diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index e71cfbd..efa2a73 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1774,18 +1774,33 @@
 	return 0;
 }
 
+/*
+ * submit buffers for write.
+ *
+ * When we have a large buffer list, we do not want to hold all the buffers
+ * locked while we block on the request queue waiting for IO dispatch. To avoid
+ * this problem, we lock and submit buffers in groups of 50, thereby minimising
+ * the lock hold times for lists which may contain thousands of objects.
+ *
+ * To do this, we sort the buffer list before we walk the list to lock and
+ * submit buffers, and we plug and unplug around each group of buffers we
+ * submit.
+ */
 static int
-__xfs_buf_delwri_submit(
+xfs_buf_delwri_submit_buffers(
 	struct list_head	*buffer_list,
-	struct list_head	*io_list,
-	bool			wait)
+	struct list_head	*wait_list)
 {
-	struct blk_plug		plug;
 	struct xfs_buf		*bp, *n;
+	LIST_HEAD		(submit_list);
 	int			pinned = 0;
+	struct blk_plug		plug;
 
+	list_sort(NULL, buffer_list, xfs_buf_cmp);
+
+	blk_start_plug(&plug);
 	list_for_each_entry_safe(bp, n, buffer_list, b_list) {
-		if (!wait) {
+		if (!wait_list) {
 			if (xfs_buf_ispinned(bp)) {
 				pinned++;
 				continue;
@@ -1808,25 +1823,21 @@
 			continue;
 		}
 
-		list_move_tail(&bp->b_list, io_list);
 		trace_xfs_buf_delwri_split(bp, _RET_IP_);
-	}
-
-	list_sort(NULL, io_list, xfs_buf_cmp);
-
-	blk_start_plug(&plug);
-	list_for_each_entry_safe(bp, n, io_list, b_list) {
-		bp->b_flags &= ~(_XBF_DELWRI_Q | XBF_ASYNC | XBF_WRITE_FAIL);
-		bp->b_flags |= XBF_WRITE | XBF_ASYNC;
 
 		/*
-		 * we do all Io submission async. This means if we need to wait
-		 * for IO completion we need to take an extra reference so the
-		 * buffer is still valid on the other side.
+		 * We do all IO submission async. This means if we need
+		 * to wait for IO completion we need to take an extra
+		 * reference so the buffer is still valid on the other
+		 * side. We need to move the buffer onto the io_list
+		 * at this point so the caller can still access it.
 		 */
-		if (wait)
+		bp->b_flags &= ~(_XBF_DELWRI_Q | XBF_ASYNC | XBF_WRITE_FAIL);
+		bp->b_flags |= XBF_WRITE | XBF_ASYNC;
+		if (wait_list) {
 			xfs_buf_hold(bp);
-		else
+			list_move_tail(&bp->b_list, wait_list);
+		} else
 			list_del_init(&bp->b_list);
 
 		xfs_buf_submit(bp);
@@ -1849,8 +1860,7 @@
 xfs_buf_delwri_submit_nowait(
 	struct list_head	*buffer_list)
 {
-	LIST_HEAD		(io_list);
-	return __xfs_buf_delwri_submit(buffer_list, &io_list, false);
+	return xfs_buf_delwri_submit_buffers(buffer_list, NULL);
 }
 
 /*
@@ -1865,15 +1875,15 @@
 xfs_buf_delwri_submit(
 	struct list_head	*buffer_list)
 {
-	LIST_HEAD		(io_list);
+	LIST_HEAD		(wait_list);
 	int			error = 0, error2;
 	struct xfs_buf		*bp;
 
-	__xfs_buf_delwri_submit(buffer_list, &io_list, true);
+	xfs_buf_delwri_submit_buffers(buffer_list, &wait_list);
 
 	/* Wait for IO to complete. */
-	while (!list_empty(&io_list)) {
-		bp = list_first_entry(&io_list, struct xfs_buf, b_list);
+	while (!list_empty(&wait_list)) {
+		bp = list_first_entry(&wait_list, struct xfs_buf, b_list);
 
 		list_del_init(&bp->b_list);