From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED.blaine.gmane.org!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.devel Subject: Re: Lost or corrupted `undo-tree' history Date: Fri, 10 Jan 2020 11:31:05 +0200 Message-ID: <831rs7ac9y.fsf@gnu.org> References: <1631cfa6-91e2-1fc9-85b8-fdb55a4aa765@Alexander.Shukaev.name> <835zhjag4g.fsf@gnu.org> <64a45342-251e-06b3-d836-6a0f19e3c114@Alexander.Shukaev.name> Injection-Info: blaine.gmane.org; posting-host="blaine.gmane.org:195.159.176.226"; logging-data="54611"; mail-complaints-to="usenet@blaine.gmane.org" Cc: emacs-devel@gnu.org To: Alexander Shukaev Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Jan 10 10:36:12 2020 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by blaine.gmane.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1ipqeV-000zWN-1I for ged-emacs-devel@m.gmane-mx.org; Fri, 10 Jan 2020 10:32:23 +0100 Original-Received: from localhost ([::1]:43030 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ipqeT-0007lu-6P for ged-emacs-devel@m.gmane-mx.org; Fri, 10 Jan 2020 04:32:21 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:43016) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ipqdH-0006fz-0T for emacs-devel@gnu.org; Fri, 10 Jan 2020 04:31:08 -0500 Original-Received: from fencepost.gnu.org ([2001:470:142:3::e]:43718) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ipqdG-0005Px-S9; Fri, 10 Jan 2020 04:31:06 -0500 Original-Received: from [176.228.60.248] (port=2121 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_256_CBC_SHA1:256) (Exim 4.82) (envelope-from ) id 1ipqdG-0005jb-9m; Fri, 10 Jan 2020 04:31:06 -0500 In-reply-to: <64a45342-251e-06b3-d836-6a0f19e3c114@Alexander.Shukaev.name> (message from Alexander Shukaev on Fri, 10 Jan 2020 10:19:15 +0100) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.23 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-mx.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:244171 Archived-At: > Cc: emacs-devel@gnu.org > From: Alexander Shukaev > Date: Fri, 10 Jan 2020 10:19:15 +0100 > > > IMO, it would be a very bad mantra for a Lisp package operating on > > this low level to disable GC, because that could cause the user's > > system to run out of memory, and Emacs be killed by the likes of OOM > > killer agents. Disabling GC is barely a good idea on the > > user-customization level, certainly not in packages such as undo-tree. > > Maybe. I was under impression that for a "short-running" function this > might be fine to prevent GC from running in-between some Emacs Lisp > instructions. You can never know whether a given function is "short-running" or not in Emacs, not with the multitude of hooks and advices we have. You _might_ be able to make that assumption safely on the C level, but even there, it's non-trivial to prove to ourselves no Lisp could ever run in between. For Lisp code, this is simply impossible to prove. > Having said that, I agree that disabling GC sometimes may be dangerous > practice. I remember how after reading [1], I tried that suggestion for > minibuffer. After some time I noticed that I keep running out of > memory. What was interesting is the actual test case. For example, I > could run some search command which pushes matches into minibuffer, say > up to 100 000 matches. As this is happening (and `gc-cons-threshold' is > `most-positive-fixnum'), I can see memory consumption of Emacs growing > rapidly say from 500MB up to 8GB at which point I cancel the search and > exit the minibuffer command. As a result, `gc-cons-threshold' comes > back to the default value and garbage collecting starts immediately. > However, the memory consumption of Emacs does not fall back to 500MB, > but rather goes down to only e.g. 6GB, which afterwards are never ever > reclaimed. I believe this is the expected behavior of memory allocation routines on GNU/Linux. Freed memory is not necessarily returned to the system, but kept in the process's address space as free memory to be used for future allocations. > If I repeat the test, the memory consumption would immediately > continue to grow off 6GB further as if those 6GB are not reused and > are somehow stuck holding something that cannot be reclaimed > anymore. Hence, you can see that if I way same amount of time, the > memory consumption would go to around 14GB. This is how one can > quickly run out of memory as if there would be some memory leaks > related to GC. There are no memory leaks. Just don't set gc-cons-threshold too high, that's all. > Nevertheless, the second suggestion (for speeding up initialization > code) from [1], IMO, is a good example of temporarily blowing > `gc-cons-threshold' which I still use. I disagree. Kids, don't try that at home! I posted several times on reddit and elsewhere the procedure I propose to follow to raise the threshold in a conservative and controlled way, to satisfy the personal needs of any particular user, without risking any system-wide degradation in memory pressure.