[PATCH 02/12] bcache: fix sequential large write IO bypass

Coly Li
2017-09-06T06:25:52Z

From: Tang Junhui <tang.junhui@zte.com.cn>

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 &&
mode == CACHE_MODE_WRITEBACK &&
op_is_write(bio_op(bio)) &&
(bio-＞bi_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@zte.com.cn>
Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Eric Wheeler <bcache@linux.ewheeler.net>
Cc: stable@vger.kernel.org
---
drivers/md/bcache/request.c | 6 ------
1 file changed, 6 deletions(-)

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 019b3df9f1c6..958072a11347 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -400,12 +400,6 @@ static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
if (!congested && !dc->sequential_cutoff)
goto rescale;

- if (!congested &&
- mode == CACHE_MODE_WRITEBACK &&
- op_is_write(bio->bi_opf) &&
- op_is_sync(bio->bi_opf))
- goto rescale;
-
spin_lock(&dc->io_lock);

hlist_for_each_entry(i, iohash(dc, bio->bi_iter.bi_sector), hash)
--
2.13.5