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Re: [PATCH for-4.18 v5] xen/pdx: Make CONFIG_PDX_COMPRESSION a common Kconfig option
- To: Julien Grall <julien@xxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Fri, 6 Oct 2023 17:27:27 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Henry Wang <Henry.Wang@xxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Fri, 06 Oct 2023 15:28:06 +0000
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On Fri, Oct 06, 2023 at 04:09:19PM +0100, Julien Grall wrote:
>
>
> On 06/10/2023 15:44, Andrew Cooper wrote:
> > From: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
> >
> > Adds a new compile-time flag to allow disabling PDX compression and
> > compiles out compression-related code/data. It also shorts the pdx<->pfn
> > conversion macros and creates stubs for masking functions.
> >
> > While at it, removes the old arch-defined CONFIG_HAS_PDX flag. Despite the
> > illusion of choice, it was not optional.
> >
> > There are ARM and PPC platforms with sparse RAM banks - leave compression
> > active by default there. OTOH, there are no known production x86 systems
> > with
> > sparse RAM banks, so disable compression. This decision can be revisited if
> > such a platform comes along.
>
> (Process remarks rather than the code itself)
>
> Jan is away this week so I want to make sure this doesn't go in without him
> having a say.
>
> While I don't particularly care about the approach taken for x86, Jan voiced
> concerned with this approach and so far I didn't see any conclusion. If
> there is any, then please point me to them.
>
> For the record, the objections from Jan are in [1]. If we want to ignore
> them, then I think we need a vote. Possibly only from the x86 folks (?).
I would be fine in leaving the option to be selected if we knew that
such x86 systems might be feasible, but so far we have seen 0 x86
systems with sparse RAM. That said, I don't have a strong opinion, but
the hiding on x86 seems fine to me. Interested parties can always
forcefully select the option, and a case can be made to make it
available again on Kconfig.
I'm fine with waiting for Jan, in case he has more to add.
Thanks, Roger.
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