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=-1.0 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS 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 0EB38C04ABB for ; Tue, 11 Sep 2018 19:53:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AD9E920865 for ; Tue, 11 Sep 2018 19:53:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AD9E920865 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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 S1726897AbeILAyM (ORCPT ); Tue, 11 Sep 2018 20:54:12 -0400 Received: from mailout.easymail.ca ([64.68.200.34]:37237 "EHLO mailout.easymail.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726689AbeILAyM (ORCPT ); Tue, 11 Sep 2018 20:54:12 -0400 Received: from localhost (localhost [127.0.0.1]) by mailout.easymail.ca (Postfix) with ESMTP id 8E20040FBD; Tue, 11 Sep 2018 19:53:20 +0000 (UTC) Received: from mailout.easymail.ca ([127.0.0.1]) by localhost (emo03-pco.easydns.vpn [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id XWLeDU2E6e-J; Tue, 11 Sep 2018 19:53:20 +0000 (UTC) Received: from [192.168.1.87] (c-24-9-64-241.hsd1.co.comcast.net [24.9.64.241]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mailout.easymail.ca (Postfix) with ESMTPSA id C793740CE3; Tue, 11 Sep 2018 19:53:09 +0000 (UTC) Subject: Re: [PATCH] arm64: add NUMA emulation support To: Will Deacon 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, Shuah Khan 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> <20180911165029.GA15022@arm.com> From: Shuah Khan Message-ID: <4c6ae739-28f9-3859-123a-8fde9294d918@kernel.org> Date: Tue, 11 Sep 2018 13:53:08 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180911165029.GA15022@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/11/2018 10:50 AM, Will Deacon wrote: > 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. > That is what is this patch is doing in some ways. Instead of hacking the firmware tables, it provides a command line option to split the flat machine into specified number of NUMA memory nodes. In addition to the new config option and new command line handling, I added one init routine that handles the NUMA emulation and after that normal NUMA code is leveraged. The only change is the following added to arm64_numa_init() if (!numa_init(arm64_numa_emu_init)) + return; arm64_numa_emu_init() does nothing unless the kernel is booted with the new "numa=fake=N" Please note that I am not adding any new NUMA code other than just this init routine. When the command line is specified, instead of going down the dummy_numa_init() path it will create NUMA emulation nodes. I was very careful in identifying the minimal amount of code needed to add this support. The change is limited to two existing routines: numa_parse_early_param() and arm64_numa_init(). numa_init() which is common for all the variants including the fallback dummy_numa_init() This allows a cleaner way to split the memory and leverage all of the NUMA code. This makes it easier to debug problems as opposed to hacked firmware tables. thanks, -- Shuah