On Thu, Jan 25, 2024 at 12:02 AM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > > > // lru list lock held > > > shrink_memcg_cb() > > > swpentry = entry->swpentry > > > // Don't isolate entry from lru list here, just use list_lru_putback() > > > spin_unlock(lru list lock) > > > > > > folio = __read_swap_cache_async(swpentry) > > > if (!folio) > > > return > > > > > > if (!folio_was_allocated) > > > folio_put(folio) > > > return > > > > > > // folio is locked, swapcache is secured against swapoff > > > tree = get tree from swpentry > > > spin_lock(&tree->lock) > > > > That will not work well with zswap to xarray change. We want to remove > > the tree lock and only use the xarray lock. > > The lookup should just hold xarray RCU read lock and return the entry > > with ref count increased. > > In this path, we also invalidate the zswap entry, which would require > holding the xarray lock anyway. It will drop the RCU read lock after finding the entry and re-acquire the xarray spin lock on invalidation. In between there is a brief moment without locks. Chris
