git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / Atom feed
From: Junio C Hamano <gitster@pobox.com>
To: "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, peff@peff.net, avarab@gmail.com,
	jrnieder@gmail.com, Derrick Stolee <dstolee@microsoft.com>
Subject: Re: [PATCH v4 1/6] revision: add mark_tree_uninteresting_sparse
Date: Fri, 11 Jan 2019 12:25:45 -0800
Message-ID: <xmqqva2vx7p2.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <xmqqzhs7x9nm.fsf@gitster-ct.c.googlers.com> (Junio C. Hamano's message of "Fri, 11 Jan 2019 11:43:25 -0800")

Junio C Hamano <gitster@pobox.com> writes:

>> In preparation for a new algorithm that walks fewer trees when
>> creating a pack from a set of revisions, create a method that
>> takes an oidset of tree oids and marks reachable objects as
>> UNINTERESTING.
>> ...
>> There is one new assumption in this approach: we are also given
>> the oids of the interesting trees. This implementation does not
>> use those trees at the moment, but we will use them in a later
>> rewrite of this method.

Ahh....


> The proposed log message claims that the method takes an oidset and
> marks reachable objects as uninteresting, but the implementation
> only marks those that are reachable from already uninteresting
> trees.  Either one of them must be wrong.
>
> Did you mean to have this instead?
>
> 		if (!tree)
> 			continue;
> 		/*
> 		 * Force traversal of the tree, even if it has been
> 		 * already marked as UNINTERESTING.
> 		 */
> 		tree->object.flags &= ~UNINTERESTING;
> 		mark_tree_uninteresting(r, tree);

So, I assumed that the implementation was wrong, but it is the other
way around.  You do mean to pick only already uninteresting trees
out of "set" and mark its reachables.

One thing that would make me worried is what help the callers of
this function will get (or they may have to devise the way
themselves) to avoid having to traverse the same tree number of
times.  A tree can be made uninteresting after a traversal of
another tree that contains it, but the logic in this function

> +		if (tree->object.flags & UNINTERESTING) {
> +			/*
> +			 * Remove the flag so the next call
> +			 * is not a no-op. The flag is added
> +			 * in mark_tree_unintersting().
> +			 */
> +			tree->object.flags ^= UNINTERESTING;
> +			mark_tree_uninteresting(r, tree);
> +		}

ignores the fact that it is already UNINTERESTING (in fact, in a
sense it is even worse---it cannot be used to make a not-yet
UNINTERESTING one into UNINTERESTING), drops the UNINTERESING bit
and forces the traversal of that tree.  The only thing I see that
would work as a saving grace is that mark_tree_uninteresting()
itself would honor existing UNINTERESING bit and refuses to recurse
into its subtrees, but that means blobs at the top-level of such a
tree would be marked UNINTERESING while those in its subtrees can be
left not-UNINTERESING, which sounds like inviting a mess.

It does *not* immediately mean this function is misdesigned.  It
just means that the caller needs to carefully follow whatever
calling convention this series will establish in the later patches
(which we haven't seen yet at this point).

> By the way, one of the bigger reasons why I have to ask, instead of
> making an educated guess, is because "struct oidset *set" parameter
> does not give any useful information with the variable name to the
> readers.  We know it is a set because its type is oidset; readers
> need to know what meaning the 'set' has, what it is used for, why
> the caller wants to (or decides not to) place a tree object in the
> set when it calls it.  None of that can be read from its name.

