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Subject[PATCH v3 1/3] mm, oom: refactor dump_tasks for memcg OOMs
From
dump_tasks() traverses all the existing processes even for the memcg OOM
context which is not only unnecessary but also wasteful. This imposes
a long RCU critical section even from a contained context which can be
quite disruptive.

Change dump_tasks() to be aligned with select_bad_process and use
mem_cgroup_scan_tasks to selectively traverse only processes of the
target memcg hierarchy during memcg OOM.

Signed-off-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>

---
Changelog since v2:
- Updated the commit message.

Changelog since v1:
- Divide the patch into two patches.

mm/oom_kill.c | 68 ++++++++++++++++++++++++++++++---------------------
1 file changed, 40 insertions(+), 28 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 05aaa1a5920b..bd80997e0969 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -385,10 +385,38 @@ static void select_bad_process(struct oom_control *oc)
oc->chosen_points = oc->chosen_points * 1000 / oc->totalpages;
}

+static int dump_task(struct task_struct *p, void *arg)
+{
+ struct oom_control *oc = arg;
+ struct task_struct *task;
+
+ if (oom_unkillable_task(p, NULL, oc->nodemask))
+ return 0;
+
+ task = find_lock_task_mm(p);
+ if (!task) {
+ /*
+ * This is a kthread or all of p's threads have already
+ * detached their mm's. There's no need to report
+ * them; they can't be oom killed anyway.
+ */
+ return 0;
+ }
+
+ pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n",
+ task->pid, from_kuid(&init_user_ns, task_uid(task)),
+ task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
+ mm_pgtables_bytes(task->mm),
+ get_mm_counter(task->mm, MM_SWAPENTS),
+ task->signal->oom_score_adj, task->comm);
+ task_unlock(task);
+
+ return 0;
+}
+
/**
* dump_tasks - dump current memory state of all system tasks
- * @memcg: current's memory controller, if constrained
- * @nodemask: nodemask passed to page allocator for mempolicy ooms
+ * @oc: pointer to struct oom_control
*
* Dumps the current memory state of all eligible tasks. Tasks not in the same
* memcg, not in the same cpuset, or bound to a disjoint set of mempolicy nodes
@@ -396,37 +424,21 @@ static void select_bad_process(struct oom_control *oc)
* State information includes task's pid, uid, tgid, vm size, rss,
* pgtables_bytes, swapents, oom_score_adj value, and name.
*/
-static void dump_tasks(struct mem_cgroup *memcg, const nodemask_t *nodemask)
+static void dump_tasks(struct oom_control *oc)
{
- struct task_struct *p;
- struct task_struct *task;
-
pr_info("Tasks state (memory values in pages):\n");
pr_info("[ pid ] uid tgid total_vm rss pgtables_bytes swapents oom_score_adj name\n");
- rcu_read_lock();
- for_each_process(p) {
- if (oom_unkillable_task(p, memcg, nodemask))
- continue;

- task = find_lock_task_mm(p);
- if (!task) {
- /*
- * This is a kthread or all of p's threads have already
- * detached their mm's. There's no need to report
- * them; they can't be oom killed anyway.
- */
- continue;
- }
+ if (is_memcg_oom(oc))
+ mem_cgroup_scan_tasks(oc->memcg, dump_task, oc);
+ else {
+ struct task_struct *p;

- pr_info("[%7d] %5d %5d %8lu %8lu %8ld %8lu %5hd %s\n",
- task->pid, from_kuid(&init_user_ns, task_uid(task)),
- task->tgid, task->mm->total_vm, get_mm_rss(task->mm),
- mm_pgtables_bytes(task->mm),
- get_mm_counter(task->mm, MM_SWAPENTS),
- task->signal->oom_score_adj, task->comm);
- task_unlock(task);
+ rcu_read_lock();
+ for_each_process(p)
+ dump_task(p, oc);
+ rcu_read_unlock();
}
- rcu_read_unlock();
}

static void dump_oom_summary(struct oom_control *oc, struct task_struct *victim)
@@ -458,7 +470,7 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
dump_unreclaimable_slab();
}
if (sysctl_oom_dump_tasks)
- dump_tasks(oc->memcg, oc->nodemask);
+ dump_tasks(oc);
if (p)
dump_oom_summary(oc, p);
}
--
2.22.0.410.gd8fdbe21b5-goog
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