Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967234AbdLSMqw (ORCPT ); Tue, 19 Dec 2017 07:46:52 -0500 Received: from mx2.suse.de ([195.135.220.15]:36078 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966054AbdLSMqt (ORCPT ); Tue, 19 Dec 2017 07:46:49 -0500 Date: Tue, 19 Dec 2017 13:46:46 +0100 From: Michal Hocko To: David Laight Cc: "'Edward Napierala'" , Andrew Morton , "linux-api@vger.kernel.org" , Khalid Aziz , Michael Ellerman , Russell King - ARM Linux , Andrea Arcangeli , "linux-mm@kvack.org" , LKML , "linux-arch@vger.kernel.org" , Florian Weimer , John Hubbard , Matthew Wilcox , Abdul Haleem , Joel Stanley , Kees Cook , "jasone@google.com" , "davidtgoldblatt@gmail.com" Subject: Re: [PATCH v2 0/2] mm: introduce MAP_FIXED_SAFE Message-ID: <20171219124646.GR2787@dhcp22.suse.cz> References: <20171213092550.2774-1-mhocko@kernel.org> <20171213163210.6a16ccf8753b74a6982ef5b6@linux-foundation.org> <20171214131526.GM16951@dhcp22.suse.cz> <20171214145443.GA2202@brick> <0ca2620ce7534c5491e69416621ac41b@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0ca2620ce7534c5491e69416621ac41b@AcuMS.aculab.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1785 Lines: 39 On Tue 19-12-17 12:40:16, David Laight wrote: > From: Edward Napierala > > Sent: 14 December 2017 14:55 > > > > On 1214T1415, Michal Hocko wrote: > > > On Thu 14-12-17 12:44:17, Edward Napierala wrote: > > > > Regarding the name - how about adopting MAP_EXCL? It was introduced in > > > > FreeBSD, > > > > and seems to do exactly this; quoting mmap(2): > > > > > > > > MAP_FIXED Do not permit the system to select a different address > > > > than the one specified. If the specified address > > > > cannot be used, mmap() will fail. If MAP_FIXED is > > > > specified, addr must be a multiple of the page size. > > > > If MAP_EXCL is not specified, a successful MAP_FIXED > > > > request replaces any previous mappings for the > > > > process' pages in the range from addr to addr + len. > > > > In contrast, if MAP_EXCL is specified, the request > > > > will fail if a mapping already exists within the > > > > range. > > > > > > I am not familiar with the FreeBSD implementation but from the above it > > > looks like MAP_EXCL is a MAP_FIXED mofifier which is not how we are > > > going to implement it in linux due to reasons mentioned in this cover > > > letter. Using the same name would be more confusing than helpful I am > > > afraid. > > > > Sorry, missed that. Indeed, reusing a name with a different semantics > > would be a bad idea. > > I don't remember any discussion about using MAP_FIXED | MAP_EXCL ? > > Why not match the prior art?? See the cover letter which explains why an extension is not backward compatible. -- Michal Hocko SUSE Labs