linux-kernel - [PATCH 1/3] doc: memcontrol: fix the obsolete content about force empty

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Message-Id: <1546459533-36247-2-git-send-email-yang.shi@linux.alibaba.com>
Date:   Thu,  3 Jan 2019 04:05:31 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     mhocko@...e.com, hannes@...xchg.org, akpm@...ux-foundation.org
Cc:     yang.shi@...ux.alibaba.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] 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.

Cc: Michal Hocko <mhocko@...e.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
---
 Documentation/cgroup-v1/memory.txt | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/Documentation/cgroup-v1/memory.txt b/Documentation/cgroup-v1/memory.txt
index 3682e99..8e2cb1d 100644
--- 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.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)
@@ -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().
-  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
-- 
1.8.3.1