[dm-devel] [PATCH 2/2] dm thin: support for non power of 2 pool blocksize

[Mike Snitzer]

Non power of 2 blocksize support is needed to properly align thinp IO
on storage that has non power of 2 optimal IO sizes (e.g. RAID6 10+2).

Use do_div wrappers to support non power of 2 blocksize for the pool's
data device.  do_div provides comparable performance to the power of 2
math that was performed until now (as tested on modern x86_64 hardware).

Verify that the pool's blocksize is a multiple of 64K and that the
pool's data device is a multiple of blocksize.

Eliminate pool structure's 'sectors_per_block', 'block_shift' and
remaining 4 byte holes.

Signed-off-by: Mike Snitzer <snitzer at redhat.com>
---
 drivers/md/dm-thin.c |   56 +++++++++++++++++++++++++++++++++----------------
 1 files changed, 38 insertions(+), 18 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index ce7dd80..91644b4 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -507,10 +507,8 @@ struct pool {
 	struct block_device *md_dev;
 	struct dm_pool_metadata *pmd;
 
-	uint32_t sectors_per_block;
-	unsigned block_shift;
-	dm_block_t offset_mask;
 	dm_block_t low_water_blocks;
+	uint32_t sectors_per_block;
 
 	struct pool_features pf;
 	unsigned low_water_triggered:1;	/* A dm event has been sent */
@@ -523,8 +521,8 @@ struct pool {
 	struct work_struct worker;
 	struct delayed_work waker;
 
-	unsigned ref_count;
 	unsigned long last_commit_jiffies;
+	unsigned ref_count;
 
 	spinlock_t lock;
 	struct bio_list deferred_bios;
@@ -673,9 +671,27 @@ static void requeue_io(struct thin_c *tc)
  * target.
  */
 
+/*
+ * do_div wrappers that don't modify the dividend
+ */
+static inline sector_t dm_thin_do_div(sector_t a, __u32 b)
+{
+	sector_t r = a;
+
+	do_div(r, b);
+	return r;
+}
+
+static inline sector_t dm_thin_do_mod(sector_t a, __u32 b)
+{
+	sector_t tmp = a;
+
+	return do_div(tmp, b);
+}
+
 static dm_block_t get_bio_block(struct thin_c *tc, struct bio *bio)
 {
-	return bio->bi_sector >> tc->pool->block_shift;
+	return dm_thin_do_div(bio->bi_sector, tc->pool->sectors_per_block);
 }
 
 static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
@@ -683,8 +699,8 @@ static void remap(struct thin_c *tc, struct bio *bio, dm_block_t block)
 	struct pool *pool = tc->pool;
 
 	bio->bi_bdev = tc->pool_dev->bdev;
-	bio->bi_sector = (block << pool->block_shift) +
-		(bio->bi_sector & pool->offset_mask);
+	bio->bi_sector = (block * pool->sectors_per_block) +
+		dm_thin_do_mod(bio->bi_sector, pool->sectors_per_block);
 }
 
 static void remap_to_origin(struct thin_c *tc, struct bio *bio)
@@ -929,9 +945,8 @@ static void process_prepared(struct pool *pool, struct list_head *head,
  */
 static int io_overlaps_block(struct pool *pool, struct bio *bio)
 {
-	return !(bio->bi_sector & pool->offset_mask) &&
+	return !dm_thin_do_mod(bio->bi_sector, pool->sectors_per_block) &&
 		(bio->bi_size == (pool->sectors_per_block << SECTOR_SHIFT));
-
 }
 
 static int io_overwrites_block(struct pool *pool, struct bio *bio)
@@ -1234,8 +1249,8 @@ static void process_discard(struct thin_c *tc, struct bio *bio)
 			 * part of the discard that is in a subsequent
 			 * block.
 			 */
-			sector_t offset = bio->bi_sector - (block << pool->block_shift);
-			unsigned remaining = (pool->sectors_per_block - offset) << 9;
+			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);
@@ -1696,8 +1711,6 @@ static struct pool *pool_create(struct mapped_device *pool_md,
 
 	pool->pmd = pmd;
 	pool->sectors_per_block = block_size;
-	pool->block_shift = ffs(block_size) - 1;
-	pool->offset_mask = block_size - 1;
 	pool->low_water_blocks = 0;
 	pool_features_init(&pool->pf);
 	pool->prison = prison_create(PRISON_CELLS);
@@ -1941,12 +1954,18 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	if (kstrtoul(argv[2], 10, &block_size) || !block_size ||
 	    block_size < DATA_DEV_BLOCK_SIZE_MIN_SECTORS ||
 	    block_size > DATA_DEV_BLOCK_SIZE_MAX_SECTORS ||
-	    !is_power_of_2(block_size)) {
+	    dm_thin_do_mod(block_size, DATA_DEV_BLOCK_SIZE_MIN_SECTORS)) {
 		ti->error = "Invalid block size";
 		r = -EINVAL;
 		goto out;
 	}
 
+	if (dm_thin_do_mod(ti->len, block_size)) {
+		ti->error = "Data device is not a multiple of block size";
+		r = -EINVAL;
+		goto out;
+	}
+
 	if (kstrtoull(argv[3], 10, (unsigned long long *)&low_water_blocks)) {
 		ti->error = "Invalid low water mark";
 		r = -EINVAL;
@@ -2089,7 +2108,7 @@ static int pool_preresume(struct dm_target *ti)
 	if (r)
 		return r;
 
-	data_size = ti->len >> pool->block_shift;
+	data_size = dm_thin_do_div(ti->len, pool->sectors_per_block);
 	r = dm_pool_get_data_dev_size(pool->pmd, &sb_data_size);
 	if (r) {
 		DMERR("failed to retrieve data device size");
@@ -2709,17 +2728,18 @@ static int thin_iterate_devices(struct dm_target *ti,
 {
 	dm_block_t blocks;
 	struct thin_c *tc = ti->private;
+	struct pool *pool = tc->pool;
 
 	/*
 	 * We can't call dm_pool_get_data_dev_size() since that blocks.  So
 	 * we follow a more convoluted path through to the pool's target.
 	 */
-	if (!tc->pool->ti)
+	if (!pool->ti)
 		return 0;	/* nothing is bound */
 
-	blocks = tc->pool->ti->len >> tc->pool->block_shift;
+	blocks = dm_thin_do_div(pool->ti->len, pool->sectors_per_block);
 	if (blocks)
-		return fn(ti, tc->pool_dev, 0, tc->pool->sectors_per_block * blocks, data);
+		return fn(ti, tc->pool_dev, 0, pool->sectors_per_block * blocks, data);
 
 	return 0;
 }
-- 
1.7.1