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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C55D8C433EF for ; Wed, 9 Mar 2022 14:22:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233501AbiCIOXs (ORCPT ); Wed, 9 Mar 2022 09:23:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34568 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233506AbiCIOXn (ORCPT ); Wed, 9 Mar 2022 09:23:43 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 792D6106CA4 for ; Wed, 9 Mar 2022 06:22:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646835758; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=eBdr36BGk28rRgdEtMTExffYNjapNYQlJHsocuTv1h0=; b=Qq/u3Cy5BYxH1q+I8LWNQkhqW8VE0XSVhCqapSqIzWMNKwRxEya83I1u4EdK1luY15UFux 1UKLnn75TyszoWO1QO7cuiyVCnq/ZngOBiy4yyGPksBaHP12Qz50KTcwkX5fgpLjgKlFch lzkz0uxJ+9/X41FQNAdOdooVB0W/bLo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-656-79oIyWLvPSKnb0LlI_EVJA-1; Wed, 09 Mar 2022 09:22:33 -0500 X-MC-Unique: 79oIyWLvPSKnb0LlI_EVJA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 79551824FA6; Wed, 9 Mar 2022 14:22:31 +0000 (UTC) Received: from [10.22.18.30] (unknown [10.22.18.30]) by smtp.corp.redhat.com (Postfix) with ESMTP id D937923760; Wed, 9 Mar 2022 14:22:30 +0000 (UTC) Message-ID: <45202ef8-1c4a-0f08-d394-b6e0de1307c1@redhat.com> Date: Wed, 9 Mar 2022 09:22:30 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH-mm v2] mm/list_lru: Optimize memcg_reparent_list_lru_node() Content-Language: en-US To: Roman Gushchin Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song References: <20220309011824.1454619-1-longman@redhat.com> <54ea34a9-e261-3521-ce11-efc59c9a803c@redhat.com> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/8/22 23:46, Roman Gushchin wrote: > On Tue, Mar 08, 2022 at 10:12:48PM -0500, Waiman Long wrote: >> On 3/8/22 21:13, Roman Gushchin wrote: >>> On Tue, Mar 08, 2022 at 08:18:24PM -0500, Waiman Long wrote: >>>> Since commit 2c80cd57c743 ("mm/list_lru.c: fix list_lru_count_node() >>>> to be race free"), we are tracking the total number of lru >>>> entries in a list_lru_node in its nr_items field. In the case of >>>> memcg_reparent_list_lru_node(), there is nothing to be done if nr_items >>>> is 0. We don't even need to take the nlru->lock as no new lru entry >>>> could be added by a racing list_lru_add() to the draining src_idx memcg >>>> at this point. >>>> >>>> Signed-off-by: Waiman Long >>>> --- >>>> mm/list_lru.c | 6 ++++++ >>>> 1 file changed, 6 insertions(+) >>>> >>>> diff --git a/mm/list_lru.c b/mm/list_lru.c >>>> index ba76428ceece..c669d87001a6 100644 >>>> --- a/mm/list_lru.c >>>> +++ b/mm/list_lru.c >>>> @@ -394,6 +394,12 @@ static void memcg_reparent_list_lru_node(struct list_lru *lru, int nid, >>>> int dst_idx = dst_memcg->kmemcg_id; >>>> struct list_lru_one *src, *dst; >>>> + /* >>>> + * If there is no lru entry in this nlru, we can skip it immediately. >>>> + */ >>>> + if (!READ_ONCE(nlru->nr_items)) >>>> + return; >>> This is a per-node counter, not a per-memcg, right? >> Right. list_lru_node is a per-node structure inside list_lru. >>> If so, do we optimize for the case when all lru items belong to one node and >>> others are empty? >> That is actually the case that I am trying to optimize for. >> >> If a system has many containers. It is also likely each container may mount >> one or more container specific filesystems. Since a container likely use >> just a few cpus, it is highly that only the list_lru_node that contains >> those cpus will be utilized while the rests may be empty. >> >> I got the idea of doing this patch when I was looking at a crash dump >> related to the list_lru code. That particular crash dump has more than 13k >> list_lru's and thousands of mount points. I had notice even if nr_items of a >> list_lru_node is 0, it still tries to transfer lru entries from source idx >> to dest idx. Without doing an lock/unlock and loading a cacheline from the >> memcg_lrus, it can save some time. That can be substantial saving if we are >> talking about thousands of list_lru's. > Cool! Makes total sense to me. Thanks for the explanation! > Would you mind to add this text to the commit log? > > Reviewed-by: Roman Gushchin Sure. I will add some of it into the commit log. Cheers, Longman