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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 9CF06CA9EAE for ; Wed, 23 Oct 2019 06:40:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 70C9A214B2 for ; Wed, 23 Oct 2019 06:40:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571812817; bh=cci2MAyDo2x1juJvQngAS/UOXi0AVk3gw+p92j0xu1s=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=pfXCOuSs1Yy7Z/1FuaiG6MaDCySAfmpGUvNIQCsexjF6Q6Gldnmncixql+bwAbD1h UdmcX+V5MushgpmZlPRGyWzqaFujkc/bCTZz0OEkm6+HnUGlSeT2wwwjcSuZD7Ek/O ppBl3yikodUd1JInzklV/kvNXyzP/tPch0li2fWg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389315AbfJWGkQ (ORCPT ); Wed, 23 Oct 2019 02:40:16 -0400 Received: from mx2.suse.de ([195.135.220.15]:60402 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728697AbfJWGkQ (ORCPT ); Wed, 23 Oct 2019 02:40:16 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 9AD87B3F4; Wed, 23 Oct 2019 06:40:13 +0000 (UTC) Date: Wed, 23 Oct 2019 08:40:12 +0200 From: Michal Hocko To: Johannes Weiner Cc: Andrew Morton , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, netdev@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] mm: memcontrol: fix network errors from failing __GFP_ATOMIC charges Message-ID: <20191023064012.GB754@dhcp22.suse.cz> References: <20191022233708.365764-1-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191022233708.365764-1-hannes@cmpxchg.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 22-10-19 19:37:08, Johannes Weiner wrote: > While upgrading from 4.16 to 5.2, we noticed these allocation errors > in the log of the new kernel: > > [ 8642.253395] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC) > [ 8642.269170] cache: tw_sock_TCPv6(960:helper-logs), object size: 232, buffer size: 240, default order: 1, min order: 0 > [ 8642.293009] node 0: slabs: 5, objs: 170, free: 0 > > slab_out_of_memory+1 > ___slab_alloc+969 > __slab_alloc+14 > kmem_cache_alloc+346 > inet_twsk_alloc+60 > tcp_time_wait+46 > tcp_fin+206 > tcp_data_queue+2034 > tcp_rcv_state_process+784 > tcp_v6_do_rcv+405 > __release_sock+118 > tcp_close+385 > inet_release+46 > __sock_release+55 > sock_close+17 > __fput+170 > task_work_run+127 > exit_to_usermode_loop+191 > do_syscall_64+212 > entry_SYSCALL_64_after_hwframe+68 > > accompanied by an increase in machines going completely radio silent > under memory pressure. This is really worrying because that suggests that something depends on GFP_ATOMIC allocation which is fragile and broken. > One thing that changed since 4.16 is e699e2c6a654 ("net, mm: account > sock objects to kmemcg"), which made these slab caches subject to > cgroup memory accounting and control. > > The problem with that is that cgroups, unlike the page allocator, do > not maintain dedicated atomic reserves. As a cgroup's usage hovers at > its limit, atomic allocations - such as done during network rx - can > fail consistently for extended periods of time. The kernel is not able > to operate under these conditions. > > We don't want to revert the culprit patch, because it indeed tracks a > potentially substantial amount of memory used by a cgroup. > > We also don't want to implement dedicated atomic reserves for cgroups. > There is no point in keeping a fixed margin of unused bytes in the > cgroup's memory budget to accomodate a consumer that is impossible to > predict - we'd be wasting memory and get into configuration headaches, > not unlike what we have going with min_free_kbytes. We do this for > physical mem because we have to, but cgroups are an accounting game. > > Instead, account these privileged allocations to the cgroup, but let > them bypass the configured limit if they have to. This way, we get the > benefits of accounting the consumed memory and have it exert pressure > on the rest of the cgroup, but like with the page allocator, we shift > the burden of reclaimining on behalf of atomic allocations onto the > regular allocations that can block. On the other hand this would allow to break the isolation by an unpredictable amount. Should we put a simple cap on how much we can go over the limit. If the memcg limit reclaim is not able to keep up with those overflows then even __GFP_ATOMIC allocations have to fail. What do you think? > Cc: stable@kernel.org # 4.18+ > Fixes: e699e2c6a654 ("net, mm: account sock objects to kmemcg") > Signed-off-by: Johannes Weiner > --- > mm/memcontrol.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 8090b4c99ac7..c7e3e758c165 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2528,6 +2528,15 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > goto retry; > } > > + /* > + * Memcg doesn't have a dedicated reserve for atomic > + * allocations. But like the global atomic pool, we need to > + * put the burden of reclaim on regular allocation requests > + * and let these go through as privileged allocations. > + */ > + if (gfp_mask & __GFP_ATOMIC) > + goto force; > + > /* > * Unlike in global OOM situations, memcg is not in a physical > * memory shortage. Allow dying and OOM-killed tasks to > -- > 2.23.0 > -- Michal Hocko SUSE Labs