On Thu 15-12-22 09:58:12, Wei Xu wrote: > On Wed, Dec 14, 2022 at 2:23 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Tue 13-12-22 11:29:45, Mina Almasry wrote: > > > On Tue, Dec 13, 2022 at 6:03 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > > > On Tue 13-12-22 14:30:40, Johannes Weiner wrote: > > > > > On Tue, Dec 13, 2022 at 02:30:57PM +0800, Huang, Ying wrote: > > > > [...] > > > > > > After these discussion, I think the solution maybe use different > > > > > > interfaces for "proactive demote" and "proactive reclaim". That is, > > > > > > reconsider "memory.demote". In this way, we will always uncharge the > > > > > > cgroup for "memory.reclaim". This avoid the possible confusion there. > > > > > > And, because demotion is considered aging, we don't need to disable > > > > > > demotion for "memory.reclaim", just don't count it. > > > > > > > > > > Hm, so in summary: > > > > > > > > > > 1) memory.reclaim would demote and reclaim like today, but it would > > > > > change to only count reclaimed pages against the goal. > > > > > > > > > > 2) memory.demote would only demote. > > > > > > > > > > > If the above 2 points are agreeable then yes, this sounds good to me > > > and does address our use case. > > > > > > > > a) What if the demotion targets are full? Would it reclaim or fail? > > > > > > > > > > > Wei will chime in if he disagrees, but I think we _require_ that it > > > fails, not falls back to reclaim. The interface is asking for > > > demotion, and is called memory.demote. For such an interface to fall > > > back to reclaim would be very confusing to userspace and may trigger > > > reclaim on a high priority job that we want to shield from proactive > > > reclaim. > > > > But what should happen if the immediate demotion target is full but > > lower tiers are still usable. Should the first one demote before > > allowing to demote from the top tier? > > In that case, the demotion will fall back to the lower tiers. See > node_get_allowed_targets() and establish_demotion_targets().. I am not talking about an implicit behavior that we do not want to cast into interface. If we want to allow a fine grained control over demotion then the implementation shouldn't rely on the current behavior. [...] > > Is there any strong reason for that? We do not have any interface to > > control NUMA balancing from userspace. Why cannot we use the interface > > for that purpose? > > A demotion interface such as memory.demote will trigger the demotion > code path in the kernel, which depends on multiple memory tiers. Demotion is just a fancy name of a directed migration. There is no realy dependency on the HW nor the technology. > I think what you are getting is a more general page migration > interface for memcg, which will need both source and target nodes as > arguments. I think this can be a great idea. It should be able to > support our demotion use cases as well. yes. -- Michal Hocko SUSE Labs
