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Date: Tue, 17 Feb 2009 07:44:32 -0800 (PST)
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
cc: Nick Piggin <npiggin@suse.de>, Jens Axboe <jens.axboe@oracle.com>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Ingo Molnar <mingo@elte.hu>, Rusty Russell <rusty@rustcorp.com.au>,
       Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
       Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH 2/4] generic-smp: remove kmalloc usage
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On Tue, 17 Feb 2009, Peter Zijlstra wrote:
> 
> Ah, no, I don't actually. I remove the kmalloc+call_rcu stuff in 2, not
> the newly cfd mini rcu thing.

I'm not talking about the "mini-rcu", I'm talking about the _existing_ rcu 
code that you play games with, just before you then remove it.

See here:

 - patch 1/4:

	@@ -25,8 +40,11 @@ struct call_function_data {
	        struct call_single_data csd;
	        spinlock_t lock;
	        unsigned int refs;
	-       struct rcu_head rcu_head;
	-       unsigned long cpumask_bits[];
	+       union {
	+               struct rcu_head rcu_head;
	+               struct list_head free_list;
	+       };
	+       struct cpumask cpumask;
	 };

 - patch 2/4:

	 struct call_function_data {
	        struct call_single_data csd;
	        spinlock_t lock;
	        unsigned int refs;
	-       union {
	-               struct rcu_head rcu_head;
	-               struct list_head free_list;
	-       };
	+       struct list_head free_list;
	        struct cpumask cpumask;
	 };

ie that ugly/complex/subtle union of rcu_head that you added in 1/4 you 
then remove immediately in 2/4. Making the patches just harder to read. 

Just remove it. I'd say fold 1+2 into one patch, instead of playing games 
with that thing. Just make the patch remove the kmalloc.

Or at least get rid of the _games_ you play with that union. Now it just 
makes the patch unreadable.

		Linus