From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755542AbbHZNlq (ORCPT ); Wed, 26 Aug 2015 09:41:46 -0400 Received: from outbound-smtp01.blacknight.com ([81.17.249.7]:51169 "EHLO outbound-smtp01.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751737AbbHZNlp (ORCPT ); Wed, 26 Aug 2015 09:41:45 -0400 Date: Wed, 26 Aug 2015 14:41:41 +0100 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Johannes Weiner , Rik van Riel , David Rientjes , Joonsoo Kim , Michal Hocko , Linux-MM , LKML Subject: Re: [PATCH 04/12] mm, page_alloc: Only check cpusets when one exists that can be mem-controlled Message-ID: <20150826134141.GN12432@techsingularity.net> References: <1440418191-10894-1-git-send-email-mgorman@techsingularity.net> <1440418191-10894-5-git-send-email-mgorman@techsingularity.net> <55DB1015.4080103@suse.cz> <20150824131616.GK12432@techsingularity.net> <55DB8451.4000102@suse.cz> <20150825103300.GM12432@techsingularity.net> <55DC4CEF.7060104@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <55DC4CEF.7060104@suse.cz> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 25, 2015 at 01:09:35PM +0200, Vlastimil Babka wrote: > On 08/25/2015 12:33 PM, Mel Gorman wrote: > >On Mon, Aug 24, 2015 at 10:53:37PM +0200, Vlastimil Babka wrote: > >>On 24.8.2015 15:16, Mel Gorman wrote: > >>>>> > >>>>> return read_seqcount_retry(¤t->mems_allowed_seq, seq); > >>>>>@@ -139,7 +141,7 @@ static inline void set_mems_allowed(nodemask_t nodemask) > >>>>> > >>>>> #else /* !CONFIG_CPUSETS */ > >>>>> > >>>>>-static inline bool cpusets_enabled(void) { return false; } > >>>>>+static inline bool cpusets_mems_enabled(void) { return false; } > >>>>> > >>>>> static inline int cpuset_init(void) { return 0; } > >>>>> static inline void cpuset_init_smp(void) {} > >>>>>diff --git a/mm/page_alloc.c b/mm/page_alloc.c > >>>>>index 62ae28d8ae8d..2c1c3bf54d15 100644 > >>>>>--- a/mm/page_alloc.c > >>>>>+++ b/mm/page_alloc.c > >>>>>@@ -2470,7 +2470,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags, > >>>>> if (IS_ENABLED(CONFIG_NUMA) && zlc_active && > >>>>> !zlc_zone_worth_trying(zonelist, z, allowednodes)) > >>>>> continue; > >>>>>- if (cpusets_enabled() && > >>>>>+ if (cpusets_mems_enabled() && > >>>>> (alloc_flags & ALLOC_CPUSET) && > >>>>> !cpuset_zone_allowed(zone, gfp_mask)) > >>>>> continue; > >>>> > >>>>Here the benefits are less clear. I guess cpuset_zone_allowed() is > >>>>potentially costly... > >>>> > >>>>Heck, shouldn't we just start the static key on -1 (if possible), so that > >>>>it's enabled only when there's 2+ cpusets? > >> > >>Hm wait a minute, that's what already happens: > >> > >>static inline int nr_cpusets(void) > >>{ > >> /* jump label reference count + the top-level cpuset */ > >> return static_key_count(&cpusets_enabled_key) + 1; > >>} > >> > >>I.e. if there's only the root cpuset, static key is disabled, so I think this > >>patch is moot after all? > >> > > > >static_key_count is an atomic read on a field in struct static_key where > >as static_key_false is a arch_static_branch which can be eliminated. The > >patch eliminates an atomic read so I didn't think it was moot. > > Sorry I wasn't clear enough. My point is that AFAICS cpusets_enabled() will > only return true if there are more cpusets than the root (top-level) one. > So the current cpusets_enabled() checks should be enough. Checking that > "nr_cpusets() > 1" only duplicates what is already covered by > cpusets_enabled() - see the nr_cpusets() listing above. I.e. David's premise > was wrong. > /me slaps self I should have spotted that. Thanks. -- Mel Gorman SUSE Labs