Re: [PATCH v3 4/4] pdx: Add CONFIG_PDX_COMPRESSION as a common Kconfig option

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/09/2023 10:46 am, Roger Pau Monné wrote:
> On Mon, Sep 25, 2023 at 08:36:03AM +0200, Jan Beulich wrote:
>> On 22.09.2023 22:03, Andrew Cooper wrote:
>>> On 08/08/2023 2:02 pm, Alejandro Vallejo wrote:
>>>> --- a/xen/common/Kconfig
>>>> +++ b/xen/common/Kconfig
>>>> @@ -23,6 +23,16 @@ config GRANT_TABLE
>>>>  
>>>>      If unsure, say Y.
>>>>  
>>>> +config PDX_COMPRESSION
>>>> +  bool "PDX (Page inDeX) compression support" if EXPERT
>>> This still needs hiding on x86.  The minimal hack for 4.18 is "if EXPERT
>>> && !X86".
>> If you insist on complete hiding and I insist on allowing it to be used by
>> people who want to play with exotic hardware, then this won't go anywhere.
>> I think I've come far enough with accepting a compromise, and so I think
>> it's your turn now to also take a step from your original position.
> Just because I'm not familiar with this, is there any x86 hardware
> that has such sparse memory map that would benefit from PDX?

There is one known system which never shipped.  Xen's implementation was
from the anticipation of that system shipping.  Nothing else known.

None of the other major kernels have facilities such as this, which is
very likely a contributory factor to the system not shipping.

> Wouldn't anyone doing bring up on such exotic hardware also likely need to
> perform other adjustments to Xen, and hence commenting out the !X86 in
> Kconfig be acceptable? (we would likely make it selectable at that
> point if such platforms exist).

People with bizarre hardware can cover the cost of bringing it up.  And
that includes tweaking Kconfig so they can select this option.

~Andrew