[PATCH 15/15] writeback: use spin_trylock() in bdi_writeback_all() for WB_SYNC_NONE

[Jens Axboe <jens.axboe@oracle.com>]

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
---
 fs/fs-writeback.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e15a3fa..98bac71 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -517,9 +517,17 @@ void bdi_writeback_all(struct super_block *sb, struct writeback_control *wbc)
 	struct bdi_work *work;
 	LIST_HEAD(list);
 
-restart:
-	spin_lock(&bdi_lock);
+	/*
+	 * If this isn't a data integrity writeback, just drop it if
+	 * someone is already holding the bdi_lock
+	 */
+	if (!spin_trylock(&bdi_lock)) {
+		if (!must_wait)
+			return;
+		spin_lock(&bdi_lock);
+	}
 
+restart:
 	list_for_each_entry_safe(bdi, tmp, &bdi_list, bdi_list) {
 		struct bdi_work *work;
 
@@ -540,6 +548,7 @@ restart:
 			spin_unlock(&bdi_lock);
 			wbc->bdi = bdi;
 			generic_sync_bdi_inodes(sb, wbc);
+			spin_lock(&bdi_lock);
 			goto restart;
 		}
 		if (must_wait)
-- 
1.6.3.rc0.1.gf800