Re: [PATCH] mm: Use WQ_HIGHPRI for mm_percpu_wq.

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

Tejun Heo wrote:
> On Fri, Sep 01, 2017 at 07:07:25AM +0900, Tetsuo Handa wrote:
> > cond_resched() from !PF_WQ_WORKER threads is sufficient for PF_WQ_WORKER threads to run.
> > But cond_resched() is not sufficient for rescuer threads to start processing a pending work.
> > An explicit scheduling (e.g. schedule_timeout_*()) by PF_WQ_WORKER threads is needed for
> > rescuer threads to start processing a pending work.
> 
> I'm not even sure this is the case.  Unless I'm mistaken, in your
> workqueue dumps, the available workers couldn't even leave idle which
> means that they likely didn't get scheduled at all.  It looks like
> genuine multi minute starvation by competing direct reclaims.  What's
> the load number like while these events are in progress?

I don't know the load number because the system is unresponsive due to global
OOM. All information I can collect is via printk() from SysRq. But I guess that
it is genuine multi minute starvation by competing direct reclaims, for
I ran 1024 threads on 4 or 8 CPUs / 4GB RAM / no swap in order to test heavy
memory pressure situation where WQ_MEM_RECLAIM mm_percpu_wq work will stay
pending when I check for SysRq-t.

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