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dm cache: submit writethrough writes in parallel to origin and cache 

Discontinue issuing writethrough write IO in series to the origin and
then cache.

Use bio_clone_fast() to create a new origin clone bio that will be
mapped to the origin device and then bio_chain() it to the bio that gets
remapped to the cache device.  The origin clone bio does _not_ have a
copy of the per_bio_data -- as such check_if_tick_bio_needed() will not
be called.

The cache bio (parent bio) will not complete until the origin bio has
completed -- this fulfills bio_clone_fast()'s requirements as well as
the requirement to not complete the original IO until the write IO has
completed to both the origin and cache device.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
hifive-unleashed-5.1
Mike Snitzer 2017-10-19 17:16:54 -04:00
parent 8e3c382777
commit 2df3bae9a6
1 changed files with 37 additions and 17 deletions
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54
drivers/md/dm-cache-target.c
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@ -450,6 +450,7 @@ struct cache {
struct work_struct migration_worker;
struct delayed_work waker;
struct dm_bio_prison_v2 *prison;
struct bio_set *bs;
mempool_t *migration_pool;
@ -868,16 +869,23 @@ static void check_if_tick_bio_needed(struct cache *cache, struct bio *bio)
spin_unlock_irqrestore(&cache->lock, flags);
}
static void remap_to_origin_clear_discard(struct cache *cache, struct bio *bio,
dm_oblock_t oblock)
static void __remap_to_origin_clear_discard(struct cache *cache, struct bio *bio,
dm_oblock_t oblock, bool bio_has_pbd)
{
// FIXME: this is called way too much.
check_if_tick_bio_needed(cache, bio);
if (bio_has_pbd)
check_if_tick_bio_needed(cache, bio);
remap_to_origin(cache, bio);
if (bio_data_dir(bio) == WRITE)
clear_discard(cache, oblock_to_dblock(cache, oblock));
}
static void remap_to_origin_clear_discard(struct cache *cache, struct bio *bio,
dm_oblock_t oblock)
{
// FIXME: check_if_tick_bio_needed() is called way too much through this interface
__remap_to_origin_clear_discard(cache, bio, oblock, true);
}
static void remap_to_cache_dirty(struct cache *cache, struct bio *bio,
dm_oblock_t oblock, dm_cblock_t cblock)
{
@ -971,23 +979,25 @@ static void writethrough_endio(struct bio *bio)
}
/*
* FIXME: send in parallel, huge latency as is.
* When running in writethrough mode we need to send writes to clean blocks
* to both the cache and origin devices. In future we'd like to clone the
* bio and send them in parallel, but for now we're doing them in
* series as this is easier.
* to both the cache and origin devices. Clone the bio and send them in parallel.
*/
static void remap_to_origin_then_cache(struct cache *cache, struct bio *bio,
dm_oblock_t oblock, dm_cblock_t cblock)
static void remap_to_origin_and_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, PB_DATA_SIZE_WT);
struct bio *origin_bio = bio_clone_fast(bio, GFP_NOIO, cache->bs);
pb->cache = cache;
pb->cblock = cblock;
dm_hook_bio(&pb->hook_info, bio, writethrough_endio, NULL);
dm_bio_record(&pb->bio_details, bio);
BUG_ON(!origin_bio);
remap_to_origin_clear_discard(pb->cache, bio, oblock);
bio_chain(origin_bio, bio);
/*
* Passing false to __remap_to_origin_clear_discard() skips
* all code that might use per_bio_data (since clone doesn't have it)
*/
__remap_to_origin_clear_discard(cache, origin_bio, oblock, false);
submit_bio(origin_bio);
remap_to_cache(cache, bio, cblock);
}
/*----------------------------------------------------------------
@ -1873,7 +1883,7 @@ static int map_bio(struct cache *cache, struct bio *bio, dm_oblock_t block,
} else {
if (bio_data_dir(bio) == WRITE && writethrough_mode(cache) &&
!is_dirty(cache, cblock)) {
remap_to_origin_then_cache(cache, bio, block, cblock);
remap_to_origin_and_cache(cache, bio, block, cblock);
accounted_begin(cache, bio);
} else
remap_to_cache_dirty(cache, bio, block, cblock);
@ -2132,6 +2142,9 @@ static void destroy(struct cache *cache)
kfree(cache->ctr_args[i]);
kfree(cache->ctr_args);
if (cache->bs)
bioset_free(cache->bs);
kfree(cache);
}
@ -2578,6 +2591,13 @@ static int cache_create(struct cache_args *ca, struct cache **result)
cache->features = ca->features;
ti->per_io_data_size = get_per_bio_data_size(cache);
if (writethrough_mode(cache)) {
/* Create bioset for writethrough bios issued to origin */
cache->bs = bioset_create(BIO_POOL_SIZE, 0, 0);
if (!cache->bs)
goto bad;
}
cache->callbacks.congested_fn = cache_is_congested;
dm_table_add_target_callbacks(ti->table, &cache->callbacks);