memcg: avoid oom during moving charge

This move-charge-at-task-migration feature has extra charges on
"to"(pre-charges) and "from"(left-over charges) during moving charge.
This means unnecessary oom can happen.

This patch tries to avoid such oom.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 51 insertions, 2 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f5fb9917787c..589084f00b70 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -254,7 +254,11 @@ static struct move_charge_struct {
         struct mem_cgroup *to;
         unsigned long precharge;
         unsigned long moved_charge;
-} mc;
+        struct task_struct *moving_task;        /* a task moving charges */
+        wait_queue_head_t waitq;                /* a waitq for other context */
+} mc = {
+        .waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
+};
 
 /*
  * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
@@ -1508,6 +1512,48 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
                 if (mem_cgroup_check_under_limit(mem_over_limit))
                         continue;
 
+                /* try to avoid oom while someone is moving charge */
+                if (mc.moving_task && current != mc.moving_task) {
+                        struct mem_cgroup *from, *to;
+                        bool do_continue = false;
+                        /*
+                         * There is a small race that "from" or "to" can be
+                         * freed by rmdir, so we use css_tryget().
+                         */
+                        rcu_read_lock();
+                        from = mc.from;
+                        to = mc.to;
+                        if (from && css_tryget(&from->css)) {
+                                if (mem_over_limit->use_hierarchy)
+                                        do_continue = css_is_ancestor(
+                                                        &from->css,
+                                                        &mem_over_limit->css);
+                                else
+                                        do_continue = (from == mem_over_limit);
+                                css_put(&from->css);
+                        }
+                        if (!do_continue && to && css_tryget(&to->css)) {
+                                if (mem_over_limit->use_hierarchy)
+                                        do_continue = css_is_ancestor(
+                                                        &to->css,
+                                                        &mem_over_limit->css);
+                                else
+                                        do_continue = (to == mem_over_limit);
+                                css_put(&to->css);
+                        }
+                        rcu_read_unlock();
+                        if (do_continue) {
+                                DEFINE_WAIT(wait);
+                                prepare_to_wait(&mc.waitq, &wait,
+                                                        TASK_INTERRUPTIBLE);
+                                /* moving charge context might have finished. */
+                                if (mc.moving_task)
+                                        schedule();
+                                finish_wait(&mc.waitq, &wait);
+                                continue;
+                        }
+                }
+
                 if (!nr_retries--) {
                         if (oom) {
                                 mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);
@@ -3381,7 +3427,6 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
                         INIT_WORK(&stock->work, drain_local_stock);
                 }
                 hotcpu_notifier(memcg_stock_cpu_callback, 0);
-
         } else {
                 parent = mem_cgroup_from_cont(cont->parent);
                 mem->use_hierarchy = parent->use_hierarchy;
@@ -3641,6 +3686,8 @@ static void mem_cgroup_clear_mc(void)
         }
         mc.from = NULL;
         mc.to = NULL;
+        mc.moving_task = NULL;
+        wake_up_all(&mc.waitq);
 }
 
 static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
@@ -3666,10 +3713,12 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
                         VM_BUG_ON(mc.to);
                         VM_BUG_ON(mc.precharge);
                         VM_BUG_ON(mc.moved_charge);
+                        VM_BUG_ON(mc.moving_task);
                         mc.from = from;
                         mc.to = mem;
                         mc.precharge = 0;
                         mc.moved_charge = 0;
+                        mc.moving_task = current;
 
                         ret = mem_cgroup_precharge_mc(mm);
                         if (ret)