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 4A357C1B0F2 for ; Wed, 20 Jun 2018 15:31:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02CE6208B9 for ; Wed, 20 Jun 2018 15:31:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 02CE6208B9 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 S1754207AbeFTPbw (ORCPT ); Wed, 20 Jun 2018 11:31:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:35514 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754113AbeFTPbv (ORCPT ); Wed, 20 Jun 2018 11:31:51 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext-too.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 9FF93ADCA; Wed, 20 Jun 2018 15:31:49 +0000 (UTC) Date: Wed, 20 Jun 2018 17:31:48 +0200 From: Michal Hocko To: Johannes Weiner Cc: linux-mm@kvack.org, Greg Thelen , Shakeel Butt , Andrew Morton , LKML Subject: Re: [RFC PATCH] memcg, oom: move out_of_memory back to the charge path Message-ID: <20180620153148.GO13685@dhcp22.suse.cz> References: <20180620103736.13880-1-mhocko@kernel.org> <20180620151812.GA2441@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180620151812.GA2441@cmpxchg.org> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 20-06-18 11:18:12, Johannes Weiner wrote: > On Wed, Jun 20, 2018 at 12:37:36PM +0200, Michal Hocko wrote: [...] > > -static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order) > > +enum oom_status { > > + OOM_SUCCESS, > > + OOM_FAILED, > > + OOM_ASYNC, > > + OOM_SKIPPED > > Either SUCCESS & FAILURE, or SUCCEEDED & FAILED ;) sure, I will go with later. > We're not distinguishing ASYNC and SKIPPED anywhere below, but I > cannot think of a good name to communicate them both without this > function making assumptions about the charge function's behavior. > So it's a bit weird, but probably the best way to go. Yeah, that was what I was fighting with. My original proposal which simply ENOMEM in the failure case was a simple bool but once we have those different sates and failure behavior I think it is better to comunicate that and let the caller do whatever it finds reasonable. > > > +static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order) > > { > > - if (!current->memcg_may_oom || order > PAGE_ALLOC_COSTLY_ORDER) > > - return; > > + if (order > PAGE_ALLOC_COSTLY_ORDER) > > + return OOM_SKIPPED; > > /* > > * We are in the middle of the charge context here, so we > > * don't want to block when potentially sitting on a callstack > > * that holds all kinds of filesystem and mm locks. > > * > > - * Also, the caller may handle a failed allocation gracefully > > - * (like optional page cache readahead) and so an OOM killer > > - * invocation might not even be necessary. > > + * cgroup1 allows disabling the OOM killer and waiting for outside > > + * handling until the charge can succeed; remember the context and put > > + * the task to sleep at the end of the page fault when all locks are > > + * released. > > + * > > + * On the other hand, in-kernel OOM killer allows for an async victim > > + * memory reclaim (oom_reaper) and that means that we are not solely > > + * relying on the oom victim to make a forward progress and we can > > + * invoke the oom killer here. > > * > > - * That's why we don't do anything here except remember the > > - * OOM context and then deal with it at the end of the page > > - * fault when the stack is unwound, the locks are released, > > - * and when we know whether the fault was overall successful. > > + * Please note that mem_cgroup_oom_synchronize might fail to find a > > + * victim and then we have rely on mem_cgroup_oom_synchronize otherwise > > + * we would fall back to the global oom killer in pagefault_out_of_memory > > */ > > + if (!memcg->oom_kill_disable) { > > + if (mem_cgroup_out_of_memory(memcg, mask, order)) > > + return OOM_SUCCESS; > > + > > + WARN(!current->memcg_may_oom, > > + "Memory cgroup charge failed because of no reclaimable memory! " > > + "This looks like a misconfiguration or a kernel bug."); > > + return OOM_FAILED; > > + } > > + > > + if (!current->memcg_may_oom) > > + return OOM_SKIPPED; > > memcg_may_oom was introduced to distinguish between userspace faults > that can OOM and contexts that return -ENOMEM. Now we're using it > slightly differently and it's confusing. > > 1) Why warn for kernel allocations, but not userspace ones? This > should have a comment at least. I am not sure I understand. We do warn for all allocations types of mem_cgroup_out_of_memory fails as long as we are not in a legacy - oom_disabled case. > 2) We invoke the OOM killer when !memcg_may_oom. We want to OOM kill > in either case, but only set up the mem_cgroup_oom_synchronize() for > userspace faults. So the code makes sense, but a better name would be > in order -- current->in_user_fault? in_user_fault is definitely better than memcg_may_oom. > > css_get(&memcg->css); > > current->memcg_in_oom = memcg; > > current->memcg_oom_gfp_mask = mask; > > current->memcg_oom_order = order; > > + > > + return OOM_ASYNC; > > In terms of code flow, it would be much clearer to handle the > memcg->oom_kill_disable case first, as a special case with early > return, and make the OOM invocation the main code of this function, > given its name. This? if (order > PAGE_ALLOC_COSTLY_ORDER) return OOM_SKIPPED; /* * We are in the middle of the charge context here, so we * don't want to block when potentially sitting on a callstack * that holds all kinds of filesystem and mm locks. * * cgroup1 allows disabling the OOM killer and waiting for outside * handling until the charge can succeed; remember the context and put * the task to sleep at the end of the page fault when all locks are * released. * * On the other hand, in-kernel OOM killer allows for an async victim * memory reclaim (oom_reaper) and that means that we are not solely * relying on the oom victim to make a forward progress and we can * invoke the oom killer here. * * Please note that mem_cgroup_oom_synchronize might fail to find a * victim and then we have rely on mem_cgroup_oom_synchronize otherwise * we would fall back to the global oom killer in pagefault_out_of_memory */ if (memcg->oom_kill_disable) { if (!current->memcg_may_oom) return OOM_SKIPPED; css_get(&memcg->css); current->memcg_in_oom = memcg; current->memcg_oom_gfp_mask = mask; current->memcg_oom_order = order; return OOM_ASYNC; } if (mem_cgroup_out_of_memory(memcg, mask, order)) return OOM_SUCCESS; WARN(!current->memcg_may_oom, "Memory cgroup charge failed because of no reclaimable memory! " "This looks like a misconfiguration or a kernel bug."); return OOM_FAILED; Thanks! -- Michal Hocko SUSE Labs