bcache: Fix a writeback performance regression
Background writeback works by scanning the btree for dirty data and
adding those keys into a fixed size buffer, then for each dirty key in
the keybuf writing it to the backing device.
When read_dirty() finishes and it's time to scan for more dirty data, we
need to wait for the outstanding writeback IO to finish - they still
take up slots in the keybuf (so that foreground writes can check for
them to avoid races) - without that wait, we'll continually rescan when
we'll be able to add at most a key or two to the keybuf, and that takes
locks that starves foreground IO. Doh.
Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: linux-stable <stable@vger.kernel.org> # >= v3.10
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index b39f6f0..0f12382 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -498,7 +498,7 @@
*/
atomic_t has_dirty;
- struct ratelimit writeback_rate;
+ struct bch_ratelimit writeback_rate;
struct delayed_work writeback_rate_update;
/*
@@ -507,10 +507,9 @@
*/
sector_t last_read;
- /* Number of writeback bios in flight */
- atomic_t in_flight;
+ /* Limit number of writeback bios in flight */
+ struct semaphore in_flight;
struct closure_with_timer writeback;
- struct closure_waitlist writeback_wait;
struct keybuf writeback_keys;