xfs: convert the xfsaild threads to a workqueue

Similar to the xfssyncd, the per-filesystem xfsaild threads can be
converted to a global workqueue and run periodically by delayed
works. This makes sense for the AIL pushing because it uses
variable timeouts depending on the work that needs to be done.

By removing the xfsaild, we simplify the AIL pushing code and
remove the need to spread the code to implement the threading
and pushing across multiple files.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>

1 files changed, 73 insertions, 60 deletions

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 12aff95..cb3aeac 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -28,6 +28,8 @@
 #include "xfs_trans_priv.h"
 #include "xfs_error.h"
 
+struct workqueue_struct	*xfs_ail_wq;	/* AIL workqueue */
+
 STATIC void xfs_ail_splice(struct xfs_ail *, struct list_head *, xfs_lsn_t);
 STATIC void xfs_ail_delete(struct xfs_ail *, xfs_log_item_t *);
 STATIC xfs_log_item_t * xfs_ail_min(struct xfs_ail *);
@@ -69,36 +71,6 @@ xfs_trans_ail_tail(
 }
 
 /*
- * xfs_trans_push_ail
- *
- * This routine is called to move the tail of the AIL forward.  It does this by
- * trying to flush items in the AIL whose lsns are below the given
- * threshold_lsn.
- *
- * the push is run asynchronously in a separate thread, so we return the tail
- * of the log right now instead of the tail after the push. This means we will
- * either continue right away, or we will sleep waiting on the async thread to
- * do its work.
- *
- * We do this unlocked - we only need to know whether there is anything in the
- * AIL at the time we are called. We don't need to access the contents of
- * any of the objects, so the lock is not needed.
- */
-void
-xfs_trans_ail_push(
-	struct xfs_ail	*ailp,
-	xfs_lsn_t	threshold_lsn)
-{
-	xfs_log_item_t	*lip;
-
-	lip = xfs_ail_min(ailp);
-	if (lip && !XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
-		if (XFS_LSN_CMP(threshold_lsn, ailp->xa_target) > 0)
-			xfsaild_wakeup(ailp, threshold_lsn);
-	}
-}
-
-/*
  * AIL traversal cursor initialisation.
  *
  * The cursor keeps track of where our current traversal is up
@@ -236,16 +208,16 @@ out:
 }
 
 /*
- * xfsaild_push does the work of pushing on the AIL.  Returning a timeout of
- * zero indicates that the caller should sleep until woken.
+ * xfs_ail_worker does the work of pushing on the AIL. It will requeue itself
+ * to run at a later time if there is more work to do to complete the push.
  */
-long
-xfsaild_push(
-	struct xfs_ail	*ailp,
-	xfs_lsn_t	*last_lsn)
+STATIC void
+xfs_ail_worker(
+	struct work_struct *work)
 {
-	long		tout = 0;
-	xfs_lsn_t	last_pushed_lsn = *last_lsn;
+	struct xfs_ail	*ailp = container_of(to_delayed_work(work),
+					struct xfs_ail, xa_work);
+	long		tout;
 	xfs_lsn_t	target =  ailp->xa_target;
 	xfs_lsn_t	lsn;
 	xfs_log_item_t	*lip;
@@ -256,15 +228,15 @@ xfsaild_push(
 
 	spin_lock(&ailp->xa_lock);
 	xfs_trans_ail_cursor_init(ailp, cur);
-	lip = xfs_trans_ail_cursor_first(ailp, cur, *last_lsn);
+	lip = xfs_trans_ail_cursor_first(ailp, cur, ailp->xa_last_pushed_lsn);
 	if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
 		/*
 		 * AIL is empty or our push has reached the end.
 		 */
 		xfs_trans_ail_cursor_done(ailp, cur);
 		spin_unlock(&ailp->xa_lock);
-		*last_lsn = 0;
-		return tout;
+		ailp->xa_last_pushed_lsn = 0;
+		return;
 	}
 
 	XFS_STATS_INC(xs_push_ail);
@@ -301,13 +273,13 @@ xfsaild_push(
 		case XFS_ITEM_SUCCESS:
 			XFS_STATS_INC(xs_push_ail_success);
 			IOP_PUSH(lip);
-			last_pushed_lsn = lsn;
+			ailp->xa_last_pushed_lsn = lsn;
 			break;
 
 		case XFS_ITEM_PUSHBUF:
 			XFS_STATS_INC(xs_push_ail_pushbuf);
 			IOP_PUSHBUF(lip);
-			last_pushed_lsn = lsn;
+			ailp->xa_last_pushed_lsn = lsn;
 			push_xfsbufd = 1;
 			break;
 
