Re: [PATCH v3 2/2] powerpc/mm/hugetlb: Add support for 1G huge pages

[Aneesh Kumar K.V]

On Thursday 18 May 2017 02:17 PM, Michael Ellerman wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes:
>
> > On Thursday 18 May 2017 10:51 AM, Michael Ellerman wrote:
> > > "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> writes:
> > >
> > > > POWER9 supports hugepages of size 2M and 1G in radix MMU mode. This patch
> > > > enables the usage of 1G page size for hugetlbfs. This also update the helper
> > > > such we can do 1G page allocation at runtime.
> > > >
> > > > We still don't enable 1G page size on DD1 version. This is to avoid doing
> > > > workaround mentioned in commit: 6d3a0379ebdc8 (powerpc/mm: Add
> > > > radix__tlb_flush_pte_p9_dd1()
> > > >
> > > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >    arch/powerpc/include/asm/book3s/64/hugetlb.h | 10 ++++++++++
> > > >    arch/powerpc/mm/hugetlbpage.c                |  7 +++++--
> > > >    arch/powerpc/platforms/Kconfig.cputype       |  1 +
> > > >    3 files changed, 16 insertions(+), 2 deletions(-)
> > >
> > > I think this patch is OK, but it's very confusing because it doesn't
> > > mention that it's only talking about *generic* gigantic page support.
> >
> > What you mean by generic gigantic page ? what is supported here is the
> > gigantic page with size 1G alone ?
>
> What about 16G pages on pseries.
>
> And all the other gigantic page sizes that Book3E supports?

None of that is supported w.r.t runtime allocation of hugepages. ie, we 
cannot echo nr_hugepages w.r.t them.  For 16GB i am not sure it make 
sense, because we will rarely get such large contiguous region. W.r.t 
page size supported for Book3E, may be we can. But I don't have a 
facility to test those. Hence didn't include that.

-aneesh