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 S1751730Ab3LLVEh (ORCPT <rfc822;w@1wt.eu>);
	Thu, 12 Dec 2013 16:04:37 -0500
Received: from relay1.sgi.com ([192.48.179.29]:59032 "EHLO relay.sgi.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751526Ab3LLVEe (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 12 Dec 2013 16:04:34 -0500
Date: Thu, 12 Dec 2013 15:04:32 -0600
From: Alex Thorlton <athorlton@sgi.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Rik van Riel <riel@redhat.com>, Wanpeng Li <liwanp@linux.vnet.ibm.com>,
        Mel Gorman <mgorman@suse.de>, Michel Lespinasse <walken@google.com>,
        Benjamin LaHaise <bcrl@kvack.org>, Oleg Nesterov <oleg@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        David Rientjes <rientjes@google.com>,
        Zhang Yanfei <zhangyanfei@cn.fujitsu.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@suse.cz>,
        Jiang Liu <jiang.liu@huawei.com>,
        Cody P Schafer <cody@linux.vnet.ibm.com>,
        Glauber Costa <glommer@parallels.com>,
        Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 2/3] Add tunable to control THP behavior
Message-ID: <20131212210432.GB6034@sgi.com>
References: <cover.1386790423.git.athorlton@sgi.com>
 <20131212180050.GC134240@sgi.com>
 <CALCETrWfFRhjuoK8T9G8hecxsRxFPQ+qA0x7azoof1X5tuxruA@mail.gmail.com>
 <20131212204950.GA6034@sgi.com>
 <CALCETrWgVViOK8mp5wort9T6VWBAAN_MCGmoAGddudsWfr2Ypw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALCETrWgVViOK8mp5wort9T6VWBAAN_MCGmoAGddudsWfr2Ypw@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> Right.  I like that behavior for my workload.  (Although I currently
> allocate huge pages -- when I wrote that code, THP interacted so badly
> with pagecache that it was a non-starter.  I think it's fixed now,
> though.)

In that case, it's probably best to just stick with current behavior,
and leave the threshold at 1, unless we implement something like I
discuss below.

> In that case, I guess I misunderstood your description.  Are saying
> that, once any node accesses this many pages in the potential THP,
> then the whole THP will be mapped?

Well, right now, this patch completely gives up on mapping a THP if two
different nodes take a page from our chunk before the threshold is hit,
so I think you're mostly understanding it correctly.

One thing we could consider is adding an option to map the THP on
the node with the *most* references to the potential THP, instead of
giving up on mapping the THP when multiple nodes reference it.  That
might be a good middle ground, but I can see some performance issues
coming into play there if the threshold is set too high, since we'll
have to move all the pages in the chunk to the node that hit the
threshold.

- Alex