On zoned filesystems, btrfs uses per-FS zoned_meta_io_lock to serialize
the metadata write IOs.
Even with this serialization, write bios sent from btree_write_cache_pages
can be reordered by async checksum workers as these workers are per CPU and
not per zone.
To preserve write BIO ordering, we disable async metadata checksum on a
zoned filesystem. This does not result in lower performance with HDDs as a
single CPU core is fast enough to do checksum for a single zone write
stream with the maximum possible bandwidth of the device. If multiple zones
are being written simultaneously, HDD seek overhead lowers the achievable
maximum bandwidth, resulting again in a per zone checksum serialization not
affecting the performance.
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
fs/btrfs/disk-io.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 458bb27e0327..6e16f556ed75 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -871,6 +871,8 @@ static blk_status_t btree_submit_bio_start(struct inode *inode, struct bio *bio,
static int check_async_write(struct btrfs_fs_info *fs_info,
struct btrfs_inode *bi)
{
+ if (btrfs_is_zoned(fs_info))
+ return 0;
if (atomic_read(&bi->sync_writers))
return 0;
if (test_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags))
--
2.30.0
