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bcache: fix sequential large write IO bypass

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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
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Tang Junhui 2017-09-06 14:25:52 +08:00 committed by Jens Axboe
parent 4b758df21e
commit c81ffa32a2
1 changed files with 0 additions and 6 deletions
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6
drivers/md/bcache/request.c
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@ -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)