"Derrick Stolee via GitGitGadget" [off-list ref] writes:
This patch series performs a decently-sized refactoring of the revision-walk
machinery. Well, "refactoring" is probably the wrong word, as I don't
actually remove the old code. Instead, when we see certain options in the
'rev_info' struct, we redirect the commit-walk logic to a new set of methods
that distribute the workload differently. By using generation numbers in the
commit-graph, we can significantly improve 'git log --graph' commands (and
the underlying 'git rev-list --topo-order').
Finally ;-).