[v11 3/6] mm, oom: cgroup-aware OOM killer

Roman Gushchin
2017-10-05T13:04:51Z

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.

Under OOM conditions, it 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 well, 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 leaf memory cgroups.
Due to memcg statistics implementation a special algorithm
is used for estimating it's oom_score: we define it as maximum
oom_score of the belonging tasks.

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: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>
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 | 17 +++++
include/linux/oom.h | 12 +++-
mm/memcontrol.c | 172 +++++++++++++++++++++++++++++++++++++++++++++
mm/oom_kill.c | 70 +++++++++++++-----
4 files changed, 251 insertions(+), 20 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 69966c461d1c..75b63b68846e 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 {
@@ -342,6 +343,11 @@ 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)

@@ -480,6 +486,8 @@ 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
@@ -744,6 +752,10 @@ 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,
@@ -936,6 +948,11 @@ 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 76aac4ce39bc..ca78e2d5956e 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -9,6 +9,13 @@
#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;
@@ -39,7 +46,8 @@ 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;
};

@@ -101,6 +109,8 @@ extern void oom_killer_enable(void);

extern struct task_struct *find_lock_task_mm(struct task_struct *p);

+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 41d71f665550..191b70735f1f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2670,6 +2670,178 @@ 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;
+
+ /*
+ * We don't have necessary stats for the root memcg,
+ * so we define it's oom_score as the maximum oom_score
+ * of the belonging tasks.
+ *
+ * As tasks in the root memcg unlikely are parts of a
+ * single workload, and we don't have to implement
+ * group killing, this approximation is reasonable.
+ *
+ * But if we will have necessary stats for the root memcg,
+ * we might switch to the approach which is used for all
+ * other memcgs.
+ */
+ if (memcg == root_mem_cgroup) {
+ struct css_task_iter it;
+ struct task_struct *task;
+ long score, max_score = 0;
+
+ css_task_iter_start(&memcg->css, 0, &it);
+ while ((task = css_task_iter_next(&it))) {
+ score = oom_badness(task, memcg, nodemask,
+ totalpages);
+ if (score > max_score)
+ max_score = score;
+ }
+ css_task_iter_end(&it);
+
+ return max_score;
+ }
+
+ 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;
+
+ /*
+ * 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 ccdb7d34cd13..20e62ec32ba8 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -310,7 +310,7 @@ 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;
@@ -344,26 +344,26 @@ 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)
{
@@ -926,7 +926,7 @@ 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;
@@ -987,6 +987,27 @@ 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.
*/
@@ -1039,6 +1060,7 @@ 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;
@@ -1083,27 +1105,37 @@ bool out_of_memory(struct oom_control *oc)
current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
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) && oom_kill_memcg_victim(oc)) {
+ delay = true;
+ goto out;
+ }
+
select_bad_process(oc);
/* 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;
}

/*
--
2.13.6

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