Re: [PATCH 02/11] xen/page_alloc: Remove `claim` from domain_set_outstanding_pages()

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

On Tue, Jun 10, 2025 at 02:23:26PM +0200, Jan Beulich wrote:
> On 05.06.2025 18:42, Roger Pau Monné wrote:
> > On Fri, Mar 14, 2025 at 05:24:53PM +0000, Alejandro Vallejo wrote:
> >> With a single global count for the claims it's easy to substract
> >> domain_tot_pages() from the claim so the number given in the hypercall
> >> is the real reservation of the domain. This is the current behaviour.
> >>
> >> However, a later patch introduces exact-node claims and those interact
> >> very poorly with such a scheme. Since accounting domain_tot_pages() in
> >> one case but not the other seems strictly worse than not accounting them
> >> at all (which is at least consistent), this patch stops substracting
> >> tot_pages from the claim and instead checks that claimed memory +
> >> allocated memory don't exceed max_mem.
> > 
> > Hm, while I don't have any specific interest in keeping the current
> > behavior, XENMEM_claim_pages is part of the stable ABI (it's not a
> > domctl), and hence should be stable.
> 
> Is that true? It sits inside a
> 
> #if defined(__XEN__) || defined(__XEN_TOOLS__)
> 
> which generally de-marks unstable (tools-only) interfaces.

Ops, my bad, I didn't realize it was inside such region.

> >  Note also the comment above the
> > definition of XENMEM_claim_pages how it states the specific behavior
> > that you are trying to change (and which should have been adjusted as
> > part of this change).
> 
> This is the more important part, imo.

I see.  Well, it's in a kind of a weird position then, because there's
no equivalent of XEN_DOMCTL_INTERFACE_VERSION that we could use to
signal callers of the changed interface, like we do for domctl.

Thanks, Roger.