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Subject: Re: [thisops uV3 07/18] highmem: Use this_cpu_xx_return()
 operations
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: akpm@linux-foundation.org, Pekka Enberg <penberg@cs.helsinki.fi>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-kernel@vger.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Tejun Heo <tj@kernel.org>, linux-mm@kvack.org
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Date: Tue, 30 Nov 2010 20:29:51 +0100
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Le mardi 30 novembre 2010 à 13:26 -0600, Christoph Lameter a écrit :
> On Tue, 30 Nov 2010, Eric Dumazet wrote:
> 
> > >  {
> > > -	int idx = --__get_cpu_var(__kmap_atomic_idx);
> > > +	int idx = __this_cpu_dec_return(__kmap_atomic_idx);
> >
> > __this_cpu_dec_return() is only needed if CONFIG_DEBUG_HIGHMEM
> >
> > >  #ifdef CONFIG_DEBUG_HIGHMEM
> > >  	BUG_ON(idx < 0);
> > >  #endif
> > >
> >
> > You could change kmap_atomic_idx_pop() to return void, and use
> > __this_cpu_dec(__kmap_atomic_idx)
> 
> The following would do?
> 
> 
> Subject: highmem: Use this_cpu_dec instead of __this_cpu_dec_return if !DEBUG_HIGHMEM
> 
> Signed-off-by: Christoph Lameter <cl@linux.com>
> 
> ---
>  include/linux/highmem.h |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/include/linux/highmem.h
> ===================================================================
> --- linux-2.6.orig/include/linux/highmem.h	2010-11-30 13:23:44.000000000 -0600
> +++ linux-2.6/include/linux/highmem.h	2010-11-30 13:24:54.000000000 -0600
> @@ -95,14 +95,19 @@ static inline int kmap_atomic_idx(void)
>  	return __this_cpu_read(__kmap_atomic_idx) - 1;
>  }
> 
> +#ifdef CONFIG_DEBUG_HIGHMEM
>  static inline int kmap_atomic_idx_pop(void)
>  {
>  	int idx = __this_cpu_dec_return(__kmap_atomic_idx);
> -#ifdef CONFIG_DEBUG_HIGHMEM
>  	BUG_ON(idx < 0);
> -#endif
>  	return idx;
>  }
> +#else
> +static inline void kmap_atomic_idx_pop(void)
> +{
> +	__this_cpu_dec(__kmap_atomic_idx);
> +}
> +#endif
> 
>  #endif
> 


well maybe a single prototype ;)

static inline void kmap_atomic_idx_pop(void)
{
#ifdef CONFIG_DEBUG_HIGHMEM
	int idx = __this_cpu_dec_return(__kmap_atomic_idx);
	BUG_ON(idx < 0);
#else
      __this_cpu_dec(__kmap_atomic_idx);
#endif
}