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-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI, RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id E46221F45E for ; Tue, 18 Feb 2020 20:05:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727742AbgBRUFE (ORCPT ); Tue, 18 Feb 2020 15:05:04 -0500 Received: from cloud.peff.net ([104.130.231.41]:47124 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1728908AbgBRUCU (ORCPT ); Tue, 18 Feb 2020 15:02:20 -0500 Received: (qmail 20004 invoked by uid 109); 18 Feb 2020 20:02:20 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with SMTP; Tue, 18 Feb 2020 20:02:20 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 22036 invoked by uid 111); 18 Feb 2020 20:11:20 -0000 Received: from coredump.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.2) by peff.net (qpsmtpd/0.94) with (TLS_AES_256_GCM_SHA384 encrypted) ESMTPS; Tue, 18 Feb 2020 15:11:20 -0500 Authentication-Results: peff.net; auth=none Date: Tue, 18 Feb 2020 15:02:19 -0500 From: Jeff King To: Derrick Stolee Cc: git@vger.kernel.org, Junio C Hamano Subject: Re: [PATCH v2 02/15] pack-bitmap: fix leak of haves/wants object lists Message-ID: <20200218200219.GC21774@coredump.intra.peff.net> References: <20200214182147.GA654525@coredump.intra.peff.net> <20200214182211.GB150965@coredump.intra.peff.net> <28c2f199-e9eb-4405-9044-92a0af7632ec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <28c2f199-e9eb-4405-9044-92a0af7632ec@gmail.com> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Tue, Feb 18, 2020 at 12:58:10PM -0500, Derrick Stolee wrote: > On 2/14/2020 1:22 PM, Jeff King wrote: > > When we do a bitmap-aware revision traversal, we create an object_list > > for each of the "haves" and "wants" tips. After creating the result > > bitmaps these are no longer needed or used, but we never free the list > > memory. > > It's surprising that we got away with this for so long. Is it > possible that this loop of freeing memory could provide significant > performance drawbacks? I'm assuming that the free() loop is much > faster than the malloc() loop, so the impact is negligible. I don't think it's surprising. We're only talking about leaking hundreds or perhaps thousands of structs. So maybe a few kilobytes at most. And we'd typically only run one such bitmap traversal per program. Meanwhile rev-list is generally storing that same set of objects in a pending array, and I think we don't generally clean up after it (nor is there even a convenient function to do so). So I think it's sort of a drop in the bucket of Git's "eh, this pretty much lasts about the whole program anyway" leaks. I don't think there's much performance difference either way in freeing or not. It's mostly just a cleanliness thing. (I do one day dream of being able to run the test suite through a leakchecker, but we're still a ways off, I think). -Peff