From: Mikulas Patocka dm-thin will be most likely used with a block size that is a power of two. So it should be optimized for this case. This patch changes division and modulo operations to shifts and bit masks if block size is a power of two. A test that bi_sector is divisible by a block size is removed from io_overlaps_block. Device mapper never sends bios that span a block boundary. Consequently, if we tested that bi_size is equivalent to block size, bi_sector must already be on a block boundary. Signed-off-by: Mikulas Patocka Signed-off-by: Alasdair G Kergon --- drivers/md/dm-thin.c | 23 ++++++++++++++++------- 1 file changed, 16 insertions(+), 7 deletions(-) Index: linux/drivers/md/dm-thin.c =================================================================== --- linux.orig/drivers/md/dm-thin.c +++ linux/drivers/md/dm-thin.c @@ -512,6 +512,7 @@ struct pool { dm_block_t low_water_blocks; uint32_t sectors_per_block; + int sectors_per_block_shift; struct pool_features pf; unsigned low_water_triggered:1; /* A dm event has been sent */ @@ -679,7 +680,10 @@ static dm_block_t get_bio_block(struct t { sector_t block_nr = bio->bi_sector; - (void) sector_div(block_nr, tc->pool->sectors_per_block); + if (tc->pool->sectors_per_block_shift < 0) + (void) sector_div(block_nr, tc->pool->sectors_per_block); + else + block_nr >>= tc->pool->sectors_per_block_shift; return block_nr; } @@ -690,8 +694,12 @@ static void remap(struct thin_c *tc, str sector_t bi_sector = bio->bi_sector; bio->bi_bdev = tc->pool_dev->bdev; - bio->bi_sector = (block * pool->sectors_per_block) + - sector_div(bi_sector, pool->sectors_per_block); + if (tc->pool->sectors_per_block_shift < 0) + bio->bi_sector = (block * pool->sectors_per_block) + + sector_div(bi_sector, pool->sectors_per_block); + else + bio->bi_sector = (block << pool->sectors_per_block_shift) | + (bi_sector & (pool->sectors_per_block - 1)); } static void remap_to_origin(struct thin_c *tc, struct bio *bio) @@ -936,10 +944,7 @@ static void process_prepared(struct pool */ static int io_overlaps_block(struct pool *pool, struct bio *bio) { - sector_t bi_sector = bio->bi_sector; - - return !sector_div(bi_sector, pool->sectors_per_block) && - (bio->bi_size == (pool->sectors_per_block << SECTOR_SHIFT)); + return bio->bi_size == (pool->sectors_per_block << SECTOR_SHIFT); } static int io_overwrites_block(struct pool *pool, struct bio *bio) @@ -1721,6 +1726,10 @@ static struct pool *pool_create(struct m pool->pmd = pmd; pool->sectors_per_block = block_size; + if (block_size & (block_size - 1)) + pool->sectors_per_block_shift = -1; + else + pool->sectors_per_block_shift = __ffs(block_size); pool->low_water_blocks = 0; pool_features_init(&pool->pf); pool->prison = prison_create(PRISON_CELLS);