From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joe Thornber Subject: Re: A patchset to limit the number of outstanding bios Date: Mon, 13 Oct 2014 17:03:18 +0100 Message-ID: <20141013160317.GD27596@debian> 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: Mikulas Patocka Cc: Ondrej Kozina , Mike Snitzer , dm-devel@redhat.com, "Alasdair G. Kergon" List-Id: dm-devel.ids On Mon, Oct 13, 2014 at 11:27:20AM -0400, Mikulas Patocka wrote: > Hi > > I'm announcing the release of a patchset that limits the number of > outstanding bios in the device mapper. Interesting; Mike and I were considering this for throttling io to thinp a couple of weeks ago. The reason we didn't go with this was, for thinp, there are cheap bios (eg, a quick remap) and expensive bios (eg, one that triggers a copy on write exception). This means it's very hard to come up with a single number that represents too many bios. Instead I throttle by looking at how long it's taking the worker thread to get through it's work queue. Could you make this limit optional please? eg, setting the limit to 0 turns it off, and I'd prefer a default of 0/off. - Joe