mm, oom: introduce memory.oom.group

For some workloads an intervention from the OOM killer can be painful.
Killing a random task can bring the workload into an inconsistent state.

Historically, there are two common solutions for this
problem:
1) enabling panic_on_oom,
2) using a userspace daemon to monitor OOMs and kill
   all outstanding processes.

Both approaches have their downsides: rebooting on each OOM is an obvious
waste of capacity, and handling all in userspace is tricky and requires a
userspace agent, which will monitor all cgroups for OOMs.

In most cases an in-kernel after-OOM cleaning-up mechanism can eliminate
the necessity of enabling panic_on_oom.  Also, it can simplify the cgroup
management for userspace applications.

This commit introduces a new knob for cgroup v2 memory controller:
memory.oom.group.  The knob determines whether the cgroup should be
treated as an indivisible workload by the OOM killer.  If set, all tasks
belonging to the cgroup or to its descendants (if the memory cgroup is not
a leaf cgroup) are killed together or not at all.

To determine which cgroup has to be killed, we do traverse the cgroup
hierarchy from the victim task's cgroup up to the OOMing cgroup (or root)
and looking for the highest-level cgroup with memory.oom.group set.

Tasks with the OOM protection (oom_score_adj set to -1000) are treated as
an exception and are never killed.

This patch doesn't change the OOM victim selection algorithm.

Link: http://lkml.kernel.org/r/20180802003201.817-4-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 0 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 0e6c515fb698..652f602167df 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -225,6 +225,11 @@ struct mem_cgroup {
 	 */
 	bool use_hierarchy;
 
+	/*
+	 * Should the OOM killer kill all belonging tasks, had it kill one?
+	 */
+	bool oom_group;
+
 	/* protected by memcg_oom_lock */
 	bool		oom_lock;
 	int		under_oom;
@@ -542,6 +547,9 @@ static inline bool task_in_memcg_oom(struct task_struct *p)
 }
 
 bool mem_cgroup_oom_synchronize(bool wait);
+struct mem_cgroup *mem_cgroup_get_oom_group(struct task_struct *victim,
+					    struct mem_cgroup *oom_domain);
+void mem_cgroup_print_oom_group(struct mem_cgroup *memcg);
 
 #ifdef CONFIG_MEMCG_SWAP
 extern int do_swap_account;
@@ -1001,6 +1009,16 @@ static inline bool mem_cgroup_oom_synchronize(bool wait)
 	return false;
 }
 
+static inline struct mem_cgroup *mem_cgroup_get_oom_group(
+	struct task_struct *victim, struct mem_cgroup *oom_domain)
+{
+	return NULL;
+}
+
+static inline void mem_cgroup_print_oom_group(struct mem_cgroup *memcg)
+{
+}
+
 static inline unsigned long memcg_page_state(struct mem_cgroup *memcg,
 					     int idx)
 {