linux-kernel - Re: [PATCH] oom: add sysctl to enable slab memory dump

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Message-ID: <alpine.DEB.2.00.1202221028340.10258@router.home>
Date:	Wed, 22 Feb 2012 10:29:40 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Rafael Aquini <aquini@...hat.com>
cc:	linux-mm@...ck.org, Randy Dunlap <rdunlap@...otime.net>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>, Rik van Riel <riel@...hat.com>,
	Josef Bacik <josef@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] oom: add sysctl to enable slab memory dump

On Wed, 22 Feb 2012, Rafael Aquini wrote:

> On Wed, Feb 22, 2012 at 07:55:16AM -0600, Christoph Lameter wrote:
> >
> > Please use node_nr_objects() instead of directly accessing total_objects.
> > total_objects are only available if debugging support was compiled in.
> >
> Shame on me! I've wrongly assumed that it would be safe accessing
> the element because SLUB_DEBUG is turned on by default when slub is chosen.
>
> Considering your note on my previous mistake, shall I assume now that it
> would be better having this whole dump feature dependable on CONFIG_SLUB_DEBUG,
> instead of just CONFIG_SLUB ?

That is certainly one solution. If CONFIG_SLUB_DEBUG is not set then
support for maintaining a total count is not compiled in. You can of
course still approximate that from the total number of slabs allocated and
multiply that number by the # of objs per slab page.

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