On Mon, Jul 04, 2022 at 05:07:30PM +0200, Michal Hocko wrote: > On Sat 02-07-22 08:39:14, Roman Gushchin wrote: > > On Fri, Jul 01, 2022 at 10:50:40PM -0700, Shakeel Butt wrote: > > > On Fri, Jul 1, 2022 at 8:35 PM Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote: > > > > > > > > Yafang Shao reported an issue related to the accounting of bpf > > > > memory: if a bpf map is charged indirectly for memory consumed > > > > from an interrupt context and allocations are enforced, MEMCG_MAX > > > > events are not raised. > > > > > > > > It's not/less of an issue in a generic case because consequent > > > > allocations from a process context will trigger the reclaim and > > > > MEMCG_MAX events. However a bpf map can belong to a dying/abandoned > > > > memory cgroup, so it might never happen. > > > > > > The patch looks good but the above sentence is confusing. What might > > > never happen? Reclaim or MAX event on dying memcg? > > > > Direct reclaim and MAX events. I agree it might be not clear without > > looking into the code. How about something like this? > > > > "It's not/less of an issue in a generic case because consequent > > allocations from a process context will trigger the direct reclaim > > and MEMCG_MAX events will be raised. However a bpf map can belong > > to a dying/abandoned memory cgroup, so there will be no allocations > > from a process context and no MEMCG_MAX events will be triggered." > > Could you expand little bit more on the situation? Can those charges to > offline memcg happen indefinetely? Yes. > How can it ever go away then? Bpf map should be deleted by a user first. > Also is this something that we actually want to encourage? Not really. We can implement reparenting (probably objcg-based), I think it's a good idea in general. I can take a look, but can't promise it will be fast. In thory we can't forbid deleting cgroups with associated bpf maps, but I don't thinks it's a good idea. > In other words shouldn't those remote charges be redirected when the > target memcg is offline? Reparenting is the best answer I have. Thanks!
