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

["Roger Pau Monné" <roger.pau@citrix.com>]

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.  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).

I have no idea why this was made a xenmem rather than a domctl
hypercall, but if you want to change the semantics I think the only
option is introducing a new hypercall.

Thanks, Roger.