linux-kernel - Re: [PATCH UPDATED] percpu: use dynamic percpu allocator as the default percpu allocator

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Message-ID: <20090401225754.GN8014@parisc-linux.org>
Date:	Wed, 1 Apr 2009 16:57:54 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>, Tejun Heo <tj@...nel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	rusty@...tcorp.com.au, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	Paul Mundt <lethal@...ux-sh.org>, rmk@....linux.org.uk,
	starvik@...s.com, ralf@...ux-mips.org, davem@...emloft.net,
	cooloney@...nel.org, kyle@...artin.ca, grundler@...isc-linux.org,
	takata@...ux-m32r.org, benh@...nel.crashing.org, rth@...ddle.net,
	ink@...assic.park.msu.ru, heiko.carstens@...ibm.com,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH UPDATED] percpu: use dynamic percpu allocator as the default percpu allocator

On Thu, Apr 02, 2009 at 12:32:41AM +0200, Ingo Molnar wrote:
> And free_percpu(NULL) does this:
> 
> void free_percpu(void *ptr)
> {
>         void *addr = __pcpu_ptr_to_addr(ptr);
>         struct pcpu_chunk *chunk;
>         unsigned long flags;
>         int off;
> 
>         if (!ptr)
>                 return;

Why don't we rewrite this as:

-	void *addr = __pcpu_ptr_to_addr(ptr);
+	void *addr;
...
	if (!ptr)
		return;
	addr = __pcpu_ptr_to_addr(ptr);

if kfree(NULL) is really that important, we should avoid doing this
extra work, not just rely on the variable being cache-hot.

-- 
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."
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