On Mon, Nov 25, 2019 at 10:42 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > > On Mon, Nov 25, 2019 at 03:21:50PM +0100, Michal Hocko wrote: > > On Mon 25-11-19 22:11:15, Yafang Shao wrote: > > > When there're no processes, we don't need to protect the pages. You > > > can consider it as 'fault tolerance' . > > > > I have already tried to explain why this is a bold statement that > > doesn't really hold universally and that the kernel doesn't really have > > enough information to make an educated guess. > > I agree, this is not obviously true. And the kernel shouldn't try to > guess whether the explicit userspace configuration is still desirable > to userspace or not. Should we also delete the cgroup when it becomes > empty for example? > > It's better to implement these kinds of policy decisions from > userspace. > > There is a cgroup.events file that can be polled, and its "populated" > field shows conveniently whether there are tasks in a subtree or > not. You can use that to clear protection settings. Why isn't force_empty supported in cgroup2 ? In this case we can free the protected file pages immdiately with force_empty. The advantage of it is to avoid scaning all other memcgs in kswapd/direct reclaim paths, because currently the reclaimer will fairly scan all memcgs and reclaim pages from them. What's the problem with force_empty ? Thanks Yafang
