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

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Date:	Fri, 05 Apr 2013 11:48:07 +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

On 04/05/2013 11:45 AM, Ric Mason wrote:
> 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?

s/why/why not

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

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