[PATCH v13 3/7] mm, oom: cgroup-aware OOM killer

[Roman Gushchin]

Traditionally, the OOM killer is operating on a process level.
Under oom conditions, it finds a process with the highest oom score
and kills it.

This behavior doesn't suit well the system with many running
containers:

1) There is no fairness between containers. A small container with
few large processes will be chosen over a large one with huge
number of small processes.

2) Containers often do not expect that some random process inside
will be killed. In many cases much safer behavior is to kill
all tasks in the container. Traditionally, this was implemented
in userspace, but doing it in the kernel has some advantages,
especially in a case of a system-wide OOM.

To address these issues, the cgroup-aware OOM killer is introduced.

This patch introduces the core functionality: an ability to select
a memory cgroup as an OOM victim. Under OOM conditions the OOM killer
looks for the biggest leaf memory cgroup and kills the biggest
task belonging to it.

The following patches will extend this functionality to consider
non-leaf memory cgroups as OOM victims, and also provide an ability
to kill all tasks belonging to the victim cgroup.

The root cgroup is treated as a leaf memory cgroup, so it's score
is compared with other leaf memory cgroups.
Due to memcg statistics implementation a special approximation
is used for estimating oom_score of root memory cgroup: we sum
oom_score of the belonging processes (or, to be more precise,
tasks owning their mm structures).

Signed-off-by: Roman Gushchin <guro@xxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: kernel-team@xxxxxx
Cc: cgroups@xxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
 include/linux/memcontrol.h |  17 +++++
 include/linux/oom.h        |  12 ++-
 mm/memcontrol.c            | 181 +++++++++++++++++++++++++++++++++++++++++++++
 mm/oom_kill.c              |  84 +++++++++++++++------
 4 files changed, 272 insertions(+), 22 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 882046863581..cb4db659a8b5 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -35,6 +35,7 @@ struct mem_cgroup;
 struct page;
 struct mm_struct;
 struct kmem_cache;
+struct oom_control;
 
 /* Cgroup-specific page state, on top of universal node page state */
 enum memcg_stat_item {
@@ -344,6 +345,11 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *css){
 	return css ? container_of(css, struct mem_cgroup, css) : NULL;
 }
 
+static inline void mem_cgroup_put(struct mem_cgroup *memcg)
+{
+	css_put(&memcg->css);
+}
+
 #define mem_cgroup_from_counter(counter, member)	\
 	container_of(counter, struct mem_cgroup, member)
 
@@ -482,6 +488,8 @@ static inline bool task_in_memcg_oom(struct task_struct *p)
 
 bool mem_cgroup_oom_synchronize(bool wait);
 
+bool mem_cgroup_select_oom_victim(struct oom_control *oc);
+
 #ifdef CONFIG_MEMCG_SWAP
 extern int do_swap_account;
 #endif
@@ -781,6 +789,10 @@ static inline bool task_in_mem_cgroup(struct task_struct *task,
 	return true;
 }
 
+static inline void mem_cgroup_put(struct mem_cgroup *memcg)
+{
+}
+
 static inline struct mem_cgroup *
 mem_cgroup_iter(struct mem_cgroup *root,
 		struct mem_cgroup *prev,
@@ -973,6 +985,11 @@ static inline
 void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx)
 {
 }
+
+static inline bool mem_cgroup_select_oom_victim(struct oom_control *oc)
+{
+	return false;
+}
 #endif /* CONFIG_MEMCG */
 
 /* idx can be of type enum memcg_stat_item or node_stat_item */
diff --git a/include/linux/oom.h b/include/linux/oom.h
index 27cd36b762b5..10f495c8454d 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -10,6 +10,13 @@
 #include <linux/sched/coredump.h> /* MMF_* */
 #include <linux/mm.h> /* VM_FAULT* */
 
+
+/*
+ * Special value returned by victim selection functions to indicate
+ * that are inflight OOM victims.
+ */
+#define INFLIGHT_VICTIM ((void *)-1UL)
+
 struct zonelist;
 struct notifier_block;
 struct mem_cgroup;
@@ -51,7 +58,8 @@ struct oom_control {
 
