linux-kernel - [PATCH 13/19] btrfs: avoid sync IO prioritization on checksum in HMZONED mode

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Date:   Fri,  7 Jun 2019 22:10:19 +0900
From:   Naohiro Aota <naohiro.aota@....com>
To:     linux-btrfs@...r.kernel.org, David Sterba <dsterba@...e.com>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        Qu Wenruo <wqu@...e.com>, Nikolay Borisov <nborisov@...e.com>,
        linux-kernel@...r.kernel.org, Hannes Reinecke <hare@...e.com>,
        linux-fsdevel@...r.kernel.org,
        Damien Le Moal <damien.lemoal@....com>,
        Matias Bjørling <mb@...htnvm.io>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Bart Van Assche <bvanassche@....org>,
        Naohiro Aota <naohiro.aota@....com>
Subject: [PATCH 13/19] btrfs: avoid sync IO prioritization on checksum in HMZONED mode

Btrfs prioritize sync I/Os to be handled by async checksum worker earlier.
As a result, checksumming sync I/Os to larger logical extent address can
finish faster than checksumming non-sync I/Os to smaller logical extent
address.

Since we have upper limit of number of checksum worker, it is possible that
sync I/Os to wait forever for non-starting checksum of I/Os for smaller
address.

This situation can be reproduced by e.g. fstests btrfs/073.

To avoid such disordering, disable sync IO prioritization for now. Note
that sync I/Os anyway must wait for I/Os to smaller address to finish. So,
actually prioritization have no benefit in HMZONED mode.

Signed-off-by: Naohiro Aota <naohiro.aota@....com>
---
 fs/btrfs/disk-io.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 56a416902ce7..6651986da470 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -838,7 +838,7 @@ blk_status_t btrfs_wq_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio,

 	async->status = 0;

-	if (op_is_sync(bio->bi_opf))
+	if (op_is_sync(bio->bi_opf) && !btrfs_fs_incompat(fs_info, HMZONED))
 		btrfs_set_work_high_priority(&async->work);

 	btrfs_queue_work(fs_info->workers, &async->work);
-- 
2.21.0