Subject: Re: [PATCH -V7 08/10] powerpc/THP: Enable THP on PPC64

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Sat, 04 May 2013 00:19:03 +0530

David Gibson <[email-masked]> writes:

> On Mon, Apr 29, 2013 at 01:21:49AM +0530, Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <[email-masked]>
>> 
>> We enable only if the we support 16MB page size.
>> 
>> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
>> ---
>>  arch/powerpc/include/asm/pgtable-ppc64.h |  3 +--
>>  arch/powerpc/mm/pgtable_64.c             | 28 ++++++++++++++++++++++++++++
>>  2 files changed, 29 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
>> index 97fc839..d65534b 100644
>> --- a/arch/powerpc/include/asm/pgtable-ppc64.h
>> +++ b/arch/powerpc/include/asm/pgtable-ppc64.h
>> @@ -426,8 +426,7 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
>>  	return pmd_val(pmd) >> PTE_RPN_SHIFT;
>>  }
>>  
>> -/* We will enable it in the last patch */
>> -#define has_transparent_hugepage() 0
>> +extern int has_transparent_hugepage(void);
>>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>  
>>  static inline int pmd_young(pmd_t pmd)
>> diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
>> index 54216c1..b742d6f 100644
>> --- a/arch/powerpc/mm/pgtable_64.c
>> +++ b/arch/powerpc/mm/pgtable_64.c
>> @@ -754,6 +754,34 @@ void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long addr,
>>  	return;
>>  }
>>  
>> +int has_transparent_hugepage(void)
>> +{
>> +	if (!mmu_has_feature(MMU_FTR_16M_PAGE))
>> +		return 0;
>> +	/*
>> +	 * We support THP only if HPAGE_SHIFT is 16MB.
>> +	 */
>> +	if (!HPAGE_SHIFT || (HPAGE_SHIFT != mmu_psize_defs[MMU_PAGE_16M].shift))
>> +		return 0;
>
> Again, THP should not be dependent on the value of HPAGE_SHIFT.  Just
> checking that mmu_psize_defsz[MMU_PAGE_16M].shift == 24 should be
> sufficient (i.e. that 16M hugepages are supported).

done

+	/*
+	 * We support THP only if PMD_SIZE is 16MB.
+	 */
+	if (mmu_psize_defs[MMU_PAGE_16M].shift != PMD_SHIFT)
+		return 0;
+	/*

>
>> +	/*
>> +	 * We need to make sure that we support 16MB hugepage in a segement
>> +	 * with base page size 64K or 4K. We only enable THP with a PAGE_SIZE
>> +	 * of 64K.
>> +	 */
>> +	/*
>> +	 * If we have 64K HPTE, we will be using that by default
>> +	 */
>> +	if (mmu_psize_defs[MMU_PAGE_64K].shift &&
>> +	    (mmu_psize_defs[MMU_PAGE_64K].penc[MMU_PAGE_16M] == -1))
>> +		return 0;
>> +	/*
>> +	 * Ok we only have 4K HPTE
>> +	 */
>> +	if (mmu_psize_defs[MMU_PAGE_4K].penc[MMU_PAGE_16M] == -1)
>> +		return 0;
>
> Except you don't actually support THP on 4K base page size yet.

That is 64K linux page size and 4K HPTE . We do support that. The Linux
page size part is taken care by Kconfig. 

>
>> +
>> +	return 1;
>> +}
>>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>  
>>  pmd_t pmdp_get_and_clear(struct mm_struct *mm,
>

-aneesh