On Thu, Dec 21, 2023 at 03:19:12AM +0000, Pasha Tatashin wrote: > This series frees empty page tables on unmaps. It intends to be a > low overhead feature. > > The read-writer lock is used to synchronize page table, but most of > time the lock is held is reader. It is held as a writer for short > period of time when unmapping a page that is bigger than the current > iova request. For all other cases this lock is read-only. > > page->refcount is used in order to track number of entries at each page > table. Have I not put enough DANGER signs up around the page refcount? * If you want to use the refcount field, it must be used in such a way * that other CPUs temporarily incrementing and then decrementing the * refcount does not cause problems. On receiving the page from * alloc_pages(), the refcount will be positive. You can't use refcount for your purpose, and honestly I'm shocked you haven't seen any of your WARNings trigger.
