[PATCH 3.16 098/133] bcache: fix sequential large write IO bypass

From: Ben Hutchings
Date: Tue Nov 21 2017 - 21:48:04 EST

3.16.51-rc1 review patch. If anyone has any objections, please let me know.


From: Tang Junhui <tang.junhui@xxxxxxxxxx>

commit c81ffa32a214c84b08900fbc9d432187bd948eba upstream.

Sequential write IOs were tested with bs=1M by FIO in writeback cache
mode, these IOs were expected to be bypassed, but actually they did not.
We debug the code, and find in check_should_bypass():
if (!congested &&
op_is_write(bio_op(bio)) &&
(bio-ïbi_opf & REQ_SYNC))
goto rescale
that means, If in writeback mode, a write IO with REQ_SYNC flag will not
be bypassed though it is a sequential large IO, It's not a correct thing
to do actually, so this patch remove these codes.

Signed-off-by: tang.junhui <tang.junhui@xxxxxxxxxx>
Reviewed-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Reviewed-by: Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
[bwh: Backported to 3.16: deleted code is slightly different]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
drivers/md/bcache/request.c | 6 ------
1 file changed, 6 deletions(-)

--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -395,12 +395,6 @@ static bool check_should_bypass(struct c
if (!congested && !dc->sequential_cutoff)
goto rescale;

- if (!congested &&
- (bio->bi_rw & REQ_WRITE) &&
- (bio->bi_rw & REQ_SYNC))
- goto rescale;

hlist_for_each_entry(i, iohash(dc, bio->bi_iter.bi_sector), hash)