On Wed, Jun 14, 2017 at 11:34:42AM +0900, Daeho Jeong wrote:
> Now, when we mount ext4 filesystem with '-o discard' option, we have to
> issue all the discard commands for the blocks to be deallocated and
> wait for the completion of the commands on the commit complete phase.
> Because this procedure might involve a lot of sequential combinations of
> issuing discard commands and waiting for that, the delay of this
> procedure might be too much long, even to 17.0s in our test,
> and it results in long commit delay and fsync() performance degradation.
>
> To reduce this kind of delay, instead of adding callback for each
> extent and handling all of them in a sequential manner on commit phase,
> we instead add a separate list of extents to free to the superblock and
> then process this list at once after transaction commits so that
> we can issue all the discard commands in a parallel manner like XFS
> filesystem.
>
> Finally, we could enhance the discard command handling performance.
> The result was such that 17.0s delay of a single commit in the worst
> case has been enhanced to 4.8s.
>
> Signed-off-by: Daeho Jeong <daeho.jeong@xxxxxxxxxxx>
> Tested-by: Hobin Woo <hobin.woo@xxxxxxxxxxx>
> Tested-by: Kitae Lee <kitae87.lee@xxxxxxxxxxx>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
Thanks, applied. Since the one-line summary was longer than 80
characters, I shortened it to:
ext4: send parallel discards on commit completions
- Ted
