bcache: don't set max writeback rate if gc is running

When gc is running, user space I/O processes may wait inside
bcache code, so no new I/O coming. Indeed this is not a real idle
time, maximum writeback rate should not be set in such situation.
Otherwise a faster writeback thread may compete locks with gc thread
and makes garbage collection slower, which results a longer I/O
freeze period.

This patch checks c->gc_mark_valid in set_at_max_writeback_rate(). If
c->gc_mark_valid is 0 (gc running), set_at_max_writeback_rate() returns
false, then update_writeback_rate() will not set writeback rate to
maximum value even c->idle_counter reaches an idle threshold.

Now writeback thread won't interfere gc thread performance.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 73f0efac2b9f703fe686c82572a599f8a5642494..262f7ef20992a626c605e8b67f9274ef79ff8b69 100644 (file)
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -122,6 +122,9 @@ static void __update_writeback_rate(struct cached_dev *dc)
 static bool set_at_max_writeback_rate(struct cache_set *c,
                                       struct cached_dev *dc)
 {
+       /* Don't set max writeback rate if gc is running */
+       if (!c->gc_mark_valid)
+               return false;
        /*
         * Idle_counter is increased everytime when update_writeback_rate() is
         * called. If all backing devices attached to the same cache set have