From b1092c9af9ed88dd2fc8345d987dfb7efe7be8f0 Mon Sep 17 00:00:00 2001 From: Michael Lyle Date: Mon, 8 Jan 2018 12:21:24 -0800 Subject: bcache: allow quick writeback when backing idle If the control system would wait for at least half a second, and there's been no reqs hitting the backing disk for awhile: use an alternate mode where we have at most one contiguous set of writebacks in flight at a time. (But don't otherwise delay). If front-end IO appears, it will still be quick, as it will only have to contend with one real operation in flight. But otherwise, we'll be sending data to the backing disk as quickly as it can accept it (with one op at a time). Signed-off-by: Michael Lyle Reviewed-by: Tang Junhui Acked-by: Coly Li Signed-off-by: Jens Axboe --- drivers/md/bcache/writeback.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'drivers/md/bcache/writeback.c') diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 6e1d2fde43df..f82ffb2e9b9b 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -356,6 +356,27 @@ static void read_dirty(struct cached_dev *dc) delay = writeback_delay(dc, size); + /* If the control system would wait for at least half a + * second, and there's been no reqs hitting the backing disk + * for awhile: use an alternate mode where we have at most + * one contiguous set of writebacks in flight at a time. If + * someone wants to do IO it will be quick, as it will only + * have to contend with one operation in flight, and we'll + * be round-tripping data to the backing disk as quickly as + * it can accept it. + */ + if (delay >= HZ / 2) { + /* 3 means at least 1.5 seconds, up to 7.5 if we + * have slowed way down. + */ + if (atomic_inc_return(&dc->backing_idle) >= 3) { + /* Wait for current I/Os to finish */ + closure_sync(&cl); + /* And immediately launch a new set. */ + delay = 0; + } + } + while (!kthread_should_stop() && delay) { schedule_timeout_interruptible(delay); delay = writeback_delay(dc, 0); -- cgit v1.2.3-59-g8ed1b