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    Subject[PATCH 2/2] f2fs: avoid IO split due to mixed WB_SYNC_ALL and WB_SYNC_NONE
    Date
    If two threads try to flush dirty pages in different inodes respectively,
    f2fs_write_data_pages() will produce WRITE and WRITE_SYNC one at a time,
    resulting in a lot of 4KB seperated IOs.

    So, this patch gives higher priority to WB_SYNC_ALL IOs and gathers write
    IOs with a big WRITE_SYNC'ed bio.

    Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
    ---
    fs/f2fs/data.c | 15 +++++++++++++--
    fs/f2fs/f2fs.h | 3 +++
    fs/f2fs/super.c | 2 ++
    3 files changed, 18 insertions(+), 2 deletions(-)

    diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
    index 8f36080b47c4..b1cac6d85bcb 100644
    --- a/fs/f2fs/data.c
    +++ b/fs/f2fs/data.c
    @@ -1605,8 +1605,10 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
    last_idx = page->index;
    }

    - if (--wbc->nr_to_write <= 0 &&
    - wbc->sync_mode == WB_SYNC_NONE) {
    + /* give a priority to WB_SYNC threads */
    + if ((atomic_read(&F2FS_M_SB(mapping)->wb_sync_req) ||
    + --wbc->nr_to_write <= 0) &&
    + wbc->sync_mode == WB_SYNC_NONE) {
    done = 1;
    break;
    }
    @@ -1662,9 +1664,18 @@ 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)
    + atomic_inc(&sbi->wb_sync_req);
    + else if (atomic_read(&sbi->wb_sync_req))
    + goto skip_write;
    +
    blk_start_plug(&plug);
    ret = f2fs_write_cache_pages(mapping, wbc);
    blk_finish_plug(&plug);
    +
    + if (wbc->sync_mode == WB_SYNC_ALL)
    + atomic_dec(&sbi->wb_sync_req);
    /*
    * if some pages were truncated, we cannot guarantee its mapping->host
    * to detect pending bios.
    diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
    index 32d6f674c114..fd39db681226 100644
    --- a/fs/f2fs/f2fs.h
    +++ b/fs/f2fs/f2fs.h
    @@ -888,6 +888,9 @@ struct f2fs_sb_info {
    /* # of allocated blocks */
    struct percpu_counter alloc_valid_block_count;

    + /* writeback control */
    + atomic_t wb_sync_req; /* count # of WB_SYNC threads */
    +
    /* valid inode count */
    struct percpu_counter total_valid_inode_count;

    diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
    index 2d78f3c76d18..cb65e6d0d275 100644
    --- a/fs/f2fs/super.c
    +++ b/fs/f2fs/super.c
    @@ -1566,6 +1566,8 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
    for (i = 0; i < NR_COUNT_TYPE; i++)
    atomic_set(&sbi->nr_pages[i], 0);

    + atomic_set(&sbi->wb_sync_req, 0);
    +
    INIT_LIST_HEAD(&sbi->s_list);
    mutex_init(&sbi->umount_mutex);
    mutex_init(&sbi->wio_mutex[NODE]);
    --
    2.11.0
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