1 Threads (Tasks (threads) versus processes)
cgroup v1 可以单独操作进程中的线程, man cgroups :
In cgroups v1, a distinction is drawn between processes and tasks. In this view, a process can con‐ sist of multiple tasks (more commonly called threads, from a user-space perspective, and called such in the remainder of this man page). In cgroups v1, it is possible to independently manipulate the cgroup memberships of the threads in a process.
v2 中起初移除了线程支持，然后在后期又将其中的功能 “有限的” 加了回来：
The cgroups v1 ability to split threads across different cgroups caused problems in some cases. For example, it made no sense for the memory controller, since all of the threads of a process share a single address space. Because of these problems, the ability to independently manipulate the cgroup memberships of the threads in a process was removed in the initial cgroups v2 implementation, and subsequently restored in a more limited form (see the discussion of “thread mode” below).
1.1 cgroup v2 线程限制
Linux 4.14 为 cgroup v2 增加了线程模式，该模式可以：
• The creation of threaded subtrees in which the threads of a process may be spread across cgroups inside the tree. (A threaded subtree may contain multiple multithreaded processes.)
• The concept of threaded controllers, which can distribute resources across the cgroups in a threaded subtree.
• A relaxation of the “no internal processes rule”, so that, within a threaded subtree, a cgroup can both contain member threads and exercise resource control over child cgroups.