From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.6 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id CAA5420437 for ; Fri, 13 Oct 2017 14:10:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758396AbdJMOKX (ORCPT ); Fri, 13 Oct 2017 10:10:23 -0400 Received: from cloud.peff.net ([104.130.231.41]:52122 "HELO cloud.peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1758390AbdJMOKV (ORCPT ); Fri, 13 Oct 2017 10:10:21 -0400 Received: (qmail 22805 invoked by uid 109); 13 Oct 2017 14:10:20 -0000 Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with SMTP; Fri, 13 Oct 2017 14:10:20 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 25588 invoked by uid 111); 13 Oct 2017 14:10:23 -0000 Received: from sigill.intra.peff.net (HELO sigill.intra.peff.net) (10.0.0.7) by peff.net (qpsmtpd/0.94) with SMTP; Fri, 13 Oct 2017 10:10:23 -0400 Authentication-Results: peff.net; auth=none Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Fri, 13 Oct 2017 10:10:18 -0400 Date: Fri, 13 Oct 2017 10:10:18 -0400 From: Jeff King To: Derrick Stolee Cc: Constantine , Junio C Hamano , Christian Couder , Mike Hommey , git Subject: Re: git-clone causes out of memory Message-ID: <20171013141018.62zvezivkkhloc5d@sigill.intra.peff.net> References: <20171013103722.rvr7536mu2hoo4wb@glandium.org> <2f9b8856-dacc-768d-32c2-985f5f145ba7@yandex.ru> <20171013124456.qsbaol7txdgdb6wq@sigill.intra.peff.net> <20171013135058.q7vhufdtin42ddic@sigill.intra.peff.net> <53f98311-3c5f-9863-5f6c-bc4f25fad317@gmail.com> <20171013135636.o2vhktt7aqx6luuy@sigill.intra.peff.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20171013135636.o2vhktt7aqx6luuy@sigill.intra.peff.net> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Fri, Oct 13, 2017 at 09:56:36AM -0400, Jeff King wrote: > On Fri, Oct 13, 2017 at 09:55:15AM -0400, Derrick Stolee wrote: > > > > We should be comparing an empty tree and d0/d0/d0/d0 (or however deep > > > your pathspec goes). We should be able to see immediately that the entry > > > is not present between the two and not bother descending. After all, > > > we've set the QUICK flag in init_revisions(). So the real question is > > > why QUICK is not kicking in. > > > > I'm struggling to understand your meaning. We want to walk from root to > > d0/d0/d0/d0, but there is no reason to walk beyond that tree. But maybe > > that's what the QUICK flag is supposed to do. > > Yes, that's exactly what it is for. When we see the first difference we > should say "aha, the caller only wanted to know whether there was a > difference, not what it was" and return immediately. See > diff_can_quit_early(). Hmm. So this patch makes it go fast: diff --git a/revision.c b/revision.c index d167223e69..b52ea4e9d8 100644 --- a/revision.c +++ b/revision.c @@ -409,7 +409,7 @@ static void file_add_remove(struct diff_options *options, int diff = addremove == '+' ? REV_TREE_NEW : REV_TREE_OLD; tree_difference |= diff; - if (tree_difference == REV_TREE_DIFFERENT) + if (tree_difference & REV_TREE_DIFFERENT) DIFF_OPT_SET(options, HAS_CHANGES); } But that essentially makes the conditional a noop (since we know we set either NEW or OLD above and DIFFERENT is the union of those flags). I'm not sure I understand why file_add_remove() would ever want to avoid setting HAS_CHANGES (certainly its companion file_change() always does). This goes back to Junio's dd47aa3133 (try-to-simplify-commit: use diff-tree --quiet machinery., 2007-03-14). Maybe I am missing something, but AFAICT this was always buggy. But since it only affects adds and deletes, maybe nobody noticed? I'm also not sure if it only causes a slowdown, or if this could cause us to erroneously mark something as TREESAME which isn't (I _do_ think people would have noticed that). -Peff