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dm writecache: don't split bios when overwriting contiguous cache content

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[ 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>
This commit is contained in:
Mikulas Patocka 2021-05-26 10:29:45 -04:00 committed by Greg Kroah-Hartman
parent 65e780667c
commit 939f750215
1 changed files with 30 additions and 8 deletions
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38
drivers/md/dm-writecache.c
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@ -1360,14 +1360,18 @@ static int writecache_map(struct dm_target *ti, struct bio *bio)
} 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 @@ static int writecache_map(struct dm_target *ti, struct bio *bio)
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;
}