block: adjust blkdev_issue_discard for swap

Two mods to blkdev_issue_discard(), thinking ahead to its use on swap:

1. Add gfp_mask argument, so swap allocation can use it where GFP_KERNEL
   might deadlock but GFP_NOIO is safe.

2. Enlarge nr_sects argument from unsigned to sector_t: unsigned long is
   enough to cover a whole swap area, but sector_t suits any partition.

Change sb_issue_discard()'s nr_blocks to sector_t too; but no need seen
for a gfp_mask there, just pass GFP_KERNEL down to blkdev_issue_discard().

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index 988b634..5c99ff8 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -332,12 +332,13 @@
  * @bdev:	blockdev to issue discard for
  * @sector:	start sector
  * @nr_sects:	number of sectors to discard
+ * @gfp_mask:	memory allocation flags (for bio_alloc)
  *
  * Description:
  *    Issue a discard request for the sectors in question. Does not wait.
  */
-int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
-			 unsigned nr_sects)
+int blkdev_issue_discard(struct block_device *bdev,
+			 sector_t sector, sector_t nr_sects, gfp_t gfp_mask)
 {
 	struct request_queue *q;
 	struct bio *bio;
@@ -354,7 +355,7 @@
 		return -EOPNOTSUPP;
 
 	while (nr_sects && !ret) {
-		bio = bio_alloc(GFP_KERNEL, 0);
+		bio = bio_alloc(gfp_mask, 0);
 		if (!bio)
 			return -ENOMEM;