Maybe, int madvise5(addr, length, MADV_DONTNEED|MADV_LAZY|MADV_SIGBUS,
&purged, &ret);
Another reason to make it hard is that madvise(2) is tight coupled with
with vmas split/merge. It needs mmap_sem's write-side lock and it hurt
anon-vrange test performance much heavily and userland might want to
make volatile range with small unit like "page size" so it's undesireable
to make it with vma. Then, we should filter out to avoid vma split/merge
in implementation if only MADV_LAZY case? Doable but it could make code
complicated and lost consistency with other variant of madvise.