Commit f9a8e0cd authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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dm thin: optimize power of two block size 



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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 49296309

drivers/md/dm-thin.c

+16 −7
Original line number Diff line number Diff line
@@ -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 thin_c *tc, struct bio *bio) 
{

	sector_t block_nr = bio->bi_sector;



	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, struct bio *bio, dm_block_t block) 
	sector_t bi_sector = bio->bi_sector;



	bio->bi_bdev = tc->pool_dev->bdev;

	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 *pool, struct list_head *head, 
 */

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 mapped_device *pool_md, 


	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);

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