On 3/25/19 11:37 AM, Michael S. Tsirkin wrote:
> On Mon, Mar 25, 2019 at 10:27:46AM -0400, Nitesh Narayan Lal wrote:
>> I performed some experiments to see if the current implementation of
>> hinting breaks THP. I used AnonHugePages to track the THP pages
>> currently in use and memhog as the guest workload.
>> Setup:
>> Host Size: 30GB (No swap)
>> Guest Size: 15GB
>> THP Size: 2MB
>> Process: Guest is installed with different kernels to hint different
>> granularities(MAX_ORDER - 1, MAX_ORDER - 2 and MAX_ORDER - 3). Memhog 
>> 15G is run multiple times in the same guest to see AnonHugePages usage
>> in the host.
>>
>> Observation:
>> There is no THP split for order MAX_ORDER - 1 & MAX_ORDER - 2 whereas
>> for hinting granularity MAX_ORDER - 3 THP does split irrespective of
>> MADVISE_FREE or MADVISE_DONTNEED.
>> -- 
>> Regards
>> Nitesh
>>
> This is on x86 right?
Yes.
>  So THP is 2M and MAX_ORDER is 8M.
> MAX_ORDER - 3 ==> 1M.
> Seems to work out.
>
>
-- 
Regards
Nitesh