[PATCH] Btrfs: do not async submit for nodatacsum inodes

[PATCH] Btrfs: do not async submit for nodatacsum inodes

[Liu Bo]

While we submit direct writes, if the inode is flagged with nodatasum,
there's no benefit to submit asynchronously, because

a) we don't have to calculate checksum across processors,

b) and direct IO has started a plug, but async submit makes us queue
IO on each device's scheduled IO list instead of DIO's plug list, so
that IOs get much less merges in general.

Lets use sync submit for nodatasum inodes.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 95c2120..f4a48d8 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8467,7 +8467,7 @@ static inline int __btrfs_submit_dio_bio(struct bio *bio, struct inode *inode,
 			goto err;
 	}
 map:
-	ret = btrfs_map_bio(fs_info, bio, 0, async_submit);
+	ret = btrfs_map_bio(fs_info, bio, 0, 0);
 err:
 	bio_put(bio);
 	return ret;
-- 
2.9.4

Re: [PATCH] Btrfs: do not async submit for nodatacsum inodes

[Josef Bacik]

On Fri, Aug 18, 2017 at 11:54:02AM -0600, Liu Bo wrote:
> While we submit direct writes, if the inode is flagged with nodatasum,
> there's no benefit to submit asynchronously, because
> 
> a) we don't have to calculate checksum across processors,
> 
> b) and direct IO has started a plug, but async submit makes us queue
> IO on each device's scheduled IO list instead of DIO's plug list, so
> that IOs get much less merges in general.
> 
> Lets use sync submit for nodatasum inodes.
> 
> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>

Reviewed-by: Josef Bacik <jbacik@fb.com>

Thanks,

Josef