Re: [PATCH -V3 0/3] memory tiering: hot page selection

[Huang, Ying]

Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:

> On 6/14/2022 4:16 PM, Huang Ying wrote:
>> To optimize page placement in a memory tiering system with NUMA
>> balancing, the hot pages in the slow memory nodes need to be
>> identified.  Essentially, the original NUMA balancing implementation
>> selects the mostly recently accessed (MRU) pages to promote.  But this
>> isn't a perfect algorithm to identify the hot pages.  Because the
>> pages with quite low access frequency may be accessed eventually given
>> the NUMA balancing page table scanning period could be quite long
>> (e.g. 60 seconds).  So in this patchset, we implement a new hot page
>> identification algorithm based on the latency between NUMA balancing
>> page table scanning and hint page fault.  Which is a kind of mostly
>> frequently accessed (MFU) algorithm.
>> In NUMA balancing memory tiering mode, if there are hot pages in
>> slow
>> memory node and cold pages in fast memory node, we need to
>> promote/demote hot/cold pages between the fast and cold memory nodes.
>> A choice is to promote/demote as fast as possible.  But the CPU
>> cycles
>> and memory bandwidth consumed by the high promoting/demoting
>> throughput will hurt the latency of some workload because of accessing
>> inflating and slow memory bandwidth contention.
>> A way to resolve this issue is to restrict the max
>> promoting/demoting
>> throughput.  It will take longer to finish the promoting/demoting.
>> But the workload latency will be better.  This is implemented in this
>> patchset as the page promotion rate limit mechanism.
>> The promotion hot threshold is workload and system configuration
>> dependent.  So in this patchset, a method to adjust the hot threshold
>> automatically is implemented.  The basic idea is to control the number
>> of the candidate promotion pages to match the promotion rate limit.
>> We used the pmbench memory accessing benchmark tested the patchset
>> on
>> a 2-socket server system with DRAM and PMEM installed.  The test
>> results are as follows,
>> 		pmbench score		promote rate
>> 		 (accesses/s)			MB/s
>> 		-------------		------------
>> base		  146887704.1		       725.6
>> hot selection     165695601.2		       544.0
>> rate limit	  162814569.8		       165.2
>> auto adjustment	  170495294.0                  136.9
>>  From the results above,
>> With hot page selection patch [1/3], the pmbench score increases
>> about
>> 12.8%, and promote rate (overhead) decreases about 25.0%, compared with
>> base kernel.
>> With rate limit patch [2/3], pmbench score decreases about 1.7%, and
>> promote rate decreases about 69.6%, compared with hot page selection
>> patch.
>> With threshold auto adjustment patch [3/3], pmbench score increases
>> about 4.7%, and promote rate decrease about 17.1%, compared with rate
>> limit patch.
>
> I did a simple testing with mysql on my machine which contains 1 DRAM
> node (30G) and 1 PMEM node (126G).
>
> sysbench /usr/share/sysbench/oltp_read_write.lua \
> ......
> --tables=200 \
> --table-size=1000000 \
> --report-interval=10 \
> --threads=16 \
> --time=120
>
> The tps can be improved about 5% from below data, and I think this is
> a good start to optimize the promotion. So for this series, please
> feel free to add:
>
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>
> Without this patchset:
>  transactions:                        2080188 (3466.48 per sec.)
>
> With this patch set:
>  transactions:                        2174296 (3623.40 per sec.)

Thanks a lot!

Best Regards,
Huang, Ying