Grow GC heaps independently

[Bug #21214]

If we allocate objects where one heap holds transient objects and another
holds long lived objects, then the heap with transient objects will grow
along the heap with long lived objects, causing higher memory usage.

For example, we can see this issue in this script:

    def allocate_small_object = []
    def allocate_large_object = Array.new(10)

    arys = Array.new(1_000_000) do
      # Allocate 10 small transient objects
      10.times { allocate_small_object }
      # Allocate 1 large object that is persistent
      allocate_large_object
    end

    pp GC.stat
    pp GC.stat_heap

Before this change:

    heap_live_slots: 2837243
    {0 =>
      {slot_size: 40,
       heap_eden_pages: 1123,
       heap_eden_slots: 1838807},
     2 =>
      {slot_size: 160,
       heap_eden_pages: 2449,
       heap_eden_slots: 1001149},
    }

After this change:

    heap_live_slots: 1094474
    {0 =>
      {slot_size: 40,
       heap_eden_pages: 58,
       heap_eden_slots: 94973},
     2 =>
      {slot_size: 160,
       heap_eden_pages: 2449,
       heap_eden_slots: 1001149},
    }

0 files changed, 0 insertions, 0 deletions