From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752210AbeDJIEo (ORCPT ); Tue, 10 Apr 2018 04:04:44 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36129 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751892AbeDJIEm (ORCPT ); Tue, 10 Apr 2018 04:04:42 -0400 X-Google-Smtp-Source: AIpwx4+aP8barmEbjxnga/yrSUkx2m2P9NY2BGgdo9bPmvzOPZ1WVwRZPNOQrbsqoZQ0Gf3m12JSyNqyq67OJiEz+yQ= MIME-Version: 1.0 In-Reply-To: <20180410074921.GU21835@dhcp22.suse.cz> References: <20180408084717.62ee4f9e@gandalf.local.home> <20180409094944.6399b211@gandalf.local.home> <20180409231230.1ab99e85@vmware.local.home> <20180410061447.GQ21835@dhcp22.suse.cz> <20180410074921.GU21835@dhcp22.suse.cz> From: Zhaoyang Huang Date: Tue, 10 Apr 2018 16:04:40 +0800 Message-ID: Subject: Re: [PATCH v1] ringbuffer: Don't choose the process with adj equal OOM_SCORE_ADJ_MIN To: Michal Hocko Cc: Steven Rostedt , Ingo Molnar , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 10, 2018 at 3:49 PM, Michal Hocko wrote: > On Tue 10-04-18 14:39:35, Zhaoyang Huang wrote: >> On Tue, Apr 10, 2018 at 2:14 PM, Michal Hocko wrote: >> > On Tue 10-04-18 11:41:44, Zhaoyang Huang wrote: >> >> On Tue, Apr 10, 2018 at 11:12 AM, Steven Rostedt wrote: >> >> > On Tue, 10 Apr 2018 10:32:36 +0800 >> >> > Zhaoyang Huang wrote: >> >> > >> >> >> For bellowing scenario, process A have no intension to exhaust the >> >> >> memory, but will be likely to be selected by OOM for we set >> >> >> OOM_CORE_ADJ_MIN for it. >> >> >> process A(-1000) process B >> >> >> >> >> >> i = si_mem_available(); >> >> >> if (i < nr_pages) >> >> >> return -ENOMEM; >> >> >> schedule >> >> >> ---------------> >> >> >> allocate huge memory >> >> >> <------------- >> >> >> if (user_thread) >> >> >> set_current_oom_origin(); >> >> >> >> >> >> for (i = 0; i < nr_pages; i++) { >> >> >> bpage = kzalloc_node >> >> > >> >> > Is this really an issue though? >> >> > >> >> > Seriously, do you think you will ever hit this? >> >> > >> >> > How often do you increase the size of the ftrace ring buffer? For this >> >> > to be an issue, the system has to trigger an OOM at the exact moment >> >> > you decide to increase the size of the ring buffer. That would be an >> >> > impressive attack, with little to gain. >> >> > >> >> > Ask the memory management people. If they think this could be a >> >> > problem, then I'll be happy to take your patch. >> >> > >> >> > -- Steve >> >> add Michael for review. >> >> Hi Michael, >> >> I would like suggest Steve NOT to set OOM_CORE_ADJ_MIN for the process >> >> with adj = -1000 when setting the user space process as potential >> >> victim of OOM. >> > >> > OOM_SCORE_ADJ_MIN means "hide the process from the OOM killer completely". >> > So what exactly do you want to achieve here? Because from the above it >> > sounds like opposite things. /me confused... >> > >> Steve's patch intend to have the process be OOM's victim when it >> over-allocating pages for ring buffer. I amend a patch over to protect >> process with OOM_SCORE_ADJ_MIN from doing so. Because it will make >> such process to be selected by current OOM's way of >> selecting.(consider OOM_FLAG_ORIGIN first before the adj) > > I just wouldn't really care unless there is an existing and reasonable > usecase for an application which updates the ring buffer size _and_ it > is OOM disabled at the same time. > -- > Michal Hocko > SUSE Labs There is indeed such kind of test case on my android system, which is known as CTS and Monkey etc. Furthermore, I think we should make the patch to be as safest as possible. Why do we leave a potential risk here? There is no side effect for my patch.