On Mon, Jan 25, 2021 at 7:58 AM David Rientjes <rientjes@xxxxxxxxxx> 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?
This is __not__ configurable. Seems like a comment to help others
understand this option. Like Randy said.
Thanks.
>
> > + 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
> >
