Re: [RFC PATCH 1/3] mm: support hugetlb free page reporting

[Liang Li]

> On 12/22/20 11:59 AM, Alexander Duyck wrote:
> > On Mon, Dec 21, 2020 at 11:47 PM Liang Li <liliang.opensource@xxxxxxxxx> wrote:
> >> +
> >> +       if (huge_page_order(h) > MAX_ORDER)
> >> +               budget = HUGEPAGE_REPORTING_CAPACITY;
> >> +       else
> >> +               budget = HUGEPAGE_REPORTING_CAPACITY * 32;
> >
> > Wouldn't huge_page_order always be more than MAX_ORDER? Seems like we
> > don't even really need budget since this should probably be pulling
> > out no more than one hugepage at a time.
>
> On standard x86_64 configs, 2MB huge pages are of order 9 < MAX_ORDER (11).
> What is important for hugetlb is the largest order that can be allocated
> from buddy.  Anything bigger is considered a gigantic page and has to be
> allocated differently.
>
> If the code above is trying to distinguish between huge and gigantic pages,
> it is off by 1.  The largest order that can be allocated from the buddy is
> (MAX_ORDER - 1).  So, the check should be '>='.
>
> --
> Mike Kravetz

Yes, you're right!  thanks

Liang