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Date: Mon, 15 Jun 2009 13:28:28 +0200
From: Nick Piggin <npiggin@suse.de>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>,
       Heiko Carstens <heiko.carstens@de.ibm.com>,
       torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
       akpm@linux-foundation.org, cl@linux-foundation.org,
       kamezawa.hiroyu@jp.fujitsu.com, lizf@cn.fujitsu.com, mingo@elte.hu,
       yinghai@kernel.org
Subject: Re: [GIT PULL v2] Early SLAB fixes for 2.6.31
Message-ID: <20090615112827.GC6012@wotan.suse.de>
References: <Pine.LNX.4.64.0906121624280.2937@melkki.cs.Helsinki.FI> <Pine.LNX.4.64.0906121859420.5963@melkki.cs.Helsinki.FI> <20090615081831.GA5411@osiris.boeblingen.de.ibm.com> <84144f020906150210w7fa29042xc12efb4a087e3d26@mail.gmail.com> <20090615094148.GC1314@wotan.suse.de> <1245059476.12400.7.camel@pasglop> <20090615101254.GB10294@wotan.suse.de> <1245062388.12400.17.camel@pasglop> <20090615112205.GA6012@wotan.suse.de>
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On Mon, Jun 15, 2009 at 01:22:05PM +0200, Nick Piggin wrote:
> On Mon, Jun 15, 2009 at 08:39:48PM +1000, Benjamin Herrenschmidt wrote:
> But I won't live with having it shit in our nice core code...
> Well, at least I won't throw up my hands and give up this
> early.

Just the principle, btw. The cost of this one load and
branch (when moved out to the slowpath -- in the fastpath
then adding a single cycle is like a 1% slowdown you know)
is not prohibitive, but it's a slipperly slope.

If a couple of specialised early boot code places have
to test slab_is_available() to prevent crap leaking into
our main allocators, then that's quite fine by me.