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Commit 19b0092e authored by Mike Snitzer's avatar Mike Snitzer Committed by Alasdair G Kergon
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dm cache: reduce bio front_pad size in writeback mode 



A recent patch to fix the dm cache target's writethrough mode extended
the bio's front_pad to include a 1056-byte struct dm_bio_details.
Writeback mode doesn't need this, so this patch reduces the
per_bio_data_size to 16 bytes in this case instead of 1096.

The dm_bio_details structure was added in "dm cache: fix writes to
cache device in writethrough mode" which fixed commit e2e74d61 ("dm
cache: fix race in writethrough implementation").  In writeback mode
we avoid allocating the writethrough-specific members of the
per_bio_data structure (the dm_bio_details structure included).

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent b844fe69

drivers/md/dm-cache-target.c

+34 −13
Original line number Diff line number Diff line
@@ -202,7 +202,11 @@ struct per_bio_data { 
	unsigned req_nr:2;

	struct dm_deferred_entry *all_io_entry;



	/* writethrough fields */

	/*

	 * writethrough fields.  These MUST remain at the end of this

	 * structure and the 'cache' member must be the first as it

	 * is used to determine the offsetof the writethrough fields.

	 */

	struct cache *cache;

	dm_cblock_t cblock;

	bio_end_io_t *saved_bi_end_io;
@@ -515,16 +519,28 @@ static void save_stats(struct cache *cache) 
/*----------------------------------------------------------------

 * Per bio data

 *--------------------------------------------------------------*/

static struct per_bio_data *get_per_bio_data(struct bio *bio)



/*

 * If using writeback, leave out struct per_bio_data's writethrough fields.

 */

#define PB_DATA_SIZE_WB (offsetof(struct per_bio_data, cache))

#define PB_DATA_SIZE_WT (sizeof(struct per_bio_data))



static size_t get_per_bio_data_size(struct cache *cache)

{

	return cache->features.write_through ? PB_DATA_SIZE_WT : PB_DATA_SIZE_WB;

}



static struct per_bio_data *get_per_bio_data(struct bio *bio, size_t data_size)

{

	struct per_bio_data *pb = dm_per_bio_data(bio, sizeof(struct per_bio_data));

	struct per_bio_data *pb = dm_per_bio_data(bio, data_size);

	BUG_ON(!pb);

	return pb;

}



static struct per_bio_data *init_per_bio_data(struct bio *bio)

static struct per_bio_data *init_per_bio_data(struct bio *bio, size_t data_size)

{

	struct per_bio_data *pb = get_per_bio_data(bio);

	struct per_bio_data *pb = get_per_bio_data(bio, data_size);



	pb->tick = false;

	pb->req_nr = dm_bio_get_target_bio_nr(bio);
@@ -558,7 +574,8 @@ static void remap_to_cache(struct cache *cache, struct bio *bio, 
static void check_if_tick_bio_needed(struct cache *cache, struct bio *bio)

{

	unsigned long flags;

	struct per_bio_data *pb = get_per_bio_data(bio);

	size_t pb_data_size = get_per_bio_data_size(cache);

	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);



	spin_lock_irqsave(&cache->lock, flags);

	if (cache->need_tick_bio &&
@@ -637,7 +654,7 @@ static void defer_writethrough_bio(struct cache *cache, struct bio *bio) 


static void writethrough_endio(struct bio *bio, int err)

{

	struct per_bio_data *pb = get_per_bio_data(bio);

	struct per_bio_data *pb = get_per_bio_data(bio, PB_DATA_SIZE_WT);

	bio->bi_end_io = pb->saved_bi_end_io;



	if (err) {
@@ -665,7 +682,7 @@ static void writethrough_endio(struct bio *bio, int err) 
static void remap_to_origin_then_cache(struct cache *cache, struct bio *bio,

				       dm_oblock_t oblock, dm_cblock_t cblock)

{

	struct per_bio_data *pb = get_per_bio_data(bio);

	struct per_bio_data *pb = get_per_bio_data(bio, PB_DATA_SIZE_WT);



	pb->cache = cache;

	pb->cblock = cblock;
@@ -1039,7 +1056,8 @@ static void defer_bio(struct cache *cache, struct bio *bio) 


static void process_flush_bio(struct cache *cache, struct bio *bio)

{

	struct per_bio_data *pb = get_per_bio_data(bio);

	size_t pb_data_size = get_per_bio_data_size(cache);

	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);



	BUG_ON(bio->bi_size);

	if (!pb->req_nr)
@@ -1111,7 +1129,8 @@ static void process_bio(struct cache *cache, struct prealloc *structs, 
	dm_oblock_t block = get_bio_block(cache, bio);

	struct dm_bio_prison_cell *cell_prealloc, *old_ocell, *new_ocell;

	struct policy_result lookup_result;

	struct per_bio_data *pb = get_per_bio_data(bio);

	size_t pb_data_size = get_per_bio_data_size(cache);

	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);

	bool discarded_block = is_discarded_oblock(cache, block);

	bool can_migrate = discarded_block || spare_migration_bandwidth(cache);
@@ -1885,7 +1904,6 @@ static int cache_create(struct cache_args *ca, struct cache **result) 


	cache->ti = ca->ti;

	ti->private = cache;

	ti->per_bio_data_size = sizeof(struct per_bio_data);

	ti->num_flush_bios = 2;

	ti->flush_supported = true;
@@ -1894,6 +1912,7 @@ static int cache_create(struct cache_args *ca, struct cache **result) 
	ti->discard_zeroes_data_unsupported = true;



	memcpy(&cache->features, &ca->features, sizeof(cache->features));

	ti->per_bio_data_size = get_per_bio_data_size(cache);



	cache->callbacks.congested_fn = cache_is_congested;

	dm_table_add_target_callbacks(ti->table, &cache->callbacks);
@@ -2096,6 +2115,7 @@ static int cache_map(struct dm_target *ti, struct bio *bio) 


	int r;

	dm_oblock_t block = get_bio_block(cache, bio);

	size_t pb_data_size = get_per_bio_data_size(cache);

	bool can_migrate = false;

	bool discarded_block;

	struct dm_bio_prison_cell *cell;
@@ -2112,7 +2132,7 @@ static int cache_map(struct dm_target *ti, struct bio *bio) 
		return DM_MAPIO_REMAPPED;

	}



	pb = init_per_bio_data(bio);

	pb = init_per_bio_data(bio, pb_data_size);



	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA | REQ_DISCARD)) {

		defer_bio(cache, bio);
@@ -2197,7 +2217,8 @@ static int cache_end_io(struct dm_target *ti, struct bio *bio, int error) 
{

	struct cache *cache = ti->private;

	unsigned long flags;

	struct per_bio_data *pb = get_per_bio_data(bio);

	size_t pb_data_size = get_per_bio_data_size(cache);

	struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);



	if (pb->tick) {

		policy_tick(cache->policy);