From 7fcbbaf18392f0b17c95e2f033c8ccf87eecde1d Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 22 May 2014 11:54:16 -0700 Subject: [PATCH] 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 Acked-by: Jeff Moyer Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 000a220e2a41..088358c8006b 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -257,9 +257,11 @@ static int filemap_check_errors(struct address_space *mapping) { 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; } -- 2.30.2