Re: [PATCH] mm/memcontrol: log userspace OOM wait entry and completion

[Michal Hocko]

On Tue 13-10-26 04:00:34, Rohit Ner wrote:
> When a memory cgroup hits its limit with memory.oom_control
> oom_kill_disable configured, mem_cgroup_oom_synchronize() puts the
> faulting task to sleep on memcg_oom_waitq and notifies userspace OOM
> handlers to reclaim memory, enlarge limits, or terminate tasks. On
> platforms where userspace is severely stalled under memory pressure
> before a hardware or software watchdog reset, no kernel breadcrumb is
> currently emitted when a memcg enters or exits this userspace OOM wait.

Correct, this is an inherent limitation of the feature. You rely that
the userspace OOM killer implementation is correct and memory pressure
aware.

> Log rate-limited KERN_ERR messages (pr_err_ratelimited) upon entering
> and completing the userspace OOM wait in mem_cgroup_oom_synchronize(),
> including the memcg path, memory usage/limit/unevictable stats, elapsed
> waited_ms, and whether the task exited due to a fatal signal.

Isn't this something you can achieve by adding dynamic tracepoints, bpf
progs etc.? Why do we need that for all users?

-- 
Michal Hocko
SUSE Labs