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Subject[PATCH v2: [linux-4.14.y] ] dm cache: submit writethrough writes in parallel to origin and cache
Date
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.x .

Signed-off-by: John Donnelly <john.p.donnelly@oracle.com>
Reviewed-by: Somasundaram Krishnasamy <somasundaram.krishnasamy@oracle.com>

conflicts:
drivers/md/dm-cache-target.c. - Corrected usage of
writethrough_mode(&cache->feature) that was caught by
compiler, and removed unused static functions : writethrough_endio(),
defer_writethrough_bio(), wake_deferred_writethrough_worker()
that generated warnings.
---
drivers/md/dm-cache-target.c | 94
++++++++++++++++++--------------------------
1 file changed, 38 insertions(+), 56 deletions(-)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 69cdb29ef6be..2d9566bfe08b 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1,5 +1,5 @@
/*
- * Copyright (C) 2012 Red Hat. All rights reserved.
+ i Copyright (C) 2012 Red Hat. All rights reserved.
*
* This file is released under the GPL.
*/
@@ -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
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