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Date: Fri, 20 Feb 2009 00:37:43 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Tejun Heo <tj@kernel.org>
Cc: rusty@rustcorp.com.au, tglx@linutronix.de, x86@kernel.org,
       linux-kernel@vger.kernel.org, hpa@zytor.com, jeremy@goop.org,
       cpw@sgi.com, mingo@elte.hu
Subject: Re: [PATCH UPDATED 09/10] percpu: implement new dynamic percpu
 allocator
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On Fri, 20 Feb 2009 16:30:01 +0900 Tejun Heo <tj@kernel.org> wrote:

> Impact: new scalable dynamic percpu allocator which allows dynamic
>         percpu areas to be accessed the same way as static ones
> 
> Implement scalable dynamic percpu allocator which can be used for both
> static and dynamic percpu areas.  This will allow static and dynamic
> areas to share faster direct access methods.  This feature is optional
> and enabled only when CONFIG_HAVE_DYNAMIC_PER_CPU_AREA is defined by
> arch.  Please read comment on top of mm/percpu.c for details.
> 
> ...
>
> +static int pcpu_unit_pages_shift;
> +static int pcpu_unit_pages;
> +static int pcpu_unit_shift;
> +static int pcpu_unit_size;
> +static int pcpu_chunk_size;
> +static int pcpu_nr_slots;
> +static size_t pcpu_chunk_struct_size;
> +
> +/* the address of the first chunk which starts with the kernel static area */
> +void *pcpu_base_addr;
> +EXPORT_SYMBOL_GPL(pcpu_base_addr);
> +
> +/* the size of kernel static area */
> +static int pcpu_static_size;

It would be nice to document the units of the `size' variables.  Bytes?
Pages?

Or, better: s/size/bytes/g.  

> +static int pcpu_size_to_slot(int size)
> +{
> +	int highbit = fls(size);
> +	return max(highbit - PCPU_SLOT_BASE_SHIFT + 2, 1);
> +}

See,

static int pcpu_bytes_to_slot(int bytes)
{
	int highbit = fls(bytes);
	return max(highbit - PCPU_SLOT_BASE_SHIFT + 2, 1);
}

is clearer.