[v11,30/40] btrfs: avoid async metadata checksum on ZONED mode

Commit Message

Naohiro Aota Dec. 22, 2020, 3:49 a.m. UTC

In ZONED, btrfs uses per-FS zoned_meta_io_lock to serialize the metadata
write IOs.

Even with these 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 can disable async metadata checksum on
ZONED.  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 performance.

Reviewed-by: Josef Bacik <[e-mail]>
Signed-off-by: Naohiro Aota <[e-mail]>
---
 fs/btrfs/disk-io.c | 2 ++
 1 file changed, 2 insertions(+)

Patch

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1f0523a796b4..efcf1a343732 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -814,6 +814,8 @@  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))