From: Benjamin Marzinski <bmarzins@redhat.com>
Date: Wed, 16 Jul 2008 16:20:15 -0500
Subject: [gfs2] initial write performance very slow
Message-id: 20080716212015.GA28996@ether.msp.redhat.com
O-Subject: [RHEL 5.3 PATCH] GFS2 - bz #432826: GFS2: Initial Write Performance very slow
Bugzilla: 432826
RH-Acked-by: Josef Bacik <jbacik@redhat.com>
RH-Acked-by: Bob Peterson <rpeterso@redhat.com>
RH-Acked-by: Steven Whitehouse <swhiteho@redhat.com>

BZ#432826
https://bugzilla.redhat.com/show_bug.cgi?id=432826

In GFS2, we already allows local SH locks while we hold a cached EX
glock, so here we allow DF locks as well. This works only because we
rely on the VFS's invalidation for locally cached data, and because if
we hold an EX lock, then we know that no other node can be caching data
relating to this file.

It dramatically speeds up initial writes to O_DIRECT files since we
fall back to buffered I/O for this and would otherwise bounce between DF
and EX modes on each and every write call. The lessons to be learned
from that are to ensure that (for the time being anyway) O_DIRECT files
are preallocated and that they are written to using reasonably large I/O
sizes. Even so this change fixes that corner case nicely

This patch has been submitted upstream.

-Ben

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
--
 glock.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 7ceadee..aae1b90 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -299,8 +299,12 @@ static inline int may_grant(const struct gfs2_glock *gl, const struct gfs2_holde
 		return 1;
 	if (gh->gh_flags & GL_EXACT)
 		return 0;
-	if (gh->gh_state == LM_ST_SHARED && gl->gl_state == LM_ST_EXCLUSIVE)
-		return 1;
+	if (gl->gl_state == LM_ST_EXCLUSIVE) {
+		if (gh->gh_state == LM_ST_SHARED && gh_head->gh_state == LM_ST_SHARED)
+			return 1;
+		if (gh->gh_state == LM_ST_DEFERRED && gh_head->gh_state == LM_ST_DEFERRED)
+			return 1;
+	}
 	if (gl->gl_state != LM_ST_UNLOCKED && (gh->gh_flags & LM_FLAG_ANY))
 		return 1;
 	return 0;