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    Subject[PATCH] f2fs: fix performance issue observed with multi-thread sequential read
    Date
    This reverts the commit - "b93f771 - f2fs: remove writepages lock"
    to fix the drop in sequential read throughput.

    Test: ./tiotest -t 32 -d /data/tio_tmp -f 32 -b 524288 -k 1 -k 3 -L
    device: UFS

    Before -
    read throughput: 185 MB/s
    total read requests: 85177 (of these ~80000 are 4KB size requests).
    total write requests: 2546 (of these ~2208 requests are written in 512KB).

    After -
    read throughput: 758 MB/s
    total read requests: 2417 (of these ~2042 are 512KB reads).
    total write requests: 2701 (of these ~2034 requests are written in 512KB).

    Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
    Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
    ---
    fs/f2fs/data.c | 14 ++++++++++++--
    fs/f2fs/f2fs.h | 1 +
    fs/f2fs/super.c | 1 +
    3 files changed, 14 insertions(+), 2 deletions(-)

    diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
    index 45f043ee48bd..e042d050b87d 100644
    --- a/fs/f2fs/data.c
    +++ b/fs/f2fs/data.c
    @@ -2132,6 +2132,7 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
    struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
    struct blk_plug plug;
    int ret;
    + bool locked = false;

    /* deal with chardevs and other special file */
    if (!mapping->a_ops->writepage)
    @@ -2157,15 +2158,24 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
    trace_f2fs_writepages(mapping->host, wbc, DATA);

    /* to avoid spliting IOs due to mixed WB_SYNC_ALL and WB_SYNC_NONE */
    - if (wbc->sync_mode == WB_SYNC_ALL)
    + if (wbc->sync_mode == WB_SYNC_ALL) {
    atomic_inc(&sbi->wb_sync_req[DATA]);
    - else if (atomic_read(&sbi->wb_sync_req[DATA]))
    + mutex_lock(&sbi->writepages);
    + locked = true;
    + } else if (atomic_read(&sbi->wb_sync_req[DATA])) {
    goto skip_write;
    + } else {
    + atomic_inc(&sbi->wb_sync_req[DATA]);
    + mutex_lock(&sbi->writepages);
    + }

    blk_start_plug(&plug);
    ret = f2fs_write_cache_pages(mapping, wbc, io_type);
    blk_finish_plug(&plug);

    + if (locked)
    + mutex_unlock(&sbi->writepages);
    +
    if (wbc->sync_mode == WB_SYNC_ALL)
    atomic_dec(&sbi->wb_sync_req[DATA]);
    /*
    diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
    index b1c127d8383b..29bbc55cbc0b 100644
    --- a/fs/f2fs/f2fs.h
    +++ b/fs/f2fs/f2fs.h
    @@ -1133,6 +1133,7 @@ struct f2fs_sb_info {
    struct rw_semaphore sb_lock; /* lock for raw super block */
    int valid_super_block; /* valid super block no */
    unsigned long s_flag; /* flags for sbi */
    + struct mutex writepages; /* mutex for writepages() */

    #ifdef CONFIG_BLK_DEV_ZONED
    unsigned int blocks_per_blkz; /* F2FS blocks per zone */
    diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
    index be41dbd7b261..53d70b64fea1 100644
    --- a/fs/f2fs/super.c
    +++ b/fs/f2fs/super.c
    @@ -2842,6 +2842,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
    /* init f2fs-specific super block info */
    sbi->valid_super_block = valid_super_block;
    mutex_init(&sbi->gc_mutex);
    + mutex_init(&sbi->writepages);
    mutex_init(&sbi->cp_mutex);
    init_rwsem(&sbi->node_write);
    init_rwsem(&sbi->node_change);
    --
    2.17.0.441.gb46fe60e1d-goog
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