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Commit 49296309 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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dm thin: split discards on block boundary 



This patch sets the variable "ti->split_discard_requests" for the dm thin
target so that device mapper core splits discard requests on a block
boundary.

Consequently, a discard request that spans multiple blocks is never sent
to dm-thin. The patch also removes some code in process_discard that
deals with discards that span multiple blocks.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 7acf0277

drivers/md/dm-thin.c

+7 −9
Original line number Diff line number Diff line
@@ -1238,15 +1238,10 @@ static void process_discard(struct thin_c *tc, struct bio *bio) 
			}

		} else {

			/*

			 * This path is hit if people are ignoring

			 * limits->discard_granularity.  It ignores any

			 * part of the discard that is in a subsequent

			 * block.

			 * The DM core makes sure that the discard doesn't span

			 * a block boundary.  So we submit the discard of a

			 * partial block appropriately.

			 */

			sector_t offset = bio->bi_sector - (block * pool->sectors_per_block);

			unsigned remaining = (pool->sectors_per_block - offset) << SECTOR_SHIFT;

			bio->bi_size = min(bio->bi_size, remaining);



			cell_release_singleton(cell, bio);

			cell_release_singleton(cell2, bio);

			if ((!lookup_result.shared) && pool->pf.discard_passdown)
@@ -2509,7 +2504,8 @@ static void set_discard_limits(struct pool *pool, struct queue_limits *limits) 


	/*

	 * This is just a hint, and not enforced.  We have to cope with

	 * bios that overlap 2 blocks.

	 * bios that cover a block partially.  A discard that spans a block

	 * boundary is not sent to this target.

	 */

	limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;

	limits->discard_zeroes_data = pool->pf.zero_new_blocks;
@@ -2652,6 +2648,8 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv) 
		ti->discards_supported = 1;

		ti->num_discard_requests = 1;

		ti->discard_zeroes_data_unsupported = 1;

		/* Discard requests must be split on a block boundary */

		ti->split_discard_requests = 1;

	}



	dm_put(pool_md);