 	/* Used by oom implementation, do not set */
 	unsigned long totalpages;
-	struct task_struct *chosen;
+	struct task_struct *chosen_task;
+	struct mem_cgroup *chosen_memcg;
 	unsigned long chosen_points;
 };
 
@@ -115,6 +123,8 @@ extern struct task_struct *find_lock_task_mm(struct task_struct *p);
 
 extern struct page *alloc_pages_before_oomkill(const struct oom_control *oc);
 
+extern int oom_evaluate_task(struct task_struct *task, void *arg);
+
 /* sysctls */
 extern int sysctl_oom_dump_tasks;
 extern int sysctl_oom_kill_allocating_task;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 55fbda60cef6..592ffb1c98a7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2664,6 +2664,187 @@ static inline bool memcg_has_children(struct mem_cgroup *memcg)
 	return ret;
 }
 
+static long memcg_oom_badness(struct mem_cgroup *memcg,
+			      const nodemask_t *nodemask,
+			      unsigned long totalpages)
+{
+	long points = 0;
+	int nid;
+	pg_data_t *pgdat;
+
+	for_each_node_state(nid, N_MEMORY) {
+		if (nodemask && !node_isset(nid, *nodemask))
+			continue;
+
+		points += mem_cgroup_node_nr_lru_pages(memcg, nid,
+				LRU_ALL_ANON | BIT(LRU_UNEVICTABLE));
+
+		pgdat = NODE_DATA(nid);
+		points += lruvec_page_state(mem_cgroup_lruvec(pgdat, memcg),
+					    NR_SLAB_UNRECLAIMABLE);
+	}
+
+	points += memcg_page_state(memcg, MEMCG_KERNEL_STACK_KB) /
+		(PAGE_SIZE / 1024);
+	points += memcg_page_state(memcg, MEMCG_SOCK);
+	points += memcg_page_state(memcg, MEMCG_SWAP);
+
+	return points;
+}
+
+/*
+ * Checks if the given memcg is a valid OOM victim and returns a number,
+ * which means the folowing:
+ *   -1: there are inflight OOM victim tasks, belonging to the memcg
+ *    0: memcg is not eligible, e.g. all belonging tasks are protected
+ *       by oom_score_adj set to OOM_SCORE_ADJ_MIN
+ *   >0: memcg is eligible, and the returned value is an estimation
+ *       of the memory footprint
+ */
+static long oom_evaluate_memcg(struct mem_cgroup *memcg,
+			       const nodemask_t *nodemask,
+			       unsigned long totalpages)
+{
+	struct css_task_iter it;
+	struct task_struct *task;
+	int eligible = 0;
+
+	/*
+	 * Root memory cgroup is a special case:
+	 * we don't have necessary stats to evaluate it exactly as
+	 * leaf memory cgroups, so we approximate it's oom_score
+	 * by summing oom_score of all belonging tasks, which are
+	 * owners of their mm structs.
+	 *
+	 * If there are inflight OOM victim tasks inside
+	 * the root memcg, we return -1.
+	 */
+	if (memcg == root_mem_cgroup) {
+		struct css_task_iter it;
+		struct task_struct *task;
+		long score = 0;
+
+		css_task_iter_start(&memcg->css, 0, &it);
+		while ((task = css_task_iter_next(&it))) {
+			if (tsk_is_oom_victim(task) &&
+			    !test_bit(MMF_OOM_SKIP,
