Re: [RFC PATCH v6 0/5] mm: Hot page tracking and promotion infrastructure

[Bharata B Rao]

Graph500 results

Test system details
-------------------
3 node AMD Zen5 system with 2 regular NUMA nodes (0, 1) and a CXL node (2)

$ numactl -H
available: 3 nodes (0-2)
node 0 cpus: 0-95,192-287
node 0 size: 128460 MB
node 1 cpus: 96-191,288-383
node 1 size: 128893 MB
node 2 cpus:
node 2 size: 257993 MB
node distances:
node   0   1   2
  0:  10  32  50
  1:  32  10  60
  2:  255  255  10

Hotness sources
---------------
NUMAB0 - Without NUMA Balancing in base case and with no source enabled
         in the pghot case. No migrations occur.
NUMAB2 - Existing hot page promotion for the base case and
         use of hint faults as source in the pghot case.
NUMAB3 - Enabled both regular and tiering mode of NUMA Balancing
         (kernel.numa_balancing=3)

Pghot by default promotes after two accesses but for NUMAB2 source,
promotion is done after one access to match the base behaviour.
(/sys/kernel/debug/pghot/freq_threshold=1)

Graph500 details
----------------
Command: mpirun -n 128 --bind-to core --map-by core
graph500/src/graph500_reference_bfs 28 16

After the graph creation, the processes are stopped and data is migrated
to CXL node 2 before continuing so that BFS phase starts accessing lower
tier memory.

Total memory usage is slightly over 100GB and will fit within Node 0 and 1.
Hence there is no memory pressure to induce demotions.

harmonic_mean_TEPS - Higher is better
=====================================================================================
                        Base            Base            pghot-default
pghot-precise
                        NUMAB0          NUMAB2          NUMAB2          NUMAB2
=====================================================================================
harmonic_mean_TEPS      5.07693e+08     7.08679e+08     5.56854e+08     7.39417e+08
mean_time               8.45968         6.06046         7.71283         5.80853
median_TEPS             5.08914e+08     7.23181e+08     5.51614e+08     7.58993e+08
max_TEPS                5.15226e+08     1.01654e+09     7.75233e+08     9.69136e+08

pgpromote_success       0               13797978        13746431        13752523
numa_pte_updates        0               26727341        39998363        48374479
numa_hint_faults        0               13798301        24459996        32728927
=====================================================================================
                                                        pghot-default
                                                        NUMAB3
=====================================================================================
harmonic_mean_TEPS                                      7.18678e+08
mean_time                                               5.97614
median_TEPS                                             7.376e+08
max_TEPS                                                7.47337e+08

pgpromote_success                                       13821625
numa_pte_updates                                        93534398
numa_hint_faults                                        69164048
=====================================================================================
- The base case shows a good improvement with NUMAB2 in harmonic_mean_TEPS.
- The same improvement gets maintained with pghot-precise too.
- pghot-default mode doesn't show benefit even when achieving similar page promotion
  numbers. This mode doesn't track accessing NID and by default promotes to NID=0
  which probably isn't all that beneficial as processes are running on both Node 0
  and Node 1.
- pghot-default recovers the performance when balancing between toptier nodes
  0 and 1 is enabled in addition to hot page promotion.