doc: memcontrol: fix the obsolete content about force empty

We don't do page cache reparent anymore when offlining memcg, so update
force empty related content accordingly.

Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

diff --git a/Documentation/cgroup-v1/memory.txt b/Documentation/cgroup-v1/memory.txt
index 3682e99234c2c6652ac4990504dfb14bd3873618..8e2cb1dabeb030fcb5e66334904216ef875df6ad 100644 (file)
--- a/Documentation/cgroup-v1/memory.txt
+++ b/Documentation/cgroup-v1/memory.txt
@@ -70,7 +70,7 @@ Brief summary of control files.
  memory.soft_limit_in_bytes     # set/show soft limit of memory usage
  memory.stat                    # show various statistics
  memory.use_hierarchy           # set/show hierarchical account enabled
  memory.soft_limit_in_bytes     # set/show soft limit of memory usage
  memory.stat                    # show various statistics
  memory.use_hierarchy           # set/show hierarchical account enabled

- memory.force_empty             # trigger forced move charge to parent
+ memory.force_empty             # trigger forced page reclaim

  memory.pressure_level          # set memory pressure notifications
  memory.swappiness              # set/show swappiness parameter of vmscan
                                 (See sysctl's vm.swappiness)
  memory.pressure_level          # set memory pressure notifications
  memory.swappiness              # set/show swappiness parameter of vmscan
                                 (See sysctl's vm.swappiness)


@@ -459,8 +459,9 @@ About use_hierarchy, see Section 6.
   the cgroup will be reclaimed and as many pages reclaimed as possible.
 
   The typical use case for this interface is before calling rmdir().
   the cgroup will be reclaimed and as many pages reclaimed as possible.
 
   The typical use case for this interface is before calling rmdir().

-  Because rmdir() moves all pages to parent, some out-of-use page caches can be
-  moved to the parent. If you want to avoid that, force_empty will be useful.
+  Though rmdir() offlines memcg, but the memcg may still stay there due to
+  charged file caches. Some out-of-use page caches may keep charged until
+  memory pressure happens. If you want to avoid that, force_empty will be useful.

 
   Also, note that when memory.kmem.limit_in_bytes is set the charges due to
   kernel pages will still be seen. This is not considered a failure and the
 
   Also, note that when memory.kmem.limit_in_bytes is set the charges due to
   kernel pages will still be seen. This is not considered a failure and the