Re: [PATCH v4 1/2] mm: hugetlb_vmemmap: introduce ARCH_WANT_HUGETLB_PAGE_FREE_VMEMMAP

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 3/31/22 12:26, Muchun Song wrote:
> The feature of minimizing overhead of struct page associated with each
> HugeTLB page is implemented on x86_64, however, the infrastructure of
> this feature is already there, we could easily enable it for other
> architectures.  Introduce ARCH_WANT_HUGETLB_PAGE_FREE_VMEMMAP for other
> architectures to be easily enabled.  Just select this config if they
> want to enable this feature.
> 
> Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  arch/x86/Kconfig |  1 +
>  fs/Kconfig       | 10 +++++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 9f5bd41bf660..e69d42528542 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -119,6 +119,7 @@ config X86
>  	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
>  	select ARCH_WANTS_NO_INSTR
>  	select ARCH_WANT_HUGE_PMD_SHARE
> +	select ARCH_WANT_HUGETLB_PAGE_FREE_VMEMMAP	if X86_64
>  	select ARCH_WANT_LD_ORPHAN_WARN
>  	select ARCH_WANTS_THP_SWAP		if X86_64
>  	select ARCH_HAS_PARANOID_L1D_FLUSH
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 6c7dc1387beb..f6db2af33738 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -245,9 +245,17 @@ config HUGETLBFS
>  config HUGETLB_PAGE
>  	def_bool HUGETLBFS
>  
> +#
> +# Select this config option from the architecture Kconfig, if it is preferred
> +# to enable the feature of minimizing overhead of struct page associated with
> +# each HugeTLB page.
> +#
> +config ARCH_WANT_HUGETLB_PAGE_FREE_VMEMMAP
> +	bool
> +
>  config HUGETLB_PAGE_FREE_VMEMMAP
>  	def_bool HUGETLB_PAGE
> -	depends on X86_64
> +	depends on ARCH_WANT_HUGETLB_PAGE_FREE_VMEMMAP
>  	depends on SPARSEMEM_VMEMMAP
>  
>  config HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON

Better to have platforms subscribe via ARCH_HAS/WANTS_ method instead
of direct dependency in the config itself.

LGTM.

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>