Re: [PATCH v3 8/9] commit-graph: always load commit-graph information

[Derrick Stolee <stolee@gmail.com>]

On 4/18/2018 8:02 PM, Jakub Narebski wrote:
> Derrick Stolee <dstolee@microsoft.com> writes:
>
>> Most code paths load commits using lookup_commit() and then
>> parse_commit(). In some cases, including some branch lookups, the commit
>> is parsed using parse_object_buffer() which side-steps parse_commit() in
>> favor of parse_commit_buffer().
>>
>> With generation numbers in the commit-graph, we need to ensure that any
>> commit that exists in the commit-graph file has its generation number
>> loaded.
> All right, that is nice explanation of the why behind this change.
>
>> Create new load_commit_graph_info() method to fill in the information
>> for a commit that exists only in the commit-graph file. Call it from
>> parse_commit_buffer() after loading the other commit information from
>> the given buffer. Only fill this information when specified by the
>> 'check_graph' parameter. This avoids duplicate work when we already
>> checked the graph in parse_commit_gently() or when simply checking the
>> buffer contents in check_commit().
> Couldn't this 'check_graph' parameter be a global variable similar to
> the 'commit_graph' variable?  Maybe I am not understanding it.

See the two callers at the bottom of the patch. They have different 
purposes: one needs to fill in a valid commit struct, the other needs to 
check the commit buffer is valid (then throws away the struct). They 
have different values for 'check_graph'. Also, in parse_commit_gently() 
we check parse_commit_in_graph() before we call parse_commit_buffer, so 
we do not want to repeat work; in the case of a valid commit-graph file, 
but the commit is not in the commit-graph, we would repeat our binary 
search for the same commit.

>
>> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
>> ---
>>   commit-graph.c | 51 ++++++++++++++++++++++++++++++++------------------
>>   commit-graph.h |  8 ++++++++
>>   commit.c       |  7 +++++--
>>   commit.h       |  2 +-
>>   object.c       |  2 +-
>>   sha1_file.c    |  2 +-
>>   6 files changed, 49 insertions(+), 23 deletions(-)
>>
>> diff --git a/commit-graph.c b/commit-graph.c
>> index 688d5b1801..21e853c21a 100644
>> --- a/commit-graph.c
>> +++ b/commit-graph.c
>> @@ -245,13 +245,19 @@ static struct commit_list **insert_parent_or_die(struct commit_graph *g,
>>   	return &commit_list_insert(c, pptr)->next;
>>   }
>>   
>> +static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, uint32_t pos)
>> +{
>> +	const unsigned char *commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * pos;
>> +	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
>> +}
>> +
>>   static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t pos)
>>   {
>>   	uint32_t edge_value;
>>   	uint32_t *parent_data_ptr;
>>   	uint64_t date_low, date_high;
>>   	struct commit_list **pptr;
>> -	const unsigned char *commit_data = g->chunk_commit_data + (g->hash_len + 16) * pos;
>> +	const unsigned char *commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * pos;
> I'm probably wrong, but isn't it unrelated change?

You're right. I saw this while I was in here, and there was a similar 
comment on this change in a different patch. Probably best to keep these 
cleanup things in a separate commit.

>>   	item->object.parsed = 1;
>>   	item->graph_pos = pos;
>> @@ -292,31 +298,40 @@ static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uin
>>   	return 1;
>>   }
>>   
>> +static int find_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t *pos)
>> +{
>> +	if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
>> +		*pos = item->graph_pos;
>> +		return 1;
>> +	} else {
>> +		return bsearch_graph(commit_graph, &(item->object.oid), pos);
>> +	}
>> +}
> All right (after the fix).
>
>> +
>>   int parse_commit_in_graph(struct commit *item)
>>   {
>> +	uint32_t pos;
>> +
>> +	if (item->object.parsed)
>> +		return 0;
>>   	if (!core_commit_graph)
>>   		return 0;
>> -	if (item->object.parsed)
>> -		return 1;
> Hmmm... previously the function returned 1 if item->object.parsed, now
> it returns 0 for this situation.  I don't understand this change.

The good news is that this change is unimportant (the only caller is 
parse_commit_gently() which checks item->object.parsed before calling 
parse_commit_in_graph()). I wonder why I reordered those things, anyway. 
I'll revert to simplify the patch.

