linux-kernel - Re: [PATCH] kmemleak: Do not use off-slab management with SLAB

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Date:	Fri, 16 Oct 2009 13:08:14 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	linux-kernel@...r.kernel.org,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH] kmemleak: Do not use off-slab management with
	SLAB_NOLEAKTRACE

Hi Pekka,

On Thu, 2009-10-15 at 21:59 +0300, Pekka Enberg wrote:
> Catalin Marinas wrote:
> > With the slab allocator, if off-slab management is enabled for the
> > kmem_caches used by kmemleak, it leads to recursive calls into
> > kmemleak_alloc(). Off-slab management can be triggered by other config
> > options increasing the slab size, e.g. DEBUG_PAGEALLOC.
> > 
> > Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> > Cc: Pekka Enberg <penberg@...helsinki.fi>
> > Cc: Christoph Lameter <cl@...ux-foundation.org>
> > Signed-off-by: Catalin Marinas <catalin.marinas@....com>
> 
> Forcing slabs to use on-slab management is pretty bad from memory 
> consumption point of view. Wouldn't it be better to annotate the 
> recursive calls somehow?

The are annotated using SLAB_NOLEAKTRACE but off-slab management uses a
general cachep and we cannot use this flag on them as we end up ignoring
kmalloc allocations. An alternative is to use GFP_ flag rather than a
SLAB_ one to track the recursive calls.

I could also rework the way hooks were added to slab.c but currently
they follow the same places as kmemcheck_slab_alloc and
lockdep_trace_alloc.

Anyway, the kmemleak caches only need off-slab management when
DEBUG_PAGEALLOC is enabled but in this case the memory consumption is
high anyway.

-- 
Catalin

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