Re: [PATCH v1 03/10] mm: Introduce try_vma_alloc_movable_folio()

[Yu Zhao <yuzhao@google.com>]

On Mon, Jun 26, 2023 at 8:34 PM Yu Zhao <yuzhao@google.com> wrote:
>
> On Mon, Jun 26, 2023 at 11:14 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
> >
> > Opportunistically attempt to allocate high-order folios in highmem,
> > optionally zeroed. Retry with lower orders all the way to order-0, until
> > success. Although, of note, order-1 allocations are skipped since a
> > large folio must be at least order-2 to work with the THP machinery. The
> > user must check what they got with folio_order().
> >
> > This will be used to oportunistically allocate large folios for
> > anonymous memory with a sensible fallback under memory pressure.
> >
> > For attempts to allocate non-0 orders, we set __GFP_NORETRY to prevent
> > high latency due to reclaim, instead preferring to just try for a lower
> > order. The same approach is used by the readahead code when allocating
> > large folios.
> >
> > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> > ---
> >  mm/memory.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 367bbbb29d91..53896d46e686 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -3001,6 +3001,39 @@ static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
> >         return 0;
> >  }
> >
> > +static inline struct folio *vma_alloc_movable_folio(struct vm_area_struct *vma,
> > +                               unsigned long vaddr, int order, bool zeroed)
> > +{
> > +       gfp_t gfp = order > 0 ? __GFP_NORETRY | __GFP_NOWARN : 0;
> > +
> > +       if (zeroed)
> > +               return vma_alloc_zeroed_movable_folio(vma, vaddr, gfp, order);
> > +       else
> > +               return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp, order, vma,
> > +                                                               vaddr, false);
> > +}
> > +
> > +/*
> > + * Opportunistically attempt to allocate high-order folios, retrying with lower
> > + * orders all the way to order-0, until success. order-1 allocations are skipped
> > + * since a folio must be at least order-2 to work with the THP machinery. The
> > + * user must check what they got with folio_order(). vaddr can be any virtual
> > + * address that will be mapped by the allocated folio.
> > + */
> > +static struct folio *try_vma_alloc_movable_folio(struct vm_area_struct *vma,
> > +                               unsigned long vaddr, int order, bool zeroed)
> > +{
> > +       struct folio *folio;
> > +
> > +       for (; order > 1; order--) {
> > +               folio = vma_alloc_movable_folio(vma, vaddr, order, zeroed);
> > +               if (folio)
> > +                       return folio;
> > +       }
> > +
> > +       return vma_alloc_movable_folio(vma, vaddr, 0, zeroed);
> > +}
>
> I'd drop this patch. Instead, in do_anonymous_page():
>
>   if (IS_ENABLED(CONFIG_ARCH_WANTS_PTE_ORDER))
>     folio = vma_alloc_zeroed_movable_folio(vma, addr,
> CONFIG_ARCH_WANTS_PTE_ORDER))
>
>   if (!folio)
>     folio = vma_alloc_zeroed_movable_folio(vma, addr, 0);

I meant a runtime function arch_wants_pte_order() (Its default
implementation would return 0.)