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>

fs/gfs2/glock.c

@@ -140,7 +140,7 @@ void gfs2_glock_free(struct gfs2_glock *gl)
 {
 	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
 
-	BUG_ON(atomic_read(&gl->gl_revokes));
+	BUG_ON(test_bit(GLF_REVOKES, &gl->gl_flags));
 	rhashtable_remove_fast(&gl_hash_table, &gl->gl_node, ht_parms);
 	smp_mb();
 	wake_up_glock(gl);
@@ -1801,7 +1801,7 @@ void gfs2_dump_glock(struct seq_file *seq, struct gfs2_glock *gl)
 		  state2str(gl->gl_target),
 		  state2str(gl->gl_demote_state), dtime,
 		  atomic_read(&gl->gl_ail_count),
-		  atomic_read(&gl->gl_revokes),
+		  test_bit(GLF_REVOKES, &gl->gl_flags) ? 1 : 0,
 		  (int)gl->gl_lockref.count, gl->gl_hold_time);
 
 	list_for_each_entry(gh, &gl->gl_holders, gh_list)

fs/gfs2/incore.h

@@ -345,6 +345,7 @@ enum {
 	GLF_OBJECT			= 14, /* Used only for tracing */
 	GLF_BLOCKING			= 15,
 	GLF_INODE_CREATING		= 16, /* Inode creation occurring */
+	GLF_REVOKES			= 17, /* Glock has revokes in queue */
 };
 
 struct gfs2_glock {
@@ -374,7 +375,6 @@ struct gfs2_glock {
 	struct list_head gl_lru;
 	struct list_head gl_ail_list;
 	atomic_t gl_ail_count;
-	atomic_t gl_revokes;
 	struct delayed_work gl_work;
 	union {
 		/* For inode and iopen glocks only */

fs/gfs2/log.c

@@ -606,8 +606,10 @@ void gfs2_add_revoke(struct gfs2_sbd *sdp, struct gfs2_bufdata *bd)
 	gfs2_remove_from_ail(bd); /* drops ref on bh */
 	bd->bd_bh = NULL;
 	sdp->sd_log_num_revoke++;
-	if (atomic_inc_return(&gl->gl_revokes) == 1)
+	if (!test_bit(GLF_REVOKES, &gl->gl_flags)) {
+		set_bit(GLF_REVOKES, &gl->gl_flags);
 		gfs2_glock_hold(gl);
+	}
 	set_bit(GLF_LFLUSH, &gl->gl_flags);
 	list_add(&bd->bd_list, &sdp->sd_log_le_revoke);
 }

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,

fs/gfs2/main.c

@@ -59,7 +59,6 @@ static void gfs2_init_glock_once(void *foo)
 	INIT_LIST_HEAD(&gl->gl_lru);
 	INIT_LIST_HEAD(&gl->gl_ail_list);
 	atomic_set(&gl->gl_ail_count, 0);
-	atomic_set(&gl->gl_revokes, 0);
 }
 
 static void gfs2_init_gl_aspace_once(void *foo)

fs/gfs2/super.c

@@ -1474,7 +1474,7 @@ static void gfs2_final_release_pages(struct gfs2_inode *ip)
 	truncate_inode_pages(gfs2_glock2aspace(ip->i_gl), 0);
 	truncate_inode_pages(&inode->i_data, 0);
 
-	if (atomic_read(&gl->gl_revokes) == 0) {
+	if (!test_bit(GLF_REVOKES, &gl->gl_flags)) {
 		clear_bit(GLF_LFLUSH, &gl->gl_flags);
 		clear_bit(GLF_DIRTY, &gl->gl_flags);
 	}