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

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Date:	Thu, 11 Jun 2009 18:11:59 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, mel@....ul.ie,
	Larry.Finger@...inger.net
Subject: Re: [PATCH 2/2] SLUB: Disable debugging if it increases the
 minimum page order

Hi Christoph,

On Thu, 11 Jun 2009, Pekka Enberg wrote:
> > On Thu, 2009-06-11 at 09:43 -0400, Christoph Lameter wrote:
> > > We have had that with SLAB. NO! This leads to the situation that some
> > > slabs have debug on and some have not. You just do not know which.
> >
> > I do see your point but surely we don't want to use order 1 allocations
> > in the fall-back case for kmalloc-4096? Couldn't we just add a printk
> > saying that debug was disabled for the cache? After all, my patch is
> > much better than what SLAB does.

On Thu, 2009-06-11 at 10:24 -0400, Christoph Lameter wrote:
> If we are enabling global debugging then we are looking for memory
> corruption in *all* slab caches. Disabling debugging of some cache behind
> the scenes is bad even if this leads to order 1 allocations.
> 
> We could refine the way to specify groups of slab caches that should have
> debugging on.

I think my patch is the simplest solution here: it turns off debugging
for those caches where the metadata bumps up the minimum allocation
order and I suspect that we disable cache only for 4096 in practice.

Also note that when we switch back to more aggressive page allocator
pass-through, we lose SLUB debugging support.

			Pekka

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