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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 e2e74d617e ("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: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mike Snitzer 2013-04-05 15:36:34 +01:00 committed by Alasdair G Kergon
parent b844fe6918
commit 19b0092e26
1 changed files with 34 additions and 13 deletions
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47
drivers/md/dm-cache-target.c
View File

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