Subject: Re: [RFC 4/9] powerpc/mm: Split huge_pte_alloc function for BOOK3S 64K

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 10 Mar 2016 01:25:53 +0530

Anshuman Khandual <[email-masked]> writes:

> [ text/plain ]
> From: root <[email-masked]>
>
> Currently the 'huge_pte_alloc' function has two versions, one for the
> BOOK3S and the other one for the BOOK3E platforms. This change splits
> the BOOK3S version into two parts, one for the 4K page size based
> implementation and the other one for the 64K page sized implementation.
> This change is one of the prerequisites towards enabling GENERAL_HUGETLB
> implementation for BOOK3S 64K based huge pages.

I really wish we reduce #ifdefs in C code and start splitting hash
and nonhash code out where ever we can. 

What we really want here is a book3s version and in book3s version use
powerpc specific huge_pte_alloc only if GENERAL_HUGETLB was not defined.
Don't limit it to 64k linux page size. We should select between powerpc
specific implementation and generic code using GENERAL_HUGETLB define.

>
> Signed-off-by: Anshuman Khandual <[email-masked]>
> ---
>  arch/powerpc/mm/hugetlbpage.c | 67 +++++++++++++++++++++++++++----------------
>  1 file changed, 43 insertions(+), 24 deletions(-)
>
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index 744e24b..a49c6ae 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -59,6 +59,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
>  	return __find_linux_pte_or_hugepte(mm->pgd, addr, NULL, NULL);
>  }
>
> +#if !defined(CONFIG_PPC_64K_PAGES) || !defined(CONFIG_PPC_BOOK3S_64)
>  static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
>  			   unsigned long address, unsigned pdshift, unsigned pshift)
>  {
> @@ -117,6 +118,7 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
>  	spin_unlock(&mm->page_table_lock);
>  	return 0;
>  }
> +#endif /* !defined(CONFIG_PPC_64K_PAGES) || !defined(CONFIG_PPC_BOOK3S_64) */
>
>  /*
>   * These macros define how to determine which level of the page table holds
> @@ -131,6 +133,7 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
>  #endif
>
>  #ifdef CONFIG_PPC_BOOK3S_64
> +#ifdef CONFIG_PPC_4K_PAGES
>  /*
>   * At this point we do the placement change only for BOOK3S 64. This would
>   * possibly work on other subarchs.
> @@ -146,32 +149,23 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz
>
>  	addr &= ~(sz-1);
>  	pg = pgd_offset(mm, addr);
> -
> -	if (pshift == PGDIR_SHIFT)
> -		/* 16GB huge page */
> -		return (pte_t *) pg;
> -	else if (pshift > PUD_SHIFT)
> -		/*
> -		 * We need to use hugepd table
> -		 */
> +	if (pshift > PUD_SHIFT) {
>  		hpdp = (hugepd_t *)pg;
> -	else {
> -		pdshift = PUD_SHIFT;
> -		pu = pud_alloc(mm, pg, addr);
> -		if (pshift == PUD_SHIFT)
> -			return (pte_t *)pu;
> -		else if (pshift > PMD_SHIFT)
> -			hpdp = (hugepd_t *)pu;
> -		else {
> -			pdshift = PMD_SHIFT;
> -			pm = pmd_alloc(mm, pu, addr);
> -			if (pshift == PMD_SHIFT)
> -				/* 16MB hugepage */
> -				return (pte_t *)pm;
> -			else
> -				hpdp = (hugepd_t *)pm;
> -		}
> +		goto hugepd_search;
> +	}
> +
> +	pdshift = PUD_SHIFT;
> +	pu = pud_alloc(mm, pg, addr);
> +	if (pshift > PMD_SHIFT) {
> +		hpdp = (hugepd_t *)pu;
> +		goto hugepd_search;
>  	}
> +
> +	pdshift = PMD_SHIFT;
> +	pm = pmd_alloc(mm, pu, addr);
> +	hpdp = (hugepd_t *)pm;
> +
> +hugepd_search:
>  	if (!hpdp)
>  		return NULL;
>
> @@ -184,6 +178,31 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz
>  }
>
>  #else
> +pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz)
> +{
> +	pgd_t *pg;
> +	pud_t *pu;
> +	pmd_t *pm;
> +	unsigned pshift = __ffs(sz);
> +
> +	addr &= ~(sz-1);
> +	pg = pgd_offset(mm, addr);
> +
> +	if (pshift == PGDIR_SHIFT)	/* 16GB Huge Page */
> +		return (pte_t *)pg;
> +
> +	pu = pud_alloc(mm, pg, addr);	/* NA, skipped */
> +	if (pshift == PUD_SHIFT)
> +		return (pte_t *)pu;
> +
> +	pm = pmd_alloc(mm, pu, addr);	/* 16MB Huge Page */
> +	if (pshift == PMD_SHIFT)
> +		return (pte_t *)pm;
> +
> +	return NULL;
> +}
> +#endif
> +#else
>
>  pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr, unsigned long sz)
>  {
> -- 
> 2.1.0