From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx108.postini.com [74.125.245.108]) by kanga.kvack.org (Postfix) with SMTP id C811B6B00BD for ; Wed, 14 Nov 2012 17:12:25 -0500 (EST) Message-ID: <50A41583.6060709@redhat.com> Date: Wed, 14 Nov 2012 17:04:51 -0500 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 0/2] change_protection(): Count the number of pages affected References: <1352883029-7885-1-git-send-email-mingo@kernel.org> <50A3E659.9060804@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: Ingo Molnar , Linux Kernel Mailing List , linux-mm , Paul Turner , Lee Schermerhorn , Christoph Lameter , Mel Gorman , Andrew Morton , Andrea Arcangeli , Peter Zijlstra , Thomas Gleixner , Hugh Dickins On 11/14/2012 03:52 PM, Linus Torvalds wrote: > On Wed, Nov 14, 2012 at 10:43 AM, Rik van Riel wrote: >> >>> - even *more* aggressive: if the bits become strictly more >>> restrictive > > sorry, this was meant to be "permissive", not restrictive. > My mistake - the point is that if we're changing to a strictly more > permissive mode, the old state of the page tables and TLB's are > perfectly "valid", they are just unnecessarily strict. So we'll take a > fault on some accesses, but that's fine - we can fix things up at > fault time. The patches I sent in a few weeks ago do that for do_wp_page, but I can see how we want the same for mprotect... > The question then becomes what the access patterns are. The fault > overhead may well dawrf any TLB flush costs, but it depends on whether > people tend to do large mprotect() and then just actually change a few > pages, or whether mprotect() users often then touch all of the area.. If we keep a counter of faults-after-mprotect, we may be able to figure out automatically what behaviour would be best. Of course, that gets us into premature optimization, so it is probably best to do the simple thing for now. -- All rights reversed -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org