linux-kernel - [PATCH 3/5] direct-io: honor dio->boundary a little more strictly

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Message-ID: <20100507174104.GD3360@localhost.localdomain>
Date:	Fri, 7 May 2010 13:41:04 -0400
From:	Josef Bacik <josef@...hat.com>
To:	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Cc:	hch@...radead.org, akpm@...ux-foundation.org
Subject: [PATCH 3/5] direct-io: honor dio->boundary a little more strictly

Because BTRFS needs to be able to lookup checksums when we submit the bio's, we
need to be able to look up the logical offset in the inode we're submitting the
bio for.  The way we do this is in our get_blocks function is return the map_bh
with b_blocknr of the logical offset in the file, and then in the submit path
turn that into an actual block number on the device.  This causes problems with
the DIO stuff since it will try and merge requests that look like they are
contiguous, even though they are not actually contiguous on disk.  So BTRFS sets
buffer_boundary on the map_bh.  Unfortunately if there is not a bio already
setup in the DIO stuff, dio->boundary gets cleared and then the next time a
request is made they will get merged.  So instead of clearing dio->boundary in
dio_new_bio, save the boundary value before doing anything, that way if
dio->boundary gets cleared, we still submit the IO.  Thanks,

Signed-off-by: Josef Bacik <josef@...hat.com>
---
 fs/direct-io.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 2dbf2e9..98f6f42 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -615,6 +615,7 @@ static int dio_bio_add_page(struct dio *dio)
  */
 static int dio_send_cur_page(struct dio *dio)
 {
+	int boundary = dio->boundary;
 	int ret = 0;

 	if (dio->bio) {
@@ -627,7 +628,7 @@ static int dio_send_cur_page(struct dio *dio)
 		 * Submit now if the underlying fs is about to perform a
 		 * metadata read
 		 */
-		if (dio->boundary)
+		if (boundary)
 			dio_bio_submit(dio);
 	}

@@ -644,6 +645,8 @@ static int dio_send_cur_page(struct dio *dio)
 			ret = dio_bio_add_page(dio);
 			BUG_ON(ret != 0);
 		}
+	} else if (boundary) {
+		dio_bio_submit(dio);
 	}
 out:
 	return ret;
-- 
1.6.6.1

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