From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: jca@wxcvbn.org (=?utf-8?Q?J=C3=A9r=C3=A9mie_Courr=C3=A8ges-Anglas?=) Newsgroups: gmane.emacs.devel Subject: Re: When should ralloc.c be used? Date: Fri, 28 Oct 2016 09:09:22 +0200 Message-ID: <87shrheyql.fsf@ritchie.wxcvbn.org> References: <838ttfnmev.fsf@gnu.org> <837f8znk8f.fsf@gnu.org> <83zilvm2ud.fsf@gnu.org> <83r377m0i8.fsf@gnu.org> <83eg36n6v5.fsf@gnu.org> <83shrl523p.fsf@gnu.org> <83eg354ux3.fsf@gnu.org> <4f0c2868-d408-a5c4-d5a8-90dae750eb33@dancol.org> <878tt9ggdk.fsf@ritchie.wxcvbn.org> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1477640170 8665 195.159.176.226 (28 Oct 2016 07:36:10 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 28 Oct 2016 07:36:10 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (berkeley-unix) Cc: Eli Zaretskii , eggert@cs.ucla.edu, Stefan Monnier , emacs-devel@gnu.org To: Daniel Colascione Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Oct 28 09:36:06 2016 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c01ho-00011o-Qs for ged-emacs-devel@m.gmane.org; Fri, 28 Oct 2016 09:36:00 +0200 Original-Received: from localhost ([::1]:47213 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c01hr-0004nj-C5 for ged-emacs-devel@m.gmane.org; Fri, 28 Oct 2016 03:36:03 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:41613) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1c01Iw-0001T1-C6 for emacs-devel@gnu.org; Fri, 28 Oct 2016 03:10:19 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1c01Iv-0000WK-9k for emacs-devel@gnu.org; Fri, 28 Oct 2016 03:10:18 -0400 Original-Received: from chomsky.autogeree.net ([91.216.110.36]:59725) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1c01Iq-0000U9-Kx; Fri, 28 Oct 2016 03:10:12 -0400 Original-Received: from ritchie.wxcvbn.org (localhost [127.0.0.1]) by wxcvbn.org (8.15.2/8.15.2) with ESMTP id u9S79OFa040149; Fri, 28 Oct 2016 09:09:24 +0200 (CEST) Original-Received: (from jca@localhost) by ritchie.wxcvbn.org (8.15.2/8.15.2/Submit) id u9S79Mwu026172; Fri, 28 Oct 2016 09:09:22 +0200 (CEST) Mail-Followup-To: Daniel Colascione , Eli Zaretskii , eggert@cs.ucla.edu, Stefan Monnier , emacs-devel@gnu.org In-Reply-To: (Daniel Colascione's message of "Thu, 27 Oct 2016 23:23:05 -0700") X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 91.216.110.36 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:208924 Archived-At: Daniel Colascione writes: > jca@wxcvbn.org (J=C3=A9r=C3=A9mie Courr=C3=A8ges-Anglas) writes: > >> Daniel Colascione writes: >> >>> On 10/24/2016 08:40 AM, Eli Zaretskii wrote: >>>>> From: Stefan Monnier >>>>> Cc: eggert@cs.ucla.edu, emacs-devel@gnu.org >>>>> Date: Mon, 24 Oct 2016 10:37:19 -0400 >>>>> >>>>>> Using mmap has disadvantages: when you need to enlarge buffer text, >>>>>> and that fails (because there are no more free pages/addresses after >>>>>> the already allocated region), we need to copy buffer text to the new >>>>>> allocation. >>> >>> 64-bit address spaces are *huge*. What about just making every buffer >>> allocation 2GB long or so, marked PROT_NONE? You don't actually have to >>> commit all that memory --- all you've done is set aside that address >>> space. >> >> IIUC you suggest relying on memory overcommit. That doesn't sound >> portable at all. Not all OSes do overcommit and the ones who do >> generally provide a way to disable it. > > You understand incorrectly. "Overcommit" is the practice of allowing an > operating system to lie about how much memory it's guaranteed to give > applications in the future. We're not talking about guaranteed > memory. We're talking about setting aside address space only, not asking > the OS to make guarantees about future memory availability. All major > operating systems, even ones like Windows that don't do overcommit, > provide ways to reserve address space without asking the OS to guarantee > availability of memory. Can you point at some documentation regarding those techniques? I fail to find one that would work on my "non-major", mostly POSIX OS. > That said, my idea probably isn't the best --- but it doesn't rely > on overcommit. --=20 jca | PGP : 0x1524E7EE / 5135 92C1 AD36 5293 2BDF DDCC 0DFA 74AE 1524 E7EE