mainline inclusion from mainline-5.3-rc1 commit 141df8bb5dc052f605de8f48a7aa10290e1384ae category: backport 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> --- drivers/md/bcache/writeback.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index e9ffcea1ca50..d60268fe49e1 100644 --- 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 -- 2.16.4