From cc926f78420705817b807dbec0c5d3643827eba3 Mon Sep 17 00:00:00 2001 From: KAMEZAWA Hiroyuki Date: Tue, 29 May 2012 15:07:04 -0700 Subject: memcg: move charges to root cgroup if use_hierarchy=0 Presently, at removal of cgroup, ->pre_destroy() is called and moves charges to the parent cgroup. A major reason for returning -EBUSY from ->pre_destroy() is that the 'moving' hits the parent's resource limitation. It happens only when use_hierarchy=0. Considering use_hierarchy=0, all cgroups should be flat. So, no one cannot justify moving charges to parent...parent and children are in flat configuration, not hierarchical. This patch modifes the code to move charges to the root cgroup at rmdir/force_empty if use_hierarchy==0. This will much simplify rmdir() and reduce error in ->pre_destroy. Signed-off-by: KAMEZAWA Hiroyuki Cc: Aneesh Kumar K.V Cc: Michal Hocko Cc: Johannes Weiner Cc: Frederic Weisbecker Cc: Ying Han Cc: Glauber Costa Reviewed-by: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/cgroups/memory.txt | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) (limited to 'Documentation') diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index 6a066a2..dd88540 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -376,14 +376,15 @@ cgroup might have some charge associated with it, even though all tasks have migrated away from it. (because we charge against pages, not against tasks.) -Such charges are freed or moved to their parent. At moving, both of RSS -and CACHES are moved to parent. -rmdir() may return -EBUSY if freeing/moving fails. See 5.1 also. +We move the stats to root (if use_hierarchy==0) or parent (if +use_hierarchy==1), and no change on the charge except uncharging +from the child. Charges recorded in swap information is not updated at removal of cgroup. Recorded information is discarded and a cgroup which uses swap (swapcache) will be charged as a new owner of it. +About use_hierarchy, see Section 6. 5. Misc. interfaces. @@ -396,13 +397,15 @@ will be charged as a new owner of it. Almost all pages tracked by this memory cgroup will be unmapped and freed. Some pages cannot be freed because they are locked or in-use. Such pages are - moved to parent and this cgroup will be empty. This may return -EBUSY if - VM is too busy to free/move all pages immediately. + moved to parent(if use_hierarchy==1) or root (if use_hierarchy==0) and this + cgroup will be empty. Typical use case of this interface is that calling this before 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. + About use_hierarchy, see Section 6. + 5.2 stat file memory.stat file includes following statistics -- cgit v1.1