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

[Yu Zhao <yuzhao@google.com>]

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);