[PATCH] mm/memcontrol: update documentation about invoking oom killer

[Konstantin Khlebnikov]

Since commit 29ef680ae7c2 ("memcg, oom: move out_of_memory back to the
charge path") memcg invokes oom killer not only for user page-faults.
This means 0-order allocation will either succeed or task get killed.

Fixes: 8e675f7af507 ("mm/oom_kill: count global and memory cgroup oom kills")
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
 Documentation/admin-guide/cgroup-v2.rst |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 5361ebec3361..eb47815e137b 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1219,8 +1219,13 @@ PAGE_SIZE multiple when read back.
 
 		Failed allocation in its turn could be returned into
 		userspace as -ENOMEM or silently ignored in cases like
-		disk readahead.  For now OOM in memory cgroup kills
-		tasks iff shortage has happened inside page fault.
+		disk readahead.
+
+		Before 4.19 OOM in memory cgroup killed tasks iff
+		shortage has happened inside page fault, random
+		syscall may fail with ENOMEM or EFAULT. Since 4.19
+		failed memory cgroup allocation invokes oom killer and
+		keeps retrying until it succeeds.
 
 		This event is not raised if the OOM killer is not
 		considered as an option, e.g. for failed high-order