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Re: [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache

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Hillf Danton <hillf.zj@alibaba-inc.com> writes:

> On Friday, October 28, 2016 1:56 PM Huang, Ying wrote: 
>> @@ -2016,10 +2021,12 @@ int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
>>  /* Racy check whether the huge page can be split */
>>  bool can_split_huge_page(struct page *page)
>>  {
>> -	int extra_pins = 0;
>> +	int extra_pins;
>> 
>>  	/* Additional pins from radix tree */
>> -	if (!PageAnon(page))
>> +	if (PageAnon(page))
>> +		extra_pins = PageSwapCache(page) ? HPAGE_PMD_NR : 0;
>> +	else
>>  		extra_pins = HPAGE_PMD_NR;
>
> extra_pins is computed in this newly added helper.
>
>>  	return total_mapcount(page) == page_count(page) - extra_pins - 1;
>>  }
>> @@ -2072,7 +2079,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>>  			ret = -EBUSY;
>>  			goto out;
>>  		}
>> -		extra_pins = 0;
>> +		extra_pins = PageSwapCache(head) ? HPAGE_PMD_NR : 0;
>
> It is also computed at the call site, so can we fold them into one?

Sounds reasonable.  I will add another argument to can_split_huge_page()
to return extra_pins, so we can avoid duplicated code and calculation.

Best Regards,
Huang, Ying

>>  		mapping = NULL;
>>  		anon_vma_lock_write(anon_vma);
>>  	} else {
>> --
>> 2.9.3

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[PATCH -v4 RESEND 0/9] THP swap: Delay splitting THP during swapping out "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 5/9] mm, THP, swap: Support to clear SWAP_HAS_CACHE for huge page "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 9/9] mm, THP, swap: Delay splitting THP during swap out "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 6/9] mm, THP, swap: Support to add/delete THP to/from swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
    Re: [PATCH -v4 RESEND 6/9] mm, THP, swap: Support to add/delete THP to/from swap cache "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-10-28 10:20 +0200
      Re: [PATCH -v4 RESEND 6/9] mm, THP, swap: Support to add/delete THP to/from swap cache "Huang\, Ying" <ying.huang@intel.com> - 2016-10-28 10:40 +0200
  [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
    Re: [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-10-28 12:20 +0200
      Re: [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache "Huang\, Ying" <ying.huang@intel.com> - 2016-10-31 02:30 +0100
  [PATCH -v4 RESEND 4/9] mm, THP, swap: Add get_huge_swap_page() "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 1/9] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 3/9] mm, THP, swap: Add swap cluster allocate/free functions "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 7/9] mm, THP: Add can_split_huge_page() "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:00 +0200
  [PATCH -v4 RESEND 2/9] mm, memcg: Support to charge/uncharge multiple swap entries "Huang, Ying" <ying.huang@intel.com> - 2016-10-28 08:10 +0200

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