From: Jeff King <peff@peff.net>
To: "brian m. carlson" <sandals@crustytoothpaste.net>
Cc: git@vger.kernel.org, "Martin Ågren" <martin.agren@gmail.com>,
"Junio C Hamano" <gitster@pobox.com>
Subject: Re: [PATCH 0/5] tree-walk object_id refactor
Date: Thu, 10 Jan 2019 01:40:31 -0500 [thread overview]
Message-ID: <20190110064030.GB20497@sigill.intra.peff.net> (raw)
In-Reply-To: <20190110042551.915769-1-sandals@crustytoothpaste.net>
On Thu, Jan 10, 2019 at 04:25:46AM +0000, brian m. carlson wrote:
> There are a small number of places in our codebase where we cast a
> buffer of unsigned char to a struct object_id pointer. When we have
> GIT_MAX_RAWSZ set to 32 (because we have SHA-256), one of these places
> (the buffer for tree objects) can lead to us copying too much data when
> using SHA-1 as the hash, since there are only 20 bytes to read.
>
> This was not expected to be a problem before future code was introduced,
> but due to a combination of series the issue became noticeable.
>
> This series introduces a refactor to avoid referencing the struct
> object_id directly from a buffer and instead storing an additional
> struct object_id (and an int) in struct name_entry and referring to
> that.
I think this is really the only safe and sane solution. We resisted it
because of the cost of the extra copies (especially the
update_tree_entry() one). But I don't know that anybody actually
measured it. Do you have any performance numbers before/after this
series?
-Peff
next prev parent reply other threads:[~2019-01-10 6:40 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-07 23:34 What's cooking in git.git (Jan 2019, #01; Mon, 7) Junio C Hamano
2019-01-08 9:50 ` tg/checkout-no-overlay, was " Thomas Gummerer
2019-01-08 17:51 ` Junio C Hamano
2019-01-08 17:30 ` ag/sequencer-reduce-rewriting-todo " Alban Gruin
2019-01-08 21:20 ` sb/more-repo-in-api, was " Jonathan Tan
2019-01-08 21:35 ` Junio C Hamano
2019-01-09 21:28 ` Stefan Beller
2019-01-09 7:37 ` Martin Ågren
2019-01-09 21:06 ` Martin Ågren
2019-01-10 1:02 ` brian m. carlson
2019-01-10 18:55 ` Junio C Hamano
2019-01-10 19:03 ` Martin Ågren
2019-01-10 4:25 ` [PATCH 0/5] tree-walk object_id refactor brian m. carlson
2019-01-10 4:25 ` [PATCH 1/5] tree-walk: copy object ID before use brian m. carlson
2019-01-10 4:25 ` [PATCH 2/5] match-trees: compute buffer offset correctly when splicing brian m. carlson
2019-01-10 4:25 ` [PATCH 3/5] match-trees: use hashcpy to splice trees brian m. carlson
2019-01-10 6:45 ` Jeff King
2019-01-10 23:55 ` brian m. carlson
2019-01-11 14:51 ` Jeff King
2019-01-11 14:54 ` Jeff King
2019-01-14 1:30 ` brian m. carlson
2019-01-14 15:40 ` Jeff King
2019-01-10 4:25 ` [PATCH 4/5] tree-walk: store object_id in a separate member brian m. carlson
2019-01-10 6:49 ` Jeff King
2019-01-10 23:57 ` brian m. carlson
2019-01-10 4:25 ` [PATCH 5/5] cache: make oidcpy always copy GIT_MAX_RAWSZ bytes brian m. carlson
2019-01-10 6:50 ` Jeff King
2019-01-10 6:40 ` Jeff King [this message]
2019-01-11 0:17 ` [PATCH 0/5] tree-walk object_id refactor brian m. carlson
2019-01-11 14:17 ` Jeff King
2019-01-15 0:39 ` [PATCH v2 " brian m. carlson
2019-01-15 0:39 ` [PATCH v2 1/5] tree-walk: copy object ID before use brian m. carlson
2019-01-15 0:39 ` [PATCH v2 2/5] match-trees: compute buffer offset correctly when splicing brian m. carlson
2019-01-15 0:39 ` [PATCH v2 3/5] match-trees: use hashcpy to splice trees brian m. carlson
2019-01-15 0:39 ` [PATCH v2 4/5] tree-walk: store object_id in a separate member brian m. carlson
2019-01-15 0:39 ` [PATCH v2 5/5] cache: make oidcpy always copy GIT_MAX_RAWSZ bytes brian m. carlson
2019-01-15 17:51 ` [PATCH v2 0/5] tree-walk object_id refactor Junio C Hamano
2019-01-09 10:28 ` What's cooking in git.git (Jan 2019, #01; Mon, 7) Jeff King
2019-01-10 19:05 ` Junio C Hamano
2019-01-10 19:46 ` Junio C Hamano
2019-01-10 18:02 ` Stefan Beller
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