On Tue, May 10, 2016 at 01:38:05PM -0400, Jeff Moyer wrote:
> Eryu Guan <guaneryu@xxxxxxxxx> writes:
>
> > Save one level of indention by returning error early.
> >
> > Introduce some local variables to make the code easier to read a bit,
> > and do preparation for next patch.
> >
> > Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx>
>
> Hi, Eryu,
>
> I don't think you have a full appreciation of the amount of optimization
> that goes into this code. I don't see anything wrong with what you've
> done, but I also don't want to introduce all these local variables and
> change a branch in order to find out several months down the line that
> we introduced some TPC-C regression of .5%.
Agreed, I overdid it, v2 fix doesn't need the cleanup, I realized it
after I sent it out.
>
> Look, I think this is all you need for the full fix:
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 4720377..f66754e 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -639,8 +639,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
> */
> create = dio->rw & WRITE;
> if (dio->flags & DIO_SKIP_HOLES) {
> - if (sdio->block_in_file < (i_size_read(dio->inode) >>
> - sdio->blkbits))
> + if (fs_startblk < fs_count)
> create = 0;
> }
>
>
> Can you just test that?
I tested it and it did fix both of the issues for me. But it seems that
it's a bit overkilled, in certain case block allocation should be
allowed, but it still sets 'create' to 0.
For example, append writing 8k to a 4k sparse file (so offset is also
4k), on a 4k block size filesystem, fs_startblk(1) is smaller than
fs_count(2), so it still sets 'create' to 0. But block allocation should
be allowed in this case, and both the original code and my patch do so.
So I simplified my real fix to this (updates for comments not included):
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 4720377..0cace3e 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -639,8 +639,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
*/
create = dio->rw & WRITE;
if (dio->flags & DIO_SKIP_HOLES) {
- if (sdio->block_in_file < (i_size_read(dio->inode) >>
- sdio->blkbits))
+ if (fs_startblk <= ((i_size_read(dio->inode) - 1) >>
+ i_blkbits))
create = 0;
}
Do you think it's a proper fix?
Thanks again for your time!
Eryu
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