>
>> -
>>   	prepare_commit_graph();
>> -	if (commit_graph) {
>> -		uint32_t pos;
>> -		int found;
>> -		if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
>> -			pos = item->graph_pos;
>> -			found = 1;
>> -		} else {
>> -			found = bsearch_graph(commit_graph, &(item->object.oid), &pos);
>> -		}
>> -
>> -		if (found)
>> -			return fill_commit_in_graph(item, commit_graph, pos);
>> -	}
>> -
>> +	if (commit_graph && find_commit_in_graph(item, commit_graph, &pos))
>> +		return fill_commit_in_graph(item, commit_graph, pos);
> Nice refactoring.
>
>>   	return 0;
>>   }
>>   
>> +void load_commit_graph_info(struct commit *item)
>> +{
>> +	uint32_t pos;
>> +	if (!core_commit_graph)
>> +		return;
>> +	prepare_commit_graph();
>> +	if (commit_graph && find_commit_in_graph(item, commit_graph, &pos))
>> +		fill_commit_graph_info(item, commit_graph, pos);
>> +}
> And the reason for the refactoring.
>
>> +
>>   static struct tree *load_tree_for_commit(struct commit_graph *g, struct commit *c)
>>   {
>>   	struct object_id oid;
>> diff --git a/commit-graph.h b/commit-graph.h
>> index 260a468e73..96cccb10f3 100644
>> --- a/commit-graph.h
>> +++ b/commit-graph.h
>> @@ -17,6 +17,14 @@ char *get_commit_graph_filename(const char *obj_dir);
>>    */
>>   int parse_commit_in_graph(struct commit *item);
>>   
>> +/*
>> + * It is possible that we loaded commit contents from the commit buffer,
>> + * but we also want to ensure the commit-graph content is correctly
>> + * checked and filled. Fill the graph_pos and generation members of
>> + * the given commit.
>> + */
>> +void load_commit_graph_info(struct commit *item);
>> +
>>   struct tree *get_commit_tree_in_graph(const struct commit *c);
>>   
>>   struct commit_graph {
>> diff --git a/commit.c b/commit.c
>> index a70f120878..9ef6f699bd 100644
>> --- a/commit.c
>> +++ b/commit.c
>> @@ -331,7 +331,7 @@ const void *detach_commit_buffer(struct commit *commit, unsigned long *sizep)
>>   	return ret;
>>   }
>>   
>> -int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size)
>> +int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size, int check_graph)
>>   {
>>   	const char *tail = buffer;
>>   	const char *bufptr = buffer;
>> @@ -386,6 +386,9 @@ int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long s
>>   	}
>>   	item->date = parse_commit_date(bufptr, tail);
>>   
>> +	if (check_graph)
>> +		load_commit_graph_info(item);
>> +
>>   	return 0;
>>   }
>>   
>> @@ -412,7 +415,7 @@ int parse_commit_gently(struct commit *item, int quiet_on_missing)
>>   		return error("Object %s not a commit",
>>   			     oid_to_hex(&item->object.oid));
>>   	}
>> -	ret = parse_commit_buffer(item, buffer, size);
>> +	ret = parse_commit_buffer(item, buffer, size, 0);
>>   	if (save_commit_buffer && !ret) {
>>   		set_commit_buffer(item, buffer, size);
>>   		return 0;
>> diff --git a/commit.h b/commit.h
>> index 64436ff44e..b5afde1ae9 100644
>> --- a/commit.h
>> +++ b/commit.h
>> @@ -72,7 +72,7 @@ struct commit *lookup_commit_reference_by_name(const char *name);
>>    */
>>   struct commit *lookup_commit_or_die(const struct object_id *oid, const char *ref_name);
>>   
>> -int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size);
>> +int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size, int check_graph);
>>   int parse_commit_gently(struct commit *item, int quiet_on_missing);
>>   static inline int parse_commit(struct commit *item)
>>   {
>> diff --git a/object.c b/object.c
>> index e6ad3f61f0..efe4871325 100644
>> --- a/object.c
>> +++ b/object.c
>> @@ -207,7 +207,7 @@ struct object *parse_object_buffer(const struct object_id *oid, enum object_type
>>   	} else if (type == OBJ_COMMIT) {
>>   		struct commit *commit = lookup_commit(oid);
>>   		if (commit) {
>> -			if (parse_commit_buffer(commit, buffer, size))
>> +			if (parse_commit_buffer(commit, buffer, size, 1))
>>   				return NULL;
>>   			if (!get_cached_commit_buffer(commit, NULL)) {
>>   				set_commit_buffer(commit, buffer, size);
>> diff --git a/sha1_file.c b/sha1_file.c
>> index 1b94f39c4c..0fd4f0b8b6 100644
>> --- a/sha1_file.c
>> +++ b/sha1_file.c
>> @@ -1755,7 +1755,7 @@ static void check_commit(const void *buf, size_t size)
>>   {
>>   	struct commit c;
>>   	memset(&c, 0, sizeof(c));
>> -	if (parse_commit_buffer(&c, buf, size))
>> +	if (parse_commit_buffer(&c, buf, size, 0))
>>   		die("corrupt commit");
>>   }