linux-kernel - Re: [S+Q3 00/23] SLUB: The Unified slab allocator (V3)

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Date:	Tue, 17 Aug 2010 11:02:12 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...e.de>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [S+Q3 00/23] SLUB: The Unified slab allocator (V3)

On Tue, 17 Aug 2010, Christoph Lameter wrote:

> > Ok, so this is panicking because of the error handling when trying to
> > create sysfs directories with the same name (in this case, :dt-0000064).
> > I'll look into while this isn't failing gracefully later, but I isolated
> > this to the new code that statically allocates the DMA caches in
> > kmem_cache_init_late().
> 
> Hmm.... Strange. The DMA caches should create a distinct pattern there.
> 

They do after patch 11 when you introduce dynamically sized kmalloc 
caches, but not after only patches 1-8 were applied.  Since this wasn't 
booting on my system, I bisected the problem to patch 8 where 
kmem_cache_init_late() would create two DMA caches of size 64 bytes: one 
becauses of kmalloc_caches[0] (kmem_cache_node) and one because of 
kmalloc_caches[6] (2^6 = 64).  So my fixes are necessary for patch 8 but 
obsoleted later, and then the shared cache support panics on memset().

> >  - the entire iteration in kmem_cache_init_late() needs to be protected by
> >    slub_lock.  The comment in create_kmalloc_cache() should be revised
> >    since you're no longer calling it only with irqs disabled.
> >    kmem_cache_init_late() has irqs enabled and, thus, slab_caches must be
> >    protected.
> 
> I moved it to kmem_cache_init() which is run when we only have one
> execution thread. That takes care of the issue and ensures that the dma
> caches are available as early as before.
> 

I didn't know if that was a debugging patch for me or if you wanted to 
push that as part of your series, I'm not sure if you actually need to 
move it to kmem_cache_init() now that slub_state is protected by 
slub_lock.  I'm not sure if we want to allocate DMA objects between 
kmem_cache_init() and kmem_cache_init_late().
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