From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: PAGE_SIZE (64KB), while block driver 'struct request' deals with < PAGE_SIZE (up to 44Kb). Was:Re: [RFC] Support of non-indirect grant backend on 64KB guest Date: Fri, 4 Sep 2015 23:05:28 +0100 Message-ID: <55EA15A8.3060805@citrix.com> References: <55D5906C.7070907@citrix.com> <55D5A15C.80206@citrix.com> <20150821160510.GE26663@l.oracle.com> <55D74D03.9020301@citrix.com> <20150821171022.GL26663@l.oracle.com> <55DF4E04.8010005@citrix.com> <20150904154151.GA28256@localhost.localdomain> <55E9C391.7040601@citrix.com> <20150904173211.GC2042@l.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150904173211.GC2042@l.oracle.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Konrad Rzeszutek Wilk Cc: Ian Campbell , Stefano Stabellini , "xen-devel@lists.xen.org" , axboe@fb.com, David Vrabel , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= List-Id: xen-devel@lists.xenproject.org Hi Konrad, On 04/09/2015 18:32, Konrad Rzeszutek Wilk wrote: > On Fri, Sep 04, 2015 at 05:15:13PM +0100, Julien Grall wrote: >> On 04/09/15 16:41, Konrad Rzeszutek Wilk wrote: >>>> Maybe we could fall back to the previous plan of modifying xen-blkfront >>>> for the moment? >>> >>> Which afaic need to be reposted? >> >> Right. Although I didn't see any comment on the patch. All the comments >> was about the problem. Does it mean that you and Roger are "happy" with >> the way it's done? > > There were some #idef I think? And I recall seeing the segment limit being > advertised as PAGE_SIZE / 2? There is no ifdef but a PAGE_SIZE / 2. I know about the latter and plan to replace it. It was only to have a quick patch to expose my problem. > I dug in the other block drivers to figure out what they > do when the underlaying storage cannot handle < PAGE_SIZE data. > And I couldn't find them. Which means this should be really dealt > on the drivers side (xen-blkfront) as an quirk. > > Anyhow what I am going to do is - once it is reposted, force the > driver under x86 to work under this condition. That is disable > persistent support and only use 2048 .. and then drive some IO. > If all goes well I will send it in a git pull to Jens. It will also depends on 64KB series which I plan to repost next week. I will send as follow-up. To test it properly on x86 it will be necessary to drop on BUG_ON in the code which ensure that the extra req is never use for 4KB (see BUG_ON((XEN_PAGE_SIZE == PAGE_SIZE) && require_extra_req)). Regards, -- Julien Grall