From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Steinar H. Gunderson" Subject: Re: dm-cache with zero hit rate Date: Fri, 2 Aug 2013 15:58:28 +0200 Message-ID: <20130802135828.GA12191@uio.no> References: <20130731185017.GA13215@uio.no> <20130731202522.GD18513@redhat.com> <20130802084910.GA21756@uio.no> <20130802132344.GA20629@redhat.com> 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: <20130802132344.GA20629@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mike Snitzer Cc: Heinz Mauelshagen , dm-devel@redhat.com, ejt@redhat.com List-Id: dm-devel.ids On Fri, Aug 02, 2013 at 09:23:44AM -0400, Mike Snitzer wrote: > Yes, it is surprising. Curious to know if the promotions aren't > happening due to the IO scheduler somehow merging all your random small > IO. We don't yet have a descrete counter to show the number of > migrations that were skipped due to sequential_threshold but that is > something we can add. > > But you can effectively disable the sequential_threshold by setting it > really high, e.g.: > > dmsetup message cache 0 sequential_threshold 16384 I tried this, and it still doesn't appear to promote anything at all: cache: 0 23440891904 cache 913/8192 0 7021239 0 2049048 0 0 0 0 0 2 migration_threshold 2048 4 random_threshold 8 sequential_threshold 16384 It's only been running for a few minutes, though. FWIW, earlier I ran it on only one single partition, and then it worked. So it's not like my kernel is completely broken, at least. > Please write a file that is smaller than your specified > sequential_threshold, and then read it numerous times via direct IO, > e.g.: > > dd if= of=/dev/null iflag=direct bs=16K I did, with a 16 kB file (that should certainly be small enough, right?), executing the dd command 10000 times. Still nothing cached. /* Steinar */ -- Homepage: http://www.sesse.net/