On 11/30/2012 07:21 AM, Kamezawa Hiroyuki wrote: > (2012/11/29 6:34), Tejun Heo wrote: >> Hello, guys. >> >> Depending on cgroup core locking - cgroup_mutex - is messy and makes >> cgroup prone to locking dependency problems. The current code already >> has lock dependency loop - memcg nests get_online_cpus() inside >> cgroup_mutex. cpuset the other way around. >> >> Regardless of the locking details, whatever is protecting cgroup has >> inherently to be something outer to most other locking constructs. >> cgroup calls into a lot of major subsystems which in turn have to >> perform subsystem-specific locking. Trying to nest cgroup >> synchronization inside other locks isn't something which can work >> well. >> >> cgroup now has enough API to allow subsystems to implement their own >> locking and cgroup_mutex is scheduled to be made private to cgroup >> core. This patchset makes cpuset implement its own locking instead of >> relying on cgroup_mutex. >> >> cpuset is rather nasty in this respect. Some of it seems to have come >> from the implementation history - cgroup core grew out of cpuset - but >> big part stems from cpuset's need to migrate tasks to an ancestor >> cgroup when an hotunplug event makes a cpuset empty (w/o any cpu or >> memory). >> >> This patchset decouples cpuset locking from cgroup_mutex. After the >> patchset, cpuset uses cpuset-specific cpuset_mutex instead of >> cgroup_mutex. This also removes the lockdep warning triggered during >> cpu offlining (see 0009). >> >> Note that this leaves memcg as the only external user of cgroup_mutex. >> Michal, Kame, can you guys please convert memcg to use its own locking >> too? >> > > Hmm. let me see....at quick glance cgroup_lock() is used at > hierarchy policy change > kmem_limit > migration policy change > swapiness change > oom control > > Because all aboves takes care of changes in hierarchy, > Having a new memcg's mutex in ->create() may be a way. > > Ah, hm, Costa is mentioning task-attach. is the task-attach problem in memcg ? > We disallow the kmem limit to be set if a task already exists in the cgroup. So we can't allow a new task to attach if we are setting the limit. -- 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>