From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f174.google.com (mail-wi0-f174.google.com [209.85.212.174]) by kanga.kvack.org (Postfix) with ESMTP id 3530F6B0253 for ; Tue, 25 Aug 2015 07:09:40 -0400 (EDT) Received: by wicja10 with SMTP id ja10so11554100wic.1 for ; Tue, 25 Aug 2015 04:09:39 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e1si38224805wjp.38.2015.08.25.04.09.38 for (version=TLS1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 25 Aug 2015 04:09:38 -0700 (PDT) Subject: Re: [PATCH 04/12] mm, page_alloc: Only check cpusets when one exists that can be mem-controlled 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> From: Vlastimil Babka Message-ID: <55DC4CEF.7060104@suse.cz> Date: Tue, 25 Aug 2015 13:09:35 +0200 MIME-Version: 1.0 In-Reply-To: <20150825103300.GM12432@techsingularity.net> Content-Type: text/plain; charset=iso-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , Johannes Weiner , Rik van Riel , David Rientjes , Joonsoo Kim , Michal Hocko , Linux-MM , LKML 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org