Subject: Re: [PATCH] powerpc/mm: numa pte should be handled via slow path in get_user_pages_fast

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 07 Apr 2014 09:49:33 +1000

On Wed, 2014-04-02 at 21:37 +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <[email-masked]>
> 
> We need to handle numa pte via the slow path

Is this -stable material ? If yes how far back ?

Cheers,
Ben.

> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/mm/gup.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/powerpc/mm/gup.c b/arch/powerpc/mm/gup.c
> index c5f734e20b0f..d8746684f606 100644
> --- a/arch/powerpc/mm/gup.c
> +++ b/arch/powerpc/mm/gup.c
> @@ -36,6 +36,11 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
>  	do {
>  		pte_t pte = ACCESS_ONCE(*ptep);
>  		struct page *page;
> +		/*
> +		 * Similar to the PMD case, NUMA hinting must take slow path
> +		 */
> +		if (pte_numa(pte))
> +			return 0;
>  
>  		if ((pte_val(pte) & mask) != result)
>  			return 0;
> @@ -75,6 +80,14 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
>  		if (pmd_none(pmd) || pmd_trans_splitting(pmd))
>  			return 0;
>  		if (pmd_huge(pmd) || pmd_large(pmd)) {
> +			/*
> +			 * NUMA hinting faults need to be handled in the GUP
> +			 * slowpath for accounting purposes and so that they
> +			 * can be serialised against THP migration.
> +			 */
> +			if (pmd_numa(pmd))
> +				return 0;
> +
>  			if (!gup_hugepte((pte_t *)pmdp, PMD_SIZE, addr, next,
>  					 write, pages, nr))
>  				return 0;