@@ -319,7 +291,7 @@ xfsaild_push(
 
 		case XFS_ITEM_LOCKED:
 			XFS_STATS_INC(xs_push_ail_locked);
-			last_pushed_lsn = lsn;
+			ailp->xa_last_pushed_lsn = lsn;
 			stuck++;
 			break;
 
@@ -374,9 +346,23 @@ xfsaild_push(
 		wake_up_process(mp->m_ddev_targp->bt_task);
 	}
 
+	/* assume we have more work to do in a short while */
+	tout = 10;
 	if (!count) {
 		/* We're past our target or empty, so idle */
-		last_pushed_lsn = 0;
+		ailp->xa_last_pushed_lsn = 0;
+
+		/*
+		 * Check for an updated push target before clearing the
+		 * XFS_AIL_PUSHING_BIT. If the target changed, we've got more
+		 * work to do. Wait a bit longer before starting that work.
+		 */
+		smp_rmb();
+		if (ailp->xa_target == target) {
+			clear_bit(XFS_AIL_PUSHING_BIT, &ailp->xa_flags);
+			return;
+		}
+		tout = 50;
 	} else if (XFS_LSN_CMP(lsn, target) >= 0) {
 		/*
 		 * We reached the target so wait a bit longer for I/O to
@@ -384,7 +370,7 @@ xfsaild_push(
 		 * start the next scan from the start of the AIL.
 		 */
 		tout = 50;
-		last_pushed_lsn = 0;
+		ailp->xa_last_pushed_lsn = 0;
 	} else if ((stuck * 100) / count > 90) {
 		/*
 		 * Either there is a lot of contention on the AIL or we
@@ -396,14 +382,48 @@ xfsaild_push(
 		 * continuing from where we were.
 		 */
 		tout = 20;
-	} else {
-		/* more to do, but wait a short while before continuing */
-		tout = 10;
 	}
-	*last_lsn = last_pushed_lsn;
-	return tout;
+
+	/* There is more to do, requeue us.  */
+	queue_delayed_work(xfs_syncd_wq, &ailp->xa_work,
+					msecs_to_jiffies(tout));
 }
 
+/*
+ * This routine is called to move the tail of the AIL forward.  It does this by
+ * trying to flush items in the AIL whose lsns are below the given
+ * threshold_lsn.
+ *
+ * The push is run asynchronously in a workqueue, which means the caller needs
+ * to handle waiting on the async flush for space to become available.
+ * We don't want to interrupt any push that is in progress, hence we only queue
+ * work if we set the pushing bit approriately.
+ *
+ * We do this unlocked - we only need to know whether there is anything in the
+ * AIL at the time we are called. We don't need to access the contents of
+ * any of the objects, so the lock is not needed.
+ */
+void
+xfs_trans_ail_push(
+	struct xfs_ail	*ailp,
+	xfs_lsn_t	threshold_lsn)
+{
+	xfs_log_item_t	*lip;
+
+	lip = xfs_ail_min(ailp);
+	if (!lip || XFS_FORCED_SHUTDOWN(ailp->xa_mount) ||
+	    XFS_LSN_CMP(threshold_lsn, ailp->xa_target) <= 0)
+		return;
+
+	/*
+	 * Ensure that the new target is noticed in push code before it clears
+	 * the XFS_AIL_PUSHING_BIT.
+	 */
+	smp_wmb();
+	ailp->xa_target = threshold_lsn;
+	if (!test_and_set_bit(XFS_AIL_PUSHING_BIT, &ailp->xa_flags))
+		queue_delayed_work(xfs_syncd_wq, &ailp->xa_work, 0);
+}
 
 /*
  * This is to be called when an item is unlocked that may have
@@ -615,7 +635,6 @@ xfs_trans_ail_init(
 	xfs_mount_t	*mp)
 {
 	struct xfs_ail	*ailp;
-	int		error;
 
 	ailp = kmem_zalloc(sizeof(struct xfs_ail), KM_MAYFAIL);
 	if (!ailp)
@@ -624,15 +643,9 @@ xfs_trans_ail_init(
 	ailp->xa_mount = mp;
 	INIT_LIST_HEAD(&ailp->xa_ail);
 	spin_lock_init(&ailp->xa_lock);
-	error = xfsaild_start(ailp);
-	if (error)
-		goto out_free_ailp;
+	INIT_DELAYED_WORK(&ailp->xa_work, xfs_ail_worker);
 	mp->m_ail = ailp;
 	return 0;
-
-out_free_ailp:
-	kmem_free(ailp);
-	return error;
 }
 
 void
@@ -641,7 +654,7 @@ xfs_trans_ail_destroy(
 {
 	struct xfs_ail	*ailp = mp->m_ail;
 
-	xfsaild_stop(ailp);
+	cancel_delayed_work_sync(&ailp->xa_work);
 	kmem_free(ailp);
 }