Re: [PATCH v4 0/8] commit-reach: terminate merge-base walk when one side is exhausted

> commit-reach: terminate merge-base walk when one paint side is exhausted
> 
> Optimize paint_down_to_common() for merge-base queries that hit large
> one-sided histories.
> 
> When the walk from one side reaches a commit with a very low generation
> number that the other side never paints, the walk is forced to drain most of
> the graph. A common trigger is a repository import that grafts a separate
> history with its own root, but any merge that introduces a low-generation
> commit never painted by the other side has the same effect.

> Changes since v3:
> 
>   * Fixed BUG assertion that was accidentally made unconditional in v3:
>     restored the min_generation guard so it only fires when generation-based
>     ordering is active.
> 
>   * Moved generation cutoff and single-result termination conditions into the
>     documentation in patch 1/8, since they describe existing behavior.
> 
>   * Renamed paint_state counter fields for clarity: p1_count ->
>     parent1_count, p2_count -> parent2_count, pending_merge_bases ->
>     mb_candidate_count. Changed counter types from int to size_t. (Suggested
>     by Rene Scharfe.)