linux-kernel - Re: [PATCH v7 03/15] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE

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Date:   Mon, 7 Dec 2020 13:19:25 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Muchun Song <songmuchun@...edance.com>, 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
Cc:     duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v7 03/15] mm/hugetlb: Introduce a new config
 HUGETLB_PAGE_FREE_VMEMMAP

On 30.11.20 16:18, Muchun Song wrote:
> The purpose of introducing HUGETLB_PAGE_FREE_VMEMMAP is to configure
> whether to enable the feature of freeing unused vmemmap associated
> with HugeTLB pages. And this is just for dependency check. Now only
> support x86.

x86 - i386 and x86-64? (I assume the latter only ;) )

> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  arch/x86/mm/init_64.c |  2 +-
>  fs/Kconfig            | 14 ++++++++++++++
>  2 files changed, 15 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;
>  

Why does this hunk belong into this patch? Looks like this should go
into another patch.

>  	for_each_online_node(i)
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 976e8b9033c4..4961dd488444 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -245,6 +245,20 @@ config HUGETLBFS
>  config HUGETLB_PAGE
>  	def_bool HUGETLBFS
>  
> +config HUGETLB_PAGE_FREE_VMEMMAP
> +	def_bool HUGETLB_PAGE
> +	depends on X86
> +	depends on SPARSEMEM_VMEMMAP
> +	depends on HAVE_BOOTMEM_INFO_NODE
> +	help
> +	  When using HUGETLB_PAGE_FREE_VMEMMAP, the system can save up some
> +	  memory from pre-allocated HugeTLB pages when they are not used.
> +	  6 pages per 2MB HugeTLB page and 4094 per 1GB HugeTLB page.

Calculations only apply to 4k base pages, no? (maybe generalize this a
bit or mention 4k base pages - I'm pretty sure we'll see the "depends on
X86" part fairly soon if this goes upstream)


-- 
Thanks,

David / dhildenb