linux-kernel - Re: [PATCH] oom_kill: add option to disable dump

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Message-ID: <20151027162047.GK9891@dhcp22.suse.cz>
Date:	Tue, 27 Oct 2015 17:20:47 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Aristeu Rozanski <arozansk@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Greg Thelen <gthelen@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	cgroups@...r.kernel.org
Subject: Re: [PATCH] oom_kill: add option to disable dump_stack()

On Tue 27-10-15 11:43:42, Aristeu Rozanski wrote:
> Hi Michal,
> On Tue, Oct 27, 2015 at 09:09:21AM +0100, Michal Hocko wrote:
> > On Mon 26-10-15 13:40:49, Aristeu Rozanski wrote:
> > > Hi Michal,
> > > On Mon, Oct 26, 2015 at 06:20:12PM +0100, Michal Hocko wrote:
> > [...]
> > > > Would it make more sense to distinguish different parts of the OOM
> > > > report by loglevel properly?
> > > > pr_err - killed task report
> > > > pr_warning - oom invocation + memory info
> > > > pr_notice - task list
> > > > pr_info - stack trace
> > > 
> > > That'd work, yes, but I'd think the stack trace would be pr_debug. At a
> > > point that you suspect the OOM killer isn't doing the right thing picking
> > > up tasks and you need more information.
> > 
> > Stack trace should be independent on the oom victim selection because
> > the selection should be as much deterministic as possible - so it should
> > only depend on the memory consumption. I do agree that the exact trace
> > is not very useful for the (maybe) majority of OOM reports. I am trying
> > to remember when it was really useful the last time and have trouble to
> > find an example. So I would tend to agree that pr_debug would me more
> > suitable.
> 
> Only problem I see so far with this approach is that it'll require
> reworing show_stack() on all architectures in order to be able to pass
> and use log level and I'm wondering if it's something people will find
> useful for other uses.

Yes this is a mess. But I think it is worth cleaning up.
dump_stack_print_info (arch independent) has a log level parameter.
show_stack_log_lvl (x86) has a loglevel parameter which is unused.

I haven't checked other architectures but the transition doesn't have to
be all at once I guess.
-- 
Michal Hocko
SUSE Labs
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