[RFC]blk: mark discard request sync

[Shaohua Li]

Subject: blk: mark discard request sync

discard is called in jbd for example. If discard is slowed down, all
file operations could be impacted (eg, journal is full). And we always
wait for discard to finish. So looks we should mark discard as sync.

Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
---
 block/blk-lib.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/block/blk-lib.c
===================================================================
--- linux.orig/block/blk-lib.c	2012-03-16 10:20:49.621517546 +0800
+++ linux/block/blk-lib.c	2012-03-16 10:21:55.901517256 +0800
@@ -42,7 +42,7 @@ int blkdev_issue_discard(struct block_de
 {
 	DECLARE_COMPLETION_ONSTACK(wait);
 	struct request_queue *q = bdev_get_queue(bdev);
-	int type = REQ_WRITE | REQ_DISCARD;
+	int type = REQ_WRITE | REQ_DISCARD | REQ_SYNC;
 	unsigned int max_discard_sectors;
 	struct bio_batch bb;
 	struct bio *bio;
--
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