From: Junio C Hamano <gitster@pobox.com>
To: Derrick Stolee <derrickstolee@github.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"René Scharfe" <l.s.r@web.de>, "Git List" <git@vger.kernel.org>,
"Victoria Dye" <vdye@github.com>
Subject: Re: [PATCH] cache-tree: fix strbuf growth in prime_cache_tree_rec()
Date: Mon, 06 Feb 2023 10:55:36 -0800 [thread overview]
Message-ID: <xmqq357i8vyv.fsf@gitster.g> (raw)
In-Reply-To: <b1a3e684-26f9-0053-9446-751d73e83961@github.com> (Derrick Stolee's message of "Mon, 6 Feb 2023 10:27:53 -0500")
Derrick Stolee <derrickstolee@github.com> writes:
>>> - int base_path_len = tree_path->len;
>>> + size_t base_path_len = tree_path->len;
>>> ...
>>> strbuf_setlen(tree_path, base_path_len);
>>> - strbuf_grow(tree_path, base_path_len + entry.pathlen + 1);
>>> + strbuf_grow(tree_path, entry.pathlen + 1);
>>> strbuf_add(tree_path, entry.path, entry.pathlen);
>>> ...
>>
>> The size_t conversion is trivially correct.
>
> I agree, and thanks for finding and fixing this issue.
> ...
>> One wonders if (even for this index-related code) we really need such
>> careful management of growth, and could instead do with:
>>
>> strbuf_setlen(tree_path, base_path_len);
>> strbuf_add(tree_path, entry.path, entry.pathlen);
>> strbuf_addch(tree_path, '/');
>
> This would be my preferred way to go here.
Yup. _setlen() is still very useful to truncate an existing
contents in a strbuf, but we should look at each use of _grow() with
suspicion that it might be an mistaken attempt to "optimize" where
there is not a room for optimization.
There may be cases where tight and exact allocation is desirable but
this is not such a codepath. tree_path will not be overly long that
we want to avoid extra allocation for giving us slack to prepare for
reallocation. And tree_path is passed to recusive calls to further
be grown, which is exactly why we would want to use ALLOW_GROW() kind
of allocation with slack to amortize the allocation cost.
Thanks.
next prev parent reply other threads:[~2023-02-06 18:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-04 19:10 [PATCH] cache-tree: fix strbuf growth in prime_cache_tree_rec() René Scharfe
2023-02-05 21:12 ` Ævar Arnfjörð Bjarmason
2023-02-06 15:27 ` Derrick Stolee
2023-02-06 16:18 ` Ævar Arnfjörð Bjarmason
2023-02-12 11:20 ` René Scharfe
2023-02-06 18:55 ` Junio C Hamano [this message]
2023-02-10 20:20 ` René Scharfe
2023-02-10 20:20 ` René Scharfe
2023-02-10 20:33 ` Junio C Hamano
2023-02-11 2:15 ` Jeff King
2023-02-11 2:46 ` Junio C Hamano
2023-02-10 20:20 ` [PATCH v2] " René Scharfe
2023-02-13 13:37 ` Derrick Stolee
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