From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755341Ab3AKUbv (ORCPT ); Fri, 11 Jan 2013 15:31:51 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:58985 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753347Ab3AKUbu (ORCPT ); Fri, 11 Jan 2013 15:31:50 -0500 Date: Fri, 11 Jan 2013 12:31:49 -0800 From: Andrew Morton To: paul.szabo@sydney.edu.au Cc: 695182@bugs.debian.org, dave@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC] Reproducible OOM with partial workaround Message-Id: <20130111123149.c3232a96.akpm@linux-foundation.org> In-Reply-To: <201301111151.r0BBpZt1023276@como.maths.usyd.edu.au> References: <20130111000119.8e9bdf5d.akpm@linux-foundation.org> <201301111151.r0BBpZt1023276@como.maths.usyd.edu.au> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 11 Jan 2013 22:51:35 +1100 paul.szabo@sydney.edu.au wrote: > Dear Andrew, > > > Check /proc/slabinfo, see if all your lowmem got eaten up by buffer_heads. > > Please see below: I do not know what any of that means. This machine has > been running just fine, with all my users logging in here via XDMCP from > X-terminals, dozens logged in simultaneously. (But, I think I could make > it go OOM with more processes or logins.) I'm counting 107MB in slab there. Was this dump taken when the system was at or near oom? Please send a copy of the oom-killer kernel message dump, if you still have one. > > If so, you *may* be able to work around this by setting > > /proc/sys/vm/dirty_ratio really low, so the system keeps a minimum > > amount of dirty pagecache around. Then, with luck, if we haven't > > broken the buffer_heads_over_limit logic it in the past decade (we > > probably have), the VM should be able to reclaim those buffer_heads. > > I tried setting dirty_ratio to "funny" values, that did not seem to > help. Did you try setting it as low as possible? > Did you notice my patch about bdi_position_ratio(), how it was > plain wrong half the time (for negative x)? Nope, please resend. > Anyway that did not help. > > > Alternatively, use a filesystem which doesn't attach buffer_heads to > > dirty pages. xfs or btrfs, perhaps. > > Seems there is also a problem not related to filesystem... or rather, > the essence does not seem to be filesystem or caches. The filesystem > thing now seems OK with my patch doing drop_caches. hm, if doing a regular drop_caches fixes things then that implies the problem is not with dirty pagecache. Odd.