Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 3.14 32/37] mm/filemap.c: avoid always dirtying mapping->flags on O_DIRECT | Date | Tue, 7 Oct 2014 16:19:49 -0700 |
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3.14-stable review patch. If anyone has any objections, please let me know.
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From: Jens Axboe <axboe@fb.com>
commit 7fcbbaf18392f0b17c95e2f033c8ccf87eecde1d upstream.
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@fb.com> Acked-by: Jeff Moyer <jmoyer@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/filemap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/mm/filemap.c +++ b/mm/filemap.c @@ -192,9 +192,11 @@ 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; }
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