On Tue, Nov 29, 2022 at 11:08 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > On Mon, Nov 28, 2022 at 11:59:53AM -0500, Johannes Weiner wrote: > > On Wed, Nov 23, 2022 at 10:03:00PM -0800, Hugh Dickins wrote: > > The swapcache/pagecache bit was a brainfart. We acquire the folio lock > > in move_account(), which would lock out concurrent faults. If it's not > > mapped, I don't see how it could become mapped behind our backs. But > > we do need to be prepared for it to be unmapped. > > Welp, that doesn't protect us from the inverse, where the page is > mapped elsewhere and the other ptes are going away. So this won't be > enough, unfortunately. > > > > Does that mean that we just have to reinstate the folio_mapped() checks > > > in mm/memcontrol.c i.e. revert all mm/memcontrol.c changes from the > > > commit? Or does it invalidate the whole project to remove > > > lock_page_memcg() from mm/rmap.c? > > Short of further restricting the pages that can be moved, I don't see > how we can get rid of the cgroup locks in rmap after all. :( > > We can try limiting move candidates to present ptes. But maybe it's > indeed time to deprecate the legacy charge moving altogether, and get > rid of the entire complication. > > Hugh, Shakeel, Michal, what do you think? I am on-board.
