__pud_alloc
int __pud_alloc(struct mm_struct *mm, p4d_t *p4d, unsigned long address);
return (unlikely(p4d_none(*p4d)) && __pud_alloc(mm, p4d, address)) ?
err = __pud_alloc(walk->mm, p4d, addr);
if (__pud_alloc(mm, p4d, address))