Re: [External] Re: [PATCH v7 06/15] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two

[Muchun Song]

On Wed, Dec 9, 2020 at 5:57 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 30.11.20 16:18, Muchun Song wrote:
> > We only can free the tail vmemmap pages of HugeTLB to the buddy allocator
> > when the size of struct page is a power of two.
> >
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > ---
> >  mm/hugetlb_vmemmap.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index 51152e258f39..ad8fc61ea273 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -111,6 +111,11 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> >       unsigned int nr_pages = pages_per_huge_page(h);
> >       unsigned int vmemmap_pages;
> >
> > +     if (!is_power_of_2(sizeof(struct page))) {
> > +             pr_info("disable freeing vmemmap pages for %s\n", h->name);
>
> I'd just drop that pr_info(). Users are able to observe that it's
> working (below), so they are able to identify that it's not working as well.

The below is just a pr_debug. Do you suggest converting it to pr_info?

>
> > +             return;
> > +     }
> > +
> >       vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
> >       /*
> >        * The head page and the first tail page are not to be freed to buddy
> >
>
> Please squash this patch into the enabling patch and add a comment
> instead, like
>
> /* We cannot optimize if a "struct page" crosses page boundaries. */
>

Will do. Thanks.

> --
> Thanks,
>
> David / dhildenb
>


-- 
Yours,
Muchun