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authorJan Kara <jack@suse.cz>2013-09-16 08:24:26 -0400
committerTheodore Ts'o <tytso@mit.edu>2013-09-16 08:24:26 -0400
commit9c12a831d73dd938a22418d70b39aed4feb4bdf2 (patch)
tree4de915210213ff49efd637e35c176cd4e09d426d
parentad4eec613536dc7e5ea0c6e59849e6edca634d8b (diff)
ext4: fix performance regression in writeback of random writes
The Linux Kernel Performance project guys have reported that commit 4e7ea81db5 introduces a performance regression for the following fio workload: [global] direct=0 ioengine=mmap size=1500M bs=4k pre_read=1 numjobs=1 overwrite=1 loops=5 runtime=300 group_reporting invalidate=0 directory=/mnt/ file_service_type=random:36 file_service_type=random:36 [job0] startdelay=0 rw=randrw filename=data0/f1:data0/f2 [job1] startdelay=0 rw=randrw filename=data0/f2:data0/f1 ... [job7] startdelay=0 rw=randrw filename=data0/f2:data0/f1 The culprit of the problem is that after the commit ext4_writepages() are more aggressive in writing back pages. Thus we have less consecutive dirty pages resulting in more seeking. This increased aggressivity is caused by a bug in the condition terminating ext4_writepages(). We start writing from the beginning of the file even if we should have terminated ext4_writepages() because wbc->nr_to_write <= 0. After fixing the condition the throughput of the fio workload is about 20% better than before writeback reorganization. Reported-by: "Yan, Zheng" <zheng.z.yan@intel.com> Signed-off-by: Jan Kara <jack@suse.cz> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
-rw-r--r--fs/ext4/inode.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 9115f2807515..4cf2619f007c 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2559,7 +2559,7 @@ retry:
break;
}
blk_finish_plug(&plug);
- if (!ret && !cycled) {
+ if (!ret && !cycled && wbc->nr_to_write > 0) {
cycled = 1;
mpd.last_page = writeback_index - 1;
mpd.first_page = 0;