can_merge_remove_vma
if (can_merge_right && !can_merge_remove_vma(next))
VM_WARN_ON_VMG(remove_next && !can_merge_remove_vma(next), vmg);
if (vmg->__remove_middle && !can_merge_remove_vma(middle))
if (vmg->__remove_next && !can_merge_remove_vma(next)) {