From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mtagate7.de.ibm.com ([195.212.29.156]:62512 "EHLO mtagate7.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752181AbXJZIIX (ORCPT ); Fri, 26 Oct 2007 04:08:23 -0400 Subject: Re: [patch 2/6] CONFIG_HIGHPTE vs. sub-page page tables. From: Martin Schwidefsky Reply-To: schwidefsky@de.ibm.com In-Reply-To: <1193385617.13638.3.camel@pasglop> References: <20071025181520.880272069@de.ibm.com> <20071025181901.212545095@de.ibm.com> <1193345221.7018.18.camel@pasglop> <1193384578.31831.6.camel@localhost> <1193385617.13638.3.camel@pasglop> Content-Type: text/plain Date: Fri, 26 Oct 2007 10:08:20 +0200 Message-Id: <1193386100.31831.13.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org To: benh@kernel.crashing.org Cc: linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, borntraeger@de.ibm.com List-ID: On Fri, 2007-10-26 at 18:00 +1000, Benjamin Herrenschmidt wrote: > > > Interesting. That means I don't need to have a PTE page to be a struct > > > page anymore ? I can have good use for that on powerpc as well... > > > > That would be good news. I'm curious, can you elaborate on what the use > > case is? > > When using 64K pages, we use 32K of PTEs and 32K of "extension". The > extension thing is used when using HW 4K pages, to keep track of the > subpages. On setups where that isn't needed, we can save memory by > allocating half pages... Ahh, that is exactly the same reason as for s390. Page tables with a size that is sub-page. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin.