On Tue, Dec 21, 2021 at 10:51 AM David Hildenbrand [off-list ref] wrote:

For that purpose the pincount would already kind-off work. Not precise,
but at least something ("this page cannot possibly have been pinned").

That part actually exists already, ie put_page_refs() has this:

  #ifdef CONFIG_DEBUG_VM
        if (VM_WARN_ON_ONCE_PAGE(page_ref_count(page) < refs, page))
                return;
  #endif

And yeah, it shouldn't have that '#ifdef CONFIG_DEBUG_VM' there, but I
think it's because the non-CONFIG_DEBUG_VM #define for
VM_WARN_ON_ONCE_PAGE() is broken, and doesn't return 0.

                   Linus