On 07/16/2017 10:07 PM, Tejun Heo wrote: > > +Threads > +~~~~~~~ > + > +cgroup v2 supports thread granularity for a subset of controllers to > +support use cases requiring hierarchical resource distribution across > +the threads of a group of processes. By default, all threads of a > +process belong to the same cgroup, which also serves as the resource > +domain to host resource consumptions which are not specific to a > +process or thread. The thread mode allows threads to be spread across > +a subtree while still maintaining the common resource domain for them. > + > +Controllers which support thread mode are called threaded controllers. > +The ones which don't are called domain controllers. > + > +Marking a cgroup threaded makes it join the resource domain of its > +parent as a threaded cgroup. The parent may be another threaded > +cgroup whose resource domain is further up in the hierarchy. The root > +of a threaded subtree, that is, the nearest ancestor which is not > +threaded, is called threaded domain and serves as the resource domain > +for the entire subtree.
The cgroup code uses the term "thread root" in quite a number of places. So a developer may be confused when comparing the code and the documentation. I would recommend either introducing "thread root" as an alias for threaded domain here in the documentation or documenting that "threaded domain = thread root" in the code. > + cgroup.type > + > + A read-write single value file which exists on non-root > + cgroups. > + > + When read, it indicates the current type of the cgroup, which > + can be one of the following values. > + > + - "domain" : A normal valid domain cgroup. > + > + - "domain (threaded)" : A threaded domain cgroup which is > + serving as the root of a threaded subtree. > + > + - "domain (invalid)" : A cgroup which is in an invalid state. > + It can't be populated or have controllers enabled. It may > + be allowed to become a threaded cgroup. > + > + - "threaded" : A threaded cgroup which is a member of a > + threaded subtree. > + > + A cgroup can be turned into a threaded cgroup by writing > + "threaded" to this file. > + > cgroup.procs > A read-write new-line separated values file which exists on > all cgroups. Do we need to document that cgroup.procs isn't writable in a threaded cgroup? > @@ -4301,6 +4606,7 @@ static struct cgroup *cgroup_create(struct cgroup > *parent) > cgrp->self.parent = &parent->self; > cgrp->root = root; > cgrp->level = level; > + cgrp->dom_cgrp = cgrp->dom_cgrp; It is a no-op. I think it is better to modify it to + cgrp->dom_cgrp = cgroup_is_threaded(parent) ? parent->dom_cgrp : cgrp; Then we won't have an invalid domain state. Cheers, Longman
