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Date: Thu, 5 Oct 2017 16:29:14 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Roman Gushchin <guro@...com>
Cc: linux-mm@...ck.org, Vladimir Davydov <vdavydov.dev@...il.com>,
Johannes Weiner <hannes@...xchg.org>,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
David Rientjes <rientjes@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Tejun Heo <tj@...nel.org>, kernel-team@...com,
cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [v11 4/6] mm, oom: introduce memory.oom_group
On Thu 05-10-17 14:04:52, Roman Gushchin wrote:
> The cgroup-aware OOM killer treats leaf memory cgroups as memory
> consumption entities and performs the victim selection by comparing
> them based on their memory footprint. Then it kills the biggest task
> inside the selected memory cgroup.
>
> But there are workloads, which are not tolerant to a such behavior.
> Killing a random task may leave the workload in a broken state.
>
> To solve this problem, memory.oom_group knob is introduced.
> It will define, whether a memory group should be treated as an
> indivisible memory consumer, compared by total memory consumption
> with other memory consumers (leaf memory cgroups and other memory
> cgroups with memory.oom_group set), and whether all belonging tasks
> should be killed if the cgroup is selected.
>
> If set on memcg A, it means that in case of system-wide OOM or
> memcg-wide OOM scoped to A or any ancestor cgroup, all tasks,
> belonging to the sub-tree of A will be killed. If OOM event is
> scoped to a descendant cgroup (A/B, for example), only tasks in
> that cgroup can be affected. OOM killer will never touch any tasks
> outside of the scope of the OOM event.
>
> Also, tasks with oom_score_adj set to -1000 will not be killed because
> this has been a long established way to protect a particular process
> from seeing an unexpected SIGKILL from the OOM killer. Ignoring this
> user defined configuration might lead to data corruptions or other
> misbehavior.
>
> The default value is 0.
I still believe that oc->chosen_task == INFLIGHT_VICTIM check in
oom_kill_memcg_victim should go away.
>
> Signed-off-by: Roman Gushchin <guro@...com>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Vladimir Davydov <vdavydov.dev@...il.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: kernel-team@...com
> Cc: cgroups@...r.kernel.org
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-mm@...ck.org
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> include/linux/memcontrol.h | 17 +++++++++++
> mm/memcontrol.c | 75 +++++++++++++++++++++++++++++++++++++++++++---
> mm/oom_kill.c | 49 +++++++++++++++++++++++-------
> 3 files changed, 127 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 75b63b68846e..84ac10d7e67d 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -200,6 +200,13 @@ struct mem_cgroup {
> /* OOM-Killer disable */
> int oom_kill_disable;
>
> + /*
> + * Treat the sub-tree as an indivisible memory consumer,
> + * kill all belonging tasks if the memory cgroup selected
> + * as OOM victim.
> + */
> + bool oom_group;
> +
> /* handle for "memory.events" */
> struct cgroup_file events_file;
>
> @@ -488,6 +495,11 @@ bool mem_cgroup_oom_synchronize(bool wait);
>
> bool mem_cgroup_select_oom_victim(struct oom_control *oc);
>
> +static inline bool mem_cgroup_oom_group(struct mem_cgroup *memcg)
> +{
> + return memcg->oom_group;
> +}
> +
> #ifdef CONFIG_MEMCG_SWAP
> extern int do_swap_account;
> #endif
> @@ -953,6 +965,11 @@ static inline bool mem_cgroup_select_oom_victim(struct oom_control *oc)
> {
> return false;
> }
> +
> +static inline bool mem_cgroup_oom_group(struct mem_cgroup *memcg)
> +{
> + return false;
> +}
> #endif /* CONFIG_MEMCG */
>
> /* idx can be of type enum memcg_stat_item or node_stat_item */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 191b70735f1f..d5acb278b11a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2776,19 +2776,51 @@ static long oom_evaluate_memcg(struct mem_cgroup *memcg,
>
> static void select_victim_memcg(struct mem_cgroup *root, struct oom_control *oc)
> {
> - struct mem_cgroup *iter;
> + struct mem_cgroup *iter, *group = NULL;
> + long group_score = 0;
>
> oc->chosen_memcg = NULL;
> oc->chosen_points = 0;
>
> /*
> + * If OOM is memcg-wide, and the memcg has the oom_group flag set,
> + * all tasks belonging to the memcg should be killed.
> + * So, we mark the memcg as a victim.
