Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756903Ab0HaK1P (ORCPT ); Tue, 31 Aug 2010 06:27:15 -0400 Received: from daytona.panasas.com ([67.152.220.89]:34128 "EHLO daytona.int.panasas.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752855Ab0HaK1N (ORCPT ); Tue, 31 Aug 2010 06:27:13 -0400 Message-ID: <4C7CD8F8.4050409@panasas.com> Date: Tue, 31 Aug 2010 13:27:04 +0300 From: Boaz Harrosh User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-2.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Tejun Heo CC: Jan Kara , Jeff Moyer , Christoph Hellwig , jaxboe@fusionio.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, linux-raid@vger.kernel.org, James.Bottomley@suse.de, tytso@mit.edu, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp, dm-devel@redhat.com, vst@vlnb.net, rwheeler@redhat.com, hare@suse.de, neilb@suse.de, rusty@rustcorp.com.au, mst@redhat.com, jeremy@goop.org, snitzer@redhat.com, k-ueda@ct.jp.nec.com, Christoph Hellwig Subject: Re: [PATCH 26/30] ext4: do not send discards as barriers References: <1282751267-3530-1-git-send-email-tj@kernel.org> <1282751267-3530-27-git-send-email-tj@kernel.org> <20100825155842.GA3229@lst.de> <20100825160032.GC3229@lst.de> <4C753D75.2010305@kernel.org> <20100825200223.GE2738@quack.suse.cz> <4C76250B.6060800@kernel.org> <20100827173147.GA12374@quack.suse.cz> <20100830202034.GB12226@quack.quadriga.com> <4C7CB936.8010509@kernel.org> <4C7CD47B.1050409@panasas.com> <4C7CD5D0.40007@kernel.org> In-Reply-To: <4C7CD5D0.40007@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 31 Aug 2010 10:27:12.0366 (UTC) FILETIME=[1308D8E0:01CB48F7] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1605 Lines: 41 On 08/31/2010 01:13 PM, Tejun Heo wrote: > Hello, > > On 08/31/2010 12:07 PM, Boaz Harrosh wrote: >> I don't know all the specifics of the virtio driver and the KVM backend but >> don't the KVM target io is eventually directed to a local file or device? >> If so the scsi device has disappeard but the bulk of the data is in host cache >> at the backstore (file or bdev). Once all files are closed the data is synced >> to disk. >> >> Is it not the same as Ric's problem of disconnecting the sata cable but >> not dropping power to the drive. The main of the cache is still intact. > > There are two layers of caching there. > > drive cache - host page cache - guest > > When guest issues FLUSH, qemu will translate it into fdatasync which > will flush the host page cache followed by FLUSH to the drive which > will flush the drive cache to the media. If you delete the host disk > device, it will be detached w/o host page cache flushed. So, although > it's not complete, it will lose good part of cache. With out write > out timeout increased and/or with laptop mode enabled, it will > probably lose most of cache. > Ha, ok you meant that device. So if you have a dedicated physical device for backstore that would be a very nice scriptable way. Thanks, that's a much better automated test than pulling drives out of sockets. > Thanks. > Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/