linux-kernel - Re: lockdep complaints in slab allocator

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Message-ID: <20091124182506.GG6831@linux.vnet.ibm.com>
Date:	Tue, 24 Nov 2009 10:25:06 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Matt Mackall <mpm@...enic.com>,
	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org,
	cl@...ux-foundation.org, LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>
Subject: Re: lockdep complaints in slab allocator

On Tue, Nov 24, 2009 at 07:14:19PM +0100, Peter Zijlstra wrote:
> On Tue, 2009-11-24 at 11:12 -0600, Matt Mackall wrote:
> > On Tue, 2009-11-24 at 09:00 -0800, Paul E. McKenney wrote:
> > > On Tue, Nov 24, 2009 at 05:33:26PM +0100, Peter Zijlstra wrote:
> > > > On Mon, 2009-11-23 at 21:13 +0200, Pekka Enberg wrote:
> > > > > Matt Mackall wrote:
> > > > > > This seems like a lot of work to paper over a lockdep false positive in
> > > > > > code that should be firmly in the maintenance end of its lifecycle? I'd
> > > > > > rather the fix or papering over happen in lockdep.
> > > > > 
> > > > > True that. Is __raw_spin_lock() out of question, Peter?-) Passing the 
> > > > > state is pretty invasive because of the kmem_cache_free() call in 
> > > > > slab_destroy(). We re-enter the slab allocator from the outer edges 
> > > > > which makes spin_lock_nested() very inconvenient.
> > > > 
> > > > I'm perfectly fine with letting the thing be as it is, its apparently
> > > > not something that triggers very often, and since slab will be killed
> > > > off soon, who cares.
> > > 
> > > Which of the alternatives to slab should I be testing with, then?
> > 
> > I'm guessing your system is in the minority that has more than $10 worth
> > of RAM, which means you should probably be evaluating SLUB.
> 
> Well, I was rather hoping that'd die too ;-)
> 
> Weren't we going to go with SLQB?

Well, I suppose I could make my scripts randomly choose the memory
allocator, but I would rather not.  ;-)

More seriously, I do have a number of configurations that I test, and I
suppose I can chose different allocators for the different configurations.

							Thanx, Paul
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