linux-kernel - Re: [PATCH v14 2/8] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE

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Date:   Thu, 4 Feb 2021 19:44:12 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Muchun Song <songmuchun@...edance.com>
CC:     <duanxiongchun@...edance.com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <corbet@....net>,
        <mike.kravetz@...cle.com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>, <x86@...nel.org>,
        <hpa@...or.com>, <dave.hansen@...ux.intel.com>, <luto@...nel.org>,
        <peterz@...radead.org>, <viro@...iv.linux.org.uk>,
        <akpm@...ux-foundation.org>, <paulmck@...nel.org>,
        <mchehab+huawei@...nel.org>, <pawan.kumar.gupta@...ux.intel.com>,
        <rdunlap@...radead.org>, <oneukum@...e.com>,
        <anshuman.khandual@....com>, <jroedel@...e.de>,
        <almasrymina@...gle.com>, <rientjes@...gle.com>,
        <willy@...radead.org>, <osalvador@...e.de>, <mhocko@...e.com>,
        <song.bao.hua@...ilicon.com>, <david@...hat.com>,
        <naoya.horiguchi@....com>
Subject: Re: [PATCH v14 2/8] mm: hugetlb: introduce a new config
 HUGETLB_PAGE_FREE_VMEMMAP

Hi:
On 2021/2/4 11:50, Muchun Song wrote:
> 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.
> 
> 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@...edance.com>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Acked-by: Mike Kravetz <mike.kravetz@...cle.com>

LGTM. Thanks.
Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

> ---
>  arch/x86/mm/init_64.c | 2 +-
>  fs/Kconfig            | 6 ++++++
>  2 files changed, 7 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 97e7b77c9309..de87f234f1e9 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -237,6 +237,12 @@ 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
> +
>  config MEMFD_CREATE
>  	def_bool TMPFS || HUGETLBFS
>  
>