Re: [PATCH/RFC 1/6] numa: Use Generic Per-cpu Variables for numa_node_id()

[Matthew Wilcox <matthew@wil.cx>]

On Mon, Nov 30, 2009 at 03:28:40PM -0500, Lee Schermerhorn wrote:
> linux/topology.h now depends on */percpu.h to implement numa_node_id()
> and numa_mem_id().  Not so much an issue for x86 because its
> asm/topology.h already depended on its asm/percpu.h.  But ia64, for
> instance--maybe any arch that doesn't already implement numa_node_id()
> as a percpu variable--didn't define this_cpu_read() for
> linux/topology.h.
> 
> So, I included <linux/percpu.h>.
> 
> linux/percpu.h, for reasons of its own, includes linux/swap.h which

typo there ... slab.h, not swap.h.  I thought we might be able to break
the cycle here, but slab.h is more reasonable than swap.h.

We could move __alloc_percpu out of line ... it's only inline for the
!SMP case.

> includes linux/gfp.h which includes linux/topology.h for the definition
> of numa_node_id().  topology.h hasn't gotten around to defining
> numa_node_id() yet--it's still including percpu.h.  ...
> 
> Looking at other asm/foo.h and asm-generic/foo.h relationships, I see
> that some define the generic version of the api in the asm-generic
> header if the arch asm header hasn't already defined it.  asm/topology.h
> is an instance of this.  It includes asm-generic/topology.h after
> defining arch specific versions of some of the api.
> 
> Following this model, I moved the generic definitions of the percpu api
> back to the asm-generic version where it would be available without the
> inclusion of swap.h, et al. 
> 
> I tried including <asm/percpu.h> in linux/topology.h but the was advised
> to use the generic header.  So I followed the model of the x86
> asm/topology.h and included asm/percpu.h in the ia64 asm/topology.h,
> making the definitions visible to linux/topology.h.
> 
> This reminds me that I should add to the patch description a 3rd item
> required for an arch to use the generic percpu numa_node_id()
> implementation:  make the percpu variable access interface visible via
> asm/topology.h.
> 
> Does that sound reasonable?
> 
> Lee
> 
> 
> 
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-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."