Re: [PATCH v1 09/10] arm64: mm: Declare support for large anonymous folios

[Yu Zhao]

On Mon, Jun 26, 2023 at 11:15 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote:
>
> For the unhinted case, when THP is not permitted for the vma, don't
> allow anything bigger than 64K. This means we don't waste too much
> memory. Additionally, for 4K pages this is the contpte size, and for
> 16K, this is (usually) the HPA size when the uarch feature is
> implemented. For the hinted case, when THP is permitted for the vma,
> allow the contpte size for all page size configurations; 64K for 4K, 2M
> for 16K and 2M for 64K.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> ---
>  arch/arm64/Kconfig | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 343e1e1cae10..0e91b5bc8cd9 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -243,6 +243,7 @@ config ARM64
>         select TRACE_IRQFLAGS_SUPPORT
>         select TRACE_IRQFLAGS_NMI_SUPPORT
>         select HAVE_SOFTIRQ_ON_OWN_STACK
> +       select ARCH_SUPPORTS_LARGE_ANON_FOLIO
>         help
>           ARM 64-bit (AArch64) Linux support.
>
> @@ -281,6 +282,18 @@ config ARM64_CONT_PMD_SHIFT
>         default 5 if ARM64_16K_PAGES
>         default 4
>
> +config ARCH_LARGE_ANON_FOLIO_NOTHP_ORDER_MAX
> +       int
> +       default 0 if ARM64_64K_PAGES    # 64K (1 page)
> +       default 2 if ARM64_16K_PAGES    # 64K (4 pages; benefits from HPA where HW supports it)
> +       default 4 if ARM64_4K_PAGES     # 64K (16 pages; eligible for contpte-mapping)
> +
> +config ARCH_LARGE_ANON_FOLIO_THP_ORDER_MAX
> +       int
> +       default 5 if ARM64_64K_PAGES    # 2M  (32 page; eligible for contpte-mapping)
> +       default 7 if ARM64_16K_PAGES    # 2M  (128 pages; eligible for contpte-mapping)
> +       default 4 if ARM64_4K_PAGES     # 64K (16 pages; eligible for contpte-mapping)
> +
>  config ARCH_MMAP_RND_BITS_MIN
>         default 14 if ARM64_64K_PAGES
>         default 16 if ARM64_16K_PAGES

Can we please just add one Kconfig for the large anon folio feature,
i.e., ARCH_WANTS_PTE_ORDER, for now?

Feel free to add as many as you wish for arm specific features like
HPA and contpte.