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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7F320C433F5 for ; Wed, 9 Mar 2022 02:14:06 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CF7A98D0012; Tue, 8 Mar 2022 21:13:49 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id CA6918D0001; Tue, 8 Mar 2022 21:13:49 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B70388D0012; Tue, 8 Mar 2022 21:13:49 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.26]) by kanga.kvack.org (Postfix) with ESMTP id AA1A98D0001 for ; Tue, 8 Mar 2022 21:13:49 -0500 (EST) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 8064621BEB for ; Wed, 9 Mar 2022 02:13:49 +0000 (UTC) X-FDA: 79223226978.10.33BFEAC Received: from out1.migadu.com (out1.migadu.com [91.121.223.63]) by imf22.hostedemail.com (Postfix) with ESMTP id C352AC000F for ; Wed, 9 Mar 2022 02:13:48 +0000 (UTC) Date: Tue, 8 Mar 2022 18:13:41 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1646792027; 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: in-reply-to:in-reply-to:references:references; bh=AZyBLdCR0kgX9arBffEGB7+wNon6htqyedlw61KqXnI=; b=wzx2F4Am1rKGCYm836F+pUCYe5wjescsJQG4khVSUmpuIrWbdj1TQm+EyIJVFm3xrfzu42 rd2jrtdzAn/Hb20VuzGa2LA4lmU7db5g20d8GB1Eaarq5vEJOj0h1JlFnzCv4rN5unukZD 3bl0yqWQm+/oyPOJrW4gaKcYnD0YST4= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Waiman Long Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song Subject: Re: [PATCH-mm v2] mm/list_lru: Optimize memcg_reparent_list_lru_node() Message-ID: References: <20220309011824.1454619-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220309011824.1454619-1-longman@redhat.com> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev X-Rspamd-Queue-Id: C352AC000F X-Stat-Signature: dxnj1zdnzjf8u85134efnau5dufj7egj X-Rspam-User: Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=wzx2F4Am; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf22.hostedemail.com: domain of roman.gushchin@linux.dev designates 91.121.223.63 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev X-Rspamd-Server: rspam03 X-HE-Tag: 1646792028-205425 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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? If so, do we optimize for the case when all lru items belong to one node and others are empty?