Date: Wed, 22 Feb 2012 10:29:40 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
To: Rafael Aquini <aquini@redhat.com>
cc: linux-mm@kvack.org, Randy Dunlap <rdunlap@xenotime.net>,
        Pekka Enberg <penberg@kernel.org>, Matt Mackall <mpm@selenic.com>,
        Rik van Riel <riel@redhat.com>, Josef Bacik <josef@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] oom: add sysctl to enable slab memory dump
In-Reply-To: <20120222161440.GB1986@x61.redhat.com>
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References: <20120222115320.GA3107@x61.redhat.com> <alpine.DEB.2.00.1202220754140.21637@router.home> <20120222161440.GB1986@x61.redhat.com>
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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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