block: add plug for blkdev_issue_discard

Last post of this patch appears lost, so I resend this.

Now discard merge works, add plug for blkdev_issue_discard. This will help
discard request merge especially for raid0 case. In raid0, a big discard
request is split to small requests, and if correct plug is added, such small
requests can be merged in low layer.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 3 insertions, 0 deletions

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 5677fd33d7d2..b3a1f2b70b31 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -48,6 +48,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
         struct bio_batch bb;
         struct bio *bio;
         int ret = 0;
+        struct blk_plug plug;
 
         if (!q)
                 return -ENXIO;
@@ -82,6 +83,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
         bb.flags = 1 << BIO_UPTODATE;
         bb.wait = &wait;
 
+        blk_start_plug(&plug);
         while (nr_sects) {
                 unsigned int req_sects;
                 sector_t end_sect, tmp;
@@ -120,6 +122,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
                 atomic_inc(&bb.done);
                 submit_bio(type, bio);
         }
+        blk_finish_plug(&plug);
 
         /* Wait for bios in-flight */
         if (!atomic_dec_and_test(&bb.done))