[PATCH v4: {linux-4.14.y} ] dm cache: submit writethrough writes in parallel to origin and cache

From: john.p.donnelly@oracle.com
To: linux-kernel@vger.kernel.org
Subject: [PATCH v4: {linux-4.14.y} ] dm cache: submit writethrough writes in parallel to origin and cache
Date: Tue,  4 Aug 2020 17:07:46 -0700	[thread overview]
Message-ID: <20200805000746.53112-1-john.p.donnelly@oracle.com> (raw)

From: Mike Snitzer <snitzer@redhat.com>

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>

(cherry picked from commit 2df3bae9a6543e90042291707b8db0cbfbae9ee9)

Fixes: 4ec34f2196d125ff781170ddc6c3058c08ec5e73 (dm bio record:
save/restore bi_end_io and bi_integrity )

4ec34f21 introduced a mkfs.ext4 hang on a LVM device that has been
modified with lvconvert --cachemode=writethrough.

CC:stable@vger.kernel.org for 4.14.y

Signed-off-by: John Donnelly <john.p.donnelly@oracle.com>
Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>
---
 drivers/md/dm-cache-target.c | 92 ++++++++++++++++++--------------------------
 1 file changed, 37 insertions(+), 55 deletions(-)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 69cdb29ef6be..2732d1df05fa 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -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;
 
@@ -537,11 +538,6 @@ static void wake_deferred_bio_worker(struct cache *cache)
 	queue_work(cache->wq, &cache->deferred_bio_worker);
 }
 
-static void wake_deferred_writethrough_worker(struct cache *cache)
-{
-	queue_work(cache->wq, &cache->deferred_writethrough_worker);
-}
-
 static void wake_migration_worker(struct cache *cache)
 {
 	if (passthrough_mode(&cache->features))
@@ -868,16 +864,23 @@ 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)
 {
@@ -937,57 +940,26 @@ static void issue_op(struct bio *bio, void *context)
 	accounted_request(cache, bio);
 }
 
-static void defer_writethrough_bio(struct cache *cache, struct bio *bio)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&cache->lock, flags);
-	bio_list_add(&cache->deferred_writethrough_bios, bio);
-	spin_unlock_irqrestore(&cache->lock, flags);
-
-	wake_deferred_writethrough_worker(cache);
-}
-
-static void writethrough_endio(struct bio *bio)
-{
-	struct per_bio_data *pb = get_per_bio_data(bio, PB_DATA_SIZE_WT);
-
-	dm_unhook_bio(&pb->hook_info, bio);
-
-	if (bio->bi_status) {
-		bio_endio(bio);
-		return;
-	}
-
-	dm_bio_restore(&pb->bio_details, bio);
-	remap_to_cache(pb->cache, bio, pb->cblock);
-
-	/*
-	 * We can't issue this bio directly, since we're in interrupt
-	 * context.  So it gets put on a bio list for processing by the
-	 * worker thread.
-	 */
-	defer_writethrough_bio(pb->cache, 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);
+
+	BUG_ON(!origin_bio);
 
-	pb->cache = cache;
-	pb->cblock = cblock;
-	dm_hook_bio(&pb->hook_info, bio, writethrough_endio, NULL);
-	dm_bio_record(&pb->bio_details, bio);
+	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_origin_clear_discard(pb->cache, bio, oblock);
+	remap_to_cache(cache, bio, cblock);
 }
 
 /*----------------------------------------------------------------
@@ -1873,7 +1845,7 @@ static int map_bio(struct cache *cache, struct bio *bio, dm_oblock_t block,
 		} else {
 			if (bio_data_dir(bio) == WRITE && writethrough_mode(&cache->features) &&
 			    !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 +2104,9 @@ static void destroy(struct cache *cache)
 		kfree(cache->ctr_args[i]);
 	kfree(cache->ctr_args);
 
+	if (cache->bs)
+		bioset_free(cache->bs);
+
 	kfree(cache);
 }
 
@@ -2589,6 +2564,13 @@ 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->features)) {
+		/* 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);
 
-- 
1.8.3.1

