git@vger.kernel.org mailing list mirror (one of many)
 help / color / mirror / code / Atom feed
From: Derrick Stolee <stolee@gmail.com>
To: Junio C Hamano <gitster@pobox.com>,
	Derrick Stolee <dstolee@microsoft.com>
Cc: "git@vger.kernel.org" <git@vger.kernel.org>,
	"peff@peff.net" <peff@peff.net>,
	"avarab@gmail.com" <avarab@gmail.com>,
	"sbeller@google.com" <sbeller@google.com>,
	"larsxschneider@gmail.com" <larsxschneider@gmail.com>,
	"bmwill@google.com" <bmwill@google.com>
Subject: Re: [PATCH v2 06/10] commit.c: use generation to halt paint walk
Date: Wed, 11 Apr 2018 09:24:01 -0400	[thread overview]
Message-ID: <cc58d8c1-f8de-4841-934f-56e4ad7729aa@gmail.com> (raw)
In-Reply-To: <xmqq604yzbqe.fsf@gitster-ct.c.googlers.com>

On 4/10/2018 11:02 PM, Junio C Hamano wrote:
> Derrick Stolee <dstolee@microsoft.com> writes:
>
>> @@ -800,17 +810,26 @@ static struct commit_list *paint_down_to_common(struct commit *one, int n, struc
>>   		return result;
>>   	}
>>   	prio_queue_put(&queue, one);
>> +	if (one->generation < min_nonstale_gen)
>> +		min_nonstale_gen = one->generation;
>>   
>>   	for (i = 0; i < n; i++) {
>>   		twos[i]->object.flags |= PARENT2;
>>   		prio_queue_put(&queue, twos[i]);
>> +		if (twos[i]->generation < min_nonstale_gen)
>> +			min_nonstale_gen = twos[i]->generation;
>>   	}
>>   
>> -	while (queue_has_nonstale(&queue)) {
>> +	while (queue_has_nonstale(&queue, min_nonstale_gen)) {
>>   		struct commit *commit = prio_queue_get(&queue);
>>   		struct commit_list *parents;
>>   		int flags;
>>   
>> +		if (commit->generation > last_gen)
>> +			BUG("bad generation skip");
>> +
>> +		last_gen = commit->generation;
>> +
>>   		flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
>>   		if (flags == (PARENT1 | PARENT2)) {
>>   			if (!(commit->object.flags & RESULT)) {
>> @@ -830,6 +849,10 @@ static struct commit_list *paint_down_to_common(struct commit *one, int n, struc
>>   				return NULL;
>>   			p->object.flags |= flags;
> Hmph.  Can a commit that used to be not stale (and contributed to
> the current value of min_nonstale_gen) become stale here by getting
> visited twice, invalidating the value in min_nonstale_gen?

min_nonstale_gen can be "wrong" in the way you say, but fits the 
definition from the commit message:

"To properly take advantage of this condition, track the minimum 
generation number of a commit that **enters the queue** with nonstale 
status." (Emphasis added)

You make an excellent point about how this can be problematic. I was 
confused by the lack of clear performance benefits here, but I think 
that whatever benefits making queue_has_nonstale() be O(1) were removed 
by walking more commits than necessary.

Consider the following commit graph, where M is a parent of both A and 
B, S is a parent of M and B, and there is a large set of commits 
reachable from M with generation number larger than gen(S).

A    B
| __/|
|/   |
M    |
|\   |
. |  |
. |  |
. |_/
|/
S

Between A and B, the true merge base is M. Anything reachable from M is 
marked as stale. When S is added to the queue, it is only reachable from 
B, so it is non-stale. However, it is marked stale after M is walked. 
The old code would detect this as a termination condition, but the new 
code would not.

I think this data shape is actually common (not exactly, as it may be 
that some ancestor of M provides a second path to S) especially in the 
world of pull requests and users merging master into their topic branches.

I'll remove this commit in the next version, but use the new prototype 
for queue_has_nonstale() in "commit: add short-circuit to 
paint_down_to_common()" using the given 'min_generation' instead of 
'min_nonstale_gen'.

Thanks,
-Stolee

  reply	other threads:[~2018-04-11 13:24 UTC|newest]

