linux-kernel - [PATCH] mm: lru_cache_disable: use synchronize_rcu

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Message-ID: <YpToHCmnx/HEcVyR@fuller.cnet>
Date:   Mon, 30 May 2022 12:51:56 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Michael Larabel <Michael@...haellarabel.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH] mm: lru_cache_disable: use synchronize_rcu_expedited 


commit ff042f4a9b050895a42cae893cc01fa2ca81b95c replaced
lru_cache_disable's usage of work queues with synchronize_rcu.

Some users reported performance regressions due to this commit, for example:
https://lore.kernel.org/all/20220521234616.GO1790663@paulmck-ThinkPad-P17-Gen-1/T/

Switching to synchronize_rcu_expedited fixes the problem.

Tested-by: Stefan Wahren <stefan.wahren@...e.com> 
Tested-by: Michael Larabel <Michael@...haelLarabel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

diff --git a/mm/swap.c b/mm/swap.c
index bceff0cb559c..04a8bbf9817a 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -879,7 +879,7 @@ void lru_cache_disable(void)
 	 * lru_disable_count = 0 will have exited the critical
 	 * section when synchronize_rcu() returns.
 	 */
-	synchronize_rcu();
+	synchronize_rcu_expedited();
 #ifdef CONFIG_SMP
 	__lru_add_drain_all(true);
 #else