cgroup, memcg: move cgroup_event implementation to memcg

cgroup_event is way over-designed and tries to build a generic
flexible event mechanism into cgroup - fully customizable event
specification for each user of the interface.  This is utterly
unnecessary and overboard especially in the light of the planned
unified hierarchy as there's gonna be single agent.  Simply generating
events at fixed points, or if that's too restrictive, configureable
cadence or single set of configureable points should be enough.

Thankfully, memcg is the only user and gets to keep it.  Replacing it
with something simpler on sane_behavior is strongly recommended.

This patch moves cgroup_event and "cgroup.event_control"
implementation to mm/memcontrol.c.  Clearing of events on cgroup
destruction is moved from cgroup_destroy_locked() to
mem_cgroup_css_offline(), which shouldn't make any noticeable
difference.

cgroup_css() and __file_cft() are exported to enable the move;
however, this will soon be reverted once the event code is updated to
be memcg specific.

Note that "cgroup.event_control" will now exist only on the hierarchy
with memcg attached to it.  While this change is visible to userland,
it is unlikely to be noticeable as the file has never been meaningful
outside memcg.

Aside from the above change, this is pure code relocation.

v2: Per Li Zefan's comments, init/Kconfig updated accordingly and
    poll.h inclusion moved from cgroup.c to memcontrol.c.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 3ecd8a1178f1..3ca5b8110b0c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -861,7 +861,6 @@ config NUMA_BALANCING
 
 menuconfig CGROUPS
         boolean "Control Group support"
-        depends on EVENTFD
         help
           This option adds support for grouping sets of processes together, for
           use with process control subsystems such as Cpusets, CFS, memory
@@ -928,6 +927,7 @@ config MEMCG
         bool "Memory Resource Controller for Control Groups"
         depends on RESOURCE_COUNTERS
         select MM_OWNER
+        select EVENTFD
         help
           Provides a memory resource controller that manages both anonymous
           memory and page cache. (See Documentation/cgroups/memory.txt)
@@ -1167,7 +1167,6 @@ config UIDGID_STRICT_TYPE_CHECKS
 
 config SCHED_AUTOGROUP
         bool "Automatic process group scheduling"
-        select EVENTFD
         select CGROUPS
         select CGROUP_SCHED
         select FAIR_GROUP_SCHED