On 2012/7/21 4:05, Tejun Heo wrote: > Hey, Peter. > > On Fri, Jul 20, 2012 at 05:45:40PM +0200, Peter Zijlstra wrote: >>> So, Peter, why does cpuset mangle with cgroup_mutex? What guarantees >>> does it need? Why can't it work on "changed" notification while >>> caching the current css like blkcg does? >> >> I've no clue sorry.. /me goes stare at this stuff.. Looks like something >> Paul Menage did when he created cgroups. I'll have to have a hard look >> at all that to untangle this. Not something obvious to me. > > Yeah, it would be great if this can be untangled. I really don't see > any other reasonable way out of this circular locking mess. If cpuset > needs stable css association across certain period, the RTTD is > caching the css by holding its ref and synchronize modifications to > that cache, rather than synchronizing cgroup operations themselves. > The cgroup core was extracted from cpuset, so they are deeply tangled. There are several issues to resolve with regard to removing cgroup lock from cpuset. - there are places that the cgroup hierarchy is travelled. This should be easy, as cpuset can be made to maintain its hierarchy. - cpuset disallows clearing cpuset.mems/cpuset.cpus if the cgroup is not empty, which can be guaranteed only by cgroup lock. - cpuset disallows a task be attached to a cgroup with empty cpuset.mems/cpuset.cpus, which again can be guarantted only by cgroup lock. - cpuset may move tasks from a cgroup to another cgroup (Glauber mentioned this). - maybe other cases I overlooked.. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>