uvm_rb_gap
KASSERT(prev_entry->gap == uvm_rb_gap(prev_entry));
KASSERT(entry->gap == uvm_rb_gap(entry));
KDASSERT(parent->gap == uvm_rb_gap(parent));
KDASSERT(brother->gap == uvm_rb_gap(brother));
entry->gap = entry->maxgap = uvm_rb_gap(entry);
entry->prev->gap = uvm_rb_gap(entry->prev);
entry->prev->gap = uvm_rb_gap(entry->prev);
if (tmp->gap != uvm_rb_gap(tmp)) {
(ulong)tmp->gap, (ulong)uvm_rb_gap(tmp),