linux-kernel - Re: [thisops uV3 07/18] highmem: Use this_cpu_xx

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Date:	Tue, 30 Nov 2010 13:26:39 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Tejun Heo <tj@...nel.org>, linux-mm@...ck.org
Subject: Re: [thisops uV3 07/18] highmem: Use this_cpu_xx_return()
 operations

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@...ux.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

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