+				      &task->signal->oom_mm->flags)) {
+				score = -1;
+				break;
+			}
+
+			task_lock(task);
+			if (!task->mm || task->mm->owner != task) {
+				task_unlock(task);
+				continue;
+			}
+			task_unlock(task);
+
+			score += oom_badness(task, memcg, nodemask,
+					     totalpages);
+		}
+		css_task_iter_end(&it);
+
+		return score;
+	}
+
+	/*
+	 * Memcg is OOM eligible if there are OOM killable tasks inside.
+	 *
+	 * We treat tasks with oom_score_adj set to OOM_SCORE_ADJ_MIN
+	 * as unkillable.
+	 *
+	 * If there are inflight OOM victim tasks inside the memcg,
+	 * we return -1.
+	 */
+	css_task_iter_start(&memcg->css, 0, &it);
+	while ((task = css_task_iter_next(&it))) {
+		if (!eligible &&
+		    task->signal->oom_score_adj != OOM_SCORE_ADJ_MIN)
+			eligible = 1;
+
+		if (tsk_is_oom_victim(task) &&
+		    !test_bit(MMF_OOM_SKIP, &task->signal->oom_mm->flags)) {
+			eligible = -1;
+			break;
+		}
+	}
+	css_task_iter_end(&it);
+
+	if (eligible <= 0)
+		return eligible;
+
+	return memcg_oom_badness(memcg, nodemask, totalpages);
+}
+
+static void select_victim_memcg(struct mem_cgroup *root, struct oom_control *oc)
+{
+	struct mem_cgroup *iter;
+
+	oc->chosen_memcg = NULL;
+	oc->chosen_points = 0;
+
+	/*
+	 * The oom_score is calculated for leaf memory cgroups (including
+	 * the root memcg).
+	 */
+	rcu_read_lock();
+	for_each_mem_cgroup_tree(iter, root) {
+		long score;
+
+		if (memcg_has_children(iter) && iter != root_mem_cgroup)
+			continue;
+
+		score = oom_evaluate_memcg(iter, oc->nodemask, oc->totalpages);
+
+		/*
+		 * Ignore empty and non-eligible memory cgroups.
+		 */
+		if (score == 0)
+			continue;
+
+		/*
+		 * If there are inflight OOM victims, we don't need
+		 * to look further for new victims.
+		 */
+		if (score == -1) {
+			oc->chosen_memcg = INFLIGHT_VICTIM;
+			mem_cgroup_iter_break(root, iter);
+			break;
+		}
+
+		if (score > oc->chosen_points) {
+			oc->chosen_points = score;
+			oc->chosen_memcg = iter;
+		}
+	}
+
+	if (oc->chosen_memcg && oc->chosen_memcg != INFLIGHT_VICTIM)
+		css_get(&oc->chosen_memcg->css);
+
+	rcu_read_unlock();
+}
+
+bool mem_cgroup_select_oom_victim(struct oom_control *oc)
+{
+	struct mem_cgroup *root;
+
+	if (mem_cgroup_disabled())
+		return false;
+
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return false;
+
+	if (oc->memcg)
+		root = oc->memcg;
+	else
+		root = root_mem_cgroup;
+
+	select_victim_memcg(root, oc);
+
+	return oc->chosen_memcg;
+}
+
 /*
  * Reclaims as many pages from the given memcg as possible.
  *
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index f041534d77d3..bcfa92f29407 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -309,7 +309,7 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 	return CONSTRAINT_NONE;
 }
 
