(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 ? Thanks, -Kame > This patchset contains the following thirteen patches. > > 0001-cpuset-remove-unused-cpuset_unlock.patch > 0002-cpuset-remove-fast-exit-path-from-remove_tasks_in_em.patch > 0003-cpuset-introduce-css_on-offline.patch > 0004-cpuset-introduce-CS_ONLINE.patch > 0005-cpuset-introduce-cpuset_for_each_child.patch > 0006-cpuset-cleanup-cpuset-_can-_attach.patch > 0007-cpuset-drop-async_rebuild_sched_domains.patch > 0008-cpuset-reorganize-CPU-memory-hotplug-handling.patch > 0009-cpuset-don-t-nest-cgroup_mutex-inside-get_online_cpu.patch > 0010-cpuset-make-CPU-memory-hotplug-propagation-asynchron.patch > 0011-cpuset-pin-down-cpus-and-mems-while-a-task-is-being-.patch > 0012-cpuset-schedule-hotplug-propagation-from-cpuset_atta.patch > 0013-cpuset-replace-cgroup_mutex-locking-with-cpuset-inte.patch > > 0001-0006 are prep patches. > > 0007-0009 make cpuset nest get_online_cpus() inside cgroup_mutex, not > the other way around. > > 0010-0012 plug holes which would be exposed by switching to > cpuset-specific locking. > > 0013 replaces cgroup_mutex with cpuset_mutex. > > This patchset is on top of cgroup/for-3.8 (fddfb02ad0) and also > available in the following git branch. > > git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-cpuset-locking > > diffstat follows. > > kernel/cpuset.c | 750 +++++++++++++++++++++++++++++++------------------------- > 1 file changed, 423 insertions(+), 327 deletions(-) > > Thanks. > > -- > tejun > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- 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>