Re: [PATCH] kmemleak: Do not use off-slab management with SLAB_NOLEAKTRACE

[Catalin Marinas <catalin.marinas@arm.com>]

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@I-love.SAKURA.ne.jp>
> > Cc: Pekka Enberg <penberg@cs.helsinki.fi>
> > Cc: Christoph Lameter <cl@linux-foundation.org>
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.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