On Tue Jun 10, 2025 at 2:23 PM CEST, 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. > >> 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.
Ugh. I missed that. Regardless, the current scheme is highly counterintuitive and works only because toolstack colaborates in removing the claim after dom creation. > >> 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. > > It _is_ a memory operation, and it re-uses one of the interface structs > there. (Yes, none of these would technically have prevented it from > being a domctl.) > > Jan As Jan mentions, my understanding was that __XEN_TOOLS__ effectively meant unstable. It is quite hard to keep the previous semantics for one hypercall while introducing a new one that behaves slightly differently. Cheers, Alejandro
