[PATCH] Btrfs: skip checksum verification if IO error occurs

[PATCH] Btrfs: skip checksum verification if IO error occurs

[Liu Bo]

Currently dio read also goes to verify checksum if -EIO has been returned,
although it usually fails on checksum, it's not necessary at all, we could
directly check if there is another copy to read.

And with this, the behavior of dio read is now consistent with that of
buffered read.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/inode.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 5e71f1e..632b616 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8030,6 +8030,7 @@ static int __btrfs_subio_endio_read(struct inode *inode,
 	unsigned int pgoff;
 	int csum_pos;
 	int i;
+	int uptodate = !!(err == 0);
 	int ret;
 
 	fs_info = BTRFS_I(inode)->root->fs_info;
@@ -8044,12 +8045,14 @@ static int __btrfs_subio_endio_read(struct inode *inode,
 
 		pgoff = bvec->bv_offset;
 next_block:
-		csum_pos = BTRFS_BYTES_TO_BLKS(fs_info, offset);
-		ret = __readpage_endio_check(inode, io_bio, csum_pos,
-					bvec->bv_page, pgoff, start,
-					sectorsize);
-		if (likely(!ret))
-			goto next;
+		if (uptodate) {
+			csum_pos = BTRFS_BYTES_TO_BLKS(fs_info, offset);
+			ret = __readpage_endio_check(inode, io_bio, csum_pos,
+						     bvec->bv_page, pgoff,
+						     start, sectorsize);
+			if (likely(!ret))
+				goto next;
+		}
 try_again:
 		done.uptodate = 0;
 		done.start = start;
-- 
2.5.5

Re: [PATCH] Btrfs: skip checksum verification if IO error occurs

[David Sterba]

On Thu, Apr 13, 2017 at 06:11:48PM -0700, Liu Bo wrote:
> Currently dio read also goes to verify checksum if -EIO has been returned,
> although it usually fails on checksum, it's not necessary at all, we could
> directly check if there is another copy to read.
> 
> And with this, the behavior of dio read is now consistent with that of
> buffered read.
> 
> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>

Reviewed-by: David Sterba <dsterba@suse.com>

> @@ -8030,6 +8030,7 @@ static int __btrfs_subio_endio_read(struct inode *inode,
>  	unsigned int pgoff;
>  	int csum_pos;
>  	int i;
> +	int uptodate = !!(err == 0);

I've switched that to bool and dropped !!.