block: allow large discard requests

Currently we set the bio size to the byte equivalent of the blocks to
be trimmed when submitting the initial DISCARD ioctl.  That means it
is subject to the max_hw_sectors limitation of the HBA which is
much lower than the size of a DISCARD request we can support.
Add a separate max_discard_sectors tunable to limit the size for discard
requests.

We limit the max discard request size in bytes to 32bit as that is the
limit for bio->bi_size.  This could be much larger if we had a way to pass
that information through the block layer.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index 21f5025c3945..8873b9b439ff 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -385,6 +385,8 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 
         while (nr_sects && !ret) {
                 unsigned int sector_size = q->limits.logical_block_size;
+                unsigned int max_discard_sectors =
+                        min(q->limits.max_discard_sectors, UINT_MAX >> 9);
 
                 bio = bio_alloc(gfp_mask, 1);
                 if (!bio)
@@ -411,10 +413,10 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
                  * touch many more blocks on disk than the actual payload
                  * length.
                  */
-                if (nr_sects > queue_max_hw_sectors(q)) {
-                        bio->bi_size = queue_max_hw_sectors(q) << 9;
-                        nr_sects -= queue_max_hw_sectors(q);
-                        sector += queue_max_hw_sectors(q);
+                if (nr_sects > max_discard_sectors) {
+                        bio->bi_size = max_discard_sectors << 9;
+                        nr_sects -= max_discard_sectors;
+                        sector += max_discard_sectors;
                 } else {
                         bio->bi_size = nr_sects << 9;
                         nr_sects = 0;