From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964823AbVHaOcE (ORCPT ); Wed, 31 Aug 2005 10:32:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964825AbVHaOcE (ORCPT ); Wed, 31 Aug 2005 10:32:04 -0400 Received: from dvhart.com ([64.146.134.43]:59782 "EHLO localhost.localdomain") by vger.kernel.org with ESMTP id S964823AbVHaOcC (ORCPT ); Wed, 31 Aug 2005 10:32:02 -0400 Date: Wed, 31 Aug 2005 07:31:52 -0700 From: "Martin J. Bligh" Reply-To: "Martin J. Bligh" To: Hugh Dickins , Arjan van de Ven Cc: Dave McCracken , Andrew Morton , Linux Kernel , Linux Memory Management Subject: Re: [PATCH 1/1] Implement shared page tables Message-ID: <16640000.1125498711@[10.10.2.4]> In-Reply-To: References: <7C49DFF721CB4E671DB260F9@[10.1.1.4]> <1125489077.3213.12.camel@laptopd505.fenrus.org> X-Mailer: Mulberry/2.2.1 (Linux/x86) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --Hugh Dickins wrote (on Wednesday, August 31, 2005 14:42:38 +0100): > On Wed, 31 Aug 2005, Arjan van de Ven wrote: >> On Wed, 2005-08-31 at 12:44 +0100, Hugh Dickins wrote: >> > I was going to say, doesn't randomize_va_space take away the rest of >> > the point? But no, it appears "randomize_va_space", as it currently >> > appears in mainline anyway, is somewhat an exaggeration: it just shifts >> > the stack a little, with no effect on the rest of the va space. >> >> it also randomizes mmaps > > Ah, via PF_RANDOMIZE, yes, thanks: so long as certain conditions are > fulfilled - and my RLIM_INFINITY RLIMIT_STACK has been preventing it. > > And mmaps include shmats: so unless the process specifies non-NULL > shmaddr to attach at, it'll choose a randomized address for that too > (subject to those various conditions). > > Which is indeed a further disincentive against shared page tables. Or shared pagetables a disincentive to randomizing the mmap space ;-) They're incompatible, but you could be left to choose one or the other via config option. 3% on "a certain industry-standard database benchmark" (cough) is huge, and we expect the benefit for PPC64 will be larger as we can share the underlying hardware PTEs without TLB flushing as well. M.