From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Andrea Corallo via "Emacs development discussions." Newsgroups: gmane.emacs.devel Subject: Re: New GC concept Date: Fri, 04 Jun 2021 08:56:43 +0000 Message-ID: References: Reply-To: Andrea Corallo Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="13420"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) Cc: emacs-devel@gnu.org To: Daniel Colascione Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Jun 04 10:57:27 2021 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1lp5dv-0003K7-AP for ged-emacs-devel@m.gmane-mx.org; Fri, 04 Jun 2021 10:57:27 +0200 Original-Received: from localhost ([::1]:46518 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lp5du-0001cd-DN for ged-emacs-devel@m.gmane-mx.org; Fri, 04 Jun 2021 04:57:26 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:36304) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lp5dP-0000wz-I3 for emacs-devel@gnu.org; Fri, 04 Jun 2021 04:56:55 -0400 Original-Received: from mx.sdf.org ([205.166.94.24]:58047) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lp5dN-00059g-AG for emacs-devel@gnu.org; Fri, 04 Jun 2021 04:56:55 -0400 Original-Received: from mab (ma.sdf.org [205.166.94.33]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 1548uhw1021798 (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO); Fri, 4 Jun 2021 08:56:44 GMT In-Reply-To: (Daniel Colascione's message of "Thu, 3 Jun 2021 20:30:26 -0700") Received-SPF: pass client-ip=205.166.94.24; envelope-from=akrl@sdf.org; helo=mx.sdf.org X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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.io gmane.emacs.devel:270364 Archived-At: Daniel Colascione writes: > Emacs has had the same GC for a decent amount of time now (since the > 1980s, really). I spent some time in 2020 rewriting it from scratch. I > haven't had time to work on the new GC recently, but I figure I'd > throw it out here to get some feedback on the general concept. > > Check out > https://github.com/dcolascione/emacs-1/blob/newgc-wip/src/alloc.c, > specifically the big doc comment on top > > The new GC basically replaces alloc.c and a few other things. It has a > few cool features: > > * fully copying and compacting > > * special treatment of sxhash to preserve object identify even while > we move it around in memory > > * generational > > * contiguous storage of mark bits separately from the data heap > > * concurrent (in design, not current implementation): idea is that we > do concurrent marking and barely pause for sweep > > * small string optimization > > * bump pointer allocation of new objects > > * heap enumeration support > > * hard requirement on pdumper > > * specialized GC spaces for conses, strings, arrays, and so on: no > stupid header word for cons cells bloating memory use by 50%! > > * cool modern C implementation that relies heavily on compiler > inlining and constant propagation > > The current implementation is deficient in many ways. Honestly, I'm > not even sure whether that specific revision compiles. But like I > said, I haven't had time recently to continue work on it. > > Still, I'm still curious about what people think of the overall > effort. It might work nicely with the new native compilation stuff, > giving us a managed code execution environment kind-of, sort-of on par > with the big modern managed-code runtimes. Sounds cool! The only comment I've so far is that IMO *the* important feature for a new Emacs GC is to have it concurrent (or say concurrent as much as possible). Emacs user experience is often dictated by its reactivity, we need to head towards a GC that is concurrent prioritizing in the design this feature over others, I wouldn't mind sacrificing some efficiency for that. I like the idea of a moving/generational GC but possibily porting what we have to a tri-color mark and sweep would solve already the problem with less impact. This is what I would have tried if I had time. Thanks for this work! Andrea