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From: Josef Bacik on 11 May 2010 20:10
On Fri, May 07, 2010 at 01:41:04PM -0400, Josef Bacik wrote:
> 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(a)redhat.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;

Self-NACK on this one. Seems to have an unwanted side-effect of forcing every
page to be submitted individually. I'm going to fix this a different way.
Thanks,

Josef
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