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Re: [PATCH v3 4/4] pdx: Add CONFIG_PDX_COMPRESSION as a common Kconfig option
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 25 Sep 2023 11:59:49 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>, Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 25 Sep 2023 09:59:58 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 25.09.2023 11:46, 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?
>
> 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).
As mentioned before, the reason PDX was introduced was to actually make Xen
work on such exotic x86 hardware. While I can't tell for sure, that hardware
probably has never made it into production. Yet still things were known to
work there after the original adjustments, so no, I would not expect other
adjustments to be necessary (provided there was no bitrot).
Jan
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