Re: [Xen-devel] [PATCH 2/2] domain: use PGC_extra domheap page for shared_info

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 06 March 2020 13:46
> To: Paul Durrant <xadimgnik@xxxxxxxxx>
> Cc: sstabellini@xxxxxxxxxx; julien@xxxxxxx; Volodymyr_Babchuk@xxxxxxxx; 
> wl@xxxxxxx;
> konrad.wilk@xxxxxxxxxx; andrew.cooper3@xxxxxxxxxx; ian.jackson@xxxxxxxxxxxxx;
> george.dunlap@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx; 'David Woodhouse' 
> <dwmw2@xxxxxxxxxxxxx>
> Subject: Re: [PATCH 2/2] domain: use PGC_extra domheap page for shared_info
> 
> On 06.03.2020 14:41, Paul Durrant wrote:
> >> -----Original Message-----
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: 06 March 2020 13:36
> >> To: Paul Durrant <xadimgnik@xxxxxxxxx>
> >> Cc: sstabellini@xxxxxxxxxx; julien@xxxxxxx; Volodymyr_Babchuk@xxxxxxxx; 
> >> wl@xxxxxxx;
> >> konrad.wilk@xxxxxxxxxx; andrew.cooper3@xxxxxxxxxx; 
> >> ian.jackson@xxxxxxxxxxxxx;
> >> george.dunlap@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxxx; 'David 
> >> Woodhouse' <dwmw2@xxxxxxxxxxxxx>
> >> Subject: Re: [PATCH 2/2] domain: use PGC_extra domheap page for shared_info
> >>
> >> On 06.03.2020 14:26, Paul Durrant wrote:
> >>>> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of 
> >>>> Jan Beulich
> >>>> Sent: 06 March 2020 13:24
> >>>>
> >>>> On 06.03.2020 14:13, Paul Durrant wrote:
> >>>>> My aim is to make the separation abundantly obvious by getting rid
> >>>>> of shared xenheap pages (for non-system domains at least) but I
> >>>>> can't do that before converting shared_info and grant shared/status
> >>>>> frames to domheap.
> >>>>
> >>>> Following David's various replies - instead of going this route of
> >>>> replacing the sharing of xenheap pages by different logic, the
> >>>> same ought to be achievable by making the backing allocations come
> >>>> from the correct pool?
> >>>>
> >>>
> >>> I still prefer the simplification of not having to clean up the
> >>> shared xenheap page list in domain_kill() so IMO it is still worth
> >>> it for that alone.
> >>
> >> I don't see anything very special with the cleaning up in
> >> domain_kill() / domain_relinquish_resources(). What I'd view as
> >> more desirable in this regard is the general fact of needing
> >> two lists. But you realize there's a downside to this as well?
> >> dump_pageframe_info() will reliably show _all_ Xen heap pages
> >> associated with a domain, but it will only ever show up to 10
> >> pages on ->page_list for a domain that's not already being
> >> cleaned up.
> >
> > That's not much of a downside though I don't think. The xenheap
> > (or PGC_extra domheap pages) are 'special' and so info about
> > them ought to be available via an alternate dump function anyway
> > (and if not already, it can be added).
> 
> Whatever you'd add, the logic would need to either traverse the
> entire ->page_list (can take very long) or have/use out of band
> information where such pages may have a record (fragile).
> 

But the shared xenheap pages in question are only shared info, or grant table, 
so their information can be dumped separately.
I guess it makes more sense to add another patch into the series to do explicit 
dump of shared_info and then exclude 'special' pages from dump_pageframe_info().

  Paul

> Jan


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