diff options
authorDave Chinner <>2010-02-05 16:45:25 +1100
committerSteven Whitehouse <>2010-03-01 14:08:26 +0000
commite5884636da3a128617032747654284ae7badc7ff (patch)
parent1ccaba3056796ab1f933736d763ffcd1958866cd (diff)
GFS2: ordered writes are backwards
When we queue data buffers for ordered write, the buffers are added to the head of the ordered write list. When the log needs to push these buffers to disk, it also walks the list from the head. The result is that the the ordered buffers are submitted to disk in reverse order. For large writes, this means that whenever the log flushes large streams of reverse sequential order buffers are pushed down into the block layers. The elevators don't handle this particularly well, so IO rates tend to be significantly lower than if the IO was issued in ascending block order. Queue new ordered buffers to the tail of the ordered buffer list to ensure that IO is dispatched in the order it was submitted. This should significantly improve large sequential write speeds. On a disk capable of 85MB/s, speeds increase from 50MB/s to 65MB/s for noop and from 38MB/s to 50MB/s for cfq. Signed-off-by: Dave Chinner <> Signed-off-by: Steven Whitehouse <>
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index de97632ba32..adc260fbea9 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -528,9 +528,9 @@ static void databuf_lo_add(struct gfs2_sbd *sdp, struct gfs2_log_element *le)
gfs2_pin(sdp, bd->bd_bh);
- list_add(&le->le_list, &sdp->sd_log_le_databuf);
+ list_add_tail(&le->le_list, &sdp->sd_log_le_databuf);
} else {
- list_add(&le->le_list, &sdp->sd_log_le_ordered);
+ list_add_tail(&le->le_list, &sdp->sd_log_le_ordered);