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dm cache: promotion optimisation for writes 

If a write block triggers promotion and covers a whole block we can
avoid a copy.

Introduce dm_{hook,unhook}_bio to simplify saving and restoring bio
fields (bi_private is now used by overwrite).  Switch writethrough
support over to using these helpers too.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Joe Thornber 2013-10-31 13:55:48 -04:00 committed by Mike Snitzer
parent c86c30706c
commit c9d28d5d09
1 changed files with 87 additions and 6 deletions
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93
drivers/md/dm-cache-target.c
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@ -61,6 +61,34 @@ static void free_bitset(unsigned long *bits)
/*----------------------------------------------------------------*/
/*
* There are a couple of places where we let a bio run, but want to do some
* work before calling its endio function. We do this by temporarily
* changing the endio fn.
*/
struct dm_hook_info {
bio_end_io_t *bi_end_io;
void *bi_private;
};
static void dm_hook_bio(struct dm_hook_info *h, struct bio *bio,
bio_end_io_t *bi_end_io, void *bi_private)
{
h->bi_end_io = bio->bi_end_io;
h->bi_private = bio->bi_private;
bio->bi_end_io = bi_end_io;
bio->bi_private = bi_private;
}
static void dm_unhook_bio(struct dm_hook_info *h, struct bio *bio)
{
bio->bi_end_io = h->bi_end_io;
bio->bi_private = h->bi_private;
}
/*----------------------------------------------------------------*/
#define PRISON_CELLS 1024
#define MIGRATION_POOL_SIZE 128
#define COMMIT_PERIOD HZ
@ -214,7 +242,7 @@ struct per_bio_data {
*/
struct cache *cache;
dm_cblock_t cblock;
bio_end_io_t *saved_bi_end_io;
struct dm_hook_info hook_info;
struct dm_bio_details bio_details;
};
@ -231,6 +259,7 @@ struct dm_cache_migration {
bool writeback:1;
bool demote:1;
bool promote:1;
bool requeue_holder:1;
struct dm_bio_prison_cell *old_ocell;
struct dm_bio_prison_cell *new_ocell;
@ -666,7 +695,8 @@ 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, PB_DATA_SIZE_WT);
bio->bi_end_io = pb->saved_bi_end_io;
dm_unhook_bio(&pb->hook_info, bio);
if (err) {
bio_endio(bio, err);
@ -697,9 +727,8 @@ static void remap_to_origin_then_cache(struct cache *cache, struct bio *bio,
pb->cache = cache;
pb->cblock = cblock;
pb->saved_bi_end_io = bio->bi_end_io;
dm_hook_bio(&pb->hook_info, bio, writethrough_endio, NULL);
dm_bio_record(&pb->bio_details, bio);
bio->bi_end_io = writethrough_endio;
remap_to_origin_clear_discard(pb->cache, bio, oblock);
}
@ -841,7 +870,12 @@ static void migration_success_post_commit(struct dm_cache_migration *mg)
cleanup_migration(mg);
} else {
cell_defer(cache, mg->new_ocell, true);
if (mg->requeue_holder)
cell_defer(cache, mg->new_ocell, true);
else {
bio_endio(mg->new_ocell->holder, 0);
cell_defer(cache, mg->new_ocell, false);
}
clear_dirty(cache, mg->new_oblock, mg->cblock);
cleanup_migration(mg);
}
@ -892,6 +926,42 @@ static void issue_copy_real(struct dm_cache_migration *mg)
}
}
static void overwrite_endio(struct bio *bio, int err)
{
struct dm_cache_migration *mg = bio->bi_private;
struct cache *cache = mg->cache;
size_t pb_data_size = get_per_bio_data_size(cache);
struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
unsigned long flags;
if (err)
mg->err = true;
spin_lock_irqsave(&cache->lock, flags);
list_add_tail(&mg->list, &cache->completed_migrations);
dm_unhook_bio(&pb->hook_info, bio);
mg->requeue_holder = false;
spin_unlock_irqrestore(&cache->lock, flags);
wake_worker(cache);
}
static void issue_overwrite(struct dm_cache_migration *mg, struct bio *bio)
{
size_t pb_data_size = get_per_bio_data_size(mg->cache);
struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
dm_hook_bio(&pb->hook_info, bio, overwrite_endio, mg);
remap_to_cache_dirty(mg->cache, bio, mg->new_oblock, mg->cblock);
generic_make_request(bio);
}
static bool bio_writes_complete_block(struct cache *cache, struct bio *bio)
{
return (bio_data_dir(bio) == WRITE) &&
(bio->bi_size == (cache->sectors_per_block << SECTOR_SHIFT));
}
static void avoid_copy(struct dm_cache_migration *mg)
{
atomic_inc(&mg->cache->stats.copies_avoided);
@ -906,9 +976,17 @@ static void issue_copy(struct dm_cache_migration *mg)
if (mg->writeback || mg->demote)
avoid = !is_dirty(cache, mg->cblock) ||
is_discarded_oblock(cache, mg->old_oblock);
else
else {
struct bio *bio = mg->new_ocell->holder;
avoid = is_discarded_oblock(cache, mg->new_oblock);
if (!avoid && bio_writes_complete_block(cache, bio)) {
issue_overwrite(mg, bio);
return;
}
}
avoid ? avoid_copy(mg) : issue_copy_real(mg);
}
@ -998,6 +1076,7 @@ static void promote(struct cache *cache, struct prealloc *structs,
mg->writeback = false;
mg->demote = false;
mg->promote = true;
mg->requeue_holder = true;
mg->cache = cache;
mg->new_oblock = oblock;
mg->cblock = cblock;
@ -1019,6 +1098,7 @@ static void writeback(struct cache *cache, struct prealloc *structs,
mg->writeback = true;
mg->demote = false;
mg->promote = false;
mg->requeue_holder = true;
mg->cache = cache;
mg->old_oblock = oblock;
mg->cblock = cblock;
@ -1042,6 +1122,7 @@ static void demote_then_promote(struct cache *cache, struct prealloc *structs,
mg->writeback = false;
mg->demote = true;
mg->promote = true;
mg->requeue_holder = true;
mg->cache = cache;
mg->old_oblock = old_oblock;
mg->new_oblock = new_oblock;