GFS2: skip dlm_unlock calls in unmount

When unmounting, gfs2 does a full dlm_unlock operation on every
cached lock.  This can create a very large amount of work and can
take a long time to complete.  However, the vast majority of these
dlm unlock operations are unnecessary because after all the unlocks
are done, gfs2 leaves the dlm lockspace, which automatically clears
the locks of the leaving node, without unlocking each one individually.
So, gfs2 can skip explicit dlm unlocks, and use dlm_release_lockspace to
remove the locks implicitly.  The one exception is when the lock's lvb is
being used.  In this case, dlm_unlock is called because it may update the
lvb of the resource.
Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glock.c

@@ -1526,6 +1526,7 @@ static void dump_glock_func(struct gfs2_glock *gl)
 
 void gfs2_gl_hash_clear(struct gfs2_sbd *sdp)
 {
+	set_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags);
 	glock_hash_walk(clear_glock, sdp);
 	flush_workqueue(glock_workqueue);
 	wait_event(sdp->sd_glock_wait, atomic_read(&sdp->sd_glock_disposal) == 0);

fs/gfs2/incore.h

@@ -539,6 +539,7 @@ enum {
 	SDF_DEMOTE		= 5,
 	SDF_NOJOURNALID		= 6,
 	SDF_RORECOVERY		= 7, /* read only recovery */
+	SDF_SKIP_DLM_UNLOCK	= 8,
 };
 
 #define GFS2_FSNAME_LEN		256

fs/gfs2/lock_dlm.c

@@ -289,6 +289,14 @@ static void gdlm_put_lock(struct gfs2_glock *gl)
 	gfs2_glstats_inc(gl, GFS2_LKS_DCOUNT);
 	gfs2_sbstats_inc(gl, GFS2_LKS_DCOUNT);
 	gfs2_update_request_times(gl);
+
+	/* don't want to skip dlm_unlock writing the lvb when lock is ex */
+	if (test_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags) &&
+	    gl->gl_state != LM_ST_EXCLUSIVE) {
+		gfs2_glock_free(gl);
+		return;
+	}
+
 	error = dlm_unlock(ls->ls_dlm, gl->gl_lksb.sb_lkid, DLM_LKF_VALBLK,
 			   NULL, gl);
 	if (error) {