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

[Aneesh Kumar K.V]

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 ?

> We have existing support for gigantic pages on powerpc, on several
> platforms. This patch appears to break that, but I think doesn't in
> practice?

What is broken ?


> So can you make it a bit clearer in the commit message, and the code,
> that this is only about enabling the generic gigantic page support, and
> is unrelated to the arch-specific gigantic page support.
>
> cheers
>
> > diff --git a/arch/powerpc/include/asm/book3s/64/hugetlb.h b/arch/powerpc/include/asm/book3s/64/hugetlb.h
> > index 6666cd366596..5c28bd6f2ae1 100644
> > --- a/arch/powerpc/include/asm/book3s/64/hugetlb.h
> > +++ b/arch/powerpc/include/asm/book3s/64/hugetlb.h
> > @@ -50,4 +50,14 @@ static inline pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
> >   	else
> >   		return entry;
> >   }
> > +
> > +#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
> > +static inline bool gigantic_page_supported(void)
> > +{
> > +	if (radix_enabled())
> > +		return true;
> > +	return false;
> > +}
> > +#endif
> > +
> >   #endif
> > diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> > index a4f33de4008e..80f6d2ed551a 100644
> > --- a/arch/powerpc/mm/hugetlbpage.c
> > +++ b/arch/powerpc/mm/hugetlbpage.c
> > @@ -763,8 +763,11 @@ static int __init add_huge_page_size(unsigned long long size)
> >   	 * Hash: 16M and 16G
> >   	 */
> >   	if (radix_enabled()) {
> > -		if (mmu_psize != MMU_PAGE_2M)
> > -			return -EINVAL;
> > +		if (mmu_psize != MMU_PAGE_2M) {
> > +			if (cpu_has_feature(CPU_FTR_POWER9_DD1) ||
> > +			    (mmu_psize != MMU_PAGE_1G))
> > +				return -EINVAL;
> > +		}
> >   	} else {
> >   		if (mmu_psize != MMU_PAGE_16M && mmu_psize != MMU_PAGE_16G)
> >   			return -EINVAL;
> > diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
> > index 684e886eaae4..b76ef6637016 100644
> > --- a/arch/powerpc/platforms/Kconfig.cputype
> > +++ b/arch/powerpc/platforms/Kconfig.cputype
> > @@ -344,6 +344,7 @@ config PPC_STD_MMU_64
> >   config PPC_RADIX_MMU
> >   	bool "Radix MMU Support"
> >   	depends on PPC_BOOK3S_64
> > +	select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
> >   	default y
> >   	help
> >   	  Enable support for the Power ISA 3.0 Radix style MMU. Currently this
> > --
> > 2.7.4