From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: When should ralloc.c be used? Date: Tue, 25 Oct 2016 10:12:23 -0400 Message-ID: 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> <83pomp35ch.fsf@gnu.org> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: blaine.gmane.org 1477404808 26251 195.159.176.226 (25 Oct 2016 14:13:28 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 25 Oct 2016 14:13:28 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.2.50 (gnu/linux) To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Oct 25 16:13:24 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 1bz2TQ-0004EG-3a for ged-emacs-devel@m.gmane.org; Tue, 25 Oct 2016 16:13:04 +0200 Original-Received: from localhost ([::1]:54805 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bz2TS-0000vH-Ap for ged-emacs-devel@m.gmane.org; Tue, 25 Oct 2016 10:13:06 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:43234) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bz2TG-0000sG-Dz for emacs-devel@gnu.org; Tue, 25 Oct 2016 10:12:58 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bz2TC-0005jm-HX for emacs-devel@gnu.org; Tue, 25 Oct 2016 10:12:54 -0400 Original-Received: from [195.159.176.226] (port=45016 helo=blaine.gmane.org) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1bz2TC-0005jX-9g for emacs-devel@gnu.org; Tue, 25 Oct 2016 10:12:50 -0400 Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1bz2Sx-00017d-E2 for emacs-devel@gnu.org; Tue, 25 Oct 2016 16:12:35 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 17 Original-X-Complaints-To: usenet@blaine.gmane.org Cancel-Lock: sha1:qUaUH/JFjyiYX++GTGV7nB5d0eo= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 195.159.176.226 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:208764 Archived-At: >> That's why I said "basically". Yes, in theory it can sometimes >> return memory. In practice, this is rare. In contrast, with mmap, >> returning memory to the OS is the rule rather than the exception. > How so? Releasing memory in both cases requires basically the same > situation: a large enough block of contiguous memory not in use. IIUC releasing memory with sbrk can only be done if that memory is at the end of the heap. > It seems ralloc is actually at an advantage, because relocating blocks > helps collect together a larger free block. mmap can always free what it has allocated before, without any need to relocate anything. Stefan