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References: <20230626171430.3167004-1-ryan.roberts@arm.com> <20230626171430.3167004-4-ryan.roberts@arm.com>
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From:   Yu Zhao <yuzhao@google.com>
Date:   Mon, 26 Jun 2023 20:34:18 -0600
Message-ID: <CAOUHufZKM+aS_hYQ5nDUHh74UQwWipJ27Na5Sw4n+RDqnwyWHA@mail.gmail.com>
Subject: Re: [PATCH v1 03/10] mm: Introduce try_vma_alloc_movable_folio()
To:     Ryan Roberts <ryan.roberts@arm.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Yin Fengwei <fengwei.yin@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-alpha@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-s390@vger.kernel.org
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On Mon, Jun 26, 2023 at 11:14=E2=80=AFAM 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 v=
m_fault *vmf)
>         return 0;
>  }
>
> +static inline struct folio *vma_alloc_movable_folio(struct vm_area_struc=
t *vma,
> +                               unsigned long vaddr, int order, bool zero=
ed)
> +{
> +       gfp_t gfp =3D order > 0 ? __GFP_NORETRY | __GFP_NOWARN : 0;
> +
> +       if (zeroed)
> +               return vma_alloc_zeroed_movable_folio(vma, vaddr, gfp, or=
der);
> +       else
> +               return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | gfp, order,=
 vma,
> +                                                               vaddr, fa=
lse);
> +}
> +
> +/*
> + * Opportunistically attempt to allocate high-order folios, retrying wit=
h 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 vi=
rtual
> + * 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 zero=
ed)
> +{
> +       struct folio *folio;
> +
> +       for (; order > 1; order--) {
> +               folio =3D vma_alloc_movable_folio(vma, vaddr, order, zero=
ed);
> +               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 =3D vma_alloc_zeroed_movable_folio(vma, addr,
CONFIG_ARCH_WANTS_PTE_ORDER))

  if (!folio)
    folio =3D vma_alloc_zeroed_movable_folio(vma, addr, 0);