From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 113F6C47255 for ; Mon, 11 May 2020 21:03:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E3F082078A for ; Mon, 11 May 2020 21:03:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732445AbgEKVDG (ORCPT ); Mon, 11 May 2020 17:03:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44100 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1732034AbgEKU74 (ORCPT ); Mon, 11 May 2020 16:59:56 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A8B6C061A0C; Mon, 11 May 2020 13:59:56 -0700 (PDT) Received: from [5.158.153.53] (helo=tip-bot2.lab.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jYFWj-0005x4-KZ; Mon, 11 May 2020 22:59:53 +0200 Received: from [127.0.1.1] (localhost [IPv6:::1]) by tip-bot2.lab.linutronix.de (Postfix) with ESMTP id 795B61C086B; Mon, 11 May 2020 22:59:39 +0200 (CEST) Date: Mon, 11 May 2020 20:59:39 -0000 From: "tip-bot2 for Joel Fernandes (Google)" Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: core/rcu] rcu/tree: Count number of batched kfree_rcu() locklessly Cc: "Joel Fernandes (Google)" , "Paul E. McKenney" , x86 , LKML MIME-Version: 1.0 Message-ID: <158923077939.390.4370771202419476177.tip-bot2@tip-bot2> X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the core/rcu branch of tip: Commit-ID: a6a82ce18ba443186545d3fefbee8b9419a859dc Gitweb: https://git.kernel.org/tip/a6a82ce18ba443186545d3fefbee8b9419a859dc Author: Joel Fernandes (Google) AuthorDate: Mon, 16 Mar 2020 12:32:28 -04:00 Committer: Paul E. McKenney CommitterDate: Mon, 27 Apr 2020 11:02:50 -07:00 rcu/tree: Count number of batched kfree_rcu() locklessly We can relax the correctness of counting of number of queued objects in favor of not hurting performance, by locklessly sampling per-cpu counters. This should be Ok since under high memory pressure, it should not matter if we are off by a few objects while counting. The shrinker will still do the reclaim. Signed-off-by: Joel Fernandes (Google) [ paulmck: Remove unused "flags" variable. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e299cd0..3f1f574 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2939,7 +2939,7 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp) krcp->head = NULL; } - krcp->count = 0; + WRITE_ONCE(krcp->count, 0); /* * One work is per one batch, so there are two "free channels", @@ -3077,7 +3077,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) krcp->head = head; } - krcp->count++; + WRITE_ONCE(krcp->count, krcp->count + 1); // Set timer to drain after KFREE_DRAIN_JIFFIES. if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && @@ -3097,15 +3097,13 @@ static unsigned long kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) { int cpu; - unsigned long flags, count = 0; + unsigned long count = 0; /* Snapshot count of all CPUs */ for_each_online_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); - spin_lock_irqsave(&krcp->lock, flags); - count += krcp->count; - spin_unlock_irqrestore(&krcp->lock, flags); + count += READ_ONCE(krcp->count); } return count;