linux-kernel - Re: next-20130204 - bisected slab problem to "slab: Common constants for kmalloc boundaries"

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Message-ID: <0000013ca82f61e2-592bc561-c5ae-4193-8007-bef820f2734d-000000@email.amazonses.com>
Date:	Tue, 5 Feb 2013 02:29:03 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Stephen Warren <swarren@...dotorg.org>
cc:	James Hogan <james.hogan@...tec.com>,
	linux-next <linux-next@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>, linux-mm@...ck.org
Subject: Re: next-20130204 - bisected slab problem to "slab: Common constants
 for kmalloc boundaries"

On Mon, 4 Feb 2013, Stephen Warren wrote:

> Here, if defined(ARCH_DMA_MINALIGN), then KMALLOC_MIN_SIZE isn't
> relative-to/derived-from KMALLOC_SHIFT_LOW, so the two may become
> inconsistent.

Right. And kmalloc_index() will therefore return KMALLOC_SHIFT_LOW which
will dereference a NULL pointer since only the later cache pointers are
populated. KMALLOC_SHIFT_LOW needs to be set correctly.

> > diff --git a/mm/slub.c b/mm/slub.c
> > index ba2ca53..d0f72ee 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2775,7 +2775,7 @@ init_kmem_cache_node(struct kmem_cache_node *n)
> >  static inline int alloc_kmem_cache_cpus(struct kmem_cache *s)
> >  {
> >  	BUILD_BUG_ON(PERCPU_DYNAMIC_EARLY_SIZE <
> > -			SLUB_PAGE_SHIFT * sizeof(struct kmem_cache_cpu));
> > +			KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu));
>
> Should that also be (KMALLOC_SHIFT_HIGH + 1)?

That is already a pretty fuzzy test. The nr of kmem_cache_cpu allocated is
lower than KMALLOC_SHIFT_HIGH since several index positions will not be
occupied.
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