linux-kernel - Re: [PATCH 2/4] generic-smp: remove kmalloc usage

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Date:	Tue, 17 Feb 2009 07:44:32 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	Nick Piggin <npiggin@...e.de>, Jens Axboe <jens.axboe@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 2/4] generic-smp: remove kmalloc usage



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
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