  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-28 21:52 [PATCH 0/5] Add a new "sparse" tree walk algorithm Derrick Stolee via GitGitGadget
2018-11-28 21:52 ` [PATCH 1/5] revision: add mark_tree_uninteresting_sparse Derrick Stolee via GitGitGadget
2018-11-28 21:52 ` [PATCH 2/5] list-objects: consume sparse tree walk Derrick Stolee via GitGitGadget
2018-11-28 21:52 ` [PATCH 3/5] pack-objects: add --sparse option Derrick Stolee via GitGitGadget
2018-11-28 22:11   ` Stefan Beller
2018-11-29 14:20     ` Derrick Stolee
2018-11-30  2:39       ` Junio C Hamano
2018-11-30 15:53         ` Derrick Stolee
2018-11-28 21:52 ` [PATCH 4/5] revision: implement sparse algorithm Derrick Stolee via GitGitGadget
2018-11-28 21:52 ` [PATCH 5/5] pack-objects: create pack.useSparse setting Derrick Stolee via GitGitGadget
2018-11-28 22:18 ` [PATCH 0/5] Add a new "sparse" tree walk algorithm Ævar Arnfjörð Bjarmason
2018-11-29  4:05   ` Derrick Stolee
2018-11-29 14:24 ` [PATCH v2 0/6] " Derrick Stolee via GitGitGadget
2018-11-29 14:24   ` [PATCH v2 1/6] revision: add mark_tree_uninteresting_sparse Derrick Stolee via GitGitGadget
2018-11-29 14:24   ` [PATCH v2 2/6] list-objects: consume sparse tree walk Derrick Stolee via GitGitGadget
2018-11-29 14:24   ` [PATCH v2 3/6] pack-objects: add --sparse option Derrick Stolee via GitGitGadget
2018-11-29 14:24   ` [PATCH v2 4/6] revision: implement sparse algorithm Derrick Stolee via GitGitGadget
2018-11-29 14:24   ` [PATCH v2 5/6] pack-objects: create pack.useSparse setting Derrick Stolee via GitGitGadget
2018-11-29 14:24   ` [PATCH v2 6/6] pack-objects: create GIT_TEST_PACK_SPARSE Derrick Stolee via GitGitGadget
2018-12-10 16:42   ` [PATCH v3 0/6] Add a new "sparse" tree walk algorithm Derrick Stolee via GitGitGadget
2018-12-10 16:42     ` [PATCH v3 1/6] revision: add mark_tree_uninteresting_sparse Derrick Stolee via GitGitGadget
2018-12-10 16:42     ` [PATCH v3 2/6] list-objects: consume sparse tree walk Derrick Stolee via GitGitGadget
2018-12-10 16:42     ` [PATCH v3 3/6] pack-objects: add --sparse option Derrick Stolee via GitGitGadget
2018-12-10 16:42     ` [PATCH v3 4/6] revision: implement sparse algorithm Derrick Stolee via GitGitGadget
2018-12-10 16:42     ` [PATCH v3 5/6] pack-objects: create pack.useSparse setting Derrick Stolee via GitGitGadget
2018-12-10 16:42     ` [PATCH v3 6/6] pack-objects: create GIT_TEST_PACK_SPARSE Derrick Stolee via GitGitGadget
2018-12-14 21:22     ` [PATCH v4 0/6] Add a new "sparse" tree walk algorithm Derrick Stolee via GitGitGadget
2018-12-14 21:22       ` [PATCH v4 1/6] revision: add mark_tree_uninteresting_sparse Derrick Stolee via GitGitGadget
2019-01-11 19:43         ` Junio C Hamano
2019-01-11 20:25           ` Junio C Hamano [this message]
2019-01-11 22:05             ` Derrick Stolee
2018-12-14 21:22       ` [PATCH v4 2/6] list-objects: consume sparse tree walk Derrick Stolee via GitGitGadget
2019-01-11 23:20         ` Junio C Hamano
2018-12-14 21:22       ` [PATCH v4 3/6] pack-objects: add --sparse option Derrick Stolee via GitGitGadget
2019-01-11 22:30         ` Junio C Hamano
2019-01-15 15:06           ` Derrick Stolee
2019-01-15 18:23             ` Junio C Hamano
2018-12-14 21:22       ` [PATCH v4 4/6] revision: implement sparse algorithm Derrick Stolee via GitGitGadget
2018-12-14 23:32         ` Ævar Arnfjörð Bjarmason
2018-12-17 14:20           ` Derrick Stolee
2018-12-17 14:26             ` Ævar Arnfjörð Bjarmason
2018-12-17 14:50               ` Derrick Stolee
2019-01-11 23:20         ` Junio C Hamano
2018-12-14 21:22       ` [PATCH v4 5/6] pack-objects: create pack.useSparse setting Derrick Stolee via GitGitGadget
2018-12-14 21:22       ` [PATCH v4 6/6] pack-objects: create GIT_TEST_PACK_SPARSE Derrick Stolee via GitGitGadget
2019-01-16 18:25       ` [PATCH v5 0/5] Add a new "sparse" tree walk algorithm Derrick Stolee via GitGitGadget
2019-01-16 18:25         ` [PATCH v5 1/5] revision: add mark_tree_uninteresting_sparse Derrick Stolee via GitGitGadget
2019-01-16 18:25         ` [PATCH v5 2/5] list-objects: consume sparse tree walk Derrick Stolee via GitGitGadget
2019-01-16 18:25         ` [PATCH v5 3/5] revision: implement sparse algorithm Derrick Stolee via GitGitGadget
2019-01-16 18:26         ` [PATCH v5 4/5] pack-objects: create pack.useSparse setting Derrick Stolee via GitGitGadget
2019-01-16 18:26         ` [PATCH v5 5/5] pack-objects: create GIT_TEST_PACK_SPARSE Derrick Stolee via GitGitGadget

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=xmqqva2vx7p2.fsf@gitster-ct.c.googlers.com \
    --to=gitster@pobox.com \
    --cc=avarab@gmail.com \
    --cc=dstolee@microsoft.com \
    --cc=git@vger.kernel.org \
    --cc=gitgitgadget@gmail.com \
    --cc=jrnieder@gmail.com \
    --cc=peff@peff.net \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

git@vger.kernel.org list mirror (unofficial, one of many)

Archives are clonable:
	git clone --mirror https://public-inbox.org/git
	git clone --mirror http://ou63pmih66umazou.onion/git
	git clone --mirror http://czquwvybam4bgbro.onion/git
	git clone --mirror http://hjrcffqmbrq6wope.onion/git

Example config snippet for mirrors

Newsgroups are available over NNTP:
	nntp://news.public-inbox.org/inbox.comp.version-control.git
	nntp://ou63pmih66umazou.onion/inbox.comp.version-control.git
	nntp://czquwvybam4bgbro.onion/inbox.comp.version-control.git
	nntp://hjrcffqmbrq6wope.onion/inbox.comp.version-control.git
	nntp://news.gmane.io/gmane.comp.version-control.git

 note: .onion URLs require Tor: https://www.torproject.org/

AGPL code for this site: git clone https://public-inbox.org/public-inbox.git