From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Nelles Subject: Re: DM-Cache Writeback & Direct IO? Date: Thu, 09 Jul 2015 18:51:55 +0200 Message-ID: <559EA6AB.2080603@evilazrael.de> References: <559CE76E.6020504@evilazrael.de> <20150708144829.GA5058@rh-vpn> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150708144829.GA5058@rh-vpn> 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 List-Id: dm-devel.ids Hello Joe, I updated to the latest kernel from Ubuntu mainline (4.2.0-040200rc1) and will rerun the same fio command over the night. Currently it shows the same behaviour. The fio command i use is fio --name=test --filename=/dev/mapper/dmcache --rw=randwrite --filesize=16G --bs=64k --ioengine=libaio --direct=1 --iodepth=1000 After 4 runs, the status for the device mapper looks like this: dmcache: 0 6442450943 cache 8 6029/4161600 512 2283/2913051 1517 119 25120 1294780 0 2283 1484 1 writeback 2 migration_threshold 2048 smq 0 rw Regards Christoph Am 08.07.2015 um 16:48 schrieb Joe Thornber: > On Wed, Jul 08, 2015 at 11:03:42AM +0200, Christoph Nelles wrote: >> Hi, >> >> Can the dm-cache writeback cache buffer direct IO or goes direct IO >> always immediately to the origin device? > Yes, the device mapper layer knows nothing about direct IO vs page > cache IO. > >> I am currently performing tests and see that random direct write IO >> never hits the cache, even after overwriting the same region over >> and over. > Could you try with the latest kernels and the new smq policy please? > > - Joe > > -- > dm-devel mailing list > dm-devel@redhat.com > https://www.redhat.com/mailman/listinfo/dm-devel