Re: [RFC PATCH v2 12/47] hugetlb: add hugetlb_hgm_walk and hugetlb_walk_step

[Jane Chu]

On 1/4/2023 4:57 PM, Jane Chu wrote:
> > + * @stop_at_none determines what we do when we encounter an empty 
> > PTE. If true,
> > + * we return that PTE. If false and @sz is less than the current 
> > PTE's size,
> > + * we make that PTE point to the next level down, going until @sz is 
> > the same
> > + * as our current PTE.
> [..]
> > +int hugetlb_hgm_walk(struct mm_struct *mm, struct vm_area_struct *vma,
> > +             struct hugetlb_pte *hpte, unsigned long addr,
> > +             unsigned long sz, bool stop_at_none)
> > +{

Also here below, the way 'stop_at_none' is used when HGM isn't enabled
is puzzling.  Could you elaborate please?

+	if (!hugetlb_hgm_enabled(vma)) {
+		if (stop_at_none)
+			return 0;
+		return sz == huge_page_size(hstate_vma(vma)) ? 0 : -EINVAL;
+	}

> [..]
> > +    while (hugetlb_pte_size(hpte) > sz && !ret) {
> > +        pte = huge_ptep_get(hpte->ptep);
> > +        if (!pte_present(pte)) {
> > +            if (stop_at_none)
> > +                return 0;
> > +            if (unlikely(!huge_pte_none(pte)))
> > +                return -EEXIST;
>
> If 'stop_at_none' means settling down on the just encountered empty PTE,
> should the above two "if" clauses switch order?  I thought Peter has
> raised this question too, but I'm not seeing a response.
>
> Regards,
> -jane
>
>
> > +        } else if (hugetlb_pte_present_leaf(hpte, pte))
> > +            return 0;
> > +        ret = hugetlb_walk_step(mm, hpte, addr, sz);
> > +    }
> > +
> > +    return ret;
> > +}
> > +

thanks,
-jane