linux-kernel - Re: [PATCH -v3 08/10] mm, THP: Add can_split_huge

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Message-ID: <87h99q5npc.fsf@yhuang-mobile.sh.intel.com>
Date:   Thu, 08 Sep 2016 10:02:55 -0700
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Huang\, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <tim.c.chen@...el.com>, <dave.hansen@...el.com>,
        <andi.kleen@...el.com>, <aaron.lu@...el.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ebru Akagunduz <ebru.akagunduz@...il.com>
Subject: Re: [PATCH -v3 08/10] mm, THP: Add can_split_huge_page()

Hi, Kirill,

Thanks for your comments!

"Kirill A. Shutemov" <kirill@...temov.name> writes:
> On Wed, Sep 07, 2016 at 09:46:07AM -0700, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@...el.com>
>> 
>> Separates checking whether we can split the huge page from
>> split_huge_page_to_list() into a function.  This will help to check that
>> before splitting the THP (Transparent Huge Page) really.
>> 
>> This will be used for delaying splitting THP during swapping out.  Where
>> for a THP, we will allocate a swap cluster, add the THP into the swap
>> cache, then split the THP.  To avoid the unnecessary operations for the
>> un-splittable THP, we will check that firstly.
>> 
>> There is no functionality change in this patch.
>> 
>> Cc: Andrea Arcangeli <aarcange@...hat.com>
>> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>> Cc: Ebru Akagunduz <ebru.akagunduz@...il.com>
>> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
>> ---
>>  include/linux/huge_mm.h |  6 ++++++
>>  mm/huge_memory.c        | 13 ++++++++++++-
>>  2 files changed, 18 insertions(+), 1 deletion(-)
>> 
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 9b9f65d..a0073e7 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -94,6 +94,7 @@ extern unsigned long thp_get_unmapped_area(struct file *filp,
>>  extern void prep_transhuge_page(struct page *page);
>>  extern void free_transhuge_page(struct page *page);
>>  
>> +bool can_split_huge_page(struct page *page);
>>  int split_huge_page_to_list(struct page *page, struct list_head *list);
>>  static inline int split_huge_page(struct page *page)
>>  {
>> @@ -176,6 +177,11 @@ static inline void prep_transhuge_page(struct page *page) {}
>>  
>>  #define thp_get_unmapped_area	NULL
>>  
>> +static inline bool
>> +can_split_huge_page(struct page *page)
>> +{
>
> BUILD_BUG() should be appropriate here.

Yes.  Will add it.

>> +	return false;
>> +}

Best Regards,
Huang, Ying