Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Message-ID: <a4df1a4d-79b6-5a69-77a2-df9a36653c89@arm.com>
Date:   Mon, 4 Apr 2022 14:35:08 +0530
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [PATCH v4 1/2] mm: hugetlb_vmemmap: introduce
 ARCH_WANT_HUGETLB_PAGE_FREE_VMEMMAP
Content-Language: en-US
To:     Muchun Song <songmuchun@bytedance.com>, will@kernel.org,
        akpm@linux-foundation.org, david@redhat.com, bodeddub@amazon.com,
        osalvador@suse.de, mike.kravetz@oracle.com, rientjes@google.com,
        mark.rutland@arm.com, catalin.marinas@arm.com, james.morse@arm.com,
        21cnbao@gmail.com
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, duanxiongchun@bytedance.com,
        fam.zheng@bytedance.com, smuchun@gmail.com
References: <20220331065640.5777-1-songmuchun@bytedance.com>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
In-Reply-To: <20220331065640.5777-1-songmuchun@bytedance.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk


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>