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authorTejun Heo <tj@kernel.org>2014-07-08 18:02:57 -0400
committerTejun Heo <tj@kernel.org>2014-07-08 18:02:57 -0400
commitaf0ba6789c8e43518635606d0af1ff475ba7471a (patch)
treee191c511bc1102149d4e44b196ec96691179f67f /Documentation/cgroups
parentb4536f0cab2b18414e26101a2b9d484c5cbea0c0 (diff)
cgroup: implement cgroup_subsys->depends_on
Currently, the blkio subsystem attributes all of writeback IOs to the root. One of the issues is that there's no way to tell who originated a writeback IO from block layer. Those IOs are usually issued asynchronously from a task which didn't have anything to do with actually generating the dirty pages. The memory subsystem, when enabled, already keeps track of the ownership of each dirty page and it's desirable for blkio to piggyback instead of adding its own per-page tag. blkio piggybacking on memory is an implementation detail which preferably should be handled automatically without requiring explicit userland action. To achieve that, this patch implements cgroup_subsys->depends_on which contains the mask of subsystems which should be enabled together when the subsystem is enabled. The previous patches already implemented the support for enabled but invisible subsystems and cgroup_subsys->depends_on can be easily implemented by updating cgroup_refresh_child_subsys_mask() so that it calculates cgroup->child_subsys_mask considering cgroup_subsys->depends_on of the explicitly enabled subsystems. Documentation/cgroups/unified-hierarchy.txt is updated to explain that subsystems may not become immediately available after being unused from userland and that dependency could be a factor in it. As subsystems may already keep residual references, this doesn't significantly change how subsystem rebinding can be used. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Diffstat (limited to 'Documentation/cgroups')
-rw-r--r--Documentation/cgroups/unified-hierarchy.txt23
1 files changed, 20 insertions, 3 deletions
diff --git a/Documentation/cgroups/unified-hierarchy.txt b/Documentation/cgroups/unified-hierarchy.txt
index 324b182e6000..a7a2205539a7 100644
--- a/Documentation/cgroups/unified-hierarchy.txt
+++ b/Documentation/cgroups/unified-hierarchy.txt
@@ -97,9 +97,26 @@ change soon.
All controllers which are not bound to other hierarchies are
automatically bound to unified hierarchy and show up at the root of
it. Controllers which are enabled only in the root of unified
-hierarchy can be bound to other hierarchies at any time. This allows
-mixing unified hierarchy with the traditional multiple hierarchies in
-a fully backward compatible way.
+hierarchy can be bound to other hierarchies. This allows mixing
+unified hierarchy with the traditional multiple hierarchies in a fully
+backward compatible way.
+
+A controller can be moved across hierarchies only after the controller
+is no longer referenced in its current hierarchy. Because per-cgroup
+controller states are destroyed asynchronously and controllers may
+have lingering references, a controller may not show up immediately on
+the unified hierarchy after the final umount of the previous
+hierarchy. Similarly, a controller should be fully disabled to be
+moved out of the unified hierarchy and it may take some time for the
+disabled controller to become available for other hierarchies;
+furthermore, due to dependencies among controllers, other controllers
+may need to be disabled too.
+
+While useful for development and manual configurations, dynamically
+moving controllers between the unified and other hierarchies is
+strongly discouraged for production use. It is recommended to decide
+the hierarchies and controller associations before starting using the
+controllers.
2-2. cgroup.subtree_control