Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760063AbYCZA6X (ORCPT ); Tue, 25 Mar 2008 20:58:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755478AbYCZA6O (ORCPT ); Tue, 25 Mar 2008 20:58:14 -0400 Received: from lemon.ertos.nicta.com.au ([203.143.174.143]:53720 "EHLO lemon.gelato.unsw.edu.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753758AbYCZA6N (ORCPT ); Tue, 25 Mar 2008 20:58:13 -0400 Date: Wed, 26 Mar 2008 11:57:23 +1100 Message-ID: <87lk465mks.wl%peter@chubb.wattle.id.au> From: Peter Chubb To: "David Mosberger-Tang" Cc: "Peter Chubb" , "David Miller" , clameter@sgi.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org, torvalds@linux-foundation.org, ianw@gelato.unsw.edu.au In-Reply-To: References: <20080324.144356.104645106.davem@davemloft.net> <20080325.162244.61337214.davem@davemloft.net> <87tziu5q37.wl%peter@chubb.wattle.id.au> User-Agent: Wanderlust/2.15.6 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (Goj~) APEL/10.7 MULE XEmacs/21.4 (patch 20) (Double Solitaire) (i486-linux-gnu) Organization: Gelato@UNSW X-SA-Exim-Connect-IP: 203.143.174.121 X-SA-Exim-Mail-From: peterc@gelato.unsw.edu.au Subject: Re: larger default page sizes... X-SA-Exim-Version: 4.2 (built Thu, 03 Mar 2005 10:39:27 +0000) X-SA-Exim-Scanned: Yes (on lemon.gelato.unsw.edu.au) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2002 Lines: 39 >>>>> "David" == David Mosberger-Tang writes: David> On Tue, Mar 25, 2008 at 5:41 PM, Peter Chubb David> wrote: >> The main issue is that, at least on Itanium, you have to turn off >> the hardware page table walker for hugepages if you want to mix >> superpages and standard pages in the same region. (The long format >> VHPT isn't the panacea we'd like it to be because the hash function >> it uses depends on the page size). David> Why not just repeat the PTEs for super-pages? That won't work David> for huge pages, but for superpages that are a reasonable David> multiple (e.g., 16-times) the base-page size, it should work David> nicely. You end up having to repeat PTEs to fit into Linux's page table structure *anyway* (unless we can change Linux's page table). But there's no place in the short format hardware-walked page table (that reuses the leaf entries in Linux's table) for a page size. And if you use some of the holes in the format, the hardware walker doesn't understand it --- so you have to turn off the hardware walker for *any* regions where there might be a superpage. If you use the long format VHPT, you have a choice: load the hash table with just the translation that caused the miss, load all possible hash entries that could have caused the miss for the page, or preload the hash table when the page is instantiated, with all possible entries that could hash to the huge page. I don't remember the details, but I seem to remember all these being bad choices for one reason or other ... Ian, can you elaborate? -- Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au http://www.ertos.nicta.com.au ERTOS within National ICT Australia -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/