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>
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 1ab122a..1074409 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -202,7 +202,11 @@
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 @@
/*----------------------------------------------------------------
* 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 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 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 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 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 @@
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 @@
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 @@
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 @@
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 @@
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 @@
{
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);