linux-kernel - Re: [PATCH v3] mm, sysctl: make NUMA stats configurable

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Date:   Tue, 10 Oct 2017 14:34:05 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        kemi <kemi.wang@...el.com>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Christopher Lameter <cl@...ux.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tim Chen <tim.c.chen@...el.com>,
        Andi Kleen <andi.kleen@...el.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Ying Huang <ying.huang@...el.com>,
        Aaron Lu <aaron.lu@...el.com>,
        Proc sysctl <linux-fsdevel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] mm, sysctl: make NUMA stats configurable

On Tue, 10 Oct 2017 19:51:43 +0200 Michal Hocko <mhocko@...nel.org> wrote:

> On Tue 10-10-17 08:39:47, Dave Hansen wrote:
> > On 10/10/2017 07:57 AM, Michal Hocko wrote:
> > >> But, let's be honest, this leaves us with an option that nobody is ever
> > >> going to turn on.  IOW, nobody except a very small portion of our users
> > >> will ever see any benefit from this.
> > > But aren't those small groups who would like to squeeze every single
> > > cycle out from the page allocator path the targeted audience?
> > 
> > They're the reason we started looking at this.  They also care the most.
> > 
> > But, the cost of these stats, especially we get more and more cores in a
> > NUMA node is really making them show up in profiles.  It would be nice
> > to get rid of them there, too.
> 
> I am not opposing to the auto mode. I am just not sure it is a safe
> default and I also think that we should add this on top if it is really
> needed.

Yup.  Let's keep things simple unless a real need is demonstrated, please.