From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753081AbaHKLhU (ORCPT ); Mon, 11 Aug 2014 07:37:20 -0400 Received: from mail-pa0-f44.google.com ([209.85.220.44]:38884 "EHLO mail-pa0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751626AbaHKLhR (ORCPT ); Mon, 11 Aug 2014 07:37:17 -0400 Date: Mon, 11 Aug 2014 04:37:15 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Vladimir Davydov cc: Li Zefan , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Christoph Lameter , Pekka Enberg , Joonsoo Kim Subject: Re: [PATCH -mm] slab: fix cpuset check in fallback_alloc In-Reply-To: <20140811071315.GA18709@esperanza> Message-ID: References: <1407692891-24312-1-git-send-email-vdavydov@parallels.com> <20140811071315.GA18709@esperanza> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 11 Aug 2014, Vladimir Davydov wrote: > > diff --git a/mm/slab.c b/mm/slab.c > > --- a/mm/slab.c > > +++ b/mm/slab.c > > @@ -3047,16 +3047,19 @@ retry: > > * from existing per node queues. > > */ > > for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) { > > - nid = zone_to_nid(zone); > > + struct kmem_cache_node *n; > > > > - if (cpuset_zone_allowed_hardwall(zone, flags) && > > - get_node(cache, nid) && > > - get_node(cache, nid)->free_objects) { > > - obj = ____cache_alloc_node(cache, > > - flags | GFP_THISNODE, nid); > > - if (obj) > > - break; > > - } > > + nid = zone_to_nid(zone); > > + if (!cpuset_zone_allowed(zone, flags | __GFP_HARDWALL)) > > We must use softwall check here, otherwise we will proceed to > alloc_pages even if there are lots of free slabs on other nodes. > alloc_pages, in turn, may allocate from other nodes in case > cpuset.mem_hardwall=0, because it uses softwall check, so it may add yet > another free slab to another node's list even if it isn't empty. As a > result, we may get free list bloating on other nodes. I've seen a > machine with one of its nodes almost completely filled with inactive > slabs for buffer_heads (dozens of GBs) w/o any chance to drop them. So, > this is a bug that must be fixed. > Right, I understand, and my patch makes no attempt to fix that issue, it's simply collapsing the code down into a single cpuset_zone_allowed() function and the context for the allocation is controlled by the gfp flags (and hardwall is controlled by setting __GFP_HARDWALL) as it should be. I understand the issue you face, but I can't combine a cleanup with a fix and I would prefer to have your patch keep your commit description. The diffstat for my proposal removes many more lines than it adds and I think it will avoid this type of issue in the future for new callers. Your patch could then be based on the single cpuset_zone_allowed() function where you would simply have to remove the __GFP_HARDWALL above. Or, your patch could be merged first and then my cleanup on top, but it seems like your one-liner would be more clear if it is based on mine.