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SubjectRe: [PATCH v3 2/2] powerpc/mm/hugetlb: Add support for 1G huge pages
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On Thursday 18 May 2017 10:51 AM, Michael Ellerman wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> 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@linux.vnet.ibm.com>
>> ---
>> 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
>

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