Re: [PATCH 1/3] mm: introduce mm_[p4d|pud|pmd]_folded

From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Li Wang <liwang@redhat.com>, Guenter Roeck <linux@roeck-us.net>,
	Janosch Frank <frankja@linux.vnet.ibm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 1/3] mm: introduce mm_[p4d|pud|pmd]_folded
Date: Wed, 31 Oct 2018 12:02:55 +0300	[thread overview]
Message-ID: <20181031090255.bvmp3jnsdaunhzn7@kshutemo-mobl1> (raw)
In-Reply-To: <1539621759-5967-2-git-send-email-schwidefsky@de.ibm.com>

On Mon, Oct 15, 2018 at 06:42:37PM +0200, Martin Schwidefsky wrote:
> Add three architecture overrideable function to test if the
> p4d, pud, or pmd layer of a page table is folded or not.
> 
> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
> ---
>  include/linux/mm.h | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 0416a7204be3..d1029972541c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h

Shouldn't it be somewhere in asm-generic/pgtable*?

> @@ -105,6 +105,46 @@ extern int mmap_rnd_compat_bits __read_mostly;
>  #define mm_zero_struct_page(pp)  ((void)memset((pp), 0, sizeof(struct page)))
>  #endif
>  
> +/*
> + * On some architectures it depends on the mm if the p4d/pud or pmd
> + * layer of the page table hierarchy is folded or not.
> + */
> +#ifndef mm_p4d_folded
> +#define mm_p4d_folded(mm) mm_p4d_folded(mm)

Do we need to define it in generic header?

> +static inline bool mm_p4d_folded(struct mm_struct *mm)
> +{
> +#ifdef __PAGETABLE_P4D_FOLDED
> +	return 1;
> +#else
> +	return 0;
> +#endif

Maybe
	return __is_defined(__PAGETABLE_P4D_FOLDED);

?

-- 
 Kirill A. Shutemov