From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [PATCH 2/2] powerpc - Make the irq reverse mapping radix tree lockless Date: Thu, 04 Sep 2008 12:52:19 +1000 Message-ID: <1220496739.4879.20.camel@pasglop> References: <1218029429-21114-1-git-send-email-sebastien.dugue@bull.net> <1218029429-21114-3-git-send-email-sebastien.dugue@bull.net> <1219209781.21386.25.camel@pasglop> <20080903154105.7dff49db@bull.net> Reply-To: benh@kernel.crashing.org Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, paulus@samba.org, michael@ellerman.id.au, jean-pierre.dion@bull.net, gilles.carry@ext.bull.net, tinytim@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, dwalker@mvista.com To: Sebastien Dugue Return-path: Received: from gate.crashing.org ([63.228.1.57]:45389 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753527AbYIDDpj (ORCPT ); Wed, 3 Sep 2008 23:45:39 -0400 In-Reply-To: <20080903154105.7dff49db@bull.net> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On Wed, 2008-09-03 at 15:41 +0200, Sebastien Dugue wrote: > On Wed, 20 Aug 2008 15:23:01 +1000 Benjamin Herrenschmidt wrote: > > > BTW. It would be good to try to turn the GFP_ATOMIC into GFP_KERNEL, > > That would be nice indeed > > > maybe using a semaphore instead of a lock to protect insertion vs. > > initialisation. > > a semaphore? are you meaning a mutex? If not, I fail to understand what you're > implying. Right, a mutex, bad habit calling those semaphores from the old days :-) > Right, that's the problem with this new scheme and I'm still trying > to find a way to handle memory allocation failures be it for GFP_ATOMIC or > GFP_KERNEL. > > I could not think of anything simple so far and I'm open for suggestions. GFP_KERNEL should not fail, it will just block no ? If it fails, it's probably catastrophic enough not to care. You can always fallback to linear lookup. I don't know if it's worth trying to fire off a new allocation attempt later, probably not. Ben.