Re: [PATCH 03/17] mm: page_alloc: Use jump labels to avoid checking number_of_cpusets

[Mel Gorman]

On Wed, May 07, 2014 at 11:04:21AM +0200, Peter Zijlstra wrote:
> On Tue, May 06, 2014 at 11:21:18PM +0100, Mel Gorman wrote:
> > On Tue, May 06, 2014 at 10:23:50PM +0200, Peter Zijlstra wrote:
> 
> > > Why the HAVE_JUMP_LABEL and number_of_cpusets thing? When
> > > !HAVE_JUMP_LABEL the static_key thing reverts to an atomic_t and
> > > static_key_false() becomes:
> > > 
> > 
> > Because number_of_cpusets is used to size a kmalloc(). Potentially I could
> > abuse the internals of static keys and use the value of key->enabled but
> > that felt like abuse of the API.
> 
> But are those ifdefs worth the saving of 4 bytes of .data?
> 
> That said, I see no real problem adding static_key_count().

I thought it would be considered API abuse as I always viewed the labels
as being a enabled/disabled thing with the existence of the ref count
being an internal implementation detail. I'll take this approach.

Thanks.

-- 
Mel Gorman
SUSE Labs
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