From: Mikulas Patocka mpatocka@redhat.com
[ 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@redhat.com Signed-off-by: Mike Snitzer snitzer@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/dm-writecache.c | 38 ++++++++++++++++++++++++++++++-------- 1 file changed, 30 insertions(+), 8 deletions(-)
diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c index 4f72b6f66c3a..7bb4d83e90cc 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; }