Path: csiph.com!eternal-september.org!feeder.eternal-september.org!aioe.org!bofh.it!news.nic.it!robomod From: Mel Gorman Newsgroups: linux.kernel Subject: Re: [PATCH 04/12] mm, page_alloc: Only check cpusets when one exists that can be mem-controlled Date: Tue, 25 Aug 2015 12:40:02 +0200 Message-ID: References: X-Original-To: Vlastimil Babka MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 57 Organization: linux.* mail to news gateway X-Original-Cc: Andrew Morton , Johannes Weiner , Rik van Riel , David Rientjes , Joonsoo Kim , Michal Hocko , Linux-MM , LKML X-Original-Date: Tue, 25 Aug 2015 11:33:00 +0100 X-Original-Message-ID: <20150825103300.GM12432@techsingularity.net> X-Original-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> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1212940 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. -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/