From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Greg Freemyer" Subject: Re: [RFC] Disk shock protection (revisited) Date: Thu, 28 Feb 2008 12:00:21 -0500 Message-ID: <87f94c370802280900t6e099ae8q7635c275732c9c3e@mail.gmail.com> References: <87skzgd1zk.fsf@denkblock.local> <20080226123946.75dbe3d2@core> <87mypl8p49.fsf@denkblock.local> <20080228111349.6831925c@core> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from an-out-0708.google.com ([209.85.132.244]:47171 "EHLO an-out-0708.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756215AbYB1RAX (ORCPT ); Thu, 28 Feb 2008 12:00:23 -0500 Received: by an-out-0708.google.com with SMTP id d31so783081and.103 for ; Thu, 28 Feb 2008 09:00:21 -0800 (PST) In-Reply-To: <20080228111349.6831925c@core> Content-Disposition: inline Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Alan Cox Cc: Elias Oltmanns , linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe , lmb@suse.de On Thu, Feb 28, 2008 at 6:13 AM, Alan Cox wrote: > > > That sounds like a non starter. What if the box is busy, what if the > > > daemon or something you touch needs memory and causes paging ? > > > > The daemon runs mlock'd anyway, so there won't be any need for paging > > mlock does not guarantee anything of that form. A syscall by an mlocked > process which causes a memory allocation can cause paging of another > process on the system. > > > > there. As for responsiveness under heavy load, I'm not quite sure I get > > your meaning. On my system, at least, the only way I have managed to > > decrease responsiveness noticeably is to cause a lot of I/O operations > > It depends a lot on hardware but you can certainly get user space delays > in seconds as an extreme worst case. I don't know the details, but I believe the Linux-HA heartbeat daemons take significant effort to eliminate unexpected delays. See http://www.linux-ha.org/ Lars Marowsky-Bree of Novell is extremely involved in the project and he at least occasionally posts on LKML. I've cc'ed him. Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com