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From: Arnd Bergmann <arnd@arndb.de>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Ingo Molnar <mingo@elte.hu>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Manfred Spraul <manfred@colorfullife.com>
Subject: Re: [PATCH V4 1/1] rcu: introduce kfree_rcu()
Date: Tue, 15 Mar 2011 11:15:54 +0100	[thread overview]
Message-ID: <201103151115.54426.arnd@arndb.de> (raw)
In-Reply-To: <4D7F356C.8020903@cn.fujitsu.com>

On Tuesday 15 March 2011 10:46:20 Lai Jiangshan wrote:
> +static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
> +{
> +       return offset < 4096;
> +}

So this relies on the assumptions that 

a) the rcu_head is within the first 4 KB of the data structure to be freed
b) no callback ever gets called in the first 4 KB of virtual address space

It's probably a reasonable assumption, but I think it should be documented
more explicitly, especially the first one. It's entirely possible that
an RCU managed data structure is larger than 4 KB.
Another alternative might be to encode the difference between a
function pointer and an offset in one of the lower bits of the address.

	Arnd

  reply	other threads:[~2011-03-15 10:16 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-15  9:46 [PATCH V4 1/1] rcu: introduce kfree_rcu() Lai Jiangshan
2011-03-15 10:15 ` Arnd Bergmann [this message]
2011-03-15 11:27   ` Paul E. McKenney
2011-03-15 12:02     ` Arnd Bergmann
2011-03-15 12:19       ` Paul E. McKenney
2011-03-15 13:07         ` Arnd Bergmann
2011-03-16  2:58           ` Lai Jiangshan
2011-03-16  4:38             ` Paul E. McKenney
2011-03-16  4:02           ` Paul E. McKenney
2011-03-18  3:15             ` [PATCH V5 " Lai Jiangshan
2011-03-18  8:14               ` Arnd Bergmann
2011-03-16  2:23   ` [PATCH V4 " Lai Jiangshan
2011-03-15 11:30 ` Paul E. McKenney
2011-03-16  2:50   ` Lai Jiangshan
2011-03-16  4:29     ` Paul E. McKenney
2011-03-15 13:11 ` Eric Dumazet
2011-03-16  4:03   ` Paul E. McKenney
2011-03-17  9:28     ` Lai Jiangshan
2011-03-17 17:50       ` Paul E. McKenney

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