From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hubert Verstraete Subject: Re: MDP major registration Date: Wed, 26 Mar 2008 18:50:44 +0100 Message-ID: <47EA8CF4.7080201@free.fr> References: <47D90614.9040206@free.fr> <18408.36753.223347.129420@notabene.brown> <47E92EE2.1080108@free.fr> <20080326065232.GA21970@percy.comedia.it> <47EA71BF.8050800@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <47EA71BF.8050800@tmr.com> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Bill Davidsen wrote: > Luca Berra wrote: >> On Tue, Mar 25, 2008 at 05:57:06PM +0100, Hubert Verstraete wrote: >>> Neil Brown wrote: >>>> On Thursday March 13, hubskml@free.fr wrote: >>>>> Neil, >>>>> >>>>> What is the status of the major for the partitionable arrays ? >>>> >>>> automatically determined at runtime. >>>> >>>>> I see that it is 254, which is in the experimental section, >>>>> according to the official Linux device list >>>>> (http://www.lanana.org/docs/device-list/). >>>>> Will there be an official registration ? >>>> >>>> No. Is there any need? >>> >>> I got this question in mind when I saw that mkfs.xfs source code was >>> referring to the MD major to tune its parameters on an MD device, >>> while it ignores MDP devices. >>> If there were reasons to register MD, wouldn't they apply to MDP too ? >> >> i don't think so: >> bluca@percy ~ $ grep mdp /proc/devices >> 253 mdp > > Why is it important to have XFS tune its parameters for md and not for > mdp? I don't understand your conclusion here, is tuning not needed for > mdp, or so meaningless that it doesn't matter, or that XFS code reads > /proc/devices, or ??? I note that device-mapper also has a dynamic > major, what does XFS make of that? It reads from /proc/devices. > I don't know how much difference tuning makes, but if it's worth doing > at all, it should be done for mdp as well, I would think. Same thought. I wrote the patch for mkfs.xfs but did not publish it for two reasons: 1) MD is registered but not MDP. Now I understand, it's not a problem, we just need to read /proc/devices as device-mapper does. 2) Tuning XFS for MDP can be achieved through the mkfs.xfs options. With a few lines in shell, my XFS on MDP now has the same performance as XFS on MD. Hubert