Subject: + mm-filemapc-avoid-always-dirtying-mapping-flags-on-o_direct.patch added to -mm tree
To: axboe@xxxxxx,jmoyer@xxxxxxxxxx,viro@xxxxxxxxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Mon, 12 May 2014 16:07:02 -0700
The patch titled
Subject: mm/filemap.c: avoid always dirtying mapping->flags on O_DIRECT
has been added to the -mm tree. Its filename is
mm-filemapc-avoid-always-dirtying-mapping-flags-on-o_direct.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-filemapc-avoid-always-dirtying-mapping-flags-on-o_direct.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-filemapc-avoid-always-dirtying-mapping-flags-on-o_direct.patch
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------------------------------------------------------
From: Jens Axboe <axboe@xxxxxx>
Subject: mm/filemap.c: avoid always dirtying mapping->flags on O_DIRECT
In some testing I ran today (some fio jobs that spread over two nodes), we
end up spending 40% of the time in filemap_check_errors(). That smells
fishy. Looking further, this is basically what happens:
blkdev_aio_read()
generic_file_aio_read()
filemap_write_and_wait_range()
if (!mapping->nr_pages)
filemap_check_errors()
and filemap_check_errors() always attempts two test_and_clear_bit() on the
mapping flags, thus dirtying it for every single invocation. The patch
below tests each of these bits before clearing them, avoiding this issue.
In my test case (4-socket box), performance went from 1.7M IOPS to 4.0M
IOPS.
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Acked-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN mm/filemap.c~mm-filemapc-avoid-always-dirtying-mapping-flags-on-o_direct mm/filemap.c
--- a/mm/filemap.c~mm-filemapc-avoid-always-dirtying-mapping-flags-on-o_direct
+++ a/mm/filemap.c
@@ -257,9 +257,11 @@ static int filemap_check_errors(struct a
{
int ret = 0;
/* Check for outstanding write errors */
- if (test_and_clear_bit(AS_ENOSPC, &mapping->flags))
+ if (test_bit(AS_ENOSPC, &mapping->flags) &&
+ test_and_clear_bit(AS_ENOSPC, &mapping->flags))
ret = -ENOSPC;
- if (test_and_clear_bit(AS_EIO, &mapping->flags))
+ if (test_bit(AS_EIO, &mapping->flags) &&
+ test_and_clear_bit(AS_EIO, &mapping->flags))
ret = -EIO;
return ret;
}
_
Patches currently in -mm which might be from axboe@xxxxxx are
mm-filemapc-avoid-always-dirtying-mapping-flags-on-o_direct.patch
linux-next.patch
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