[LSF/MM/BPF TOPIC] Using hardware counters to determine hot/cold pages

[Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>]

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PowerPC architecture (POWER10) supports a Hot/Cold page tracking
facility that provides access counter and access affinity details at
configurable page size granularity [1]. I have been looking at using
this counter in different areas of the kernel such as

1) Page reclaim/demotion
2) THP utilization
3) Page promotion.

I have done some MGLRU integration and would like to discuss the
observation with the rest of the community. It is still not clear what
are the best ways to integrate these hardware counters in the Linux
kernel. Attached is the performance graph showing how the mongodb/ycsb
benchmark performs when using hardware counters with MGLRU aging. An
early RFC version of the code can be found at
https://github.com/kvaneesh/linux/commit/b472e2c8080823bb4114c286270aea3e18ffe221
. I also expect we can get some numbers w.r.t THP usage before the
conference.


X axis is the amount of memory that I am removing from the system so
that I can force more memory reclaims. The total memory available is
50GB/single NUMA node/64 CPUs,40GB database with 40GB cache
configuration.


[1]
https://hc32.hotchips.org/assets/program/conference/day1/HotChips2020_Server_Processors_IBM_Starke_POWER10_v33.pdf

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