From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush Date: Mon, 23 Aug 2010 14:36:37 +0200 Message-ID: <4C726B55.80503@kernel.org> References: <1281616891-5691-1-git-send-email-tj@kernel.org> <20100820132214.GA6184@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: jaxboe@fusionio.com, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, linux-kernel@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, jack@suse.cz, rwheeler@redhat.com, hare@suse.de To: Christoph Hellwig Return-path: In-Reply-To: <20100820132214.GA6184@lst.de> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hello, On 08/20/2010 03:22 PM, Christoph Hellwig wrote: > Many storage devices, especially in the consumer market, come with volatile > write back caches. That means the devices signal I/O completion to the > operating system before data actually has hit the physical medium. A bit nit picky but flash devices can also have writeback caches and the term physical medium sounds a bit off for those cases. Maybe just saying "non-volatile media" is better? > Implementation details for filesystems > -------------------------------------- > > Filesystem can simply set the REQ_FLUSH and REQ_FUA bits and do not have to > worry if the underlying devices need any explicit cache flushing and how > the Forced Unit Access is implemented. The REQ_FLUSH and REQ_FUA flags > may both be set on a single bio. It may be worthwhile to explain the sequence of operations when REQ_FLUSH + data + REQ_FUA is executed. It can be extrapolated from the previous two descriptions but I think giving examples of different sequences depending on FLUSH/FUA configuration would be helpful to help understanding the overall picture of things. Other than those, looks good to me. Thanks. -- tejun