Need way to shrink the freelist

Hi,everybody~

I found nodes in freelist can never be shrinked, it can only grow larger(like "reserve_unsafe" and "reserve" do).
The only way to reduce the capacity of freelist is destruct queue,ringbuffer or stack. But that is not convenient. Sorry I must make the memory occupy not so high affter some request burst.
Is it possible to improve that?
If cann't, then "capacity_unsafe" function to tell current capacity is needed.
I understand data structure in freelist implementation should lock free as much as possible. But it can have a flexible way like limit the max freelist capacity. Such as when return node to freelist, examine the current capacity. It doesn't need to be accurate,so "capacity" doesn't need to be a atmoic variable.
Just some my silly ideas~

Thanks~