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 10:24:35 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
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

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.

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.

> On Thu, 2009-06-11 at 09:43 -0400, Christoph Lameter wrote:
> > Note that CONFIG_SLUB_DEBUG only enables the code to debug a slab. It does
> > not enable debugging for each slab. CONFIG_SLUB_DEBUG_ON does that.
>
> True. Larry, do you have CONFIG_SLUB_DEBUG_ON enabled or are you passing
> SLUB debugging options to the kernel?


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