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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 B62EAC6778D for ; Tue, 11 Sep 2018 16:50:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 66A372086A for ; Tue, 11 Sep 2018 16:50:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 66A372086A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727873AbeIKVuX (ORCPT ); Tue, 11 Sep 2018 17:50:23 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:46694 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726622AbeIKVuX (ORCPT ); Tue, 11 Sep 2018 17:50:23 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1C0F97A9; Tue, 11 Sep 2018 09:50:14 -0700 (PDT) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id E1AD23F703; Tue, 11 Sep 2018 09:50:13 -0700 (PDT) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id 7B0C81AE3231; Tue, 11 Sep 2018 17:50:30 +0100 (BST) Date: Tue, 11 Sep 2018 17:50:30 +0100 From: Will Deacon To: Shuah Khan Cc: Michal Hocko , catalin.marinas@arm.com, sudeep.holla@arm.com, ganapatrao.kulkarni@cavium.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: add NUMA emulation support Message-ID: <20180911165029.GA15022@arm.com> References: <20180829110802.GD10349@dhcp22.suse.cz> <20180905064252.GW14951@dhcp22.suse.cz> <20180907083452.GC19621@dhcp22.suse.cz> <20180910134845.GH10951@dhcp22.suse.cz> <4d7beb50-f778-507a-4c3c-f6de92f8cfb9@kernel.org> <20180911091124.GP10951@dhcp22.suse.cz> <86aad702-9f42-c572-a8f1-74983cd1bf33@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86aad702-9f42-c572-a8f1-74983cd1bf33@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 11, 2018 at 09:27:49AM -0600, Shuah Khan wrote: > On 09/11/2018 03:11 AM, Michal Hocko wrote: > > On Mon 10-09-18 20:02:05, Shuah Khan wrote: > >> Hi Michal, > >> > >> On 09/10/2018 07:48 AM, Michal Hocko wrote: > >>> On Fri 07-09-18 16:30:59, Shuah Khan wrote: > >>>> On 09/07/2018 02:34 AM, Michal Hocko wrote: > >>>>> On Thu 06-09-18 15:53:34, Shuah Khan wrote: > >> [....] > >>>> > >>>> In addition to isolation, being able to reserve a block instead is one of the > >>>> issues I am looking to address. Unfortunately memory cgroups won't address that > >>>> issue. > >>> > >>> Could you be more specific why you need reservations other than > >>> isolation. > >>> > >> > >> Taking automotive as a specific example, there are two classes of applications: > >> 1. critical applications that must run > >> 2. Infotainment and misc. user-space. > >> > >> In this case, being able to reserve a block of memory for critical applications > >> will ensure the memory is available for them. If a critical application has to > >> restart and/or when an on-demand critical application starts, it might not be able > >> to allocate memory if it is not reserved. > >> > >> When a flat system has multiple memory blocks, with NUMA emulation in conjunction with > >> cpusets, one or more block can be reserved for critical applications configuring a set > >> of cpus and one of more memory nodes for them. > >> > >> Memory cgroups will not support such reservation. Hope this helps explain the use-case > >> I am trying to address with this patch. > > > > OK, that is more clear. I still believe that you either have to have a > > very good control over memory allocations or a good luck to not see > > unexpected kernel allocations in your reserved memory which might easily > > break guarantees you would like to accomplish. > > > > Thanks. Right. I am with you on the possibility that root cgroup can eat into > the reserved memory. However, with this solution I proposed, there is a guarantee > that the cpuset cgroup that is configured for non-critical Infotainment and misc. > user-space application will not be able to allocate from the reserved memory node. > > I am hoping the proposed patch will allow critical apps. reserving memory with the > exception that root cgroup and kernel can still allocate from it when needed. Perhaps > cpuset exclusive logic could be extended to look for non-exclusive memory nodes first > if it doesn't already do that. This is inline with the current cpuset approach is that > the critical kernel allocations aren't starved to ensure memory reservations. > > If you don't think this solution isn't ideal/good, do you have other suggestions > for solving the problem? If not would it be okay to start with what I proposed and > build on top of as needed? I still don't understand why this can't be achieved by faking up some NUMA entries in the firmware table and just using the existing NUMA code that we have. Will