linux-kernel - Re: lockdep complaints in slab allocator

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Date:	Mon, 23 Nov 2009 21:13:57 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Matt Mackall <mpm@...enic.com>
CC:	Peter Zijlstra <peterz@...radead.org>, paulmck@...ux.vnet.ibm.com,
	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

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.

> Introducing extra cacheline pressure by passing to_destroy around also
> seems like a good way to trickle away SLAB's narrow remaining
> performance advantages.

We can probably fix that to affect CONFIG_NUMA only which sucks already.

			Pekka
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