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md/raid1: don't split discard io for write behind

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Currently, discad io is treated the same as normal write io, and for
write behind case, io size is limited to:

BIO_MAX_VECS * (PAGE_SIZE >> 9)

For 0.5KB sector size and 4KB PAGE_SIZE, this is just 1MB. For
consequence, if 'WriteMostly' is set to one of the underlying disks,
then diskcard io will be splited into 1MB and it will take a long time
for the diskcard to finish.

Fix this problem by disable write behind for discard io.

Reported-by: Roman Mamedov <rm@romanrm.net>
Closes: https://lore.kernel.org/all/6a1165f7-c792-c054-b8f0-1ad4f7b8ae01@ultracoder.org/
Reported-and-tested-by: Kirill Kirilenko <kirill@ultracoder.org>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20231007112105.407449-1-yukuai1@huaweicloud.com
This commit is contained in:
Yu Kuai 2023-10-07 19:21:05 +08:00 committed by Song Liu
parent 09f894affc
commit 9e55a22fce
1 changed files with 2 additions and 1 deletions
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3
drivers/md/raid1.c
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@ -1345,6 +1345,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
int first_clone;
int max_sectors;
bool write_behind = false;
bool is_discard = (bio_op(bio) == REQ_OP_DISCARD);
if (mddev_is_clustered(mddev) &&
md_cluster_ops->area_resyncing(mddev, WRITE,
@ -1405,7 +1406,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
* write-mostly, which means we could allocate write behind
* bio later.
*/
if (rdev && test_bit(WriteMostly, &rdev->flags))
if (!is_discard && rdev && test_bit(WriteMostly, &rdev->flags))
write_behind = true;
if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {