Re: [PATCH 6/7] config: enable `pack.writeReverseIndex` by default

> They are useful in GitHub's infrastructure, where we have seen a
> dramatic increase in performance when writing ".rev" files[1]. In
> particular:
>
>   - an ~80% reduction in the time it takes to serve fetches on a popular
>     repository, Homebrew/homebrew-core.
>
>   - a ~60% reduction in the peak memory usage to serve fetches on that
>     same repository.
>
>   - a collective savings of ~35% in CPU time across all pack-objects
>     invocations serving fetches across all repositories in a single
>     datacenter.
>
> Reverse indexes are also beneficial to end-users as well as forges. For
> example, the time it takes to generate a pack containing the objects for
> the 10 most recent commits in linux.git (representing a typical push) is
> significantly faster when on-disk reverse indexes are available:
> ...
> In the more than two years since e37d0b8730 was merged, Git's
> implementation of on-disk reverse indexes has been thoroughly tested,
> both from users enabling `pack.writeReverseIndexes`, and from GitHub's
> deployment of the feature. The latter has been running without incident
> for more than two years.