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Subject[PATCH 3.16 098/133] bcache: fix sequential large write IO bypass
3.16.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

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 &&
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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[bwh: Backported to 3.16: deleted code is slightly different]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
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 &&
- mode == CACHE_MODE_WRITEBACK &&
- (bio->bi_rw & REQ_WRITE) &&
- (bio->bi_rw & REQ_SYNC))
- goto rescale;
-
spin_lock(&dc->io_lock);

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