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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 0D146C433E1 for ; Tue, 18 Aug 2020 07:43:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CD2B3207FB for ; Tue, 18 Aug 2020 07:43:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726324AbgHRHnv (ORCPT ); Tue, 18 Aug 2020 03:43:51 -0400 Received: from mx2.suse.de ([195.135.220.15]:56726 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726302AbgHRHnv (ORCPT ); Tue, 18 Aug 2020 03:43:51 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 24540ABCC; Tue, 18 Aug 2020 07:44:15 +0000 (UTC) Date: Tue, 18 Aug 2020 09:43:44 +0200 From: Michal Hocko To: "Paul E. McKenney" Cc: Uladzislau Rezki , Peter Zijlstra , Thomas Gleixner , LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Matthew Wilcox , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag Message-ID: <20200818074344.GL28270@dhcp22.suse.cz> References: <20200814141425.GM4295@paulmck-ThinkPad-P72> <20200814161106.GA13853@paulmck-ThinkPad-P72> <20200814174924.GI3982@worktop.programming.kicks-ass.net> <20200814180224.GQ4295@paulmck-ThinkPad-P72> <875z9lkoo4.fsf@nanos.tec.linutronix.de> <20200814204140.GT4295@paulmck-ThinkPad-P72> <20200814215206.GL3982@worktop.programming.kicks-ass.net> <20200816225655.GA17869@pc636> <20200817082849.GA28270@dhcp22.suse.cz> <20200817222803.GE23602@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200817222803.GE23602@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon 17-08-20 15:28:03, Paul E. McKenney wrote: > On Mon, Aug 17, 2020 at 10:28:49AM +0200, Michal Hocko wrote: > > On Mon 17-08-20 00:56:55, Uladzislau Rezki wrote: > > [ . . . ] > > > > wget ftp://vps418301.ovh.net/incoming/1000000_kmalloc_kfree_rcu_proc_percpu_pagelist_fractio_is_8.png > > > > 1/8 of the memory in pcp lists is quite large and likely not something > > used very often. > > > > Both these numbers just make me think that a dedicated pool of page > > pre-allocated for RCU specifically might be a better solution. I still > > haven't read through that branch of the email thread though so there > > might be some pretty convincing argments to not do that. > > To avoid the problematic corner cases, we would need way more dedicated > memory than is reasonable, as in well over one hundred pages per CPU. > Sure, we could choose a smaller number, but then we are failing to defend > against flooding, even on systems that have more than enough free memory > to be able to do so. It would be better to live within what is available, > taking the performance/robustness hit only if there isn't enough. Thomas had a good point that it doesn't really make much sense to optimize for flooders because that just makes them more effective. > My current belief is that we need a combination of (1) either the > GFP_NOLOCK flag or Peter Zijlstra's patch and I must have missed the patch? -- Michal Hocko SUSE Labs