xfs: bound maximum wait time for inodegc work

Currently inodegc work can sit queued on the per-cpu queue until
the workqueue is either flushed of the queue reaches a depth that
triggers work queuing (and later throttling). This means that we
could queue work that waits for a long time for some other event to
trigger flushing.

Hence instead of just queueing work at a specific depth, use a
delayed work that queues the work at a bound time. We can still
schedule the work immediately at a given depth, but we no long need
to worry about leaving a number of items on the list that won't get
processed until external events prevail.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_icache.c

@@ -440,7 +440,7 @@ xfs_inodegc_queue_all(
 	for_each_online_cpu(cpu) {
 		gc = per_cpu_ptr(mp->m_inodegc, cpu);
 		if (!llist_empty(&gc->list))
-			queue_work_on(cpu, mp->m_inodegc_wq, &gc->work);
+			mod_delayed_work_on(cpu, mp->m_inodegc_wq, &gc->work, 0);
 	}
 }
 
@@ -1841,8 +1841,8 @@ void
 xfs_inodegc_worker(
 	struct work_struct	*work)
 {
-	struct xfs_inodegc	*gc = container_of(work, struct xfs_inodegc,
-							work);
+	struct xfs_inodegc	*gc = container_of(to_delayed_work(work),
+						struct xfs_inodegc, work);
 	struct llist_node	*node = llist_del_all(&gc->list);
 	struct xfs_inode	*ip, *n;
 
@@ -2014,6 +2014,7 @@ xfs_inodegc_queue(
 	struct xfs_inodegc	*gc;
 	int			items;
 	unsigned int		shrinker_hits;
+	unsigned long		queue_delay = 1;
 
 	trace_xfs_inode_set_need_inactive(ip);
 	spin_lock(&ip->i_flags_lock);
@@ -2025,19 +2026,26 @@ xfs_inodegc_queue(
 	items = READ_ONCE(gc->items);
 	WRITE_ONCE(gc->items, items + 1);
 	shrinker_hits = READ_ONCE(gc->shrinker_hits);
-	put_cpu_ptr(gc);
 
-	if (!xfs_is_inodegc_enabled(mp))
+	/*
+	 * We queue the work while holding the current CPU so that the work
+	 * is scheduled to run on this CPU.
+	 */
+	if (!xfs_is_inodegc_enabled(mp)) {
+		put_cpu_ptr(gc);
 		return;
-
-	if (xfs_inodegc_want_queue_work(ip, items)) {
-		trace_xfs_inodegc_queue(mp, __return_address);
-		queue_work(mp->m_inodegc_wq, &gc->work);
 	}
 
+	if (xfs_inodegc_want_queue_work(ip, items))
+		queue_delay = 0;
+
+	trace_xfs_inodegc_queue(mp, __return_address);
+	mod_delayed_work(mp->m_inodegc_wq, &gc->work, queue_delay);
+	put_cpu_ptr(gc);
+
 	if (xfs_inodegc_want_flush_work(ip, items, shrinker_hits)) {
 		trace_xfs_inodegc_throttle(mp, __return_address);
-		flush_work(&gc->work);
+		flush_delayed_work(&gc->work);
 	}
 }
 
@@ -2054,7 +2062,7 @@ xfs_inodegc_cpu_dead(
 	unsigned int		count = 0;
 
 	dead_gc = per_cpu_ptr(mp->m_inodegc, dead_cpu);
-	cancel_work_sync(&dead_gc->work);
+	cancel_delayed_work_sync(&dead_gc->work);
 
 	if (llist_empty(&dead_gc->list))
 		return;
@@ -2073,12 +2081,12 @@ xfs_inodegc_cpu_dead(
 	llist_add_batch(first, last, &gc->list);
 	count += READ_ONCE(gc->items);
 	WRITE_ONCE(gc->items, count);
-	put_cpu_ptr(gc);
 
 	if (xfs_is_inodegc_enabled(mp)) {
 		trace_xfs_inodegc_queue(mp, __return_address);
-		queue_work(mp->m_inodegc_wq, &gc->work);
+		mod_delayed_work(mp->m_inodegc_wq, &gc->work, 0);
 	}
+	put_cpu_ptr(gc);
 }
 
 /*
@@ -2173,7 +2181,7 @@ xfs_inodegc_shrinker_scan(
 			unsigned int	h = READ_ONCE(gc->shrinker_hits);
 
 			WRITE_ONCE(gc->shrinker_hits, h + 1);
-			queue_work_on(cpu, mp->m_inodegc_wq, &gc->work);
+			mod_delayed_work_on(cpu, mp->m_inodegc_wq, &gc->work, 0);
 			no_items = false;
 		}
 	}

fs/xfs/xfs_mount.h

@@ -61,7 +61,7 @@ struct xfs_error_cfg {
  */
 struct xfs_inodegc {
 	struct llist_head	list;
-	struct work_struct	work;
+	struct delayed_work	work;
 
 	/* approximate count of inodes in the list */
 	unsigned int		items;

fs/xfs/xfs_super.c

@@ -1074,7 +1074,7 @@ xfs_inodegc_init_percpu(
 		gc = per_cpu_ptr(mp->m_inodegc, cpu);
 		init_llist_head(&gc->list);
 		gc->items = 0;
-		INIT_WORK(&gc->work, xfs_inodegc_worker);
+		INIT_DELAYED_WORK(&gc->work, xfs_inodegc_worker);
 	}
 	return 0;
 }