dm writecache: count number of blocks written, not number of write bios

Change dm-writecache, so that it counts the number of blocks written
instead of the number of write bios. Bios can be split and requeued
using the dm_accept_partial_bio function, so counting bios caused
inaccurate results.

Fixes: e3a35d03 ("dm writecache: add event counters")
Reported-by: Yu Kuai <yukuai1@huaweicloud.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

Documentation/admin-guide/device-mapper/writecache.rst

@@ -82,11 +82,11 @@ Status:
 4. the number of blocks under writeback
 5. the number of read blocks
 6. the number of read blocks that hit the cache
-7. the number of write requests
-8. the number of write requests that hit uncommitted block
-9. the number of write requests that hit committed block
-10. the number of write requests that bypass the cache
-11. the number of write requests that are allocated in the cache
+7. the number of write blocks
+8. the number of write blocks that hit uncommitted block
+9. the number of write blocks that hit committed block
+10. the number of write blocks that bypass the cache
+11. the number of write blocks that are allocated in the cache
 12. the number of write requests that are blocked on the freelist
 13. the number of flush requests
 14. the number of discard requests

drivers/md/dm-writecache.c

@@ -1413,6 +1413,9 @@ static void writecache_bio_copy_ssd(struct dm_writecache *wc, struct bio *bio,
 	bio->bi_iter.bi_sector = start_cache_sec;
 	dm_accept_partial_bio(bio, bio_size >> SECTOR_SHIFT);
 
+	wc->stats.writes += bio->bi_iter.bi_size >> wc->block_size_bits;
+	wc->stats.writes_allocate += (bio->bi_iter.bi_size - wc->block_size) >> wc->block_size_bits;
+
 	if (unlikely(wc->uncommitted_blocks >= wc->autocommit_blocks)) {
 		wc->uncommitted_blocks = 0;
 		queue_work(wc->writeback_wq, &wc->flush_work);
@@ -1428,9 +1431,10 @@ static enum wc_map_op writecache_map_write(struct dm_writecache *wc, struct bio
 	do {
 		bool found_entry = false;
 		bool search_used = false;
-		wc->stats.writes++;
-		if (writecache_has_error(wc))
+		if (writecache_has_error(wc)) {
+			wc->stats.writes += bio->bi_iter.bi_size >> wc->block_size_bits;
 			return WC_MAP_ERROR;
+		}
 		e = writecache_find_entry(wc, bio->bi_iter.bi_sector, 0);
 		if (e) {
 			if (!writecache_entry_is_committed(wc, e)) {
@@ -1454,9 +1458,10 @@ static enum wc_map_op writecache_map_write(struct dm_writecache *wc, struct bio
 		if (unlikely(!e)) {
 			if (!WC_MODE_PMEM(wc) && !found_entry) {
 direct_write:
-				wc->stats.writes_around++;
 				e = writecache_find_entry(wc, bio->bi_iter.bi_sector, WFE_RETURN_FOLLOWING);
 				writecache_map_remap_origin(wc, bio, e);
+				wc->stats.writes_around += bio->bi_iter.bi_size >> wc->block_size_bits;
+				wc->stats.writes += bio->bi_iter.bi_size >> wc->block_size_bits;
 				return WC_MAP_REMAP_ORIGIN;
 			}
 			wc->stats.writes_blocked_on_freelist++;
@@ -1470,6 +1475,7 @@ static enum wc_map_op writecache_map_write(struct dm_writecache *wc, struct bio
 bio_copy:
 		if (WC_MODE_PMEM(wc)) {
 			bio_copy_block(wc, bio, memory_data(wc, e));
+			wc->stats.writes++;
 		} else {
 			writecache_bio_copy_ssd(wc, bio, e, search_used);
 			return WC_MAP_REMAP;