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Subject[v5 3/4] mm, oom: introduce oom_priority for memory cgroups
Date
Introduce a per-memory-cgroup oom_priority setting: an integer number
within the [-10000, 10000] range, which defines the order in which
the OOM killer selects victim memory cgroups.

OOM killer prefers memory cgroups with larger priority if they are
populated with elegible tasks.

The oom_priority value is compared within sibling cgroups.

The root cgroup has the oom_priority 0, which cannot be changed.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: kernel-team@fb.com
Cc: cgroups@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org
---
include/linux/memcontrol.h | 3 +++
mm/memcontrol.c | 55 ++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 796666dc3282..3c1ab3aedebe 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -206,6 +206,9 @@ struct mem_cgroup {
/* cached OOM score */
long oom_score;

+ /* OOM killer priority */
+ short oom_priority;
+
/* handle for "memory.events" */
struct cgroup_file events_file;

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0b81dc55c6ac..f61e9a9c8bdc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2724,12 +2724,21 @@ static void select_victim_memcg(struct mem_cgroup *root, struct oom_control *oc)
for (;;) {
struct cgroup_subsys_state *css;
struct mem_cgroup *memcg = NULL;
+ short prio = SHRT_MIN;
long score = LONG_MIN;

css_for_each_child(css, &root->css) {
struct mem_cgroup *iter = mem_cgroup_from_css(css);

- if (iter->oom_score > score) {
+ if (iter->oom_score == 0)
+ continue;
+
+ if (iter->oom_priority > prio) {
+ memcg = iter;
+ prio = iter->oom_priority;
+ score = iter->oom_score;
+ } else if (iter->oom_priority == prio &&
+ iter->oom_score > score) {
memcg = iter;
score = iter->oom_score;
}
@@ -2796,7 +2805,15 @@ bool mem_cgroup_select_oom_victim(struct oom_control *oc)
* For system-wide OOMs we should consider tasks in the root cgroup
* with oom_score larger than oc->chosen_points.
*/
- if (!oc->memcg) {
+ if (!oc->memcg && !(oc->chosen_memcg &&
+ oc->chosen_memcg->oom_priority > 0)) {
+ /*
+ * Root memcg has priority 0, so if chosen memcg has lower
+ * priority, any task in root cgroup is preferable.
+ */
+ if (oc->chosen_memcg && oc->chosen_memcg->oom_priority < 0)
+ oc->chosen_points = 0;
+
select_victim_root_cgroup_task(oc);

if (oc->chosen && oc->chosen_memcg) {
@@ -5392,6 +5409,34 @@ static ssize_t memory_oom_kill_all_tasks_write(struct kernfs_open_file *of,
return nbytes;
}

+static int memory_oom_priority_show(struct seq_file *m, void *v)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
+
+ seq_printf(m, "%d\n", memcg->oom_priority);
+
+ return 0;
+}
+
+static ssize_t memory_oom_priority_write(struct kernfs_open_file *of,
+ char *buf, size_t nbytes, loff_t off)
+{
+ struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
+ int oom_priority;
+ int err;
+
+ err = kstrtoint(strstrip(buf), 0, &oom_priority);
+ if (err)
+ return err;
+
+ if (oom_priority < -10000 || oom_priority > 10000)
+ return -EINVAL;
+
+ memcg->oom_priority = (short)oom_priority;
+
+ return nbytes;
+}
+
static int memory_events_show(struct seq_file *m, void *v)
{
struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
@@ -5518,6 +5563,12 @@ static struct cftype memory_files[] = {
.write = memory_oom_kill_all_tasks_write,
},
{
+ .name = "oom_priority",
+ .flags = CFTYPE_NOT_ON_ROOT,
+ .seq_show = memory_oom_priority_show,
+ .write = memory_oom_priority_write,
+ },
+ {
.name = "events",
.flags = CFTYPE_NOT_ON_ROOT,
.file_offset = offsetof(struct mem_cgroup, events_file),
--
2.13.5
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