psi-monitor: Raise default memory pressure kill threshold to 40% for EOS 5.1 #406
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The more proper way to do this would be to determine them in configure, but for such a basic C program I think we can just blindly turn them all on and error on warnings. https://phabricator.endlessm.com/T35318
Very basic `getopt_long` usage to allow adding options. https://phabricator.endlessm.com/T35318
Show the current pressure, the threshold and the recovery time when triggering an OOM to give more of a clue about what's happening. https://phabricator.endlessm.com/T35318
This will allow easier experimentation to tune the defaults. https://phabricator.endlessm.com/T35318
Current PSI monitor's default memory pressure threshold is 10%. However, after testing on 3 low end systems, it seems that this threshold is far too low. You can observe 10% full memory pressure still with a decent amount of RAM and zram available, with only minor observable effects on the UI. According to my recollection, 10% was quite generous before, but over the years this seems to have changed, perhaps due to improved ways the kernel measures things, improved behaviour under load, and innovations like multi-gen LRU. Experimenting and pushing these devices to the max, it seems like 40% is a decent threshold now, consistent over 3 devices tested. At 35% you are seeing some mouse lag but can still close apps without real difficulty. At 40% you start to lose the ability to use the mouse. https://phabricator.endlessm.com/T35318
Jian-Hong pointed out that I put the wrong number in the previous commit.
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Backport raising PSI monitor's default memory pressure threshold to 40% to EOS 5.1.
https://phabricator.endlessm.com/T35318