Jeff King [off-list ref] writes:
How frequently do you build the html branch? I always assumed it was
once in a while (every push?), not for every commit.
I don't ;-)
Every time "master" is updated to the official distribution point, i.e.,
kernel.org (which currently is down). A post-update hook runs there,
fetches the "master" branch commit into a separate repository, rebuilds
the documentation, updates "html" and "man" branches and pushes the
results back to that distribution point repository.
The mirrors will pick the result up after all that happens (or they may
lag but they will eventually catch up).