From: Jeff King <peff@peff.net>
To: "brian m. carlson" <sandals@crustytoothpaste.net>
Cc: Christian Couder <chriscool@tuxfamily.org>, git@vger.kernel.org
Subject: Re: [PATCH v2 01/24] builtin/pack-objects: make hash agnostic
Date: Sun, 23 Feb 2020 22:01:42 -0500 [thread overview]
Message-ID: <20200224030142.GA618173@coredump.intra.peff.net> (raw)
In-Reply-To: <20200223215759.GC564691@coredump.intra.peff.net>
On Sun, Feb 23, 2020 at 04:57:59PM -0500, Jeff King wrote:
> It would be nice to get rid of [nth_packed_object_sha1] entirely. In most cases,
> it's either free to do so (we end up copying the result into an oid
> anyway) or we pay for one extra hashcpy (out of the mmap into a local
> struct). But the one in pack-check.c:verify_packfile() is tricky; we
> store a pointer per object into the index mmap, and we'd have to switch
> to storing an oid per object. Given that the code isn't commonly run
> (and other operations like _generating_ the index in the first place are
> clearly OK with the extra memory hit), I think I'd be OK with that in
> the name of cleanliness.
>
> All of that is sort of orthogonal to your goals, I think, so I don't
> mind at all calling it out of scope for your series. As long as we use
> the_hash_algo->rawsz, these bare pointer accesses aren't wrong (it's
> just that it's easy to accidentally get it wrong, as this code shows).
I looked into this a bit further. It turns out that the current code in
verify_packfile() was explicitly trying to avoid that extra memory. But
the good news is that I think we can improve it further, cleaning up the
existing type-punning and using even less memory than now.
I'll prepare a separate series to do that. I had thought the cleanup
might also make this whole 20 / the_hash_algo->rawsz thing go away, but
it doesn't (the name hashwrite() made me think we ought to be using an
oidwrite(), but of course that's silly; the "hash" here is a "file with
a hash checksum" and not "an object id hash"). So the two topics really
are independent.
-Peff
next prev parent reply other threads:[~2020-02-24 3:01 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-22 20:17 [PATCH v2 00/24] SHA-256 stage 4 implementation, part 1/3 brian m. carlson
2020-02-22 20:17 ` [PATCH v2 01/24] builtin/pack-objects: make hash agnostic brian m. carlson
2020-02-23 21:57 ` Jeff King
2020-02-24 3:01 ` Jeff King [this message]
2020-02-24 3:42 ` brian m. carlson
2020-02-24 4:20 ` Jeff King
2020-02-22 20:17 ` [PATCH v2 02/24] hash: implement and use a context cloning function brian m. carlson
2020-02-22 20:17 ` [PATCH v2 03/24] hex: introduce parsing variants taking hash algorithms brian m. carlson
2020-02-22 20:17 ` [PATCH v2 04/24] hex: add functions to parse hex object IDs in any algorithm brian m. carlson
2020-02-22 20:17 ` [PATCH v2 05/24] repository: require a build flag to use SHA-256 brian m. carlson
2020-02-22 20:17 ` [PATCH v2 06/24] t: use hash-specific lookup tables to define test constants brian m. carlson
2020-02-22 20:17 ` [PATCH v2 07/24] t6300: abstract away SHA-1-specific constants brian m. carlson
2020-02-24 18:01 ` Junio C Hamano
2020-02-24 18:12 ` Jeff King
2020-02-24 20:41 ` Junio C Hamano
2020-02-22 20:17 ` [PATCH v2 08/24] t6300: make hash algorithm independent brian m. carlson
2020-02-22 20:17 ` [PATCH v2 09/24] t/helper/test-dump-split-index: initialize git repository brian m. carlson
2020-02-22 20:17 ` [PATCH v2 10/24] t/helper: initialize repository if necessary brian m. carlson
2020-02-24 18:05 ` Junio C Hamano
2020-02-25 0:05 ` brian m. carlson
2020-02-22 20:17 ` [PATCH v2 11/24] t/helper: make repository tests hash independent brian m. carlson
2020-02-22 20:17 ` [PATCH v2 12/24] setup: allow check_repository_format to read repository format brian m. carlson
2020-02-22 20:17 ` [PATCH v2 13/24] builtin/init-db: allow specifying hash algorithm on command line brian m. carlson
2020-02-24 18:14 ` Junio C Hamano
2020-02-25 0:11 ` brian m. carlson
2020-02-22 20:17 ` [PATCH v2 14/24] builtin/init-db: add environment variable for new repo hash brian m. carlson
2020-02-22 20:17 ` [PATCH v2 15/24] init-db: move writing repo version into a function brian m. carlson
2020-02-22 20:17 ` [PATCH v2 16/24] worktree: allow repository version 1 brian m. carlson
2020-02-22 20:17 ` [PATCH v2 17/24] commit: use expected signature header for SHA-256 brian m. carlson
2020-02-24 18:24 ` Junio C Hamano
2020-02-22 20:17 ` [PATCH v2 18/24] gpg-interface: improve interface for parsing tags brian m. carlson
2020-02-24 18:26 ` Junio C Hamano
2020-02-25 10:29 ` Johannes Schindelin
2020-02-25 19:25 ` Junio C Hamano
2020-02-26 3:05 ` brian m. carlson
2020-02-26 3:11 ` Junio C Hamano
2020-02-26 2:23 ` brian m. carlson
2020-02-27 13:24 ` Johannes Schindelin
2020-02-27 15:06 ` Junio C Hamano
2020-02-22 20:17 ` [PATCH v2 19/24] tag: store SHA-256 signatures in a header brian m. carlson
2020-02-24 18:30 ` Junio C Hamano
2020-02-22 20:17 ` [PATCH v2 20/24] fast-import: permit reading multiple marks files brian m. carlson
2020-06-05 16:14 ` Junio C Hamano
2020-06-05 16:26 ` Junio C Hamano
2020-06-05 22:39 ` brian m. carlson
2020-06-05 22:53 ` Junio C Hamano
2020-02-22 20:17 ` [PATCH v2 21/24] fast-import: add helper function for inserting mark object entries brian m. carlson
2020-02-22 20:17 ` [PATCH v2 22/24] fast-import: make find_marks work on any mark set brian m. carlson
2020-02-22 20:17 ` [PATCH v2 23/24] fast-import: add a generic function to iterate over marks brian m. carlson
2020-02-22 20:17 ` [PATCH v2 24/24] fast-import: add options for rewriting submodules brian m. carlson
2020-02-24 18:34 ` [PATCH v2 00/24] SHA-256 stage 4 implementation, part 1/3 Junio C Hamano
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