Re: [PATCH] mm, oom: avoid printk() iteration under RCU

[Michal Hocko <mhocko@suse.com>]

On Thu 18-07-19 22:50:14, Tetsuo Handa wrote:
> On 2019/07/18 17:30, Michal Hocko wrote:
> > On Wed 17-07-19 19:55:01, Tetsuo Handa wrote:
> >> Currently dump_tasks() might call printk() for many thousands times under
> >> RCU, which might take many minutes for slow consoles.
> > 
> > Is is even wise to enable dumping tasks on systems with thousands of
> > tasks and slow consoles? I mean you still have to call printk that is
> > slow that many times. So why do we actually care? Because of RCU stall
> > warnings?
> > 
> 
> That's a stupid question. WE DO CARE.

-ENOARGUMENT

> We are making efforts for avoid calling printk() on each thread group (e.g.
> 
>   commit 0c1b2d783cf34324 ("mm/oom_kill: remove the wrong fatal_signal_pending() check in oom_kill_process()")

removes fatal_signal_pending rather than focusing on printk

>   commit b2b469939e934587 ("proc, oom: do not report alien mms when setting oom_score_adj"))

removes a printk of a dubious value.

> ) under RCU and this patch is one of them (except that we can't remove
> printk() for dump_tasks() case).

No, this one adds a complexity for something that is not clearly a huge
win or the win is not explained properly.

-- 
Michal Hocko
SUSE Labs