On Sat, Dec 18, 2021 at 04:52:13AM +0000, Nadav Amit wrote: > Take for instance memcached and assume you overcommit memory with a very fast > swap (e.g., pmem, zram, perhaps even slower). Now, it turns out memcached > often accesses a page first for read and shortly after for write. I > encountered, in a similar scenario, that the page reference that > lru_cache_add() takes during the first faultin event (for read), causes a COW > on a write page-fault that happens shortly after [1]. So on memcached I > assume this would also trigger frequent unnecessary COWs. Why are we comparing page_count() against 1 and not 1 + PageLRU(page)? Having a reference from the LRU should be expected. Is it because of some race that we'd need to take the page lock to protect against?
