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

["Yu, Zhang" <yu.c.zhang@linux.intel.com>]

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