Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759209AbXLUEXI (ORCPT ); Thu, 20 Dec 2007 23:23:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754254AbXLUEWx (ORCPT ); Thu, 20 Dec 2007 23:22:53 -0500 Received: from smtp2.linux-foundation.org ([207.189.120.14]:34272 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752921AbXLUEWw (ORCPT ); Thu, 20 Dec 2007 23:22:52 -0500 Date: Thu, 20 Dec 2007 20:22:46 -0800 (PST) From: Linus Torvalds To: Kyle McMartin , Junio C Hamano , Git Mailing List cc: Linux Kernel Mailing List Subject: Re: Linux 2.6.24-rc6 In-Reply-To: Message-ID: References: <20071221024805.GB8535@fattire.cabal.ca> <20071221030152.GC8535@fattire.cabal.ca> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2500 Lines: 72 On Thu, 20 Dec 2007, Linus Torvalds wrote: > > The tar-ball and the git archive itself is fine, but yes, the diff from > 2.6.23 to 2.6.24-rc6 is bad. It's the "trim_common_tail()" optimization > that has caused way too much pain. Very interesting breakage. The patch was actually "correct" in a (rather limited) technical sense, but the context at the end was missing because while the trim_common_tail() code made sure to keep enough common context to allow a valid diff to be generated, the diff machinery itself could decide that it could generate the diff differently than the "obvious" solution. It only happened for a few files that had lots of repeated lines - so that the diff could literally be done multiple different ways - and in fact, the file that caused the problems really had a bogus commit that duplicated *way* too much data, and caused lots of #define's to exist twice. But the sad fact appears that the git optimization (which is very important for "git blame", which needs no context), is only really valid for that one case where we really don't need any context. I uploaded a fixed patch. And here's the git patch to avoid this optimization when there is context. Linus --- xdiff-interface.c | 12 ++++++------ 1 files changed, 6 insertions(+), 6 deletions(-) diff --git a/xdiff-interface.c b/xdiff-interface.c index 9ee877c..0b7e057 100644 --- a/xdiff-interface.c +++ b/xdiff-interface.c @@ -110,22 +110,22 @@ int xdiff_outf(void *priv_, mmbuffer_t *mb, int nbuf) static void trim_common_tail(mmfile_t *a, mmfile_t *b, long ctx) { const int blk = 1024; - long trimmed = 0, recovered = 0; + long trimmed = 0; char *ap = a->ptr + a->size; char *bp = b->ptr + b->size; long smaller = (a->size < b->size) ? a->size : b->size; + if (ctx) + return; + while (blk + trimmed <= smaller && !memcmp(ap - blk, bp - blk, blk)) { trimmed += blk; ap -= blk; bp -= blk; } - while (recovered < trimmed && 0 <= ctx) - if (ap[recovered++] == '\n') - ctx--; - a->size -= (trimmed - recovered); - b->size -= (trimmed - recovered); + a->size -= trimmed; + b->size -= trimmed; } int xdi_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp, xdemitconf_t const *xecfg, xdemitcb_t *xecb) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/