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Commit 2df3bae9 authored by Mike Snitzer's avatar Mike Snitzer
Browse files

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: default avatarMike Snitzer <snitzer@redhat.com>
parent 8e3c3827

drivers/md/dm-cache-target.c

+37 −17
Original line number Diff line number Diff line
@@ -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.

	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,

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);