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

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Date:   Thu, 18 May 2017 11:37:59 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>, akpm@...ux-foundation.org,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 2/2] powerpc/mm/hugetlb: Add support for 1G huge pages



On Thursday 18 May 2017 10:51 AM, Michael Ellerman wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.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@...ux.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
>