-static int oom_evaluate_task(struct task_struct *task, void *arg)
+int oom_evaluate_task(struct task_struct *task, void *arg)
 {
 	struct oom_control *oc = arg;
 	unsigned long points;
@@ -343,26 +343,26 @@ static int oom_evaluate_task(struct task_struct *task, void *arg)
 		goto next;
 
 	/* Prefer thread group leaders for display purposes */
-	if (points == oc->chosen_points && thread_group_leader(oc->chosen))
+	if (points == oc->chosen_points && thread_group_leader(oc->chosen_task))
 		goto next;
 select:
-	if (oc->chosen)
-		put_task_struct(oc->chosen);
+	if (oc->chosen_task)
+		put_task_struct(oc->chosen_task);
 	get_task_struct(task);
-	oc->chosen = task;
+	oc->chosen_task = task;
 	oc->chosen_points = points;
 next:
 	return 0;
 abort:
-	if (oc->chosen)
-		put_task_struct(oc->chosen);
-	oc->chosen = (void *)-1UL;
+	if (oc->chosen_task)
+		put_task_struct(oc->chosen_task);
+	oc->chosen_task = INFLIGHT_VICTIM;
 	return 1;
 }
 
 /*
  * Simple selection loop. We choose the process with the highest number of
- * 'points'. In case scan was aborted, oc->chosen is set to -1.
+ * 'points'. In case scan was aborted, oc->chosen_task is set to -1.
  */
 static void select_bad_process(struct oom_control *oc)
 {
@@ -895,7 +895,7 @@ static void __oom_kill_process(struct task_struct *victim)
 
 static void oom_kill_process(struct oom_control *oc, const char *message)
 {
-	struct task_struct *p = oc->chosen;
+	struct task_struct *p = oc->chosen_task;
 	unsigned int points = oc->chosen_points;
 	struct task_struct *victim = p;
 	struct task_struct *child;
@@ -956,6 +956,27 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 	__oom_kill_process(victim);
 }
 
+static bool oom_kill_memcg_victim(struct oom_control *oc)
+{
+
+	if (oc->chosen_memcg == NULL || oc->chosen_memcg == INFLIGHT_VICTIM)
+		return oc->chosen_memcg;
+
+	/* Kill a task in the chosen memcg with the biggest memory footprint */
+	oc->chosen_points = 0;
+	oc->chosen_task = NULL;
+	mem_cgroup_scan_tasks(oc->chosen_memcg, oom_evaluate_task, oc);
+
+	if (oc->chosen_task == NULL || oc->chosen_task == INFLIGHT_VICTIM)
+		goto out;
+
+	__oom_kill_process(oc->chosen_task);
+
+out:
+	mem_cgroup_put(oc->chosen_memcg);
+	return oc->chosen_task;
+}
+
 /*
  * Determines whether the kernel must panic because of the panic_on_oom sysctl.
  */
@@ -1008,6 +1029,7 @@ bool out_of_memory(struct oom_control *oc)
 {
 	unsigned long freed = 0;
 	enum oom_constraint constraint = CONSTRAINT_NONE;
+	bool delay = false; /* if set, delay next allocation attempt */
 
 	if (oom_killer_disabled)
 		return false;
@@ -1055,11 +1077,26 @@ bool out_of_memory(struct oom_control *oc)
 		if (oc->page)
 			return true;
 		get_task_struct(current);
-		oc->chosen = current;
+		oc->chosen_task = current;
 		oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
 		return true;
 	}
 
+	if (mem_cgroup_select_oom_victim(oc)) {
+		oc->page = alloc_pages_before_oomkill(oc);
+		if (oc->page) {
+			if (oc->chosen_memcg &&
+			    oc->chosen_memcg != INFLIGHT_VICTIM)
+				mem_cgroup_put(oc->chosen_memcg);
+			return true;
+		}
+
+		if (oom_kill_memcg_victim(oc)) {
+			delay = true;
+			goto out;
+		}
+	}
+
 	select_bad_process(oc);
 	/*
 	 * Try really last second allocation attempt after we selected an OOM
@@ -1068,25 +1105,30 @@ bool out_of_memory(struct oom_control *oc)
 	 */
 	oc->page = alloc_pages_before_oomkill(oc);
 	if (oc->page) {
-		if (oc->chosen && oc->chosen != (void *)-1UL)
-			put_task_struct(oc->chosen);
+		if (oc->chosen_task && oc->chosen_task != INFLIGHT_VICTIM)
+			put_task_struct(oc->chosen_task);
 		return true;
 	}
 	/* Found nothing?!?! Either we hang forever, or we panic. */
-	if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
+	if (!oc->chosen_task && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
 		dump_header(oc, NULL);
 		panic("Out of memory and no killable processes...\n");
 	}
-	if (oc->chosen && oc->chosen != (void *)-1UL) {
+	if (oc->chosen_task && oc->chosen_task != INFLIGHT_VICTIM) {
 		oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
 				 "Memory cgroup out of memory");
-		/*
-		 * Give the killed process a good chance to exit before trying
-		 * to allocate memory again.
-		 */
-		schedule_timeout_killable(1);
+		delay = true;
 	}
-	return !!oc->chosen;
+
+out:
+	/*
+	 * Give the killed process a good chance to exit before trying
+	 * to allocate memory again.
+	 */
+	if (delay)
+		schedule_timeout_killable(1);
+
+	return !!oc->chosen_task;
 }
 
 /*
-- 
2.14.3