From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758672AbYEEMmx (ORCPT ); Mon, 5 May 2008 08:42:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752181AbYEEMmq (ORCPT ); Mon, 5 May 2008 08:42:46 -0400 Received: from rv-out-0506.google.com ([209.85.198.232]:36769 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752142AbYEEMmp (ORCPT ); Mon, 5 May 2008 08:42:45 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=BtgeAJoqSs4sWBtsQGcFx7QCZpFELshI4EylBBJdvVlj/+YT0dLZ3ISU1AMd6eEMp9Ggx2IGZrH7Bgz+GaJiI3WT0yS1ybtKJ8pb7XFf4WRTLhG5/GIpkdB3WNEG7W1OsJF0nUmLBsEgxqOoXsZTg7bmWa2R3KZOb7basRPIjhY= Message-ID: Date: Mon, 5 May 2008 14:42:44 +0200 From: "Michael Kerrisk" To: "Nick Piggin" Subject: Re: MAP_POPULATE behavior change? Cc: lkml , mk In-Reply-To: <20080505122316.GE5018@wotan.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <4815BDF5.9070506@gmail.com> <20080505122316.GE5018@wotan.suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Nick, On Mon, May 5, 2008 at 2:23 PM, Nick Piggin wrote: > On Mon, Apr 28, 2008 at 02:07:17PM +0200, Michael Kerrisk wrote: > > In 2.6.23, you had the commit below, which seems to have changed the > > kernel-userland API. > > > > Am I right to understand that with this patch MAP_POPULATE now also works with > > MAP_PRIVATE mappings? (Formerly it only worked with MAP_SHARED mappings, but > > some very quick testing suggests that MAP_POPULATE now also has an affect for > > MAP_PRIVATE.) > > Yeah it should also set up anonymous mappings. Very observant :) Umm -- did it not work for anonymous *shared* mappings before? I understood that it did. > > Also, can you summarize the status of MAP_NONBLOCK? Is it now a no-op? > > Yes, it is. Hmm -- going back and re-reading the code, there is: if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK)) make_pages_present(addr, addr + len); That means that MAP_NONBLOCK makes *MAP_POPULATE* a no-op. Was that intended? Cheers, Michael > The problem is you need to walk the page tables, and it > is fairly annoying to have to make a special case for that to be > non blocking (after just getting rid of the ->populate special case). > > It is possible of course to implement. It might even be easier because > you could pass in a NONBLOCK flag to ->fault from get_user_pages... but > for now it is a noop. > > Thanks, > Nick > > > > > > Cheers, > > > > Michael > > > > == > > > > commit 54cb8821de07f2ffcd28c380ce9b93d5784b40d7 > > Author: Nick Piggin > > Date: Thu Jul 19 01:46:59 2007 -0700 > > > > mm: merge populate and nopage into fault (fixes nonlinear) > > > > Nonlinear mappings are (AFAIKS) simply a virtual memory concept that encodes > > the virtual address -> file offset differently from linear mappings. > > > > ->populate is a layering violation because the filesystem/pagecache code > > should need to know anything about the virtual memory mapping. The hitch here > > is that the ->nopage handler didn't pass down enough information (ie. pgoff). > > But it is more logical to pass pgoff rather than have the ->nopage function > > calculate it itself anyway (because that's a similar layering violation). > > > > Having the populate handler install the pte itself is likewise a nasty thing > > to be doing. > > > > This patch introduces a new fault handler that replaces ->nopage and > > ->populate and (later) ->nopfn. Most of the old mechanism is still in place > > so there is a lot of duplication and nice cleanups that can be removed if > > everyone switches over. > > > > The rationale for doing this in the first place is that nonlinear mappings are > > subject to the pagefault vs invalidate/truncate race too, and it seemed stupid > > to duplicate the synchronisation logic rather than just consolidate the two. > > > > After this patch, MAP_NONBLOCK no longer sets up ptes for pages present in > > pagecache. Seems like a fringe functionality anyway. > > > > NOPAGE_REFAULT is removed. This should be implemented with ->fault, and no > > users have hit mainline yet. > > > > > > > > > > -- > > Michael Kerrisk > > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > > Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html > > > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html