Detect and prevent excessive paging/swapping about nohang

[hakavlad]

$ timeout 60 stress -m 40 --vm-bytes 1G
stress: info: [398894] dispatching hogs: 0 cpu, 0 io, 40 vm, 0 hdd

$ psi2log -m2
Starting psi2log, target: SYSTEM_WIDE, mode: 2, interval: 2 sec, log file is not set, suppress output: False
PSI source dir: /proc/pressure/, source files: cpu, io, memory
All memory locked with MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT
======|=============|=============|
 cpu  |      io     |    memory   |
----- | ----------- | ----------- |
 some |  some  full |  some  full | interval
----- | ----- ----- | ----- ----- | --------
  0.7 |   0.0   0.0 |   0.0   0.0 | 2.002
  0.7 |   0.3   0.2 |   0.0   0.0 | 2.002
  0.8 |   0.4   0.3 |   0.5   0.2 | 2.002
  0.7 |   0.0   0.0 |   0.0   0.0 | 2.001
  0.9 |   0.2   0.2 |   0.0   0.0 | 2.002
  0.8 |   0.0   0.0 |   0.0   0.0 | 2.002
  0.9 |   0.0   0.0 |   0.0   0.0 | 2.002
  0.8 |   0.3   0.2 |   0.0   0.0 | 2.002
 18.0 |   0.2   0.2 |  21.8   4.0 | 2.002
 77.0 |   1.1   0.0 |  94.2  20.4 | 2.002
 80.6 |   2.1   0.0 |  92.8  23.5 | 2.002
 74.0 |   2.6   0.0 |  91.1  14.9 | 2.002
 77.1 |   2.3   0.0 |  91.9  15.6 | 2.002
 73.0 |   2.2   0.0 |  90.1  16.7 | 2.002
 78.6 |   3.6   0.0 |  90.8  14.9 | 2.003
 74.3 |   4.6   0.0 |  89.6  15.0 | 2.001
 73.7 |   4.3   0.0 |  90.7  19.8 | 2.002
 74.9 |   2.2   0.0 |  90.9  24.1 | 2.001
 78.6 |   1.1   0.0 |  88.6  14.3 | 2.002
 84.3 |   1.8   0.0 |  93.1  14.3 | 2.002
 83.0 |   5.1   0.1 |  87.7  12.9 | 2.002
 82.5 |   4.8   0.3 |  87.4  12.8 | 2.002
 84.2 |   3.9   0.0 |  90.4  14.3 | 2.002
 74.5 |   3.1   0.1 |  84.7  12.3 | 2.001
 74.5 |   2.5   0.0 |  86.1  13.3 | 2.002
 74.7 |   0.7   0.0 |  86.2  12.8 | 2.002
 74.9 |   1.7   0.0 |  88.0  14.1 | 2.002
 73.3 |   0.8   0.0 |  81.4  13.3 | 2.002
 80.0 |   1.8   0.0 |  88.5  14.8 | 2.002
 73.5 |   2.6   0.0 |  82.0  13.7 | 2.002
 66.4 |   1.5   0.0 |  76.1  14.0 | 2.002
 68.8 |   1.1   0.0 |  79.8  13.6 | 2.002
 70.1 |   1.5   0.0 |  81.8  13.6 | 2.002
 71.8 |   3.0   0.0 |  75.7  14.2 | 2.002
 71.9 |   1.4   0.0 |  83.0  14.4 | 2.002
 72.9 |   1.5   0.0 |  83.4  14.9 | 2.001
 71.7 |   1.5   0.0 |  85.7  14.7 | 2.002
 75.4 |   2.5   0.0 |  88.6  15.6 | 2.002
 83.8 |   1.1   0.0 |  70.4  11.6 | 2.002
 30.9 |   1.4   1.2 |   2.0   0.1 | 2.002
  2.9 |   3.4   3.1 |   1.3   0.0 | 2.002
^C
----- | ----- ----- | ----- ----- | --------
 84.3 |   5.1   3.1 |  94.2  24.1 | peaks

This is how PSI reacts to active swapping.

[hakavlad]

I think the PSI is already doing what it needs to do. This is probably a more accurate indicator than swapping.