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Subject: Re: [PATCH v13 02/12] mm: hugetlb: introduce a new config
 HUGETLB_PAGE_FREE_VMEMMAP
To:     Muchun Song <songmuchun@bytedance.com>
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References: <20210117151053.24600-1-songmuchun@bytedance.com>
 <20210117151053.24600-3-songmuchun@bytedance.com>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <474cca65-c184-293a-a71d-b373aae4dfb1@huawei.com>
Date:   Tue, 26 Jan 2021 10:07:10 +0800
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Hi:
On 2021/1/17 23:10, Muchun Song wrote:
> The HUGETLB_PAGE_FREE_VMEMMAP option is used to enable the freeing
> of unnecessary vmemmap associated with HugeTLB pages. The config
> option is introduced early so that supporting code can be written
> to depend on the option. The initial version of the code only
> provides support for x86-64.
> 
> Like other code which frees vmemmap, this config option depends on
> HAVE_BOOTMEM_INFO_NODE. The routine register_page_bootmem_info() is
> used to register bootmem info. Therefore, make sure
> register_page_bootmem_info is enabled if HUGETLB_PAGE_FREE_VMEMMAP
> is defined.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Acked-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
>  arch/x86/mm/init_64.c |  2 +-
>  fs/Kconfig            | 18 ++++++++++++++++++
>  2 files changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 0a45f062826e..0435bee2e172 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1225,7 +1225,7 @@ static struct kcore_list kcore_vsyscall;
>  
>  static void __init register_page_bootmem_info(void)
>  {
> -#ifdef CONFIG_NUMA
> +#if defined(CONFIG_NUMA) || defined(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP)
>  	int i;
>  
>  	for_each_online_node(i)
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 976e8b9033c4..e7c4c2a79311 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -245,6 +245,24 @@ config HUGETLBFS
>  config HUGETLB_PAGE
>  	def_bool HUGETLBFS
>  
> +config HUGETLB_PAGE_FREE_VMEMMAP
> +	def_bool HUGETLB_PAGE
> +	depends on X86_64
> +	depends on SPARSEMEM_VMEMMAP
> +	depends on HAVE_BOOTMEM_INFO_NODE
> +	help
> +	  The option HUGETLB_PAGE_FREE_VMEMMAP allows for the freeing of
> +	  some vmemmap pages associated with pre-allocated HugeTLB pages.
> +	  For example, on X86_64 6 vmemmap pages of size 4KB each can be
> +	  saved for each 2MB HugeTLB page.  4094 vmemmap pages of size 4KB
> +	  each can be saved for each 1GB HugeTLB page.
> +
> +	  When a HugeTLB page is allocated or freed, the vmemmap array
> +	  representing the range associated with the page will need to be
> +	  remapped.  When a page is allocated, vmemmap pages are freed
> +	  after remapping.  When a page is freed, previously discarded
> +	  vmemmap pages must be allocated before remapping.
> +
>  config MEMFD_CREATE
>  	def_bool TMPFS || HUGETLBFS
>  
> 

LGTM. Thanks.

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>