Re: DOM Worker: page allocation stalls (4.9.13)

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Michal Hocko wrote:
> > If you can rebuild your kernel, calling dump_tasks() in mm/oom_kill.c when
> > you hit warn_alloc() warnings might help.
> 
> I do not really see how this would help much. If anything watching for
> /proc/vmstat counters would tell us much more.

Under memory pressure, read()/write() syscalls might involve significant delay
(including reading from /sys/kernel/debug/tracing/trace_pipe and writing to
a log file). Unless all problems are contained in a cgroup (which means that
administrators can diagnose from outside of that cgroup), it is silly to try to
read memory related information of a stalling system using userspace interface.

Therefore, automatic printk() is helpful than trying to start "cat /proc/vmstat"
 from a shell. I wish there is a kernel function which does
"cat /proc/some_file" and/or "cat /sys/kernel/debug/tracing/trace_pipe" and
sends the output to printk() so that such actions will not involve significant
delay under memory pressure.

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