linux-kernel - Re: [PATCH V4 1/1] rcu: introduce kfree

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Message-Id: <201103151407.24800.arnd@arndb.de>
Date:	Tue, 15 Mar 2011 14:07:24 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: Re: [PATCH V4 1/1] rcu: introduce kfree_rcu()

On Tuesday 15 March 2011, Paul E. McKenney wrote:
> And it makes use of statically allocated structures a bit clunky.

How do statically allocated structures relate to this? I would
expect that you never call kfree_rcu on them, so it shouldn't
matter.

> Yet another approach is to use the low-order bit of the rcu_head pointer,
> given that the rcu_head structure does have to be aligned.  If this bit
> is set, then the function pointer could be interpreted as an offset.
> This approach might also allow a slab_free_rcu() to be constructed, given
> that the full 32 bits of the function pointer would be available.
> For example, if the upper 16 bits are zero, the low-order 16 bits are
> the offset.  If the upper 16 bits are 0x1, then the low-order 16 bits
> might be an index that selects the desired slab cache.

This solution sounds like a clear improvement over the patch that Lai
Jiangshan posted, without any downsides.

	Arnd
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