When running under a cgroup limit, get_cgroup() reported
stat.usage_in_bytes (memory.current on v2, memory.usage_in_bytes on v1)
as the process memory usage. That counter includes all page
cache, including cold reclaimable cache (inactive_file). For a
workload that writes logs and spool to disk, cold cache can dominate:
on a real pod memory.current was ~51GB while inactive_file was ~46GB
and the true non-cache footprint was ~1.8GB. kumod saw usage near its
limit, hit get_headroom() == 0, and ran
shrink_ready_queue_due_to_low_mem
and other reductions against pressure that was almost entirely
reclaimable cache the kernel would drop before any OOM.
Report the working set instead:
```
working_set = max(memory.current - inactive_file, anon)
```
This matches container_memory_working_set_bytes (kubelet/cAdvisor) and
the kernel's own reclaimability accounting. It still counts everything
that can drive an OOM: anonymous memory, dirty page cache, active_file,
tmpfs/shm, and slab.
Signed-off-by: Daniel Schaaff <daniel@danielschaaff.com>
closes: https://github.com/KumoCorp/kumomta/pull/549
Daniel Schaaff
c17c123402