Messages in this thread | | | Date | Wed, 24 Aug 2022 12:27:00 +0200 | From | Michal Hocko <> | Subject | Re: [RFC PATCH] memcg: use root_mem_cgroup when css is inherited |
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On Wed 24-08-22 17:34:42, Zhaoyang Huang wrote: > On Wed, Aug 24, 2022 at 3:50 PM Michal Hocko <mhocko@suse.com> wrote: > > > > On Wed 24-08-22 10:23:14, Zhaoyang Huang wrote: > > > On Tue, Aug 23, 2022 at 7:51 PM Michal Hocko <mhocko@suse.com> wrote: > > [...] > > > > One way to achieve that would be shaping the hierarchy the following way > > > > root > > > > / \ > > > > no_memcg[1] memcg[2] > > > > |||||||| ||||| > > > > app_cgroups app_cgroups > > > > > > > > with > > > > no_memcg.subtree_control = "" > > > > memcg.subtree_control = memory > > > > > > > > no? > > > According to my understanding, No as there will be no no_memcg. All > > > children groups under root would have its cgroup.controllers = memory > > > as long as root has memory enabled. > > > > Correct > > > > > Under this circumstance, all > > > descendants group under 'no_memcg' will charge memory to its parent > > > group. > > > > Correct. And why is that a problem? I thought you main concern was a per > > application LRUs. With the above configuration all app_cgroups which do > > not require an explicit memory control will share the same (no_memcg) > > LRU and they will be aged together. > I can't agree since this indicates the processes want memory free > depending on a specific hierarchy which could have been determined by > other subsys.
I really fail to understand your requirements.
> IMHO, charging the pages which out of explicitly memory > enabled group to root could solve all of the above constraints with no > harm.
This would break the hierarchical property of the controller. So a strong no no. Consider the following example
root | A controllers="memory" memory.max = 1G subtree_control="" | | | A1 A2 A3
althought A1,2,3 do not have their memory controller enabled explicitly they are still constrained by the A memcg limit. If you just charge to the root because it doesn't have memory controller enabled explicitly then you just evade that constrain. I hope you understand why that is a problem. -- Michal Hocko SUSE Labs
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