From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: When should ralloc.c be used? Date: Tue, 25 Oct 2016 19:36:54 +0300 Message-ID: <83eg34wfkp.fsf@gnu.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> <83pomp35ch.fsf@gnu.org> Reply-To: Eli Zaretskii NNTP-Posting-Host: blaine.gmane.org X-Trace: blaine.gmane.org 1477413457 1073 195.159.176.226 (25 Oct 2016 16:37:37 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 25 Oct 2016 16:37:37 +0000 (UTC) Cc: emacs-devel@gnu.org To: Stefan Monnier Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Oct 25 18:37:32 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 1bz4iy-00066t-IP for ged-emacs-devel@m.gmane.org; Tue, 25 Oct 2016 18:37:16 +0200 Original-Received: from localhost ([::1]:56445 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bz4j0-0007Jd-Sk for ged-emacs-devel@m.gmane.org; Tue, 25 Oct 2016 12:37:18 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:50251) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bz4ip-0007Io-Dj for emacs-devel@gnu.org; Tue, 25 Oct 2016 12:37:13 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bz4ik-0002sb-GW for emacs-devel@gnu.org; Tue, 25 Oct 2016 12:37:07 -0400 Original-Received: from fencepost.gnu.org ([2001:4830:134:3::e]:46307) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bz4ik-0002sX-Ct; Tue, 25 Oct 2016 12:37:02 -0400 Original-Received: from 84.94.185.246.cable.012.net.il ([84.94.185.246]:1393 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1bz4ii-0004DB-O5; Tue, 25 Oct 2016 12:37:02 -0400 In-reply-to: (message from Stefan Monnier on Tue, 25 Oct 2016 10:12:23 -0400) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2001:4830:134:3::e 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:208784 Archived-At: > From: Stefan Monnier > Date: Tue, 25 Oct 2016 10:12:23 -0400 > > >> 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. Since ralloc.c relocates blocks, it can make this happen more easily. > > 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. It makes no sense to release random pages here and there, all you get is fragmentation at address space level.