oomd

OOMKiller has a bunch of issues. Its heuristics don't apply well across the wide range of workloads Linux provides (mobile/android? webserver? Database server? build server? desktop client? Gaming machine?), each of which would require its own tuning. (more background at https://lwn.net/Kernel/Index/#Memory_management-Out-of-memor...) That's why some orgs implemented their own solutions to avoid OOMKiller having to enter the picture, like Facebook's user-space oomd [1] or Android's LMKD [2] [1] https://github.com/facebookincubator/oomd [2] https://source.android.com/devices/tech/perf/lmkd

I think the distinction is that MemoryMax= is just an interface to the cgroupv2 setting, i.e., that rule is implemented inside the kernel and invokes the kernel's OOM killer within a cgroup. The manpage for systemd-oomd says, "systemd-oomd is a system service that uses cgroups-v2 and pressure stall information (PSI) to monitor and take action on processes before an OOM occurs in kernel space." It looks like systemd-oomd is related to (based on? from the same people as?) Facebook's oomd https://github.com/facebookincubator/oomd , whose documentation gives a bunch of reasons as to why you would prefer a userspace oomd that takes in PSI data and can be configured to proactively kill misbehaving processes instead of just letting the kernel OOM killer handle it. The major reason is time to recovery: a misbehaving process can cause a system to