static int ramzswap_write(struct ramzswap *rzs, struct bio *bio)
{
        int ret, fwd_write_request = 0;
        u32 offset, index;
        size_t clen;
        struct zobj_header *zheader;
        struct page *page, *page_store;
        unsigned char *user_mem, *cmem, *src;

        rzs_stat64_inc(rzs, &rzs->stats.num_writes);

        page = bio->bi_io_vec[0].bv_page;
        index = bio->bi_sector >> SECTORS_PER_PAGE_SHIFT;

        src = rzs->compress_buffer;

        /*
         * System swaps to same sector again when the stored page
         * is no longer referenced by any process. So, its now safe
         * to free the memory that was allocated for this page.
         */
        if (rzs->table[index].page || rzs_test_flag(rzs, index, RZS_ZERO))
                ramzswap_free_page(rzs, index);

        mutex_lock(&rzs->lock);

        user_mem = kmap_atomic(page, KM_USER0);
        if (page_zero_filled(user_mem)) {
                kunmap_atomic(user_mem, KM_USER0);
                mutex_unlock(&rzs->lock);
                rzs_stat_inc(&rzs->stats.pages_zero);
                rzs_set_flag(rzs, index, RZS_ZERO);

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

        if (rzs->backing_swap &&
                (rzs->stats.compr_size > rzs->memlimit - PAGE_SIZE)) {
                kunmap_atomic(user_mem, KM_USER0);
                mutex_unlock(&rzs->lock);
                fwd_write_request = 1;
                goto out;
        }

        ret = lzo1x_1_compress(user_mem, PAGE_SIZE, src, &clen,
                                rzs->compress_workmem);

        kunmap_atomic(user_mem, KM_USER0);

        if (unlikely(ret != LZO_E_OK)) {
                mutex_unlock(&rzs->lock);
                pr_err("Compression failed! err=%d\n", ret);
                rzs_stat64_inc(rzs, &rzs->stats.failed_writes);
                goto out;
        }

        /*
         * Page is incompressible. Forward it to backing swap
         * if present. Otherwise, store it as-is (uncompressed)
         * since we do not want to return too many swap write
         * errors which has side effect of hanging the system.
         */
        if (unlikely(clen > max_zpage_size)) {
                if (rzs->backing_swap) {
                        mutex_unlock(&rzs->lock);
                        fwd_write_request = 1;
                        goto out;
                }

                clen = PAGE_SIZE;
                page_store = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
                if (unlikely(!page_store)) {
                        mutex_unlock(&rzs->lock);
                        pr_info("Error allocating memory for incompressible "
                                "page: %u\n", index);
                        rzs_stat64_inc(rzs, &rzs->stats.failed_writes);
                        goto out;
                }

                offset = 0;
                rzs_set_flag(rzs, index, RZS_UNCOMPRESSED);
                rzs_stat_inc(&rzs->stats.pages_expand);
                rzs->table[index].page = page_store;
                src = kmap_atomic(page, KM_USER0);
                goto memstore;
        }

        if (xv_malloc(rzs->mem_pool, clen + sizeof(*zheader),
                        &rzs->table[index].page, &offset,
                        GFP_NOIO | __GFP_HIGHMEM)) {
                mutex_unlock(&rzs->lock);
                pr_info("Error allocating memory for compressed "
                        "page: %u, size=%zu\n", index, clen);
                rzs_stat64_inc(rzs, &rzs->stats.failed_writes);
                if (rzs->backing_swap)
                        fwd_write_request = 1;
                goto out;
        }

memstore:
        rzs->table[index].offset = offset;

        cmem = kmap_atomic(rzs->table[index].page, KM_USER1) +
                        rzs->table[index].offset;

#if 0
        /* Back-reference needed for memory defragmentation */
        if (!rzs_test_flag(rzs, index, RZS_UNCOMPRESSED)) {
                zheader = (struct zobj_header *)cmem;
                zheader->table_idx = index;
                cmem += sizeof(*zheader);
        }
#endif

        memcpy(cmem, src, clen);

        kunmap_atomic(cmem, KM_USER1);
        if (unlikely(rzs_test_flag(rzs, index, RZS_UNCOMPRESSED)))
                kunmap_atomic(src, KM_USER0);

        /* Update stats */
        rzs->stats.compr_size += clen;
        rzs_stat_inc(&rzs->stats.pages_stored);
        if (clen <= PAGE_SIZE / 2)
                rzs_stat_inc(&rzs->stats.good_compress);

        mutex_unlock(&rzs->lock);