Thread overview: 162+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-03 16:51 [PATCH 0/6] Compute and consume generation numbers Derrick Stolee
2018-04-03 16:51 ` [PATCH 1/6] object.c: parse commit in graph first Derrick Stolee
2018-04-03 18:21   ` Jonathan Tan
2018-04-03 18:28     ` Jeff King
2018-04-03 18:32       ` Derrick Stolee
2018-04-03 16:51 ` [PATCH 2/6] commit: add generation number to struct commmit Derrick Stolee
2018-04-03 18:05   ` Brandon Williams
2018-04-03 18:28     ` Jeff King
2018-04-03 18:31       ` Derrick Stolee
2018-04-03 18:32       ` Brandon Williams
2018-04-03 18:44       ` Stefan Beller
2018-04-03 23:17       ` Ramsay Jones
2018-04-03 23:19         ` Jeff King
2018-04-03 18:24   ` Jonathan Tan
2018-04-03 16:51 ` [PATCH 3/6] commit-graph: compute generation numbers Derrick Stolee
2018-04-03 18:30   ` Jonathan Tan
2018-04-03 18:49     ` Stefan Beller
2018-04-03 16:51 ` [PATCH 4/6] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-03 18:31   ` Stefan Beller
2018-04-03 18:31   ` Jonathan Tan
2018-04-03 16:51 ` [PATCH 5/6] commit.c: use generation to halt paint walk Derrick Stolee
2018-04-03 19:01   ` Jonathan Tan
2018-04-03 16:51 ` [PATCH 6/6] commit-graph.txt: update future work Derrick Stolee
2018-04-03 19:04   ` Jonathan Tan
2018-04-03 16:56 ` [PATCH 0/6] Compute and consume generation numbers Derrick Stolee
2018-04-03 18:03 ` Brandon Williams
2018-04-03 18:29   ` Derrick Stolee
2018-04-03 18:47     ` Jeff King
2018-04-03 19:05       ` Jeff King
2018-04-04 15:45         ` [PATCH 7/6] ref-filter: use generation number for --contains Derrick Stolee
2018-04-04 15:45           ` [PATCH 8/6] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-04 15:48             ` Derrick Stolee
2018-04-04 17:01               ` Brandon Williams
2018-04-04 18:24               ` Jeff King
2018-04-04 18:53                 ` Derrick Stolee
2018-04-04 18:59                   ` Jeff King
2018-04-04 18:22           ` [PATCH 7/6] ref-filter: use generation number for --contains Jeff King
2018-04-04 19:06             ` Derrick Stolee
2018-04-04 19:16               ` Jeff King
2018-04-04 19:22                 ` Derrick Stolee
2018-04-04 19:42                   ` Jeff King
2018-04-04 19:45                     ` Derrick Stolee
2018-04-04 19:46                       ` Jeff King
2018-04-07 17:09     ` [PATCH 0/6] Compute and consume generation numbers Jakub Narebski
2018-04-07 16:55 ` Jakub Narebski
2018-04-08  1:06   ` Derrick Stolee
2018-04-11 19:32     ` Jakub Narebski
2018-04-11 19:58       ` Derrick Stolee
2018-04-14 16:52         ` Jakub Narebski
2018-04-21 20:44           ` Jakub Narebski
2018-04-23 13:54             ` Derrick Stolee
2018-04-09 16:41 ` [PATCH v2 00/10] " Derrick Stolee
2018-04-09 16:41   ` [PATCH v2 01/10] object.c: parse commit in graph first Derrick Stolee
2018-04-09 16:41   ` [PATCH v2 02/10] merge: check config before loading commits Derrick Stolee
2018-04-11  2:12     ` Junio C Hamano
2018-04-11 12:49       ` Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 03/10] commit: add generation number to struct commmit Derrick Stolee
2018-04-09 17:59     ` Stefan Beller
2018-04-11  2:31     ` Junio C Hamano
2018-04-11 12:57       ` Derrick Stolee
2018-04-11 23:28         ` Junio C Hamano
2018-04-09 16:42   ` [PATCH v2 04/10] commit-graph: compute generation numbers Derrick Stolee
2018-04-11  2:51     ` Junio C Hamano
2018-04-11 13:02       ` Derrick Stolee
2018-04-11 18:49         ` Stefan Beller
2018-04-11 19:26         ` Eric Sunshine
2018-04-09 16:42   ` [PATCH v2 05/10] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 06/10] commit.c: use generation to halt paint walk Derrick Stolee
2018-04-11  3:02     ` Junio C Hamano
2018-04-11 13:24       ` Derrick Stolee [this message]
2018-04-09 16:42   ` [PATCH v2 07/10] commit-graph.txt: update future work Derrick Stolee
2018-04-12  9:12     ` Junio C Hamano
2018-04-12 11:35       ` Derrick Stolee
2018-04-13  9:53         ` Jakub Narebski
2018-04-09 16:42   ` [PATCH v2 08/10] ref-filter: use generation number for --contains Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 09/10] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-09 16:42   ` [PATCH v2 10/10] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-04-17 17:00   ` [PATCH v3 0/9] Compute and consume generation numbers Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 1/9] commit: add generation number to struct commmit Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 2/9] commit-graph: compute generation numbers Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 3/9] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-18 14:31       ` Jakub Narebski
2018-04-18 14:46         ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 4/9] commit-graph.txt: update design document Derrick Stolee
2018-04-18 19:47       ` Jakub Narebski
2018-04-17 17:00     ` [PATCH v3 5/9] ref-filter: use generation number for --contains Derrick Stolee
2018-04-18 21:02       ` Jakub Narebski
2018-04-23 14:22         ` Derrick Stolee
2018-04-24 18:56           ` Jakub Narebski
2018-04-25 14:11             ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 6/9] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-18 22:15       ` Jakub Narebski