> + */
> + if (oc->memcg && mem_cgroup_oom_group(oc->memcg)) {
> + oc->chosen_memcg = oc->memcg;
> + css_get(&oc->chosen_memcg->css);
> + return;
> + }
> +
> + /*
> * The oom_score is calculated for leaf memory cgroups (including
> * the root memcg).
> + * Non-leaf oom_group cgroups accumulating score of descendant
> + * leaf memory cgroups.
> */
> rcu_read_lock();
> for_each_mem_cgroup_tree(iter, root) {
> long score;
>
> + /*
> + * We don't consider non-leaf non-oom_group memory cgroups
> + * as OOM victims.
> + */
> + if (memcg_has_children(iter) && iter != root_mem_cgroup &&
> + !mem_cgroup_oom_group(iter))
> + continue;
> +
> + /*
> + * If group is not set or we've ran out of the group's sub-tree,
> + * we should set group and reset group_score.
> + */
> + if (!group || group == root_mem_cgroup ||
> + !mem_cgroup_is_descendant(iter, group)) {
> + group = iter;
> + group_score = 0;
> + }
> +
> if (memcg_has_children(iter) && iter != root_mem_cgroup)
> continue;
>
> @@ -2810,9 +2842,11 @@ static void select_victim_memcg(struct mem_cgroup *root, struct oom_control *oc)
> break;
> }
>
> - if (score > oc->chosen_points) {
> - oc->chosen_points = score;
> - oc->chosen_memcg = iter;
> + group_score += score;
> +
> + if (group_score > oc->chosen_points) {
> + oc->chosen_points = group_score;
> + oc->chosen_memcg = group;
> }
> }
>
> @@ -5437,6 +5471,33 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
> return nbytes;
> }
>
> +static int memory_oom_group_show(struct seq_file *m, void *v)
> +{
> + struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
> + bool oom_group = memcg->oom_group;
> +
> + seq_printf(m, "%d\n", oom_group);
> +
> + return 0;
> +}
> +
> +static ssize_t memory_oom_group_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_group;
> + int err;
> +
> + err = kstrtoint(strstrip(buf), 0, &oom_group);
> + if (err)
> + return err;
> +
> + memcg->oom_group = oom_group;
> +
> + return nbytes;
> +}
> +
> static int memory_events_show(struct seq_file *m, void *v)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
> @@ -5557,6 +5618,12 @@ static struct cftype memory_files[] = {
> .write = memory_max_write,
> },
> {
> + .name = "oom_group",
> + .flags = CFTYPE_NOT_ON_ROOT | CFTYPE_NS_DELEGATABLE,
> + .seq_show = memory_oom_group_show,
> + .write = memory_oom_group_write,
> + },
> + {
> .name = "events",
> .flags = CFTYPE_NOT_ON_ROOT,
> .file_offset = offsetof(struct mem_cgroup, events_file),
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 20e62ec32ba8..c8fbc73c4ed3 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -851,6 +851,17 @@ static void __oom_kill_process(struct task_struct *victim)
> struct mm_struct *mm;
> bool can_oom_reap = true;
>
> + /*
> + * __oom_kill_process() is used to kill all tasks belonging to
> + * the selected memory cgroup, so we should check that we're not
> + * trying to kill an unkillable task.
> + */
> + if (is_global_init(victim) || (victim->flags & PF_KTHREAD) ||
> + victim->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
> + put_task_struct(victim);
> + return;
> + }
> +
> p = find_lock_task_mm(victim);
> if (!p) {
> put_task_struct(victim);
> @@ -987,21 +998,39 @@ 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)
> +static int oom_kill_memcg_member(struct task_struct *task, void *unused)
> {
> + get_task_struct(task);
> + __oom_kill_process(task);
> + return 0;
> +}
>
> +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);
> + /*
> + * If memory.oom_group is set, kill all tasks belonging to the sub-tree
> + * of the chosen memory cgroup, otherwise kill the task with the biggest
> + * memory footprint.
> + */
> + if (mem_cgroup_oom_group(oc->chosen_memcg)) {
> + mem_cgroup_scan_tasks(oc->chosen_memcg, oom_kill_memcg_member,
> + NULL);
> + /* We have one or more terminating processes at this point. */
> + oc->chosen_task = INFLIGHT_VICTIM;
> + } else {
> + 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);
> --
> 2.13.6
--
Michal Hocko
SUSE Labs
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