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

out:
        if (fwd_write_request) {
                rzs_stat64_inc(rzs, &rzs->stats.bdev_num_writes);
                bio->bi_bdev = rzs->backing_swap;
#if 0
                /*
                 * TODO: We currently have linear mapping of ramzswap and
                 * backing swap sectors. This is not desired since we want
                 * to optimize writes to backing swap to minimize disk seeks
                 * or have effective wear leveling (for SSDs). Also, a
                 * non-linear mapping is required to implement compressed
                 * on-disk swapping.
                 */
                 bio->bi_sector = get_backing_swap_page()
                                        << SECTORS_PER_PAGE_SHIFT;
#endif
                /*
                 * In case backing swap is a file, find the right offset within
                 * the file corresponding to logical position 'index'. For block
                 * device, this is a nop.
                 */
                bio->bi_sector = map_backing_swap_page(rzs, index)
                                        << SECTORS_PER_PAGE_SHIFT;
                return 1;
        }

        bio_io_error(bio);
        return 0;
}


/*
 * Check if request is within bounds and page aligned.
 */
static inline int valid_swap_request(struct ramzswap *rzs, struct bio *bio)
{
        if (unlikely(
                (bio->bi_sector >= (rzs->disksize >> SECTOR_SHIFT)) ||
                (bio->bi_sector & (SECTORS_PER_PAGE - 1)) ||
                (bio->bi_vcnt != 1) ||
                (bio->bi_size != PAGE_SIZE) ||
                (bio->bi_io_vec[0].bv_offset != 0))) {

                return 0;
        }

        /* swap request is valid */
        return 1;
}

/*
 * Handler function for all ramzswap I/O requests.
 */
static int ramzswap_make_request(struct request_queue *queue, struct bio *bio)
{
        int ret = 0;
        struct ramzswap *rzs = queue->queuedata;

        if (unlikely(!rzs->init_done)) {
                bio_io_error(bio);
                return 0;
        }

        if (!valid_swap_request(rzs, bio)) {
                rzs_stat64_inc(rzs, &rzs->stats.invalid_io);
                bio_io_error(bio);
                return 0;
        }

        switch (bio_data_dir(bio)) {
        case READ:
                ret = ramzswap_read(rzs, bio);
                break;

        case WRITE:
                ret = ramzswap_write(rzs, bio);
                break;
        }

        return ret;
}

static void reset_device(struct ramzswap *rzs)
{
        int is_backing_blkdev = 0;
        size_t index, num_pages;
        unsigned entries_per_page;
        unsigned long num_table_pages, entry = 0;

        /* Do not accept any new I/O request */
        rzs->init_done = 0;

        if (rzs->backing_swap && !rzs->num_extents)
                is_backing_blkdev = 1;

        num_pages = rzs->disksize >> PAGE_SHIFT;

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

        rzs->compress_workmem = NULL;
        rzs->compress_buffer = NULL;

        /* Free all pages that are still in this ramzswap device */
        for (index = 0; index < num_pages; index++) {
                struct page *page;
                u16 offset;

                page = rzs->table[index].page;
                offset = rzs->table[index].offset;

                if (!page)
                        continue;

                if (unlikely(rzs_test_flag(rzs, index, RZS_UNCOMPRESSED)))
                        __free_page(page);
                else
                        xv_free(rzs->mem_pool, page, offset);
        }

        entries_per_page = PAGE_SIZE / sizeof(*rzs->table);
        num_table_pages = DIV_ROUND_UP(num_pages * sizeof(*rzs->table),
                                        PAGE_SIZE);
        /*
         * Set page->mapping to NULL for every table page.
         * Otherwise, we will hit bad_page() during free.
         */
        while (rzs->num_extents && num_table_pages--) {
                struct page *page;
                page = vmalloc_to_page(&rzs->table[entry]);
                page->mapping = NULL;
                entry += entries_per_page;
        }
        vfree(rzs->table);
        rzs->table = NULL;

        xv_destroy_pool(rzs->mem_pool);
        rzs->mem_pool = NULL;

        /* Free all swap extent pages */
        while (!list_empty(&rzs->backing_swap_extent_list)) {
                struct page *page;
                struct list_head *entry;
                entry = rzs->backing_swap_extent_list.next;
                page = list_entry(entry, struct page, lru);
                list_del(entry);
                __free_page(page);
        }
        INIT_LIST_HEAD(&rzs->backing_swap_extent_list);
        rzs->num_extents = 0;

