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

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Message-ID: <20140528092717.GA17220@pd.tnic>
Date:	Wed, 28 May 2014 11:27:17 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Minchan Kim <minchan@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, 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@...tcorp.com.au,
	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 Wed, May 28, 2014 at 03:53:59PM +0900, Minchan Kim wrote:
> While I play inhouse patches with much memory pressure on qemu-kvm,
> 3.14 kernel was randomly crashed. The reason was kernel stack overflow.
> 
> When I investigated the problem, the callstack was a little bit deeper
> by involve with reclaim functions but not direct reclaim path.
> 
> I tried to diet stack size of some functions related with alloc/reclaim
> so did a hundred of byte but overflow was't disappeard so that I encounter
> overflow by another deeper callstack on reclaim/allocator path.
> 
> Of course, we might sweep every sites we have found for reducing
> stack usage but I'm not sure how long it saves the world(surely,
> lots of developer start to add nice features which will use stack
> agains) and if we consider another more complex feature in I/O layer
> and/or reclaim path, it might be better to increase stack size(
> meanwhile, stack usage on 64bit machine was doubled compared to 32bit
> while it have sticked to 8K. Hmm, it's not a fair to me and arm64
> already expaned to 16K. )

Hmm, stupid question: what happens when 16K is not enough too, do we
increase again? When do we stop increasing? 1M, 2M... ?

Sounds like we want to make it a config option with a couple of sizes
for everyone to be happy. :-)

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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