From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id A405E6B0044 for ; Tue, 24 Nov 2009 14:50:20 -0500 (EST) Received: from d01relay07.pok.ibm.com (d01relay07.pok.ibm.com [9.56.227.147]) by e8.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id nAOFjskk019585 for ; Tue, 24 Nov 2009 10:45:54 -0500 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay07.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id nAOJo8q21138940 for ; Tue, 24 Nov 2009 14:50:09 -0500 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id nAOJo7V0007740 for ; Tue, 24 Nov 2009 14:50:08 -0500 Date: Tue, 24 Nov 2009 11:50:07 -0800 From: "Paul E. McKenney" Subject: Re: lockdep complaints in slab allocator Message-ID: <20091124195007.GI6831@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <4B067816.6070304@cs.helsinki.fi> <1258729748.4104.223.camel@laptop> <1259002800.5630.1.camel@penberg-laptop> <1259003425.17871.328.camel@calx> <4B0ADEF5.9040001@cs.helsinki.fi> <1259080406.4531.1645.camel@laptop> <20091124170032.GC6831@linux.vnet.ibm.com> <1259082756.17871.607.camel@calx> <1259086459.4531.1752.camel@laptop> <1259090615.17871.696.camel@calx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1259090615.17871.696.camel@calx> Sender: owner-linux-mm@kvack.org To: Matt Mackall Cc: Peter Zijlstra , Pekka Enberg , linux-mm@kvack.org, cl@linux-foundation.org, LKML , Nick Piggin List-ID: On Tue, Nov 24, 2009 at 01:23:35PM -0600, Matt Mackall wrote: > On Tue, 2009-11-24 at 19:14 +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? > > News to me. Perhaps it was discussed at KS. > > My understanding of the current state of play is: > > SLUB: default allocator Not on all architectures, it appears. > SLAB: deep maintenance, will be removed if SLUB ever covers remaining > performance regressions ;-) > SLOB: useful for low-end (but high-volume!) embedded And unfortunately also depends on CONFIG_EMBEDDED, making it difficult for me to test on the available machines. My usual workaround is to patch Kconfig to remove the dependency. > SLQB: sitting in slab.git#for-next for months, has some ground to cover I will hold off testing this until it hits mainline, especially if it is where KS decided to go. > SLQB and SLUB have pretty similar target audiences, so I agree we should > eventually have only one of them. But I strongly expect performance > results to be mixed, just as they have been comparing SLUB/SLAB. > Similarly, SLQB still has of room for tuning left compared to SLUB, as > SLUB did compared to SLAB when it first emerged. It might be a while > before a clear winner emerges. Those how live by the heuristic, die by the heuristic!!! ;-) Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org