linux-kernel - Re: [PATCH 2/2] SLUB: Disable debugging if it increases the minimum page order

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Message-ID: <20090611191653.GK7302@csn.ul.ie>
Date:	Thu, 11 Jun 2009 20:16:54 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org, Larry.Finger@...inger.net
Subject: Re: [PATCH 2/2] SLUB: Disable debugging if it increases the
	minimum page order

On Thu, Jun 11, 2009 at 02:26:02PM -0400, Christoph Lameter wrote:
> On Thu, 11 Jun 2009, Mel Gorman wrote:
> 
> > "With SLUB_DEBUG, enable debug on all caches unless the increased meta-data
> > would force the minimum order up on order due to object sizes being near or
> > equal the PAGE_SIZE. If SLUB_DEBUG must be enabled, specify slub_debug=A for
> > 'All caches enable debug regardless'"
> 
> Hmmm... No SLUB_DEBUG just compiles the code in for debugging. Does not
> enable anything.
> 
> But we could make SLUB_DEBUG_ON enable debugging except on those slabs
> where the order increases (for which it does a printk saying that the
> debugging was disabled) and then have a slub_debug=A option that
> overrides the order check.

Sorry, this is what I meant and I failed to explain myself properly.

> Generally if you know that you have memory
> corruption you would want to boot with slub_debug=A. If you just want
> continuous checks then SLUB_DEBUG_ON would do the trick.
> 

That's the general idea.  It would catch a number of bugs that SLUB_DEBUG_ON
catches without creating a different class of bug report such as this
atomic-order-1 problem.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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