| From 3a4c6800f31ea8395628af5e7e490270ee5d0585 Mon Sep 17 00:00:00 2001 |
| From: Nick Piggin <npiggin@suse.de> |
| Date: Thu, 12 Feb 2009 04:34:23 +0100 |
| Subject: Fix page writeback thinko, causing Berkeley DB slowdown |
| |
| From: Nick Piggin <npiggin@suse.de> |
| |
| commit 3a4c6800f31ea8395628af5e7e490270ee5d0585 upstream. |
| |
| A bug was introduced into write_cache_pages cyclic writeout by commit |
| 31a12666d8f0c22235297e1c1575f82061480029 ("mm: write_cache_pages cyclic |
| fix"). The intention (and comments) is that we should cycle back and |
| look for more dirty pages at the beginning of the file if there is no |
| more work to be done. |
| |
| But the !done condition was dropped from the test. This means that any |
| time the page writeout loop breaks (eg. due to nr_to_write == 0), we |
| will set index to 0, then goto again. This will set done_index to |
| index, then find done is set, so will proceed to the end of the |
| function. When updating mapping->writeback_index for cyclic writeout, |
| we now use done_index == 0, so we're always cycling back to 0. |
| |
| This seemed to be causing random mmap writes (slapadd and iozone) to |
| start writing more pages from the LRU and writeout would slowdown, and |
| caused bugzilla entry |
| |
| http://bugzilla.kernel.org/show_bug.cgi?id=12604 |
| |
| about Berkeley DB slowing down dramatically. |
| |
| With this patch, iozone random write performance is increased nearly |
| 5x on my system (iozone -B -r 4k -s 64k -s 512m -s 1200m on ext2). |
| |
| Signed-off-by: Nick Piggin <npiggin@suse.de> |
| Reported-and-tested-by: Jan Kara <jack@suse.cz> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- |
| mm/page-writeback.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/mm/page-writeback.c |
| +++ b/mm/page-writeback.c |
| @@ -1001,7 +1001,7 @@ continue_unlock: |
| pagevec_release(&pvec); |
| cond_resched(); |
| } |
| - if (!cycled) { |
| + if (!cycled && !done) { |
| /* |
| * range_cyclic: |
| * We hit the last page and there is more work to be done: wrap |
