gfs2: Replace gl_revokes with a GLF flag

The gl_revokes value determines how many outstanding revokes a glock has
on the superblock revokes list; this is used to avoid unnecessary log
flushes.  However, gl_revokes is only ever tested for being zero, and it's
only decremented in revoke_lo_after_commit, which removes all revokes
from the list, so we know that the gl_revoke values of all the glocks on
the list will reach zero.  Therefore, we can replace gl_revokes with a
bit flag. This saves an atomic counter in struct gfs2_glock.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

1 files changed, 24 insertions, 9 deletions

diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index b4f0a6a3ba59..2fd61853ba63 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -662,19 +662,34 @@ static void revoke_lo_before_commit(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 static void revoke_lo_after_commit(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 {
 	struct list_head *head = &sdp->sd_log_le_revoke;
-	struct gfs2_bufdata *bd;
-	struct gfs2_glock *gl;
+	struct gfs2_bufdata *bd, *tmp;
 
-	while (!list_empty(head)) {
-		bd = list_entry(head->next, struct gfs2_bufdata, bd_list);
-		list_del_init(&bd->bd_list);
-		gl = bd->bd_gl;
-		if (atomic_dec_return(&gl->gl_revokes) == 0) {
-			clear_bit(GLF_LFLUSH, &gl->gl_flags);
-			gfs2_glock_queue_put(gl);
+	/*
+	 * Glocks can be referenced repeatedly on the revoke list, but the list
+	 * only holds one reference.  All glocks on the list will have the
+	 * GLF_REVOKES flag set initially.
+	 */
+
+	list_for_each_entry_safe(bd, tmp, head, bd_list) {
+		struct gfs2_glock *gl = bd->bd_gl;
+
+		if (test_bit(GLF_REVOKES, &gl->gl_flags)) {
+			/* Keep each glock on the list exactly once. */
+			clear_bit(GLF_REVOKES, &gl->gl_flags);
+			continue;
 		}
+		list_del(&bd->bd_list);
+		kmem_cache_free(gfs2_bufdata_cachep, bd);
+	}
+	list_for_each_entry_safe(bd, tmp, head, bd_list) {
+		struct gfs2_glock *gl = bd->bd_gl;
+
+		list_del(&bd->bd_list);
 		kmem_cache_free(gfs2_bufdata_cachep, bd);
+		clear_bit(GLF_LFLUSH, &gl->gl_flags);
+		gfs2_glock_queue_put(gl);
 	}
+	/* the list is empty now */
 }
 
 static void revoke_lo_before_scan(struct gfs2_jdesc *jd,