From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751295AbaEWUvR (ORCPT ); Fri, 23 May 2014 16:51:17 -0400 Received: from mail-ie0-f170.google.com ([209.85.223.170]:33777 "EHLO mail-ie0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750995AbaEWUvP (ORCPT ); Fri, 23 May 2014 16:51:15 -0400 Date: Fri, 23 May 2014 13:51:12 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Marcelo Tosatti cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lai Jiangshan , Mel Gorman , Tejun Heo , Christoph Lameter , Li Zefan , Andrew Morton , cgroups@vger.kernel.org Subject: Re: [PATCH] page_alloc: skip cpuset enforcement for lower zone allocations In-Reply-To: <20140523193706.GA22854@amt.cnet> Message-ID: References: <20140523193706.GA22854@amt.cnet> 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 Fri, 23 May 2014, Marcelo Tosatti wrote: > Zone specific allocations, such as GFP_DMA32, should not be restricted > to cpusets allowed node list: the zones which such allocations demand > might be contained in particular nodes outside the cpuset node list. > > The alternative would be to not perform such allocations from > applications which are cpuset restricted, which is unrealistic. > Or ensure applications that allocate from lowmem are allowed to do so, but I understand that might be hard to make sure always happens. > Fixes KVM's alloc_page(gfp_mask=GFP_DMA32) with cpuset as explained. > > Signed-off-by: Marcelo Tosatti > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 5dba293..f228039 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2698,6 +2698,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, > unsigned int cpuset_mems_cookie; > int alloc_flags = ALLOC_WMARK_LOW|ALLOC_CPUSET|ALLOC_FAIR; > struct mem_cgroup *memcg = NULL; > + nodemask_t *cpuset_mems_allowed = &cpuset_current_mems_allowed; > > gfp_mask &= gfp_allowed_mask; > > @@ -2726,9 +2727,14 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, > retry_cpuset: > cpuset_mems_cookie = read_mems_allowed_begin(); > > +#ifdef CONFIG_NUMA > + if (gfp_zone(gfp_mask) < policy_zone) > + cpuset_mems_allowed = NULL; > +#endif > + > /* The preferred zone is used for statistics later */ > first_zones_zonelist(zonelist, high_zoneidx, > - nodemask ? : &cpuset_current_mems_allowed, > + nodemask ? : cpuset_mems_allowed, > &preferred_zone); > if (!preferred_zone) > goto out; > I think this is incomplete. Correct me if I'm wrong on how this is working: preferred_zone, today, is NULL because first_zones_zonelist() is restricted to a cpuset.mems that does not include lowmem and your patch fixes that. But if the fastpath allocation with mandatory ALLOC_CPUSET fails and we go to the slowpath, which may or may not have showed up in your testing, there's still issues, particularly if __GFP_WAIT and lots of allocators do GFP_KERNEL | __GFP_DMA32. This requires ALLOC_CPUSET on all allocations and you haven't updated __cpuset_node_allowed_softwall() with this exception nor zlc_setup(). After that's done, I think all of this is really convoluted and deserves a comment to describe the ALLOC_CPUSET and __GFP_DMA32 behavior. Adding Li, the cpusets maintainer, to this as well.