Documentation/memcg: warn about incomplete kmemcg state

Kmemcg is currently under development and lacks some important features.
In particular, it does not have support of kmem reclaim on memory pressure
inside cgroup, which practically makes it unusable in real life.  Let's
warn about it in both Kconfig and Documentation to prevent complaints
arising.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 9d3585bb2a7a..4a1822a1a680 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -996,6 +996,12 @@ config MEMCG_KMEM
           the kmem extension can use it to guarantee that no group of processes
           will ever exhaust kernel resources alone.
 
+          WARNING: Current implementation lacks reclaim support. That means
+          allocation attempts will fail when close to the limit even if there
+          are plenty of kmem available for reclaim. That makes this option
+          unusable in real life so DO NOT SELECT IT unless for development
+          purposes.
+
 config CGROUP_HUGETLB
         bool "HugeTLB Resource Controller for Control Groups"
         depends on RESOURCE_COUNTERS && HUGETLB_PAGE