linux-kernel - Re: [PATCHv2, RFC 07/30] thp, mm: introduce mapping_can_have

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Message-ID: <515E48D1.2090505@gmail.com>
Date:	Fri, 05 Apr 2013 11:45:21 +0800
From:	Ric Mason <ric.masonn@...il.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2, RFC 07/30] thp, mm: introduce mapping_can_have_hugepages()
 predicate

Hi Kirill,
On 03/15/2013 01:50 AM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>
> Returns true if mapping can have huge pages. Just check for __GFP_COMP
> in gfp mask of the mapping for now.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>   include/linux/pagemap.h |   10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index e3dea75..3521b0d 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -84,6 +84,16 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
>   				(__force unsigned long)mask;
>   }
>   
> +static inline bool mapping_can_have_hugepages(struct address_space *m)
> +{
> +	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> +		gfp_t gfp_mask = mapping_gfp_mask(m);
> +		return !!(gfp_mask & __GFP_COMP);

I always see !! in kernel, but why check directly instead of have !! prefix?

> +	}
> +
> +	return false;
> +}
> +
>   /*
>    * The page cache can done in larger chunks than
>    * one page, because it allows for more efficient

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