Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932355AbcJLQWj convert rfc822-to-8bit (ORCPT ); Wed, 12 Oct 2016 12:22:39 -0400 Received: from prv-mh.provo.novell.com ([137.65.248.74]:50845 "EHLO prv-mh.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753422AbcJLQWb (ORCPT ); Wed, 12 Oct 2016 12:22:31 -0400 Message-Id: <57FE7A710200007800116D60@prv-mh.provo.novell.com> X-Mailer: Novell GroupWise Internet Agent 14.2.1 Date: Wed, 12 Oct 2016 10:01:21 -0600 From: "Jan Beulich" To: "Dan Williams" Cc: "Stefano Stabellini" , "Arnd Bergmann" , , "David Vrabel" , "Haozhong Zhang" , "Andrew Morton" , "Xiao Guangrong" , "Ross Zwisler" , , "linux-nvdimm@lists.01.org" , "Boris Ostrovsky" , "Konrad Rzeszutek Wilk" , "Juergen Gross" , "Johannes Thumshirn" , "linux-kernel@vger.kernel.org" Subject: Re: [Xen-devel] [RFC KERNEL PATCH 0/2] Add Dom0 NVDIMM support for Xen References: <57FCF26A02000078000F15E0@prv-mh.provo.novell.com> <20161011165811.GO19349@localhost.localdomain> <20161011183259.GA23193@localhost.localdomain> <20161011194810.GD25907@localhost.localdomain> <20161012103318.vq36ed5ebb5xxcom@hz-desktop> <57FE3B880200007800116A75@prv-mh.provo.novell.com> <20161012145826.wwxecoo4o3ypos5o@hz-desktop> <57FE75520200007800116D27@prv-mh.provo.novell.com> In-Reply-To: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2544 Lines: 50 >>> On 12.10.16 at 17:42, wrote: > On Wed, Oct 12, 2016 at 8:39 AM, Jan Beulich wrote: >>>>> On 12.10.16 at 16:58, wrote: >>> On 10/12/16 05:32 -0600, Jan Beulich wrote: >>>>>>> On 12.10.16 at 12:33, wrote: >>>>> The layout is shown as the following diagram. >>>>> >>>>> +---------------+-----------+-------+----------+--------------+ >>>>> | whatever used | Partition | Super | Reserved | /dev/pmem0p1 | >>>>> | by kernel | Table | Block | for Xen | | >>>>> +---------------+-----------+-------+----------+--------------+ >>>>> \_____________________ _______________________/ >>>>> V >>>>> /dev/pmem0 >>>> >>>>I have to admit that I dislike this, for not being OS-agnostic. >>>>Neither should there be any Xen-specific region, nor should the >>>>"whatever used by kernel" one be restricted to just Linux. What >>>>I could see is an OS-reserved area ahead of the partition table, >>>>the exact usage of which depends on which OS is currently >>>>running (and in the Xen case this might be both Xen _and_ the >>>>Dom0 kernel, arbitrated by a tbd protocol). After all, when >>>>running under Xen, the Dom0 may not have a need for as much >>>>control data as it has when running on bare hardware, for it >>>>controlling less (if any) of the actual memory ranges when Xen >>>>is present. >>>> >>> >>> Isn't this OS-reserved area still not OS-agnostic, as it requires OS >>> to know where the reserved area is? Or do you mean it's not if it's >>> defined by a protocol that is accepted by all OSes? >> >> The latter - we clearly won't get away without some agreement on >> where to retrieve position and size of this area. I was simply >> assuming that such a protocol already exists. >> > > No, we should not mix the struct page reservation that the Dom0 kernel > may actively use with the Xen reservation that the Dom0 kernel does > not consume. Explain again what is wrong with the partition approach? Not sure what was unclear in my previous reply. I don't think there should be apriori knowledge of whether Xen is (going to be) used on a system, and even if it gets used, but just occasionally, it would (apart from the abstract considerations already given) be a waste of resources to set something aside that could be used for other purposes while Xen is not running. Static partitioning should only be needed for persistent data. Jan