Re: [PATCH v2 19/24] pack-bitmap-write: ignore BITMAP_FLAG_REUSE

> Just because a commit happened to be bitmapped last time does not make
> it a good candidate for having a bitmap this time. In particular, we may
> choose bitmaps based on how recent they are in history, or whether a ref
> tip points to them, and those things will change. We're better off
> re-considering fresh which commits are good candidates.
> 
> Reusing the existing bitmap _is_ a reasonable thing to do to save
> computation. But only reusing exact bitmaps is a weak form of this. If
> we have an old bitmap for A and now want a new bitmap for its child, we
> should be able to compute that only by looking at trees and that are new
> to the child. But this code would consider only exact reuse (which is
> perhaps why it was eager to select those commits in the first place).

> -int rebuild_existing_bitmaps(struct bitmap_index *bitmap_git,
> -			     struct packing_data *mapping,
> -			     kh_oid_map_t *reused_bitmaps,
> -			     int show_progress)
> +uint32_t *create_bitmap_mapping(struct bitmap_index *bitmap_git,
> +				struct packing_data *mapping)