Re: [External] Re: [PATCH v13 09/12] mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap

[Muchun Song]

On Mon, Jan 25, 2021 at 8:08 PM Oscar Salvador <osalvador@xxxxxxx> wrote:
>
> On Mon, Jan 25, 2021 at 12:43:23PM +0100, David Hildenbrand wrote:
> > > -   if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> > > +   if (is_hugetlb_free_vmemmap_enabled() ||
> > > +       end - start < PAGES_PER_SECTION * sizeof(struct page))
> >
> > This looks irresponsible. You ignore any altmap, even though current
> > altmap users (ZONE_DEVICE) will not actually result in applicable
> > vmemmaps that huge pages could ever use.
> >
> > Why do you ignore the altmap completely? This has to be properly
> > documented, but IMHO it's not even the right approach to mess with
> > altmap here.
>
> The goal was not to ignore altmap but to disable PMD mapping sections
> when the feature was enabled.
> Shame on me I did not notice that with this, altmap will be ignored.
>
> Something like below maybe:

Yeah, Thanks a lot.

>
> int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
>                 struct vmem_altmap *altmap)
> {
>         int err;
>         bool populate_base_pages = false;
>
>         if ((end - start < PAGES_PER_SECTION * sizeof(struct page)) ||
>             (is_hugetlb_free_vmemmap_enabled() && !altmap))
>                 populate_base_pages = true;
>
>         if (populate_base_pages) {
>                 err = vmemmap_populate_basepages(start, end, node, NULL);
>         } else if (boot_cpu_has(X86_FEATURE_PSE)) {
>         ....
>
>
> >
> > --
> > Thanks,
> >
> > David / dhildenb
> >
> >
>
> --
> Oscar Salvador
> SUSE L3