From: Jonathan Nieder <jrnieder@gmail.com>
To: Taylor Blau <me@ttaylorr.com>
Cc: git@vger.kernel.org, jonathantanmy@google.com, gitster@pobox.com,
newren@gmail.com, Jay Conrod <jayconrod@google.com>,
Derrick Stolee <stolee@gmail.com>
Subject: Re: [PATCH v2 2/2] shallow.c: use '{commit,rollback}_shallow_file'
Date: Wed, 3 Jun 2020 13:51:51 -0700 [thread overview]
Message-ID: <20200603205151.GC253041@google.com> (raw)
In-Reply-To: <20200603051631.GA20678@syl.local>
Taylor Blau wrote:
> Ah, this only sort of has to do with the object cache. In
> 'parse_commit_buffer()' we stop parsing parents in the case that the
> repository is shallow (this goes back to 7f3140cd23 (git repack: keep
> commits hidden by a graft, 2009-07-23)).
Ah, good analysis. (In fact, the behavior is older: it's from
5da5c8f4cf4 (Teach parse_commit_buffer about grafting., 2005-07-30).)
So this is additional "cached" data that needs to be invalidated by
reset_repository_shallow.
So the question is, what other information falls into that category?
[...]
> --- a/shallow.c
> +++ b/shallow.c
> @@ -90,6 +90,9 @@ static void reset_repository_shallow(struct repository *r)
> {
> r->parsed_objects->is_shallow = -1;
> stat_validity_clear(r->parsed_objects->shallow_stat);
> +
(nit: the above two lines wouldn't be needed if r->parsed_objects is
being thrown away.)
> + parsed_object_pool_clear(r->parsed_objects);
> + r->parsed_objects = parsed_object_pool_new();
> }
Shallows don't affect the ref store. They only affect object walks.
So r->parsed_objects does seem like the only place that could be
affected.
That said, with this change I'd worry about use-after-free from any
existing references to objects in the pool.
Stepping back, what I think I would like to see is to *not* have
grafts and shallow state affect the in-memory persisted parsed
objects. Instead, act as an overlay in accessors that traverse over
them.
Lacking that, I like the idea of a "dirty bit" that gets written as
soon as we have started lying in the parsed object pool. Something
like this. What do you think?
diff --git i/commit-graph.c w/commit-graph.c
index 2ff042fbf4f..84b49ce903b 100644
--- i/commit-graph.c
+++ w/commit-graph.c
@@ -149,7 +149,8 @@ static int commit_graph_compatible(struct repository *r)
}
prepare_commit_graft(r);
- if (r->parsed_objects && r->parsed_objects->grafts_nr)
+ if (r->parsed_objects &&
+ (r->parsed_objects->grafts_nr || r->parsed_objects->substituted_parent))
return 0;
if (is_repository_shallow(r))
return 0;
diff --git i/commit.c w/commit.c
index 87686a7055b..762f09e53ae 100644
--- i/commit.c
+++ w/commit.c
@@ -423,6 +423,8 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
pptr = &item->parents;
graft = lookup_commit_graft(r, &item->object.oid);
+ if (graft)
+ r->parsed_objects->substituted_parent = 1;
while (bufptr + parent_entry_len < tail && !memcmp(bufptr, "parent ", 7)) {
struct commit *new_parent;
@@ -447,6 +449,7 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
if (graft) {
int i;
struct commit *new_parent;
+
for (i = 0; i < graft->nr_parent; i++) {
new_parent = lookup_commit(r,
&graft->parent[i]);
diff --git i/object.h w/object.h
index b22328b8383..db02fdcd6b2 100644
--- i/object.h
+++ w/object.h
@@ -26,6 +26,7 @@ struct parsed_object_pool {
char *alternate_shallow_file;
int commit_graft_prepared;
+ int substituted_parent;
struct buffer_slab *buffer_slab;
};
Thanks,
Jonathan
next prev parent reply other threads:[~2020-06-03 20:51 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-21 18:09 [PATCH] shallow.c: use 'reset_repository_shallow' when appropriate Taylor Blau
2020-04-21 20:41 ` Junio C Hamano
2020-04-21 20:45 ` Taylor Blau
2020-04-21 20:52 ` Junio C Hamano
2020-04-21 22:21 ` Taylor Blau
2020-04-21 23:06 ` Junio C Hamano
2020-04-22 18:05 ` Jonathan Tan
2020-04-22 18:02 ` Jonathan Tan
2020-04-22 18:15 ` Junio C Hamano
2020-04-23 0:14 ` Taylor Blau
2020-04-23 0:25 ` [PATCH v2 0/2] shallow.c: reset shallow-ness after updating Taylor Blau
2020-04-23 0:25 ` [PATCH v2 1/2] t5537: use test_write_lines, indented heredocs for readability Taylor Blau
2020-04-23 1:14 ` Jonathan Nieder
2020-04-24 17:11 ` Taylor Blau
2020-04-24 17:17 ` Jonathan Nieder
2020-04-24 20:45 ` Junio C Hamano
2020-04-23 0:25 ` [PATCH v2 2/2] shallow.c: use '{commit,rollback}_shallow_file' Taylor Blau
2020-04-23 1:23 ` Jonathan Nieder
2020-04-23 18:09 ` Jonathan Tan
2020-04-23 20:40 ` Junio C Hamano
2020-04-24 17:13 ` Taylor Blau
2020-06-03 3:42 ` Jonathan Nieder
2020-06-03 4:52 ` Taylor Blau
2020-06-03 5:16 ` Taylor Blau
2020-06-03 13:08 ` Derrick Stolee
2020-06-03 19:26 ` Taylor Blau
2020-06-03 21:23 ` Jonathan Nieder
2020-06-03 20:51 ` Jonathan Nieder [this message]
2020-06-03 22:14 ` Taylor Blau
2020-06-03 23:06 ` Jonathan Nieder
2020-06-04 17:45 ` Taylor Blau
2020-04-23 19:05 ` [PATCH] shallow.c: use 'reset_repository_shallow' when appropriate Junio C Hamano
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