On 11/05/2020 11.39, Michal Hocko wrote:
On Fri 08-05-20 17:16:29, Konstantin Khlebnikov wrote:
Starting from v4.19 commit 29ef680ae7c2 ("memcg, oom: move out_of_memory
back to the charge path") cgroup oom killer is no longer invoked only from
page faults. Now it implements the same semantics as global OOM killer:
allocation context invokes OOM killer and keeps retrying until success.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
Documentation/admin-guide/cgroup-v2.rst | 17 ++++++++---------
1 file changed, 8 insertions(+), 9 deletions(-)
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index bcc80269bb6a..1bb9a8f6ebe1 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1172,6 +1172,13 @@ PAGE_SIZE multiple when read back.
Under certain circumstances, the usage may go over the limit
temporarily.
+ In default configuration regular 0-order allocation always
+ succeed unless OOM killer choose current task as a victim.
+
+ Some kinds of allocations don't invoke the OOM killer.
+ Caller could retry them differently, return into userspace
+ as -ENOMEM or silently ignore in cases like disk readahead.
I would probably add -EFAULT but the less error codes we document the
better.
Yeah, EFAULT was a most obscure result of memory shortage.
Fortunately with new behaviour this shouldn't happens a lot.
Actually where it is still possible? THP always fallback to 0-order.
I mean EFAULT could appear inside kernel only if task is killed so
nobody would see it.
+
This is the ultimate protection mechanism. As long as the
high limit is used and monitored properly, this limit's
utility is limited to providing the final safety net.
@@ -1228,17 +1235,9 @@ PAGE_SIZE multiple when read back.
The number of time the cgroup's memory usage was
reached the limit and allocation was about to fail.
- Depending on context result could be invocation of OOM
- killer and retrying allocation or failing allocation.
-
- 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.
-
This event is not raised if the OOM killer is not
considered as an option, e.g. for failed high-order
- allocations.
+ allocations or if caller asked to not retry attempts.
oom_kill
The number of processes belonging to this cgroup
