On Wed, Jan 28, 2026 at 03:46:04PM +0100, Jan Beulich wrote:
> On 28.01.2026 13:03, Roger Pau Monne wrote:
> > @@ -275,7 +339,18 @@ static void populate_physmap(struct memop_args *a)
> > }
> > else
> > {
> > - page = alloc_domheap_pages(d, a->extent_order,
> > a->memflags);
> > + unsigned int scrub_start = 0;
> > + nodeid_t node =
> > + (a->memflags & MEMF_exact_node) ?
> > MEMF_get_node(a->memflags)
> > + : NUMA_NO_NODE;
> > +
> > + page = get_stashed_allocation(d, a->extent_order, node,
> > + &scrub_start);
> > +
> > + if ( !page )
> > + page = alloc_domheap_pages(d, a->extent_order,
> > + a->memflags | (d->creation_finished ? 0
> > + :
> > MEMF_no_scrub));
>
> I fear there's a more basic issue here that so far we didn't pay attention to:
> alloc_domheap_pages() is what invokes assign_page(), which in turn resets
> ->count_info for each of the pages. This reset includes setting PGC_allocated,
> which ...
>
> > @@ -286,6 +361,30 @@ static void populate_physmap(struct memop_args *a)
> > goto out;
> > }
> >
> > + if ( !d->creation_finished )
> > + {
> > + unsigned int dirty_cnt = 0;
> > +
> > + /* Check if there's anything to scrub. */
> > + for ( j = scrub_start; j < (1U << a->extent_order);
> > j++ )
> > + {
> > + if ( !test_and_clear_bit(_PGC_need_scrub,
> > + &page[j].count_info) )
> > + continue;
>
> ... means we will now scrub every page in the block, not just those which
> weren't
> scrubbed yet, and we end up clearing PGC_allocated. All because of
> PGC_need_scrub
> aliasing PGC_allocated. I wonder how this didn't end up screwing any testing
> you
> surely will have done. Or maybe I'm completely off here?
Thanks for spotting this! No, I didn't see any issues. I don't see
any check for PGC_allocated in free_domheap_pages(), which could
explain the lack of failures?
I will have to allocate with MEMF_no_owner and then do the
assign_pages() call from populate_physmap() after the scrubbing is
done. Maybe that would work. Memory allocated using MEMF_no_owner
still consumes the claim pool if a domain parameter is passed to
alloc_heap_pages().
Roger.
