This is a note to let you know that I've just added the patch titled dm writecache: don't split bios when overwriting contiguous cache content to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: dm-writecache-don-t-split-bios-when-overwriting-cont.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 02c855f35366133b1aded8e63f360e427331be79 Author: Mikulas Patocka <mpatocka@xxxxxxxxxx> Date: Wed May 26 10:29:45 2021 -0400 dm writecache: don't split bios when overwriting contiguous cache content [ Upstream commit ee50cc19d80e9b9a8283d1fb517a778faf2f6899 ] If dm-writecache overwrites existing cached data, it splits the incoming bio into many block-sized bios. The I/O scheduler does merge these bios into one large request but this needless splitting and merging causes performance degradation. Fix this by avoiding bio splitting if the cache target area that is being overwritten is contiguous. Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c index 8628c4aa2e85..64c2980aaa54 100644 --- a/drivers/md/dm-writecache.c +++ b/drivers/md/dm-writecache.c @@ -1360,14 +1360,18 @@ read_next_block: } else { do { bool found_entry = false; + bool search_used = false; if (writecache_has_error(wc)) goto unlock_error; e = writecache_find_entry(wc, bio->bi_iter.bi_sector, 0); if (e) { - if (!writecache_entry_is_committed(wc, e)) + if (!writecache_entry_is_committed(wc, e)) { + search_used = true; goto bio_copy; + } if (!WC_MODE_PMEM(wc) && !e->write_in_progress) { wc->overwrote_committed = true; + search_used = true; goto bio_copy; } found_entry = true; @@ -1404,13 +1408,31 @@ bio_copy: 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++; + if (!search_used) { + 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++; + } else { + struct wc_entry *f; + struct rb_node *next = rb_next(&e->rb_node); + if (!next) + break; + f = container_of(next, struct wc_entry, rb_node); + if (f != e + 1) + break; + if (read_original_sector(wc, f) != + read_original_sector(wc, e) + (wc->block_size >> SECTOR_SHIFT)) + break; + if (unlikely(f->write_in_progress)) + break; + if (writecache_entry_is_committed(wc, f)) + wc->overwrote_committed = true; + e = f; + } bio_size += wc->block_size; current_cache_sec += wc->block_size >> SECTOR_SHIFT; }