        /* Close backing swap device, if present */
        if (rzs->backing_swap) {
                if (is_backing_blkdev)
                        bd_release(rzs->backing_swap);
                filp_close(rzs->swap_file, NULL);
                rzs->backing_swap = NULL;
        }

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

        rzs->disksize = 0;
        rzs->memlimit = 0;
}

static int ramzswap_ioctl_init_device(struct ramzswap *rzs)
{
        int ret;
        size_t num_pages;
        struct page *page;
        union swap_header *swap_header;

        if (rzs->init_done) {
                pr_info("Device already initialized!\n");
                return -EBUSY;
        }

        ret = setup_backing_swap(rzs);
        if (ret)
                goto fail;

        if (rzs->backing_swap)
                ramzswap_set_memlimit(rzs, totalram_pages << PAGE_SHIFT);
        else
                ramzswap_set_disksize(rzs, totalram_pages << PAGE_SHIFT);

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

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

        num_pages = rzs->disksize >> PAGE_SHIFT;
        rzs->table = vmalloc(num_pages * sizeof(*rzs->table));
        if (!rzs->table) {
                pr_err("Error allocating ramzswap address table\n");
                /* To prevent accessing table entries during cleanup */
                rzs->disksize = 0;
                ret = -ENOMEM;
                goto fail;
        }
        memset(rzs->table, 0, num_pages * sizeof(*rzs->table));

        map_backing_swap_extents(rzs);

        page = alloc_page(__GFP_ZERO);
        if (!page) {
                pr_err("Error allocating swap header page\n");
                ret = -ENOMEM;
                goto fail;
        }
        rzs->table[0].page = page;
        rzs_set_flag(rzs, 0, RZS_UNCOMPRESSED);

        swap_header = kmap(page);
        ret = setup_swap_header(rzs, swap_header);
        kunmap(page);
        if (ret) {
                pr_err("Error setting swap header\n");
                goto fail;
        }

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

        /*
         * We have ident mapping of sectors for ramzswap and
         * and the backing swap device. So, this queue flag
         * should be according to backing dev.
         */
        if (!rzs->backing_swap ||
                        blk_queue_nonrot(rzs->backing_swap->bd_disk->queue))
                queue_flag_set_unlocked(QUEUE_FLAG_NONROT, rzs->disk->queue);

        rzs->mem_pool = xv_create_pool();
        if (!rzs->mem_pool) {
                pr_err("Error creating memory pool\n");
                ret = -ENOMEM;
                goto fail;
        }

        /*
         * Pages that compress to size greater than this are forwarded
         * to physical swap disk (if backing dev is provided)
         * TODO: make this configurable
         */
        if (rzs->backing_swap)
                max_zpage_size = max_zpage_size_bdev;
        else
                max_zpage_size = max_zpage_size_nobdev;
        pr_debug("Max compressed page size: %u bytes\n", max_zpage_size);

        rzs->init_done = 1;

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

fail:
        reset_device(rzs);

        pr_err("Initialization failed: err=%d\n", ret);
        return ret;
}

static int ramzswap_ioctl_reset_device(struct ramzswap *rzs)
{
        if (rzs->init_done)
                reset_device(rzs);

        return 0;
}

static int ramzswap_ioctl(struct block_device *bdev, fmode_t mode,
                        unsigned int cmd, unsigned long arg)
{
        int ret = 0;
        size_t disksize_kb, memlimit_kb;

        struct ramzswap *rzs = bdev->bd_disk->private_data;

        switch (cmd) {
        case RZSIO_SET_DISKSIZE_KB:
                if (rzs->init_done) {
                        ret = -EBUSY;
                        goto out;
                }
                if (copy_from_user(&disksize_kb, (void *)arg,
                                                _IOC_SIZE(cmd))) {
                        ret = -EFAULT;
                        goto out;
                }
                rzs->disksize = disksize_kb << 10;
                pr_info("Disk size set to %zu kB\n", disksize_kb);
                break;

