From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by dcvr.yhbt.net (Postfix) with ESMTP id 332EC1F5AE for ; Tue, 30 Jun 2020 07:13:17 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 7A59F1209E2; Tue, 30 Jun 2020 16:12:47 +0900 (JST) Received: from xtrwkhkc.outbound-mail.sendgrid.net (xtrwkhkc.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id 32FCE1209DC for ; Tue, 30 Jun 2020 16:12:44 +0900 (JST) Received: by filterdrecv-p3iad2-5b55dcd864-d2lx7 with SMTP id filterdrecv-p3iad2-5b55dcd864-d2lx7-18-5EFAE601-3F 2020-06-30 07:13:05.428537811 +0000 UTC m=+309823.080631262 Received: from herokuapp.com (unknown) by ismtpd0014p1iad2.sendgrid.net (SG) with ESMTP id srSeBxGHScai20UIpLllQQ for ; Tue, 30 Jun 2020 07:13:05.342 +0000 (UTC) Date: Tue, 30 Jun 2020 07:13:05 +0000 (UTC) From: XrXr@users.noreply.github.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 74786 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Feature X-Redmine-Issue-Id: 16984 X-Redmine-Issue-Author: alanwu X-Redmine-Sender: alanwu X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-SG-EID: =?us-ascii?Q?PWg67P6owy8ojUUZg1G=2FQM4Z0jTQ2XLCqLM8Y2L8tUvRFuUPM6+aKANjRFY5CJ?= =?us-ascii?Q?rIAqraUlX3HQidil=2FC4lhbquhFsALFfW+LG0TYs?= =?us-ascii?Q?eEfHx8NddKHzwF0b4jxCOBybOjP2Cd95O46EVcr?= =?us-ascii?Q?HuSRkbEk9ishDsW9=2Fl=2FcWaUa9Owsbk1xErPeySP?= =?us-ascii?Q?o3SHO5g8PfJE3pAAUt2adXXs6G5MMXKprTwNvxn?= =?us-ascii?Q?ErKVekrXQZ3hYTucY=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 98996 Subject: [ruby-core:98996] [Ruby master Feature#16984] Remove write barrier examption for T_ICLASS X-BeenThere: ruby-core@ruby-lang.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Ruby developers List-Id: Ruby developers List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #16984 has been updated by alanwu (Alan Wu). > Could you measure the memory/objects consumption before and after this patch if it is not difficult? I took measurements on app B. It's a large Rails app with lots of classes and modules. The amount of retained memory is not deterministic unfortunately, so I can only give a rough summary. | Change to median | Change to average | --------------------------|--------------------|---------------------| GC::Profiler "Total Size" | 7 MiB | 1 MiB | VmRSS from the /proc | 4 MiB | -5 MiB | The increase to GC heap size makes sense, I expect about 5 MiB more objects given the number of classes and modules in the app. There is not much change to RSS I guess because the patch moves what used to be on the malloc heap to the GC heap. ---------------------------------------- Feature #16984: Remove write barrier examption for T_ICLASS https://bugs.ruby-lang.org/issues/16984#change-86374 * Author: alanwu (Alan Wu) * Status: Open * Priority: Normal ---------------------------------------- Consider the following code: ```ruby module M def foo; end def bar; end end class C include M end ``` The object reference graph from running the code looks like this: ``` +---+ +-----+ | M |--------------| foo |-+ +---+ +-----+ | | +-----+ | +----------------| bar | | +-----+ | +-----------+ | | | iclass(M) |---------+ | +-----------+--------------+ ``` Applying the proposed patch, the graph becomes ``` +---+ +--------------+ +-----+ | M |---------| method table |---| foo | +---+ +--------------+ +-----+ +-----------+ | | +-----+ | iclass(M) |---------+ +-----| bar | +-----------+ +-----+ ``` This change has a similar effect on the constant table. In addition to this, T_ICLASS no longer holds a reference to a ivar table. Code that access the ivar table through iclasses are changed to access it through the object from which the iclass was made. This change impacts autoload and class variable lookup. ## Why? The main goal of this change is to make iclasses and modules write barrier protected. At the moment, they are "shady", which means the GC has to do extra work to handle them. In code bases that use modules a lot, iclasses can easily take up a significant portion of the heap and impact GC time. In the old setup, because of the way `M` and `iclass(M)` share the method table, adding a single method to `M` would create multiple edges on the object reference graph. To safely make `M` and `iclass(M)` write barrier protected, one would need to trigger a write barrier for each new edge. This would make the amount of work it takes to add a method a function of the number of times the target module is included. The new setup also factors the edges in the graph. If the number of methods in a module is `M` and the number of times the module is prepended or included is `N`, the old setup had `M * (N+1)` edges. The new setup has `M + N + 1` edges instead. For large enough `M` and `N`, the new setup produces fewer edges. Having fewer edges is better since the GC's work is proportional to the number of edges. ## Impact to GC time I measured the impact to minor GC time with the following steps: - load an application - run `GC::Profile.enable` - allocate 50 million objects - run `GC::Profile.report` Here is the impact to average minor GC time on various apps: |Application | Before | After | Speedup ratio | |------------------------|---------------|---------|---------------| |CRuby's test-all suite | 2.438ms | 2.289ms | 1.06 | |`rails new` app | 1.911ms | 1.798ms | 1.06 | |Private app A | 5.182ms | 5.168ms | 1.00 | |Private app B | 185.7ms | 107.9ms | 1.72 | Private app A's heap size is about 22 MiB compared to B's 250 MiB. App B boots up about 15% faster with this change. ## Impact to class variable lookup I included a benchmark in the patch to measure the impact to class variable lookup performance. The difference seems negligible. ## Conclusion This change seems to reduce minor GC time for real-world applications. --- Code: https://github.com/ruby/ruby/pull/3238 Credits to @tenderlovemaking for coming up with the idea for this change. -- https://bugs.ruby-lang.org/