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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 232DDC38A2B for ; Wed, 15 Apr 2020 17:20:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB4A72078B for ; Wed, 15 Apr 2020 17:20:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586971208; bh=ovMKnAPlzYZnKPMk0z75BaaEyMP8JPyVH/ZRsJypP4w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=NyEaKXxUMtHNFrDFHDpe6OG+wQiRC1ZE+tt2VF13tX3AwkBwp1yR+7aJuB04QuqrL jVAT2eNMbawJZvzum4QVSaPpgyp18tcaxqO5jsv0P4RmJ0+9OxGdPSvIvWgLA/c2bl s1OZQpaCOhDK+6EYWWa20vdel84d6AdEN6LznYG0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2410716AbgDORT4 (ORCPT ); Wed, 15 Apr 2020 13:19:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:33392 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404707AbgDORTy (ORCPT ); Wed, 15 Apr 2020 13:19:54 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3EF69214D8; Wed, 15 Apr 2020 17:19:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586971193; bh=ovMKnAPlzYZnKPMk0z75BaaEyMP8JPyVH/ZRsJypP4w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1ZZU2jx0dKEUvOrUu8gv7eFb8LeXCpuHC/ov/AcBUdT8WCImTZBxbps9PfXSzyudb +nLiJl6oLu+1upHxH8Rk3sPRNsbpaNq/dkAkLxHXsMzp1v6nxGes1FxYE6C6mM9Uqq 5q70S7cVrcJa0bwehMJdakk+68yU4Uv6d7/dhq1A= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E . McKenney" Subject: [PATCH tip/core/rcu 3/4] rcu/tree: Count number of batched kfree_rcu() locklessly Date: Wed, 15 Apr 2020 10:19:49 -0700 Message-Id: <20200415171950.9424-3-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200415171924.GA9270@paulmck-ThinkPad-P72> References: <20200415171924.GA9270@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Joel Fernandes (Google)" 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 05dcbf8..aef587e 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; -- 2.9.5