linux-kernel - Re: [PATCH] mm/thp: fix comments in transparent_hugepage

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Date:	Thu, 5 Sep 2013 11:04:22 +0800
From:	Jianguo Wu <wujianguo@...wei.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
CC:	Jianguo Wu <wujianguo106@...il.com>, <akpm@...ux-foundation.org>,
	<aarcange@...hat.com>, <kirill.shutemov@...ux.intel.com>,
	<mgorman@...e.de>, <xiaoguangrong@...ux.vnet.ibm.com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/thp: fix comments in transparent_hugepage_flags

Hi Wanpeng,

On 2013/9/5 10:11, Wanpeng Li wrote:

> Hi Jianguo,
> On Wed, Sep 04, 2013 at 09:30:22PM +0800, Jianguo Wu wrote:
>> Since commit d39d33c332(thp: enable direct defrag), defrag is enable
>> for all transparent hugepage page faults by default, not only in
>> MADV_HUGEPAGE regions.
>>
>> Signed-off-by: Jianguo Wu <wujianguo@...wei.com>
>> ---
>> mm/huge_memory.c | 6 ++----
>> 1 file changed, 2 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index a92012a..abf047e 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -28,10 +28,8 @@
>>
>> /*
>>  * By default transparent hugepage support is enabled for all mappings
> 
> This is also stale. TRANSPARENT_HUGEPAGE_ALWAYS is not configured by default in
> order that avoid to risk increase the memory footprint of applications w/o a 
> guaranteed benefit.
> 

Right, how about this:

By default transparent hugepage support is disabled in order that avoid to risk
increase the memory footprint of applications w/o a guaranteed benefit, and
khugepaged scans all mappings when transparent hugepage enabled.
Defrag is invoked by khugepaged hugepage allocations and by page faults for all
hugepage allocations.

Thanks,
Jianguo Wu

> Regards,
> Wanpeng Li 
> 
>> - * and khugepaged scans all mappings. Defrag is only invoked by
>> - * khugepaged hugepage allocations and by page faults inside
>> - * MADV_HUGEPAGE regions to avoid the risk of slowing down short lived
>> - * allocations.
>> + * and khugepaged scans all mappings. Defrag is invoked by khugepaged
>> + * hugepage allocations and by page faults for all hugepage allocations.
>>  */
>> unsigned long transparent_hugepage_flags __read_mostly =
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
>> -- 
>> 1.8.1.2
>>
>> --
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> 
> --
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> 
> 



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