+=head2 Other OS tuning knobs
+
+Linux users: the C<sys.vm.max_map_count> sysctl may need to be increased if
+handling thousands of inboxes (with L<public-inbox-extindex(1)>) to avoid
+out-of-memory errors from git.
+
+Other OSes may have similar tuning knobs (patches appreciated).
+
+=head2 Scalability to many inboxes
+
+git 2.33+ startup time is orders-of-magnitude faster and uses
+less memory when dealing with thousands of alternates required
+for thousands of inboxes.
+
+L<public-inbox-extindex(1)> allows any number of public-inboxes
+to share the same Xapian indices.
+