When dm-writecache is used with SSD as a cache device, it would submit separate bio for each written block. The I/Os would be merged by the disk scheduler, but this merging degrades performance.
This patch makes dm-writecache submit larger bios - we can submit large bio as long as there is consecutive free space on the cache device. Benchmark (arm64 with 64k page size, using /dev/ram0 as a cache device): fio --bs=512k --iodepth=32 --size=400M --direct=1 --filename=/dev/mapper/cache --rw=randwrite --numjobs=1 --name=test block old new size MiB/s MiB/s --------------------- 512 181 700 1k 347 1256 2k 644 2020 4k 1183 2759 8k 1852 3333 16k 2469 3509 32k 2974 3670 64k 3404 3810 Signed-off-by: Mikulas Patocka <[email protected]> --- drivers/md/dm-writecache.c | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-) Index: linux-2.6/drivers/md/dm-writecache.c =================================================================== --- linux-2.6.orig/drivers/md/dm-writecache.c 2020-01-14 16:11:09.000000000 +0100 +++ linux-2.6/drivers/md/dm-writecache.c 2020-01-14 21:42:44.000000000 +0100 @@ -626,7 +626,7 @@ static void writecache_add_to_freelist(s wc->freelist_size++; } -static struct wc_entry *writecache_pop_from_freelist(struct dm_writecache *wc) +static struct wc_entry *writecache_pop_from_freelist(struct dm_writecache *wc, sector_t expected_sector) { struct wc_entry *e; @@ -635,6 +635,8 @@ static struct wc_entry *writecache_pop_f if (unlikely(!wc->current_free)) return NULL; e = wc->current_free; + if (expected_sector != (sector_t)-1 && unlikely(cache_sector(wc, e) != expected_sector)) + return NULL; next = rb_next(&e->rb_node); rb_erase(&e->rb_node, &wc->freetree); if (unlikely(!next)) @@ -644,6 +646,8 @@ static struct wc_entry *writecache_pop_f if (unlikely(list_empty(&wc->freelist))) return NULL; e = container_of(wc->freelist.next, struct wc_entry, lru); + if (expected_sector != (sector_t)-1 && unlikely(cache_sector(wc, e) != expected_sector)) + return NULL; list_del(&e->lru); } wc->freelist_size--; @@ -1194,7 +1198,7 @@ read_next_block: goto bio_copy; } } - e = writecache_pop_from_freelist(wc); + e = writecache_pop_from_freelist(wc, (sector_t)-1); if (unlikely(!e)) { writecache_wait_on_freelist(wc); continue; @@ -1206,9 +1210,25 @@ bio_copy: if (WC_MODE_PMEM(wc)) { bio_copy_block(wc, bio, memory_data(wc, e)); } else { - dm_accept_partial_bio(bio, wc->block_size >> SECTOR_SHIFT); + unsigned bio_size = wc->block_size; + sector_t start_cache_sec = cache_sector(wc, e); + sector_t current_cache_sec = start_cache_sec + (bio_size >> SECTOR_SHIFT); + + while (bio_size < bio->bi_iter.bi_size) { + struct wc_entry *f = writecache_pop_from_freelist(wc, current_cache_sec); + if (!f) + break; + write_original_sector_seq_count(wc, f, bio->bi_iter.bi_sector + (bio_size >> SECTOR_SHIFT), wc->seq_count); + writecache_insert_entry(wc, f); + wc->uncommitted_blocks++; + bio_size += wc->block_size; + current_cache_sec += wc->block_size >> SECTOR_SHIFT; + } + bio_set_dev(bio, wc->ssd_dev->bdev); - bio->bi_iter.bi_sector = cache_sector(wc, e); + bio->bi_iter.bi_sector = start_cache_sec; + dm_accept_partial_bio(bio, bio_size >> SECTOR_SHIFT); + if (unlikely(wc->uncommitted_blocks >= wc->autocommit_blocks)) { wc->uncommitted_blocks = 0; queue_work(wc->writeback_wq, &wc->flush_work); -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
