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 5EFB0C433FE for ; Wed, 9 Mar 2022 03:12:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231610AbiCIDNw (ORCPT ); Tue, 8 Mar 2022 22:13:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59492 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231602AbiCIDNv (ORCPT ); Tue, 8 Mar 2022 22:13:51 -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 14CC6986E7 for ; Tue, 8 Mar 2022 19:12:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646795572; 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=nKsc/xErvV8M/cbscux0U+SiTUR+sUDjaVJnbgAGPCY=; b=WXfChX5V64A1IYyrWjRUBj2Cm/v4u9gKBRn0H4nSexB6irXcXXWE9Cvv1pEwrSUVbUO6ZV mtVVluxv+azI2w5Ne/i0tIcQhaHMSD01EoxB6DGsVTTvX+AoLS3+W4favtgwfQj0koLkdC KdC9Iscg46avsyG3gBhife88Rf5cAlA= 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-588-LcsQeoj3NWCDn-yzQSdHDA-1; Tue, 08 Mar 2022 22:12:50 -0500 X-MC-Unique: LcsQeoj3NWCDn-yzQSdHDA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7566A1006AA5; Wed, 9 Mar 2022 03:12:49 +0000 (UTC) Received: from [10.22.11.135] (unknown [10.22.11.135]) by smtp.corp.redhat.com (Postfix) with ESMTP id C73535DF21; Wed, 9 Mar 2022 03:12:48 +0000 (UTC) Message-ID: <54ea34a9-e261-3521-ce11-efc59c9a803c@redhat.com> Date: Tue, 8 Mar 2022 22:12:48 -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> From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Cheers, Longman