From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx117.postini.com [74.125.245.117]) by kanga.kvack.org (Postfix) with SMTP id 0F0D06B0073 for ; Wed, 21 Nov 2012 03:35:23 -0500 (EST) Date: Wed, 21 Nov 2012 09:35:20 +0100 From: Michal Hocko Subject: Re: [patch] mm, memcg: avoid unnecessary function call when memcg is disabled Message-ID: <20121121083505.GA8761@dhcp22.suse.cz> References: <20121120134932.055bc192.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121120134932.055bc192.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Ying Han Cc: David Rientjes , Johannes Weiner , KAMEZAWA Hiroyuki , Hugh Dickins , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org On Tue 20-11-12 13:49:32, Andrew Morton wrote: > On Mon, 19 Nov 2012 17:44:34 -0800 (PST) > David Rientjes wrote: > > > While profiling numa/core v16 with cgroup_disable=memory on the command > > line, I noticed mem_cgroup_count_vm_event() still showed up as high as > > 0.60% in perftop. > > > > This occurs because the function is called extremely often even when memcg > > is disabled. > > > > To fix this, inline the check for mem_cgroup_disabled() so we avoid the > > unnecessary function call if memcg is disabled. > > > > ... > > > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > > --- a/include/linux/memcontrol.h > > +++ b/include/linux/memcontrol.h > > @@ -181,7 +181,14 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, > > gfp_t gfp_mask, > > unsigned long *total_scanned); > > > > -void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx); > > +void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx); > > +static inline void mem_cgroup_count_vm_event(struct mm_struct *mm, > > + enum vm_event_item idx) > > +{ > > + if (mem_cgroup_disabled() || !mm) > > + return; > > + __mem_cgroup_count_vm_event(mm, idx); > > +} > > Does the !mm case occur frequently enough to justify inlining it, or > should that test remain out-of-line? Now that you've asked about it I started looking around and I cannot see how mm can ever be NULL. The condition is there since the very beginning (456f998e memcg: add the pagefault count into memcg stats) but all the callers are page fault handlers and those shouldn't have mm==NULL. Or is there anything obvious I am missing? Ying, the whole thread starts https://lkml.org/lkml/2012/11/19/545 but the primary question is why we need !mm test for mem_cgroup_count_vm_event at all. Thanks! -- Michal Hocko SUSE Labs -- 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