[Cc Tejun and Christian - this is a part of a larger discussion which is not directly related to this particular question so let me trim the original email to the bare minimum.] On Fri 18-09-20 12:40:32, Peter Xu wrote: [...] > One issue is when we charge for cgroup we probably can't do that onto the new > mm/task, since copy_namespaces() is called after copy_mm(). I don't know > enough about cgroup, I thought the child will inherit the parent's, but I'm not > sure. Or, can we change that order of copy_namespaces() && copy_mm()? I don't > see a problem so far but I'd like to ask first.. I suspect you are referring to CLONE_INTO_CGROUP, right? I have only now learned about this feature so I am not deeply familiar with all the details and I might be easily wrong. Normally all the cgroup aware resources are accounted to the parent's cgroup. For memcg that includes all the page tables, early CoW and other allocations with __GFP_ACCOUNT. IIUC CLONE_INTO_CGROUP properly then this hasn't changed as the child is associated to its new cgroup (and memcg) only in cgroup_post_fork. If that is correct then we might have quite a lot of resources bound to child's lifetime but accounted to the parent's memcg which can lead to all sorts of interesting problems (e.g. unreclaimable memory - even by the oom killer). Christian, Tejun is this the expected semantic or I am just misreading the code? -- Michal Hocko SUSE Labs
