On Thu, Feb 2, 2017 at 12:06 PM, Tejun Heo <t...@kernel.org> wrote: > Hello, > > This patchset implements cgroup v2 thread mode. It is largely based > on the discussions that we had at the plumbers last year. Here's the > rough outline.
I like this, but I have some design questions: > > * Thread mode is explicitly enabled on a cgroup by writing "enable" > into "cgroup.threads" file. The cgroup shouldn't have any child > cgroups or enabled controllers. Why do you need to manually turn it on? That is, couldn't it be automatic based on what controllers are enabled? > > * Once enabled, arbitrary sub-hierarchy can be created and threads can > be put anywhere in the subtree by writing TIDs into "cgroup.threads" > file. Process granularity and no-internal-process constraint don't > apply in a threaded subtree. I'm a bit worried that this conflates two different things. There's thread support, i.e. allowing individual threads to be placed into cgroups. There's also more flexible sub-hierarchy support, i.e. relaxing no-internal-process constraints. For the "cpuacct" controller, for example, both of these make sense. But what if someone writes a controller (directio, for example, just to make something up) for which thread granularity makes sense but relaxing no-internal-process constraints does not? --Andy
