GFS2: Don't put unlikely reclaim candidates on the reclaim list.

GFS2 was placing far too many glocks on the reclaim list that were not good
candidates for freeing up from cache.  These locks would sit there and
repeatedly get scanned to see if they could be reclaimed, wasting a lot
of time when there was memory pressure. This fix does more checks on the
locks to see if they are actually likely to be removable from cache.
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glock.c

@@ -173,6 +173,26 @@ static void gfs2_glock_hold(struct gfs2_glock *gl)
 	atomic_inc(&gl->gl_ref);
 }
 
+/**
+ * demote_ok - Check to see if it's ok to unlock a glock
+ * @gl: the glock
+ *
+ * Returns: 1 if it's ok
+ */
+
+static int demote_ok(const struct gfs2_glock *gl)
+{
+	const struct gfs2_glock_operations *glops = gl->gl_ops;
+
+	if (gl->gl_state == LM_ST_UNLOCKED)
+		return 0;
+	if (!list_empty(&gl->gl_holders))
+		return 0;
+	if (glops->go_demote_ok)
+		return glops->go_demote_ok(gl);
+	return 1;
+}
+
 /**
  * gfs2_glock_schedule_for_reclaim - Add a glock to the reclaim list
  * @gl: the glock
@@ -181,14 +201,34 @@ static void gfs2_glock_hold(struct gfs2_glock *gl)
 
 static void gfs2_glock_schedule_for_reclaim(struct gfs2_glock *gl)
 {
+	int may_reclaim;
+	may_reclaim = (demote_ok(gl) &&
+		       (atomic_read(&gl->gl_ref) == 1 ||
+			(gl->gl_name.ln_type == LM_TYPE_INODE &&
+			 atomic_read(&gl->gl_ref) <= 2)));
 	spin_lock(&lru_lock);
-	if (list_empty(&gl->gl_lru) && gl->gl_state != LM_ST_UNLOCKED) {
+	if (list_empty(&gl->gl_lru) && may_reclaim) {
 		list_add_tail(&gl->gl_lru, &lru_list);
 		atomic_inc(&lru_count);
 	}
 	spin_unlock(&lru_lock);
 }
 
+/**
+ * gfs2_glock_put_nolock() - Decrement reference count on glock
+ * @gl: The glock to put
+ *
+ * This function should only be used if the caller has its own reference
+ * to the glock, in addition to the one it is dropping.
+ */
+
+static void gfs2_glock_put_nolock(struct gfs2_glock *gl)
+{
+	if (atomic_dec_and_test(&gl->gl_ref))
+		GLOCK_BUG_ON(gl, 1);
+	gfs2_glock_schedule_for_reclaim(gl);
+}
+
 /**
  * gfs2_glock_put() - Decrement reference count on glock
  * @gl: The glock to put
@@ -214,9 +254,9 @@ int gfs2_glock_put(struct gfs2_glock *gl)
 		rv = 1;
 		goto out;
 	}
-	/* 1 for being hashed, 1 for having state != LM_ST_UNLOCKED */
-	if (atomic_read(&gl->gl_ref) == 2)
-		gfs2_glock_schedule_for_reclaim(gl);
+	spin_lock(&gl->gl_spin);
+	gfs2_glock_schedule_for_reclaim(gl);
+	spin_unlock(&gl->gl_spin);
 	write_unlock(gl_lock_addr(gl->gl_hash));
 out:
 	return rv;
@@ -398,7 +438,7 @@ static void state_change(struct gfs2_glock *gl, unsigned int new_state)
 		if (held2)
 			gfs2_glock_hold(gl);
 		else
-			gfs2_glock_put(gl);
+			gfs2_glock_put_nolock(gl);
 	}
 
 	gl->gl_state = new_state;
@@ -633,7 +673,7 @@ __acquires(&gl->gl_spin)
 out_sched:
 	gfs2_glock_hold(gl);
 	if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-		gfs2_glock_put(gl);
+		gfs2_glock_put_nolock(gl);
 out_unlock:
 	clear_bit(GLF_LOCK, &gl->gl_flags);
 	goto out;
@@ -1274,26 +1314,6 @@ void gfs2_glock_complete(struct gfs2_glock *gl, int ret)
 		gfs2_glock_put(gl);
 }
 
-/**
- * demote_ok - Check to see if it's ok to unlock a glock
- * @gl: the glock
- *
- * Returns: 1 if it's ok
- */
-
-static int demote_ok(const struct gfs2_glock *gl)
-{
-	const struct gfs2_glock_operations *glops = gl->gl_ops;
-
-	if (gl->gl_state == LM_ST_UNLOCKED)
-		return 0;
-	if (!list_empty(&gl->gl_holders))
-		return 0;
-	if (glops->go_demote_ok)
-		return glops->go_demote_ok(gl);
-	return 1;
-}
-
 
 static int gfs2_shrink_glock_memory(int nr, gfp_t gfp_mask)
 {