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Re: [Xen-devel] [RFC Design Doc] Add vNVDIMM support for Xen

>>> On 02.03.16 at 08:14, <haozhong.zhang@xxxxxxxxx> wrote:
> It means NVDIMM is very possibly mapped in page granularity, and
> hypervisor needs per-page data structures like page_info (rather than the
> range set style nvdimm_pages) to manage those mappings.
> Then we will face the problem that the potentially huge number of
> per-page data structures may not fit in the normal ram. Linux kernel
> developers came across the same problem, and their solution is to
> reserve an area of NVDIMM and put the page structures in the reserved
> area (https://lwn.net/Articles/672457/). I think we may take the similar
> solution:
> (1) Dom0 Linux kernel reserves an area on each NVDIMM for Xen usage
>     (besides the one used by Linux kernel itself) and reports the address
>     and size to Xen hypervisor.
>     Reasons to choose Linux kernel to make the reservation include:
>     (a) only Dom0 Linux kernel has the NVDIMM driver,
>     (b) make it flexible for Dom0 Linux kernel to handle all
>         reservations (for itself and Xen).
> (2) Then Xen hypervisor builds the page structures for NVDIMM pages and
>     stores them in above reserved areas.

Another argument against this being primarily Dom0-managed,
I would say. Furthermore - why would Dom0 waste space
creating per-page control structures for regions which are
meant to be handed to guests anyway?


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