linux-kernel - Re: [PATCH -mm 3/6] slub: introduce __kfree

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Message-ID: <20090307053444.GB10625@linux.vnet.ibm.com>
Date:	Fri, 6 Mar 2009 21:34:44 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Nick Piggin <npiggin@...e.de>,
	Manfred Spraul <manfred@...orfullife.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 3/6] slub: introduce __kfree_rcu

On Thu, Mar 05, 2009 at 09:39:03AM -0500, Christoph Lameter wrote:
> On Thu, 5 Mar 2009, Lai Jiangshan wrote:
> 
> > The first parameter of __kfree_rcu() is unused in slab,slub,slqb.
> > (I used it before, for CONFIG_SLUB_DEBUG=y ...etc. But I found
> > these debugging code is needless)
> >
> > Object sizes of the memory objects in slob's kmalloc-slab are various.
> > We hardly calculate the start address of the object from the rcu address.
> 
> But you can start with the descriptor at the beginning of the page and
> scan until you find the object.

Another approach would be to keep a per-page bitmap of the objects
that are awaiting a grace period.

Not sure whether or not it is worthwhile, but it does reduce the
per-object overhead to two bits (one for the objects awaiting the
current grace period, the other for objects that will await the next
grace period).

							Thanx, Paul
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