I have an application that does the following: * copy the state of all controllers attached to a hierarchy * replicate it as a child of the current level.
I would expect writes to the files to mostly succeed, since they are inheriting sane values from parents. But that is not the case for use_hierarchy. If it is set to 0, we succeed ok. If we're set to 1, the value of the file is automatically set to 1 in the children, but if userspace tries to write the very same 1, it will fail. That same situation happens if we set use_hierarchy, create a child, and then try to write 1 again. Now, there is no reason whatsoever for failing to write a value that is already there. It doesn't even match the comments, that states: /* If parent's use_hierarchy is set, we can't make any modifications * in the child subtrees... since we are not changing anything. The following patch tests the new value against the one we're storing, and automatically return 0 if we're not proposing a change. Signed-off-by: Glauber Costa <[email protected]> CC: Dhaval Giani <[email protected]> CC: Michal Hocko <[email protected]> CC: Kamezawa Hiroyuki <[email protected]> CC: Johannes Weiner <[email protected]> --- mm/memcontrol.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ac35bcc..cccebbc 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3779,6 +3779,10 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft, parent_memcg = mem_cgroup_from_cont(parent); cgroup_lock(); + + if (memcg->use_hierarchy == val) + goto out; + /* * If parent's use_hierarchy is set, we can't make any modifications * in the child subtrees. If it is unset, then the change can @@ -3795,6 +3799,8 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft, retval = -EBUSY; } else retval = -EINVAL; + +out: cgroup_unlock(); return retval; -- 1.7.10.2 _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