        case RZSIO_SET_MEMLIMIT_KB:
                if (rzs->init_done) {
                        /* TODO: allow changing memlimit */
                        ret = -EBUSY;
                        goto out;
                }
                if (copy_from_user(&memlimit_kb, (void *)arg,
                                                _IOC_SIZE(cmd))) {
                        ret = -EFAULT;
                        goto out;
                }
                rzs->memlimit = memlimit_kb << 10;
                pr_info("Memory limit set to %zu kB\n", memlimit_kb);
                break;

        case RZSIO_SET_BACKING_SWAP:
                if (rzs->init_done) {
                        ret = -EBUSY;
                        goto out;
                }

                if (copy_from_user(&rzs->backing_swap_name, (void *)arg,
                                                _IOC_SIZE(cmd))) {
                        ret = -EFAULT;
                        goto out;
                }
                rzs->backing_swap_name[MAX_SWAP_NAME_LEN - 1] = '\0';
                pr_info("Backing swap set to %s\n", rzs->backing_swap_name);
                break;

        case RZSIO_GET_STATS:
        {
                struct ramzswap_ioctl_stats *stats;
                if (!rzs->init_done) {
                        ret = -ENOTTY;
                        goto out;
                }
                stats = kzalloc(sizeof(*stats), GFP_KERNEL);
                if (!stats) {
                        ret = -ENOMEM;
                        goto out;
                }
                ramzswap_ioctl_get_stats(rzs, stats);
                if (copy_to_user((void *)arg, stats, sizeof(*stats))) {
                        kfree(stats);
                        ret = -EFAULT;
                        goto out;
                }
                kfree(stats);
                break;
        }
        case RZSIO_INIT:
                ret = ramzswap_ioctl_init_device(rzs);
                break;

        case RZSIO_RESET:
                /* Do not reset an active device! */
                if (bdev->bd_holders) {
                        ret = -EBUSY;
                        goto out;
                }

                /* Make sure all pending I/O is finished */
                if (bdev)
                        fsync_bdev(bdev);

                ret = ramzswap_ioctl_reset_device(rzs);
                break;

        default:
                pr_info("Invalid ioctl %u\n", cmd);
                ret = -ENOTTY;
        }

out:
        return ret;
}

static struct block_device_operations ramzswap_devops = {
        .ioctl = ramzswap_ioctl,
        .owner = THIS_MODULE,
};

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

        mutex_init(&rzs->lock);
        spin_lock_init(&rzs->stat64_lock);
        INIT_LIST_HEAD(&rzs->backing_swap_extent_list);

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

        blk_queue_make_request(rzs->queue, ramzswap_make_request);
        rzs->queue->queuedata = rzs;

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

        rzs->disk->major = ramzswap_major;
        rzs->disk->first_minor = device_id;
        rzs->disk->fops = &ramzswap_devops;
        rzs->disk->queue = rzs->queue;
        rzs->disk->private_data = rzs;
        snprintf(rzs->disk->disk_name, 16, "ramzswap%d", device_id);

        /*
         * Actual capacity set using RZSIO_SET_DISKSIZE_KB ioctl
         * or set equal to backing swap device (if provided)
         */
        set_capacity(rzs->disk, 0);

        blk_queue_physical_block_size(rzs->disk->queue, PAGE_SIZE);
        blk_queue_logical_block_size(rzs->disk->queue, PAGE_SIZE);

        add_disk(rzs->disk);

        rzs->init_done = 0;

out:
        return ret;
}

static void destroy_device(struct ramzswap *rzs)
{
        if (rzs->disk) {
                del_gendisk(rzs->disk);
                put_disk(rzs->disk);
        }

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

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

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

        ramzswap_major = register_blkdev(0, "ramzswap");
        if (ramzswap_major <= 0) {
                pr_warning("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);
        devices = kzalloc(num_devices * sizeof(struct ramzswap), GFP_KERNEL);
        if (!devices) {
                ret = -ENOMEM;
                goto unregister;
        }

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

        return 0;

free_devices:
        while (dev_id)
                destroy_device(&devices[--dev_id]);
unregister:
        unregister_blkdev(ramzswap_major, "ramzswap");
out:
        return ret;
}

static void __exit ramzswap_exit(void)
{
        int i;
        struct ramzswap *rzs;

        for (i = 0; i < num_devices; i++) {
                rzs = &devices[i];

                destroy_device(rzs);
                if (rzs->init_done)
                        reset_device(rzs);
        }

        unregister_blkdev(ramzswap_major, "ramzswap");

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

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

module_init(ramzswap_init);
module_exit(ramzswap_exit);

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