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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 1FF2DC32789 for ; Fri, 2 Nov 2018 16:51:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E60D02082D for ; Fri, 2 Nov 2018 16:51:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E60D02082D 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 S1728114AbeKCB7g (ORCPT ); Fri, 2 Nov 2018 21:59:36 -0400 Received: from mx2.suse.de ([195.135.220.15]:59038 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727946AbeKCB7g (ORCPT ); Fri, 2 Nov 2018 21:59:36 -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 C4EB5AE11; Fri, 2 Nov 2018 16:51:48 +0000 (UTC) Date: Fri, 2 Nov 2018 17:51:47 +0100 From: Michal Hocko To: Roman Gushchin Cc: Dexuan Cui , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Kernel Team , Shakeel Butt , Johannes Weiner , Tejun Heo , Rik van Riel , Konstantin Khlebnikov , Matthew Wilcox , "Stable@vger.kernel.org" Subject: Re: Will the recent memory leak fixes be backported to longterm kernels? Message-ID: <20181102165147.GG28039@dhcp22.suse.cz> References: <20181102005816.GA10297@tower.DHCP.thefacebook.com> <20181102073009.GP23921@dhcp22.suse.cz> <20181102154844.GA17619@tower.DHCP.thefacebook.com> <20181102161314.GF28039@dhcp22.suse.cz> <20181102162237.GB17619@tower.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181102162237.GB17619@tower.DHCP.thefacebook.com> 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 Fri 02-11-18 16:22:41, Roman Gushchin wrote: > On Fri, Nov 02, 2018 at 05:13:14PM +0100, Michal Hocko wrote: > > On Fri 02-11-18 15:48:57, Roman Gushchin wrote: > > > On Fri, Nov 02, 2018 at 09:03:55AM +0100, Michal Hocko wrote: > > > > On Fri 02-11-18 02:45:42, Dexuan Cui wrote: > > > > [...] > > > > > I totally agree. I'm now just wondering if there is any temporary workaround, > > > > > even if that means we have to run the kernel with some features disabled or > > > > > with a suboptimal performance? > > > > > > > > One way would be to disable kmem accounting (cgroup.memory=nokmem kernel > > > > option). That would reduce the memory isolation because quite a lot of > > > > memory will not be accounted for but the primary source of in-flight and > > > > hard to reclaim memory will be gone. > > > > > > In my experience disabling the kmem accounting doesn't really solve the issue > > > (without patches), but can lower the rate of the leak. > > > > This is unexpected. 90cbc2508827e was introduced to address offline > > memcgs to be reclaim even when they are small. But maybe you mean that > > we still leak in an absence of the memory pressure. Or what does prevent > > memcg from going down? > > There are 3 independent issues which are contributing to this leak: > 1) Kernel stack accounting weirdness: processes can reuse stack accounted to > different cgroups. So basically any running process can take a reference to any > cgroup. yes, but kmem accounting should rule that out, right? If not then this is a clear bug and easy to backport because that would mean to add a missing memcg_kmem_enabled check. > 2) We do forget to scan the last page in the LRU list. So if we ended up with > 1-page long LRU, it can stay there basically forever. Why /* * If the cgroup's already been deleted, make sure to * scrape out the remaining cache. */ if (!scan && !mem_cgroup_online(memcg)) scan = min(size, SWAP_CLUSTER_MAX); in get_scan_count doesn't work for that case? > 3) We don't apply enough pressure on slab objects. again kmem accounting disabled should make this moot > Because one reference is enough to keep the entire memcg structure in place, > we really have to close all three to eliminate the leak. Disabling kmem > accounting mitigates only the last one. -- Michal Hocko SUSE Labs