From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753497AbeDTFmr (ORCPT ); Fri, 20 Apr 2018 01:42:47 -0400 Received: from mail-pl0-f46.google.com ([209.85.160.46]:42816 "EHLO mail-pl0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751478AbeDTFmp (ORCPT ); Fri, 20 Apr 2018 01:42:45 -0400 X-Google-Smtp-Source: AIpwx48ppDsjLwTN/igsgSHng/LLkrKqv6aGzM+TmPkU4GiOIZc2Ux/p2FlUmaOutaGZYUe3/DEn4A== Date: Fri, 20 Apr 2018 14:42:39 +0900 From: Minchan Kim To: Michal Hocko Cc: David Rientjes , Andrew Morton , LKML , linux-mm , Johannes Weiner , Vladimir Davydov Subject: Re: [PATCH] mm:memcg: add __GFP_NOWARN in __memcg_schedule_kmem_cache_create Message-ID: <20180420054239.GA221997@rodete-desktop-imager.corp.google.com> References: <20180418022912.248417-1-minchan@kernel.org> <20180418072002.GN17484@dhcp22.suse.cz> <20180418074117.GA210164@rodete-desktop-imager.corp.google.com> <20180418075437.GP17484@dhcp22.suse.cz> <20180418132328.GB210164@rodete-desktop-imager.corp.google.com> <20180418132715.GD17484@dhcp22.suse.cz> <20180419064005.GL17484@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180419064005.GL17484@dhcp22.suse.cz> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 19, 2018 at 08:40:05AM +0200, Michal Hocko wrote: > On Wed 18-04-18 11:58:00, David Rientjes wrote: > > On Wed, 18 Apr 2018, Michal Hocko wrote: > > > > > > Okay, no problem. However, I don't feel we need ratelimit at this moment. > > > > We can do when we got real report. Let's add just one line warning. > > > > However, I have no talent to write a poem to express with one line. > > > > Could you help me? > > > > > > What about > > > pr_info("Failed to create memcg slab cache. Report if you see floods of these\n"); > > > Thanks you, Michal. However, hmm, floods is very vague to me. 100 time per sec? 10 time per hour? I guess we need more guide line to trigger user's reporting if we really want to do. > > > > Um, there's nothing actionable here for the user. Even if the message > > directed them to a specific email address, what would you ask the user for > > in response if they show a kernel log with 100 of these? > > We would have to think of a better way to create shaddow memcg caches. > > > Probably ask > > them to use sysrq at the time it happens to get meminfo. But any user > > initiated sysrq is going to reveal very different state of memory compared > > to when the kmalloc() actually failed. > > Not really. > > > If this really needs a warning, I think it only needs to be done once and > > reveal the state of memory similar to how slub emits oom warnings. But as > > the changelog indicates, the system is oom and we couldn't reclaim. We > > can expect this happens a lot on systems with memory pressure. What is > > the warning revealing that would be actionable? > > That it actually happens in real workloads and we want to know what > those workloads are. This code is quite old and yet this is the first > some somebody complains. So it is most probably rare. Maybe because most > workloads doesn't create many memcgs dynamically while low on memory. > And maybe that will change in future. In any case, having a large splat > of meminfo for GFP_NOWAIT is not really helpful. It will tell us what we > know already - the memory is low and the reclaim was prohibited. We just > need to know that this happens out there. The workload was experimenting creating memcg per app on embedded device but at this moment, I don't consider kmemcg at this moment so I can live with disabling kmemcg, even. Based on it, I cannot say whether it's real workload or not. When I see replies of this thread, it's arguble to add such one-line warn so if you want it strongly, could you handle by yourself? Sorry but I don't have any interest on the arguing. Thanks.