Re: [PATCH v2 4/8] pdx: introduce command line compression toggle

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Jun 24, 2025 at 03:40:16PM +0200, Jan Beulich wrote:
> On 20.06.2025 13:11, Roger Pau Monne wrote:
> > Introduce a command line option to allow disabling PDX compression.  The
> > disabling is done by turning pfn_pdx_add_region() into a no-op, so when
> > attempting to initialize the selected compression algorithm the array of
> > ranges to compress is empty.
> 
> While neat, this also feels fragile. It's not obvious that for any
> algorithm pfn_pdx_compression_setup() would leave compression disabled
> when there are zero ranges. In principle, if it was written differently
> for mask compression, there being no ranges could result in compression
> simply squeezing out all of the address bits. Yet as long as we think
> we're going to keep this in mind ...

It seemed to me that nr_rages == 0 (so no ranges reported) should
result in no compression, for example on x86 this means there's no
SRAT.

> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks, Roger.