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

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Date:	Thu, 15 Oct 2009 21:59:07 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Catalin Marinas <catalin.marinas@....com>
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 Catalin,

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?

			Pekka

> ---
>  mm/slab.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 7dfa481..646db30 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2261,9 +2261,11 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>  	/*
>  	 * Determine if the slab management is 'on' or 'off' slab.
>  	 * (bootstrapping cannot cope with offslab caches so don't do
> -	 * it too early on.)
> +	 * it too early on. Always use on-slab management when
> +	 * SLAB_NOLEAKTRACE to avoid recursive calls into kmemleak)
>  	 */
> -	if ((size >= (PAGE_SIZE >> 3)) && !slab_early_init)
> +	if ((size >= (PAGE_SIZE >> 3)) && !slab_early_init &&
> +	    !(flags & SLAB_NOLEAKTRACE))
>  		/*
>  		 * Size is large, assume best to place the slab management obj
>  		 * off-slab (should allow better packing of objs).
> 

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