Re: [External] Re: [RFC PATCH 03/24] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP

[Muchun Song]

On Wed, Sep 30, 2020 at 7:41 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
>
> On 9/15/20 5:59 AM, 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.
> >
> > Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > ---
> >  fs/Kconfig | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> >
> > diff --git a/fs/Kconfig b/fs/Kconfig
> > index 976e8b9033c4..61e9c08096ca 100644
> > --- a/fs/Kconfig
> > +++ b/fs/Kconfig
> > @@ -245,6 +245,21 @@ config HUGETLBFS
> >  config HUGETLB_PAGE
> >       def_bool HUGETLBFS
> >
> > +config HUGETLB_PAGE_FREE_VMEMMAP
> > +     bool "Free unused vmemmap associated with HugeTLB pages"
> > +     default n
> > +     depends on HUGETLB_PAGE
> > +     depends on SPARSEMEM_VMEMMAP
> > +     depends on HAVE_BOOTMEM_INFO_NODE
> > +     help
> > +       There are many struct page structure associated with each HugeTLB
> > +       page. But we only use a few struct page structure. In this case,
> > +       it waste some memory. It is better to free the unused struct page
> > +       structures to buddy system which can save some memory. For
> > +       architectures that support it, say Y here.
> > +
> > +       If unsure, say N.
> > +
>
> I could be wrong, but I believe the convention is introduce the config
> option at the same time code which depends on the option is introduced.
> Therefore, it might be better to combine with the next patch.

Yeah, great. Will do that. Thanks.

>
> Also, it looks like most of your development was done on x86.  Should
> this option be limited to x86 only for now?

Now only the x86 has the HAVE_BOOTMEM_INFO_NODE option. So
maybe this is enough :)

> --
> Mike Kravetz



-- 
Yours,
Muchun