Re: [PATCH] mm: respect the __GFP_NOWARN flag when warning about stalls

[Tetsuo Handa]

Vlastimil Babka wrote:
> On 09/13/2017 03:54 PM, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> >> Let's see what others think about this.
> > 
> > Whether __GFP_NOWARN should warn about stalls is not a topic to discuss.
> 
> It is the topic of this thread, which tries to address a concrete
> problem somebody has experienced. In that context, the rest of your
> concerns seem to me not related to this problem, IMHO.

I suggested replacing warn_alloc() with safe/useful one rather than tweaking
warn_alloc() about __GFP_NOWARN.

> 
> > I consider warn_alloc() for reporting stalls is broken. It fails to provide
> > backtrace of stalling location. For example, OOM lockup with oom_lock held
> > cannot be reported by warn_alloc(). It fails to provide readable output when
> > called concurrently. For example, concurrent calls can cause printk()/
> > schedule_timeout_killable() lockup with oom_lock held. printk() offloading is
> > not an option, for there will be situations where printk() offloading cannot
> > be used (e.g. queuing via printk() is faster than writing to serial consoles
> > which results in unreadable logs due to log_bug overflow).