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

[David Gibson <dwg@au1.ibm.com>]

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On Mon, Apr 29, 2013 at 01:21:49AM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> 
> We enable only if the we support 16MB page size.
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> ---
>  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).

> +	/*
> +	 * 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.

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

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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