2018-04-23 14:31         ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 7/9] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-04-18 23:19       ` Jakub Narebski
2018-04-23 14:40         ` Derrick Stolee
2018-04-23 21:38           ` Jakub Narebski
2018-04-24 12:31             ` Derrick Stolee
2018-04-19  8:32       ` Jakub Narebski
2018-04-17 17:00     ` [PATCH v3 8/9] commit-graph: always load commit-graph information Derrick Stolee
2018-04-17 17:50       ` Derrick Stolee
2018-04-19  0:02       ` Jakub Narebski
2018-04-23 14:49         ` Derrick Stolee
2018-04-17 17:00     ` [PATCH v3 9/9] merge: check config before loading commits Derrick Stolee
2018-04-19  0:04     ` [PATCH v3 0/9] Compute and consume generation numbers Jakub Narebski
2018-04-23 14:54       ` Derrick Stolee
2018-04-25 14:37     ` [PATCH v4 00/10] " Derrick Stolee
2018-04-25 14:37       ` [PATCH v4 01/10] ref-filter: fix outdated comment on in_commit_list Derrick Stolee
2018-04-28 17:54         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 02/10] commit: add generation number to struct commmit Derrick Stolee
2018-04-28 22:35         ` Jakub Narebski
2018-04-30 12:05           ` Derrick Stolee
2018-04-25 14:37       ` [PATCH v4 03/10] commit-graph: compute generation numbers Derrick Stolee
2018-04-26  2:35         ` Junio C Hamano
2018-04-26 12:58           ` Derrick Stolee
2018-04-26 13:49             ` Derrick Stolee
2018-04-29  9:08         ` Jakub Narebski
2018-05-01 12:10           ` Derrick Stolee
2018-05-02 16:15             ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 04/10] commit: use generations in paint_down_to_common() Derrick Stolee
2018-04-26  3:22         ` Junio C Hamano
2018-04-26  9:02           ` Jakub Narebski
2018-04-28 14:38             ` Jakub Narebski
2018-04-29 15:40         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 06/10] ref-filter: use generation number for --contains Derrick Stolee
2018-04-30 16:34         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 05/10] commit-graph: always load commit-graph information Derrick Stolee
2018-04-29 22:14         ` Jakub Narebski
2018-05-01 12:19           ` Derrick Stolee
2018-04-29 22:18         ` Jakub Narebski
2018-04-25 14:37       ` [PATCH v4 07/10] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-04-30 17:05         ` Jakub Narebski
2018-04-25 14:38       ` [PATCH v4 08/10] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-04-30 22:19         ` Jakub Narebski
2018-05-01 11:47           ` Derrick Stolee
2018-05-02 13:05             ` Jakub Narebski
2018-05-02 13:42               ` Derrick Stolee
2018-04-25 14:38       ` [PATCH v4 09/10] merge: check config before loading commits Derrick Stolee
2018-04-30 22:54         ` Jakub Narebski
2018-05-01 11:52           ` Derrick Stolee
2018-05-02 11:41             ` Jakub Narebski
2018-04-25 14:38       ` [PATCH v4 10/10] commit-graph.txt: update design document Derrick Stolee
2018-04-30 23:32         ` Jakub Narebski
2018-05-01 12:00           ` Derrick Stolee
2018-05-02  7:57             ` Jakub Narebski
2018-04-25 14:40       ` [PATCH v4 00/10] Compute and consume generation numbers Derrick Stolee
2018-04-28 17:28         ` Jakub Narebski
2018-05-01 12:47       ` [PATCH v5 00/11] " Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 01/11] ref-filter: fix outdated comment on in_commit_list Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 02/11] commit: add generation number to struct commmit Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 03/11] commit-graph: compute generation numbers Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 04/11] commit: use generations in paint_down_to_common() Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 05/11] commit-graph: always load commit-graph information Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 06/11] ref-filter: use generation number for --contains Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 07/11] commit: use generation numbers for in_merge_bases() Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 08/11] commit: add short-circuit to paint_down_to_common() Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 09/11] commit: use generation number in remove_redundant() Derrick Stolee
2018-05-01 15:37           ` Derrick Stolee
2018-05-03 18:45           ` Jakub Narebski
2018-05-01 12:47         ` [PATCH v5 10/11] merge: check config before loading commits Derrick Stolee
2018-05-01 12:47         ` [PATCH v5 11/11] commit-graph.txt: update design document Derrick Stolee
2018-05-03 11:18         ` [PATCH v5 00/11] Compute and consume generation numbers Jakub Narebski

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=cc58d8c1-f8de-4841-934f-56e4ad7729aa@gmail.com \
    --to=stolee@gmail.com \
    --cc=avarab@gmail.com \
    --cc=bmwill@google.com \
    --cc=dstolee@microsoft.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=larsxschneider@gmail.com \
    --cc=peff@peff.net \
    --cc=sbeller@google.com \
    /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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).