On 1/24/21 3:58 PM, David Rientjes wrote:
> On Sun, 17 Jan 2021, 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@xxxxxxxxxxxxx>
>> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
>> Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>> ---
>> 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
>
> I'm not sure I understand the rationale for providing this help text if
> this is def_bool depending on CONFIG_HUGETLB_PAGE. Are you intending that
> this is actually configurable and we want to provide guidance to the admin
> on when to disable it (which it currently doesn't)? If not, why have the
> help text?
It's good for the (non-user) Kconfig symbol's meaning to be documented somewhere,
preferably such that one does not have to go digging thru git commit logs
to find it.
>> + 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
>>
>
--
~Randy
