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>

block/blk-barrier.c

@@ -332,12 +332,13 @@ static void blkdev_discard_end_io(struct bio *bio, int err)
  * @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 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 		return -EOPNOTSUPP;
 
 	while (nr_sects && !ret) {
-		bio = bio_alloc(GFP_KERNEL, 0);
+		bio = bio_alloc(gfp_mask, 0);
 		if (!bio)
 			return -ENOMEM;
 

include/linux/blkdev.h

@@ -16,6 +16,7 @@
 #include <linux/bio.h>
 #include <linux/module.h>
 #include <linux/stringify.h>
+#include <linux/gfp.h>
 #include <linux/bsg.h>
 #include <linux/smp.h>
 
@@ -873,15 +874,15 @@ static inline struct request *blk_map_queue_find_tag(struct blk_queue_tag *bqt,
 }
 
 extern int blkdev_issue_flush(struct block_device *, sector_t *);
-extern int blkdev_issue_discard(struct block_device *, sector_t sector,
-				unsigned nr_sects);
+extern int blkdev_issue_discard(struct block_device *,
+				sector_t sector, sector_t nr_sects, gfp_t);
 
 static inline int sb_issue_discard(struct super_block *sb,
-				   sector_t block, unsigned nr_blocks)
+				   sector_t block, sector_t nr_blocks)
 {
 	block <<= (sb->s_blocksize_bits - 9);
 	nr_blocks <<= (sb->s_blocksize_bits - 9);
-	return blkdev_issue_discard(sb->s_bdev, block, nr_blocks);
+	return blkdev_issue_discard(sb->s_bdev, block, nr_blocks, GFP_KERNEL);
 }
 
 /*