linux-kernel - Re: [RFC 2/2] x86_64: expand kernel stack to 16K

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Date:	Fri, 30 May 2014 09:32:19 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K

On Fri, May 30, 2014 at 10:21:13AM +1000, Dave Chinner wrote:
> On Thu, May 29, 2014 at 08:06:49PM -0400, Dave Jones wrote:
> > On Fri, May 30, 2014 at 09:53:08AM +1000, Dave Chinner wrote:
> > 
> >  > That sounds like a plan. Perhaps it would be useful to add a
> >  > WARN_ON_ONCE(stack_usage > 8k) (or some other arbitrary depth beyond
> >  > 8k) so that we get some indication that we're hitting a deep stack
> >  > but the system otherwise keeps functioning. That gives us some
> >  > motivation to keep stack usage down but isn't a fatal problem like
> >  > it is now....
> > 
> > We have check_stack_usage() and DEBUG_STACK_USAGE for this.
> > Though it needs some tweaking if we move to 16K
> 
> Right, but it doesn't throw loud warnings when a specific threshold
> is reached - it just issues a quiet message when a process exits
> telling you what the maximum was without giving us a stack to chew
> on....

But we could enhance the inform so notice the risk to the user.
as follow

...
"kworker/u24:1 (94) used greatest stack depth: 8K bytes left, it means
there is some horrible stack hogger in your kernel. Please report it
the LKML and enable stacktrace to investigate who is culprit"


> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com
> 
> --
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-- 
Kind regards,
Minchan Kim
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