From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id E029E6B0003 for ; Fri, 2 Nov 2018 12:51:51 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id c2-v6so1494002edi.6 for ; Fri, 02 Nov 2018 09:51:51 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id w4-v6si2345043eds.451.2018.11.02.09.51.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Nov 2018 09:51:50 -0700 (PDT) Date: Fri, 2 Nov 2018 17:51:47 +0100 From: Michal Hocko 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> Sender: owner-linux-mm@kvack.org List-ID: 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" 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