From 141df8bb5dc052f605de8f48a7aa10290e1384ae Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Fri, 28 Jun 2019 19:59:24 +0800
Subject: [PATCH] bcache: don't set max writeback rate if gc is running
Git-commit: 141df8bb5dc052f605de8f48a7aa10290e1384ae
References: bsc#1140652
Patch-mainline: v5.3-rc1

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 73f0efac2b9f..262f7ef20992 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