Ruby

1. Move immutable fields from struct heaps_slot and struct sorted_heaps_slot into struct heaps_header.
   One exception is limit field, but it starts to be mutable just before freeing a heaps_header, so that it is not big issue.
2. Embed bitmap into struct heaps_slot
3. Change free_unused_heaps to free_unused_heap, so that it will not be called on every GC round, but only when page should be freed.
   While free_unused_heaps does not consume much time (it is invisible in profiler), but regular application has no need in calling this function every time.

https://github.com/ruby/ruby/pull/108
https://github.com/ruby/ruby/pull/108.patch