Re: [PATCH v2 1/2] mm: huge_memory: disallow hugepages if the system-wide THP sysfs settings are disabled

[Dev Jain]

On 06/06/25 10:19 pm, Dev Jain wrote:
> On 05/06/25 1:30 pm, Baolin Wang wrote:
> > The MADV_COLLAPSE will ignore the system-wide Anon THP sysfs 
> > settings, which
> > means that even though we have disabled the Anon THP configuration, 
> > MADV_COLLAPSE
> > will still attempt to collapse into a Anon THP. This violates the 
> > rule we have
> > agreed upon: never means never.
> >
> > Another rule for madvise, referring to David's suggestion: “allowing 
> > for collapsing
> > in a VM without VM_HUGEPAGE in the "madvise" mode would be fine".
> >
> > To address this issue, should check whether the Anon THP 
> > configuration is disabled
> > in thp_vma_allowable_orders(), even when the TVA_ENFORCE_SYSFS flag 
> > is set.
>
> Did you mean to say "even when the TVA_ENFORCE_SYSFS flag is *not* 
> set"? Because if
> is set, then we have to check the anon THP sysfs config.

Otherwise the patch itself looks good to me, so:

Reviewed-by: Dev Jain <dev.jain@xxxxxxx>


> > In summary, the current strategy is:
> >
> > 1. If always & orders == 0, and madvise & orders == 0, and 
> > hugepage_global_enabled() == false
> > (global THP settings are not enabled), it means mTHP of that orders 
> > are prohibited
> > from being used, then madvise_collapse() is forbidden for that orders.
> >
> > 2. If always & orders == 0, and madvise & orders == 0, and 
> > hugepage_global_enabled() == true
> > (global THP settings are enabled), and inherit & orders == 0, it 
> > means mTHP of that
> > orders are still prohibited from being used, thus madvise_collapse() 
> > is not allowed
> > for that orders.
> >
> > Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > ---
> >   include/linux/huge_mm.h | 23 +++++++++++++++++++----
> >   1 file changed, 19 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 2f190c90192d..199ddc9f04a1 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -287,20 +287,35 @@ unsigned long thp_vma_allowable_orders(struct 
> > vm_area_struct *vma,
> >                          unsigned long orders)
> >   {
> >       /* Optimization to check if required orders are enabled early. */
> > -    if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
> > -        unsigned long mask = READ_ONCE(huge_anon_orders_always);
> > +    if (vma_is_anonymous(vma)) {
> > +        unsigned long always = READ_ONCE(huge_anon_orders_always);
> > +        unsigned long madvise = READ_ONCE(huge_anon_orders_madvise);
> > +        unsigned long inherit = READ_ONCE(huge_anon_orders_inherit);
> > +        unsigned long mask = always | madvise;
> > +
> > +        /*
> > +         * If the system-wide THP/mTHP sysfs settings are disabled,
> > +         * then we should never allow hugepages.
> > +         */
> > +        if (!(mask & orders) && !(hugepage_global_enabled() && 
> > (inherit & orders)))
> > +            return 0;
> > +
> > +        if (!(tva_flags & TVA_ENFORCE_SYSFS))
> > +            goto skip;
> >   +        mask = always;
> >           if (vm_flags & VM_HUGEPAGE)
> > -            mask |= READ_ONCE(huge_anon_orders_madvise);
> > +            mask |= madvise;
> >           if (hugepage_global_always() ||
> >               ((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled()))
> > -            mask |= READ_ONCE(huge_anon_orders_inherit);
> > +            mask |= inherit;
> >             orders &= mask;
> >           if (!orders)
> >               return 0;
> >       }
> >   +skip:
> >       return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, 
> > orders);
> >   }