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 AAA8AC433F5 for ; Wed, 9 Mar 2022 04:46:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229514AbiCIErm (ORCPT ); Tue, 8 Mar 2022 23:47:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38400 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229480AbiCIErk (ORCPT ); Tue, 8 Mar 2022 23:47:40 -0500 Received: from out0.migadu.com (out0.migadu.com [IPv6:2001:41d0:2:267::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E0F14ECC60 for ; Tue, 8 Mar 2022 20:46:41 -0800 (PST) Date: Tue, 8 Mar 2022 20:46:33 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1646801200; 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=pwPV72PK1nbe959AqXG9dY/mbkFvNIqcqS9VHLE0tU8=; b=QtHSuJVvrFTsqhCvASuavohNw4WO/ZWGycg0/KZlAj3qVCXoZ8XMbkRahm41T0E4b7/lbs utpz03UkJt10RFWA//YLsfZxseA31jqI3uM/T8MWVY+efOFjniVPBkVtZREm/S6SVrCCFk TcTozsytGmI9G8rVj3Z7B14RjvBIb54= 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> <54ea34a9-e261-3521-ce11-efc59c9a803c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54ea34a9-e261-3521-ce11-efc59c9a803c@redhat.com> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Thanks!