From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Thornber Subject: Re: [PATCH] dm-kcopyd: monitor io activity Date: Tue, 31 May 2011 10:09:01 +0100 Message-ID: <20110531090900.GA3164@ubuntu> References: Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development Cc: "Alasdair G. Kergon" List-Id: dm-devel.ids On Mon, May 30, 2011 at 12:40:39PM -0400, Mikulas Patocka wrote: > Here I'm sending three patches that limit kcopyd speed. There is global > limit for all kcopyds running in a system. The user can set percentage of > kcopyd speed in /sys/module/dm_mod/parameters/dm_kcopyd_throttle Could you give some explanation of how to choose an appropriate value for this please? Should it be 100% unless there is an issue? How does the sys admin spot such issues? Different kcopyd clients have different performance requirements, for instance the initial sync of a new mirror leg may have less priority than a copy-on-write exception for a snapshot. This isn't something we've addressed so far, but if you're starting to slow kcopyd down (i.e. so the mirror sync doesn't saturate the system), then I think you'll get some complaints from the snapshot users. - joe