Re: [PATCH v2 24/24] pack-bitmap-write: better reuse bitmaps

> On Wed, Dec 02, 2020 at 12:08:08AM -0800, Jonathan Tan wrote:
>>> +			c_ent->maximal = 1;
>>> +			p = NULL;
>>
>> Here, we're setting maximal without also setting a bit in this commit's
>> commit_mask. This is fine because we're not propagating this commit's
>> commit_mask to any parents (we're not continuing the walk from this
>> commit), but it seems like a code smell. Suggested fix is below.
>>
>>> +		}
>>> +
>>>  		if (c_ent->maximal) {
>>>  			num_maximal++;
>>>  			ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
>>>  			bb->commits[bb->commits_nr++] = commit;
>>>  		}
>>
>> As far as I can tell, this means that this commit occupies a bit
>> position in the commit mask that it doesn't need. Could this go into a
>> separate list instead, to be appended to bb->commits at the very end?

>> We could even skip the whole maximal stuff (for commits with existing
>> bitmaps) and replace "c_ent->maximal = 1;" above with "add to list that
>> we're going to append to bb->commits at the very end". That has the
>> advantage of not having to redefine "maximal".
> 
> Hmm. I'd trust Stolee's opinion over mine here, so I'll be curious what
> he has to say.

>>>
>>> +		if (!c_ent->commit_mask)
>>> +			continue;
>>
>> I think this should be moved as far up as possible (right after
>> the call to bb_data_at()) and commented, something like:
>>
>>   If there is no commit_mask, there is no reason to iterate over this
>>   commit; it is not selected (if it were, it would not have a blank
>>   commit mask) and all its children have existing bitmaps (see the
>>   comment starting with "This commit has an existing bitmap" below), so
>>   it does not contribute anything to the final bitmap file or its
>>   descendants.
> 
> Good suggestion, thanks.