3 ms·

"earlyoom is just polling"? > systemd-oomd periodically polls PSI statistics for the system and those cgroups to decide when to take action. It's unclear if t

"earlyoom is just polling"? > systemd-oomd periodically polls PSI statistics for the system and those cgroups to decide when to take action. It's unclear if the docs for systemd-oomd are incorrect or misleading; I do see from the kernel.org link that the recommended usage pattern is to use the `poll` system call, which in this context would mean "not polling", if I understand correctly.

100721 1y ago
Unrelated to the topic, it seems awfully unintuitive to name a function ‘poll’ if the result is ‘not polling.’ I’m guessing there’s some history and maybe backwards-compatible rewrites?
- unilynx 1y ago
  Poll takes a timeout parameter. ‘Not polling’ is just a really long timeout
- friendzis 1y ago
  "Let the underlying platform do the polling and return once the condition is met"
- CGamesPlay 1y ago
  Specifically, earlyoom’s README says it repeatedly checks (“periodically polls”) the memory pressure, using CPU each time even when there is no change. The “poll” system call waits for the kernel to notify the process that the file has changed, using no CPU until the call resolves. It’s unclear what systemd-oomd does, because it uses the phrase “periodically polls”,
  - immibis 1y ago
    The "poll" system call does not wait until a file changes.
    - CGamesPlay 1y ago
      s/the file has changed/it has published new data to the file descriptor/ See https://docs.kernel.org/accounting/psi.html https://docs.kernel.org/accounting/psi.html
TheDong 1y ago
systemd-oomd, oomd, and earlyoom all do poll for when to actually take action on OOM conditions. What I was trying to say is that the actual information on when there's memory pressure is more accurate for systemd-oomd / oomd because they use PSI, which the kernel itself is updating over time, and they just poll that, while earlyoom is also internally making its own estimates at a lower granularity than the kernel does.

100721 1y ago

Unrelated to the topic, it seems awfully unintuitive to name a function ‘poll’ if the result is ‘not polling.’ I’m guessing there’s some history and maybe backwards-compatible rewrites?

unilynx 1y ago
Poll takes a timeout parameter. ‘Not polling’ is just a really long timeout
friendzis 1y ago
"Let the underlying platform do the polling and return once the condition is met"
CGamesPlay 1y ago
Specifically, earlyoom’s README says it repeatedly checks (“periodically polls”) the memory pressure, using CPU each time even when there is no change. The “poll” system call waits for the kernel to notify the process that the file has changed, using no CPU until the call resolves. It’s unclear what systemd-oomd does, because it uses the phrase “periodically polls”,
- immibis 1y ago
  The "poll" system call does not wait until a file changes.
  - CGamesPlay 1y ago
    s/the file has changed/it has published new data to the file descriptor/ See https://docs.kernel.org/accounting/psi.html https://docs.kernel.org/accounting/psi.html

TheDong 1y ago

systemd-oomd, oomd, and earlyoom all do poll for when to actually take action on OOM conditions. What I was trying to say is that the actual information on when there's memory pressure is more accurate for systemd-oomd / oomd because they use PSI, which the kernel itself is updating over time, and they just poll that, while earlyoom is also internally making its own estimates at a lower granularity than the kernel does.