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: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index f21d318..8286492 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1238,15 +1238,10 @@
}
} 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 @@
/*
* 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 @@
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);