From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Ian Pratt" Subject: RE: Reducing impact of save/restore/dump on Dom0 Date: Tue, 6 Feb 2007 23:00:17 -0000 Message-ID: <8A87A9A84C201449A0C56B728ACF491E04F46D@liverpoolst.ad.cl.cam.ac.uk> References: <342BAC0A5467384983B586A6B0B3767104A69BB9@EXNA.corp.stratus.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Return-path: Content-class: urn:content-classes:message List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: "Graham, Simon" , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org =20 > Solving this problem for save/restore is more tricky because the > on-disk/wire save format does not force the page data to be page aligned > -- my proposal would be to page align each batch of pages written, > leaving pad between the batch header and the pages themselves but I > realize that a change in on-disk/wire format is a potential > compatibility problem. The on-disk format is due to change before 3.0.5 anyhow. Page aligning the data pages is certainly something I'd like to see happen. The easiest way of doing this is to add some padding to align things at the start of the page write-out loop, then in the PV case, make sure that the page-type batches are padded to page size. (I'd reduce the max batch size slightly so that in the normal case the batch fits nicely in 1 page, or 2 for 64b). As for making the IO bypass the buffer cache, I'm not sure what the best way to do this is. There are some occasions where we want the restore image to be in the buffer cache (e.g. as used by the fault injection testing for fast domain restart) but I agree that its not helpful in the normal case. My first inclination would be O_DIRECT, but there may be a better way. Ian=20