Re: [Xen-devel] [PATCH v7 2/3] mm: make pages allocated with MEMF_no_refcount safe to assign

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 30 January 2020 11:02
> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxxxxx>;
> Ian Jackson <ian.jackson@xxxxxxxxxxxxx>; Julien Grall <julien@xxxxxxx>;
> Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; Stefano Stabellini
> <sstabellini@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Volodymyr Babchuk
> <Volodymyr_Babchuk@xxxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Subject: Re: [PATCH v7 2/3] mm: make pages allocated with MEMF_no_refcount
> safe to assign
> 
> (replying from seeing your reply on the list archives, i.e.
> threading lost/broken)
> 
> On 30.01.2020 10:40, Paul Durrant wrote:
> > This is getting very very complicated now, which makes me think that my
> > original approach using a 'normal' page and setting an initial max_pages
> in
> > domain_create() was a better approach.
> 
> I don't think so, no. I also don't thing auditing all ->{max,tot}_pages
> uses can be called "very very complicated". All I can say (again, I
> think) is that there was a reason this APIC page thing was done the
> way it was done. (It's another thing that this probably wasn't a
> _good_ reason.)
> 

I really want to get rid of shared xenheap pages though, so I will persist. 
I'll add the domain_tot_pages() helper as you suggest. I also agree that 
steal_page() ought not to encounter a PGC_extra page so I think I'll just make 
that an error case.

  Paul
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