Re: [Xen-devel] [PATCH v3 3/3] tools: introduce parameter max_wp_ram_ranges.

["Yu, Zhang" <yu.c.zhang@xxxxxxxxxxxxxxx>]

On 2/4/2016 3:12 AM, George Dunlap wrote:
> On 03/02/16 18:39, Andrew Cooper wrote:
> > On 03/02/16 18:21, George Dunlap wrote:
> > > 2. It's not technically difficult to extend the number of servers
> > > supported to something sensible, like 4 (using 4 different write_dm
> > > p2m types)
> > While technically true, spare bits in the pagetable entries are at a
> > premium, and steadily decreasing as Intel are introducing new features.
> >
> > We have 16 current p2m types, and a finite upper bound of 6 bits of p2m
> > type space, already with a push to reduce this number.
> >
> > While introducing 1 new p2m type for this purpose might be an acceptable
> > tradeoff, a using a p2m type per ioreq server is not IMO.
> It is true that we don't have a ton of elbow room to grow at the moment.
>
> But we actually already have a single p2m type -- mmio_write_dm -- that
> as far as I know is only being used by XenGT.  We don't actually need to
> add any new p2m types for my initial proposal.
>
> Going forward, we probably will, at some point, need to implement a
> parallel "p2t" structure to keep track of types -- and probably will
> whether end up implementing 4 separate write_dm types or not (for the
> reasons you describe).
Thank you, George. Could you please elaborate more about the idea of
"p2t"?

Yu

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