Re: Fix to long-standing crashes in GC

[Richard Stallman]

    With my fix, marker blocks are never freed (they remain
    on the free marker lists) -- this can be improved by keeping
    the "all free" blocks on a separate list and freeing them
    at the end of GC.  I may do that later...

It might be simpler, and not much slower, to scan the list of marker
blocks at the end of GC and check each one to see if it is all free.