Re: [PATCH 0/6] Enable parallel page migration

Balbir Singh
2017-02-22T10:52:55Z

On 22/02/17 16:55, Anshuman Khandual wrote:
> On 02/22/2017 10:34 AM, Balbir Singh wrote:
>> On Fri, Feb 17, 2017 at 04:54:47PM +0530, Anshuman Khandual wrote:
>>> This patch series is base on the work posted by Zi Yan back in
>>> November 2016 (https://lkml.org/lkml/2016/11/22/457) but includes some
>>> amount clean up and re-organization. This series depends on THP migration
>>> optimization patch series posted by Naoya Horiguchi on 8th November 2016
>>> (https://lwn.net/Articles/705879/). Though Zi Yan has recently reposted
>>> V3 of the THP migration patch series (https://lwn.net/Articles/713667/),
>>> this series is yet to be rebased.
>>>
>>> Primary motivation behind this patch series is to achieve higher
>>> bandwidth of memory migration when ever possible using multi threaded
>>> instead of a single threaded copy. Did all the experiments using a two
>>> socket X86 sytsem (Intel(R) Xeon(R) CPU E5-2650). All the experiments
>>> here have same allocation size 4K * 100000 (which did not split evenly
>>> for the 2MB huge pages). Here are the results.
>>>
>>> Vanilla:
>>>
>>> Moved 100000 normal pages in 247.000000 msecs 1.544412 GBs
>>> Moved 100000 normal pages in 238.000000 msecs 1.602814 GBs
>>> Moved 195 huge pages in 252.000000 msecs 1.513769 GBs
>>> Moved 195 huge pages in 257.000000 msecs 1.484318 GBs
>>>
>>> THP migration improvements:
>>>
>>> Moved 100000 normal pages in 302.000000 msecs 1.263145 GBs
>>
>> Is there a decrease here for normal pages?
>
> Yeah.
>
>>
>>> Moved 100000 normal pages in 262.000000 msecs 1.455991 GBs
>>> Moved 195 huge pages in 120.000000 msecs 3.178914 GBs
>>> Moved 195 huge pages in 129.000000 msecs 2.957130 GBs
>>>
>>> THP migration improvements + Multi threaded page copy:
>>>
>>> Moved 100000 normal pages in 1589.000000 msecs 0.240069 GBs **
>>
>> Ditto?
>
> Yeah, I have already mentioned about this after these data in
> the cover letter. This new flag is controlled from user space
> while invoking the system calls. Users should be careful in
> using it for scenarios where its useful and avoid it for cases
> where it hurts.

Fair enough, I wonder if _MT should be disabled for normal pages
and allow only THP migration. I think it might be worth evaluating
the overheads

>
>>
>>> Moved 100000 normal pages in 1932.000000 msecs 0.197448 GBs **
>>> Moved 195 huge pages in 54.000000 msecs 7.064254 GBs ***
>>> Moved 195 huge pages in 86.000000 msecs 4.435694 GBs ***
>>>
>>
>> Could you also comment on the CPU utilization impact of these
>> patches.
>
> Yeah, it really makes sense to analyze this impact. I have mentioned
> about this in the outstanding issues section of the series. But what
> exactly we need to analyze from CPU utilization impact point of view
> ? Like whats the probability that the work queue requested jobs will
> throw some tasks from the run queue and make them starve for some
> more time ? Could you please give some details on this ?
>

I wonder if the CPU utilization is so high that its hurting the CPU
(system time) at the cost of increased migration speeds. We may need
a trade-off (see my comment above)

Balbir Singh.