From: Mikulas Patocka There is a bug in dm_thin regarding processing discards. When dm-thin receives a discard request with size equal to block size that is not aligned on block size boundary, io_overlaps_block returns true, process_discard treats this discard as a full block discard, deletes the full block - the result is that some data that shouldn't be discarded are discarded. This patch sets the variable "ti->split_discard_requests", 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 --- drivers/md/dm-thin.c | 18 +++++++----------- drivers/md/dm-thin.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel Index: linux/drivers/md/dm-thin.c =================================================================== --- linux.orig/drivers/md/dm-thin.c +++ linux/drivers/md/dm-thin.c @@ -1243,17 +1243,10 @@ static void process_discard(struct thin_ } } 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 makes sure that the discard doesn't span + * a block boundary. So we submit the discard + * to the appropriate block. */ - sector_t offset = pool->sectors_per_block_shift >= 0 ? - bio->bi_sector & (pool->sectors_per_block - 1) : - 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) @@ -2511,7 +2504,8 @@ static void set_discard_limits(struct po /* * This is just a hint, and not enforced. We have to cope with - * bios that overlap 2 blocks. + * bios cover a block partially. A discard that spans a block boundary + * is not sent to this target. */ if (pool->sectors_per_block_shift >= 0) limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT; @@ -2655,6 +2649,8 @@ static int thin_ctr(struct dm_target *ti 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);