On Thu, Nov 09, 2017 at 05:16:16PM -0700, Liu Bo wrote:
> Setting plug can merge adjacent IOs before dispatching IOs to the disk
> driver.
>
> Without plug, it'd not be a problem for single disk usecases, but for
> multiple disks using raid profile, a large IO can be split to several
> IOs of stripe length, and plug can be helpful to bring them together
> for each disk so that we can save several disk access.
>
> Moreover, fsync issues synchronous writes, so plug can really take
> effect.
>
> Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> ---
> fs/btrfs/file.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index e43da6c..063180b 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -2018,10 +2018,13 @@ int btrfs_release_file(struct inode *inode, struct file *filp)
> static int start_ordered_ops(struct inode *inode, loff_t start, loff_t end)
> {
> int ret;
> + struct blk_plug plug;
>
> + blk_start_plug(&plug);
Can you please add a comment here? Essentially repeating the commit
message. The plug/unplug calls are never obvious so the expectations
could be documented.
> atomic_inc(&BTRFS_I(inode)->sync_writers);
> ret = btrfs_fdatawrite_range(inode, start, end);
> atomic_dec(&BTRFS_I(inode)->sync_writers);
> + blk_finish_plug(&plug);
>
> return ret;
> }
> --
> 2.9.4
>
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