From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <andi@firstfloor.org>
Received: from one.firstfloor.org (one.firstfloor.org [213.235.205.2])
	(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
	(Client did not present a certificate)
	by ozlabs.org (Postfix) with ESMTPS id CFBD2DDF31
	for <linuxppc-dev@ozlabs.org>; Thu,  7 Aug 2008 05:07:20 +1000 (EST)
To: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC] [PATCH 0/5 V2] Huge page backed user-space stacks
From: Andi Kleen <andi@firstfloor.org>
References: <cover.1216928613.git.ebmunson@us.ibm.com>
	<20080730014308.2a447e71.akpm@linux-foundation.org>
	<20080730172317.GA14138@csn.ul.ie>
	<20080730103407.b110afc2.akpm@linux-foundation.org>
Date: Wed, 06 Aug 2008 20:49:40 +0200
In-Reply-To: <20080730103407.b110afc2.akpm@linux-foundation.org> (Andrew
	Morton's message of "Wed, 30 Jul 2008 10:34:07 -0700")
Message-ID: <87fxpi567v.fsf@basil.nowhere.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Mel Gorman <mel@csn.ul.ie>, linuxppc-dev@ozlabs.org,
	libhugetlbfs-devel@lists.sourceforge.net,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.ozlabs.org>
List-Unsubscribe: <https://ozlabs.org/mailman/options/linuxppc-dev>,
	<mailto:linuxppc-dev-request@ozlabs.org?subject=unsubscribe>
List-Archive: <http://ozlabs.org/pipermail/linuxppc-dev>
List-Post: <mailto:linuxppc-dev@ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@ozlabs.org?subject=help>
List-Subscribe: <https://ozlabs.org/mailman/listinfo/linuxppc-dev>,
	<mailto:linuxppc-dev-request@ozlabs.org?subject=subscribe>

Andrew Morton <akpm@linux-foundation.org> writes:

> Do we expect that this change will be replicated in other
> memory-intensive apps?  (I do).

The catch with 2MB pages on x86 is that x86 CPUs generally have
much less 2MB TLB entries than 4K entries. So if you're unlucky
and access a lot of mappings you might actually thrash more with
them. That is why they are not necessarily an universal win.

-Andi