Commit 18421863 authored by Roman Gushchin's avatar Roman Gushchin Committed by Linus Torvalds
Browse files

docs: cgroup-v1: reflect the deprecation of the non-hierarchical mode 

Update cgroup v1 docs after the deprecation of the non-hierarchical mode
of the memory controller.

Link: https://lkml.kernel.org/r/20201110220800.929549-3-guro@fb.com


Signed-off-by: default avatarRoman Gushchin <guro@fb.com>
Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent bef8620c

Documentation/admin-guide/cgroup-v1/memcg_test.rst

+3 −5
Original line number Diff line number Diff line
@@ -219,13 +219,11 @@ Under below explanation, we assume CONFIG_MEM_RES_CTRL_SWAP=y. 


	This is an easy way to test page migration, too.



9.5 mkdir/rmdir

---------------

9.5 nested cgroups

------------------



	When using hierarchy, mkdir/rmdir test should be done.

	Use tests like the following::

	Use tests like the following for testing nested cgroups::



		echo 1 >/opt/cgroup/01/memory/use_hierarchy

		mkdir /opt/cgroup/01/child_a

		mkdir /opt/cgroup/01/child_b

Documentation/admin-guide/cgroup-v1/memory.rst

+13 −27
Original line number Diff line number Diff line
@@ -77,6 +77,8 @@ 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

                                     This knob is deprecated and shouldn't be

                                     used.

 memory.force_empty		     trigger forced page reclaim

 memory.pressure_level		     set memory pressure notifications

 memory.swappiness		     set/show swappiness parameter of vmscan
@@ -495,16 +497,13 @@ 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.)



We move the stats to root (if use_hierarchy==0) or parent (if

use_hierarchy==1), and no change on the charge except uncharging

We move the stats to parent, 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

===================
@@ -527,8 +526,6 @@ About use_hierarchy, see Section 6. 
  write will still return success. In this case, it is expected that

  memory.kmem.usage_in_bytes == memory.usage_in_bytes.



  About use_hierarchy, see Section 6.



5.2 stat file

-------------
@@ -675,31 +672,20 @@ hierarchy:: 
		      d   e



In the diagram above, with hierarchical accounting enabled, all memory

usage of e, is accounted to its ancestors up until the root (i.e, c and root),

that has memory.use_hierarchy enabled. If one of the ancestors goes over its

limit, the reclaim algorithm reclaims from the tasks in the ancestor and the

children of the ancestor.



6.1 Enabling hierarchical accounting and reclaim

------------------------------------------------



A memory cgroup by default disables the hierarchy feature. Support

can be enabled by writing 1 to memory.use_hierarchy file of the root cgroup::

usage of e, is accounted to its ancestors up until the root (i.e, c and root).

If one of the ancestors goes over its limit, the reclaim algorithm reclaims

from the tasks in the ancestor and the children of the ancestor.



	# echo 1 > memory.use_hierarchy



The feature can be disabled by::

6.1 Hierarchical accounting and reclaim

---------------------------------------



	# echo 0 > memory.use_hierarchy

Hierarchical accounting is enabled by default. Disabling the hierarchical

accounting is deprecated. An attempt to do it will result in a failure

and a warning printed to dmesg.



NOTE1:

       Enabling/disabling will fail if either the cgroup already has other

       cgroups created below it, or if the parent cgroup has use_hierarchy

       enabled.

For compatibility reasons writing 1 to memory.use_hierarchy will always pass::



NOTE2:

       When panic_on_oom is set to "2", the whole system will panic in

       case of an OOM event in any cgroup.

	# echo 1 > memory.use_hierarchy



7. Soft limits

==============