>>> On 12.10.16 at 17:42, <dan.j.willi...@intel.com> wrote: > On Wed, Oct 12, 2016 at 8:39 AM, Jan Beulich <jbeul...@suse.com> wrote: >>>>> On 12.10.16 at 16:58, <haozhong.zh...@intel.com> wrote: >>> On 10/12/16 05:32 -0600, Jan Beulich wrote: >>>>>>> On 12.10.16 at 12:33, <haozhong.zh...@intel.com> 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