On Thu 23-06-22 09:42:43, Shakeel Butt wrote: > On Thu, Jun 23, 2022 at 9:37 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > On Thu 23-06-22 09:22:35, Yosry Ahmed wrote: > > > On Thu, Jun 23, 2022 at 2:43 AM Michal Hocko <mhocko@xxxxxxxx> wrote: > > > > > > > > On Thu 23-06-22 01:35:59, Yosry Ahmed wrote: > > [...] > > > > > In our internal version of memory.reclaim that we recently upstreamed, > > > > > we do not account vmpressure during proactive reclaim (similar to how > > > > > psi is handled upstream). We want to make sure this behavior also > > > > > exists in the upstream version so that consolidating them does not > > > > > break our users who rely on vmpressure and will start seeing increased > > > > > pressure due to proactive reclaim. > > > > > > > > These are good reasons to have this patch in your tree. But why is this > > > > patch benefitial for the upstream kernel? It clearly adds some code and > > > > some special casing which will add a maintenance overhead. > > > > > > It is not just Google, any existing vmpressure users will start seeing > > > false pressure notifications with memory.reclaim. The main goal of the > > > patch is to make sure memory.reclaim does not break pre-existing users > > > of vmpressure, and doing it in a way that is consistent with psi makes > > > sense. > > > > memory.reclaim is v2 only feature which doesn't have vmpressure > > interface. So I do not see how pre-existing users of the upstream kernel > > can see any breakage. > > > > Please note that vmpressure is still being used in v2 by the > networking layer (see mem_cgroup_under_socket_pressure()) for > detecting memory pressure. I have missed this. It is hidden quite good. I thought that v2 is completely vmpressure free. I have to admit that the effect of mem_cgroup_under_socket_pressure is not really clear to me. Not to mention whether it should or shouldn't be triggered for the user triggered memory reclaim. So this would really need some explanation. > Though IMO we should deprecate vmpressure altogether. Yes it should be really limited to v1. But as I've said the effect on mem_cgroup_under_socket_pressure is not really clear to me. It really seems the v2 support has been introduced deliberately. -- Michal Hocko SUSE Labs
