Message-ID: <4B0ADEF5.9040001@cs.helsinki.fi>
Date: Mon, 23 Nov 2009 21:13:57 +0200
From: Pekka Enberg <penberg@cs.helsinki.fi>
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To: Matt Mackall <mpm@selenic.com>
CC: Peter Zijlstra <peterz@infradead.org>, paulmck@linux.vnet.ibm.com,
       linux-mm@kvack.org, cl@linux-foundation.org,
       LKML <linux-kernel@vger.kernel.org>, Nick Piggin <npiggin@suse.de>
Subject: Re: lockdep complaints in slab allocator
References: <20091118181202.GA12180@linux.vnet.ibm.com>	 <84144f020911192249l6c7fa495t1a05294c8f5b6ac8@mail.gmail.com>	 <1258709153.11284.429.camel@laptop>	 <84144f020911200238w3d3ecb38k92ca595beee31de5@mail.gmail.com>	 <1258714328.11284.522.camel@laptop>  <4B067816.6070304@cs.helsinki.fi>	 <1258729748.4104.223.camel@laptop> <1259002800.5630.1.camel@penberg-laptop> <1259003425.17871.328.camel@calx>
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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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