From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1759009Ab2CSN1N (ORCPT <rfc822;w@1wt.eu>);
	Mon, 19 Mar 2012 09:27:13 -0400
Received: from casper.infradead.org ([85.118.1.10]:42525 "EHLO
	casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1757627Ab2CSN1J convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 19 Mar 2012 09:27:09 -0400
Message-ID: <1332163594.18960.335.camel@twins>
Subject: Re: [RFC][PATCH 00/26] sched/numa
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Avi Kivity <avi@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        Paul Turner <pjt@google.com>,
        Suresh Siddha <suresh.b.siddha@intel.com>,
        Mike Galbraith <efault@gmx.de>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Lai Jiangshan <laijs@cn.fujitsu.com>, Dan Smith <danms@us.ibm.com>,
        Bharata B Rao <bharata.rao@gmail.com>,
        Lee Schermerhorn <Lee.Schermerhorn@hp.com>,
        Rik van Riel <riel@redhat.com>, Johannes Weiner <hannes@cmpxchg.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Date: Mon, 19 Mar 2012 14:26:34 +0100
In-Reply-To: <20120319130401.GI24602@redhat.com>
References: <20120316144028.036474157@chello.nl>
	 <4F670325.7080700@redhat.com> <1332155527.18960.292.camel@twins>
	 <20120319130401.GI24602@redhat.com>
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7BIT
X-Mailer: Evolution 3.2.2- 
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, 2012-03-19 at 14:04 +0100, Andrea Arcangeli wrote:

> About the cost of the actual pagetable scanner, you're not being
> rational about it. You should measure it for once, take khugepaged
> make it scan 1G of memory per millisecond and measure the cost.

Death by a thousand cuts.. 

> You keep complaining about the unaccountability of the pagetable
> scanners in terms of process load, and that's a red herring as far as
> I can tell. The irqs and ksoftirqd load in a busy server, is likely
> much higher than whatever happens at the pagetable scanner level (sure
> thing for khugepaged and by an huge order of magnitude so). 

Who says I agree with ksoftirqd? I would love to get rid of all things
softirq. And I also think workqueues are over-/ab-used.

> I don't
> think this is a relevant concern anyway because the pagetable scanners
> go over all memory in a equal amount so the cost would be evenly
> distributed for all processes over time (the same cannot be said about
> the irqs and ksoftrqid that will benefit only a few processes doing
> I/O). 

So what about the case where all I do is compile kernels and we already
have near perfect locality because everything is short running? You're
still scanning that memory, and I get no benefit.