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From: "Michał Kępień" <michal@isc.org>
To: Junio C Hamano <gitster@pobox.com>
Cc: Phillip Wood <phillip.wood123@gmail.com>, git@vger.kernel.org
Subject: Re: [PATCH v3 2/2] diff: add -I<regex> that ignores matching changes
Date: Mon, 19 Oct 2020 11:48:50 +0200	[thread overview]
Message-ID: <20201019094850.GB3717@larwa.hq.kempniu.pl> (raw)
In-Reply-To: <xmqqeelycajx.fsf@gitster.c.googlers.com>

First, thanks to Phillip for testing this.

> Yes, this is a good location to clear the diff_queue, which is
> per-invocation.  But diff_options->ignore_regex[] can and should be
> shared across multiple invocations of the diff machinery, as we are
> parsing upfront in the command line option parser just once to be
> used throughout the life of the program.  It is wrong to free them
> early like this.

Ugh, sorry, I am only now starting to see the big picture.

> I really hate to suggest this, one common API call made into the
> diff machinery from various consumers, when they are absolutely done
> with diff_options, is probably diff_result_code().  Its purpose is
> to collect bits computed to participate in the overall result into
> the final result code and anybody who ran one or more diff and wants
> to learn the outcome must call it, so it is unlikely that callers
> that matter are missing a call to finalize their uses of the diff
> machinery.  So if freeing .ignore_regex[] is really necessary, it
> could be used to tell us where to do so [*1*].
> 
> Unlike per-invocation resources that MUST be freed for repeated
> invocations of the diff machinery made in "git log" family,
> resources held for and repeatedly used during the entire session
> like this may not have to be freed, to be honest, though.

After reading your message, taking a closer look, and doing a few
Valgrind runs, I tend to agree that perhaps there is no need to free the
'ignore_regex' array after all - it does *not* get allocated repeatedly
during each invocation of the diff machinery and when Git exits, the OS
will reclaim any memory allocated by the process anyway.  On my laptop,
a Valgrind run done for a -DSUPPRESS_ANNOTATED_LEAKS build claims that
'ignore_regex' is one of 1,300+ memory blocks still reachable at exit
time, which amount to about 2.5 MB of memory in total.  Given this, it
feels slightly weird to single 'ignore_regex' out.

I will revert the diff_flush() changes in v4 unless somebody disagrees
with the above reasoning.

-- 
Best regards,
Michał Kępień

  reply	other threads:[~2020-10-19  9:48 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-01 12:06 [PATCH 0/2] " Michał Kępień
2020-10-01 12:06 ` [PATCH 1/2] " Michał Kępień
2020-10-01 18:21   ` Junio C Hamano
2020-10-07 19:48     ` Michał Kępień
2020-10-07 20:08       ` Junio C Hamano
2020-10-01 12:06 ` [PATCH 2/2] t: add -I<regex> tests Michał Kępień
2020-10-01 17:02 ` [PATCH 0/2] diff: add -I<regex> that ignores matching changes Junio C Hamano
2020-10-12  9:17 ` [PATCH v2 0/3] " Michał Kępień
2020-10-12  9:17   ` [PATCH v2 1/3] merge-base, xdiff: zero out xpparam_t structures Michał Kępień
2020-10-12 11:14     ` Johannes Schindelin
2020-10-12 17:09       ` Junio C Hamano
2020-10-12 19:52     ` Junio C Hamano
2020-10-13  6:35       ` Michał Kępień
2020-10-12  9:17   ` [PATCH v2 2/3] diff: add -I<regex> that ignores matching changes Michał Kępień
2020-10-12 11:20     ` Johannes Schindelin
2020-10-12 20:00       ` Junio C Hamano
2020-10-12 20:39         ` Johannes Schindelin
2020-10-12 21:43           ` Junio C Hamano
2020-10-13  6:37             ` Michał Kępień
2020-10-13 15:49               ` Junio C Hamano
2020-10-13  6:36       ` Michał Kępień
2020-10-13 12:02         ` Johannes Schindelin
2020-10-13 15:53           ` Junio C Hamano
2020-10-13 18:45           ` Michał Kępień
2020-10-12 18:01     ` Junio C Hamano
2020-10-13  6:38       ` Michał Kępień
2020-10-12 20:04     ` Junio C Hamano
2020-10-13  6:38       ` Michał Kępień
2020-10-12  9:17   ` [PATCH v2 3/3] t: add -I<regex> tests Michał Kępień
2020-10-12 11:49     ` Johannes Schindelin
2020-10-13  6:38       ` Michał Kępień
2020-10-13 12:00         ` Johannes Schindelin
2020-10-13 16:00           ` Junio C Hamano
2020-10-13 19:01           ` Michał Kępień
2020-10-15 11:45             ` Johannes Schindelin
2020-10-15  7:24   ` [PATCH v3 0/2] diff: add -I<regex> that ignores matching changes Michał Kępień
2020-10-15  7:24     ` [PATCH v3 1/2] merge-base, xdiff: zero out xpparam_t structures Michał Kępień
2020-10-15  7:24     ` [PATCH v3 2/2] diff: add -I<regex> that ignores matching changes Michał Kępień
2020-10-16 15:32       ` Phillip Wood
2020-10-16 18:04         ` Junio C Hamano
2020-10-19  9:48           ` Michał Kępień [this message]
2020-10-16 18:16       ` Junio C Hamano
2020-10-19  9:55         ` Michał Kępień
2020-10-19 17:29           ` Junio C Hamano
2020-10-16 10:00     ` [PATCH v3 0/2] " Johannes Schindelin
2020-10-20  6:48     ` [PATCH v4 " Michał Kępień
2020-10-20  6:48       ` [PATCH v4 1/2] merge-base, xdiff: zero out xpparam_t structures Michał Kępień
2020-10-20  6:48       ` [PATCH v4 2/2] diff: add -I<regex> that ignores matching changes Michał Kępień
2021-02-05 14:13       ` [PATCH 1/2] diff: add an API for deferred freeing Ævar Arnfjörð Bjarmason
2021-02-10 16:00         ` Johannes Schindelin
2021-02-11  3:00           ` Ævar Arnfjörð Bjarmason
2021-02-11  9:40             ` Johannes Schindelin
2021-02-11 10:21               ` Jeff King
2021-02-11 10:45                 ` [PATCH v2 0/2] " Ævar Arnfjörð Bjarmason
2021-02-11 10:45                 ` [PATCH v2 1/2] " Ævar Arnfjörð Bjarmason
2021-02-11 10:45                 ` [PATCH v2 2/2] diff: plug memory leak from regcomp() on {log,diff} -I Ævar Arnfjörð Bjarmason
2021-02-05 14:13       ` [PATCH " Ævar Arnfjörð Bjarmason

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