Refine cgroup v2 docs after latest memory.low changes.
Signed-off-by: Roman Gushchin <g...@fb.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Michal Hocko <mho...@kernel.org>
Cc: Vladimir Davydov <vdavydov....@gmail.com>
Cc: Tejun Heo <t...@kernel.org>
Cc: kernel-t...@fb.com
Cc: linux...@kvack.org
Cc: cgro...@vger.kernel.org
Cc: linux-ker...@vger.kernel.org
Cc: linux-doc@vger.kernel.org
---
Documentation/cgroup-v2.txt | 28 +++++++++++++---------------
1 file changed, 13 insertions(+), 15 deletions(-)
diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index f728e55602b2..7ee462b8a6ac 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -1006,10 +1006,17 @@ PAGE_SIZE multiple when read back.
A read-write single value file which exists on non-root
cgroups. The default is "0".
- Best-effort memory protection. If the memory usages of a
- cgroup and all its ancestors are below their low boundaries,
- the cgroup's memory won't be reclaimed unless memory can be
- reclaimed from unprotected cgroups.
+ Best-effort memory protection. If the memory usage of a
+ cgroup is within its effective low boundary, the cgroup's
+ memory won't be reclaimed unless memory can be reclaimed
+ from unprotected cgroups.
+
+ Effective low boundary is limited by memory.low values of
+ all ancestor cgroups. If there is memory.low overcommitment
+ (child cgroup or cgroups are requiring more protected memory,
+ than parent will allow), then each child cgroup will get
+ the part of parent's protection proportional to the its
+ actual memory usage below memory.low.
Putting more memory than generally available under this
protection is discouraged.
@@ -2008,17 +2015,8 @@ system performance due to overreclaim, to the point
where the feature
becomes self-defeating.
The memory.low boundary on the other hand is a top-down allocated
-reserve. A cgroup enjoys reclaim protection when it and all its
-ancestors are below their low boundaries, which makes delegation of
-subtrees possible. Secondly, new cgroups have no reserve per default
-and in the common case most cgroups are eligible for the preferred
-reclaim pass. This allows the new low boundary to be efficiently
-implemented with just a minor addition to the generic reclaim code,
-without the need for out-of-band data structures and reclaim passes.
-Because the generic reclaim code considers all cgroups except for the
-ones running low in the preferred first reclaim pass, overreclaim of
-individual groups is eliminated as well, resulting in much better
-overall workload performance.
+reserve. A cgroup enjoys reclaim protection when it's within its low,
+which makes delegation of subtrees possible.
The original high boundary, the hard limit, is defined as a strict
limit that can not budge, even if the OOM killer has to be called.
--
2.14.3
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