memcg: fix oom kill behavior

In current page-fault code,

	handle_mm_fault()
		-> ...
		-> mem_cgroup_charge()
		-> map page or handle error.
	-> check return code.

If page fault's return code is VM_FAULT_OOM, page_fault_out_of_memory() is
called.  But if it's caused by memcg, OOM should have been already
invoked.

Then, I added a patch: a636b327f731143ccc544b966cfd8de6cb6d72c6.  That
patch records last_oom_jiffies for memcg's sub-hierarchy and prevents
page_fault_out_of_memory from being invoked in near future.

But Nishimura-san reported that check by jiffies is not enough when the
system is terribly heavy.

This patch changes memcg's oom logic as.
 * If memcg causes OOM-kill, continue to retry.
 * remove jiffies check which is used now.
 * add memcg-oom-lock which works like perzone oom lock.
 * If current is killed(as a process), bypass charge.

Something more sophisticated can be added but this pactch does
fundamental things.
TODO:
 - add oom notifier
 - add permemcg disable-oom-kill flag and freezer at oom.
 - more chances for wake up oom waiter (when changing memory limit etc..)

Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: 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>

2 files changed, 107 insertions, 35 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f7b910fc14fb..7973b5221fb8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -203,7 +203,7 @@ struct mem_cgroup {
          * Should the accounting and control be hierarchical, per subtree?
          */
         bool use_hierarchy;
-        unsigned long   last_oom_jiffies;
+        atomic_t        oom_lock;
         atomic_t        refcnt;
 
         unsigned int    swappiness;
@@ -1246,32 +1246,102 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
         return total;
 }
 
-bool mem_cgroup_oom_called(struct task_struct *task)
+static int mem_cgroup_oom_lock_cb(struct mem_cgroup *mem, void *data)
 {
-        bool ret = false;
-        struct mem_cgroup *mem;
-        struct mm_struct *mm;
+        int *val = (int *)data;
+        int x;
+        /*
+         * Logically, we can stop scanning immediately when we find
+         * a memcg is already locked. But condidering unlock ops and
+         * creation/removal of memcg, scan-all is simple operation.
+         */
+        x = atomic_inc_return(&mem->oom_lock);
+        *val = max(x, *val);
+        return 0;
+}
+/*
+ * Check OOM-Killer is already running under our hierarchy.
+ * If someone is running, return false.
+ */
+static bool mem_cgroup_oom_lock(struct mem_cgroup *mem)
+{
+        int lock_count = 0;
 
-        rcu_read_lock();
-        mm = task->mm;
-        if (!mm)
-                mm = &init_mm;
-        mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
-        if (mem && time_before(jiffies, mem->last_oom_jiffies + HZ/10))
-                ret = true;
-        rcu_read_unlock();
-        return ret;
+        mem_cgroup_walk_tree(mem, &lock_count, mem_cgroup_oom_lock_cb);
+
+        if (lock_count == 1)
+                return true;
+        return false;
 }
 
-static int record_last_oom_cb(struct mem_cgroup *mem, void *data)
+static int mem_cgroup_oom_unlock_cb(struct mem_cgroup *mem, void *data)
 {
-        mem->last_oom_jiffies = jiffies;
+        /*
+         * When a new child is created while the hierarchy is under oom,
+         * mem_cgroup_oom_lock() may not be called. We have to use
+         * atomic_add_unless() here.
+         */
+        atomic_add_unless(&mem->oom_lock, -1, 0);
         return 0;
 }
 
-static void record_last_oom(struct mem_cgroup *mem)
+static void mem_cgroup_oom_unlock(struct mem_cgroup *mem)
 {
-        mem_cgroup_walk_tree(mem, NULL, record_last_oom_cb);
+        mem_cgroup_walk_tree(mem, NULL, mem_cgroup_oom_unlock_cb);
+}
+
+static DEFINE_MUTEX(memcg_oom_mutex);
+static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);
+
+/*
+ * try to call OOM killer. returns false if we should exit memory-reclaim loop.
+ */
+bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
+{
+        DEFINE_WAIT(wait);
+        bool locked;
+
+        /* At first, try to OOM lock hierarchy under mem.*/
+        mutex_lock(&memcg_oom_mutex);
+        locked = mem_cgroup_oom_lock(mem);
+        /*
+         * Even if signal_pending(), we can't quit charge() loop without
+         * accounting. So, UNINTERRUPTIBLE is appropriate. But SIGKILL
+         * under OOM is always welcomed, use TASK_KILLABLE here.
+         */
+        if (!locked)
+                prepare_to_wait(&memcg_oom_waitq, &wait, TASK_KILLABLE);
+        mutex_unlock(&memcg_oom_mutex);
+
+        if (locked)
+                mem_cgroup_out_of_memory(mem, mask);
+        else {
+                schedule();
+                finish_wait(&memcg_oom_waitq, &wait);
+        }
+        mutex_lock(&memcg_oom_mutex);
+        mem_cgroup_oom_unlock(mem);
+        /*
+         * Here, we use global waitq .....more fine grained waitq ?
+         * Assume following hierarchy.
+         * A/
+         *   01
+         *   02
+         * assume OOM happens both in A and 01 at the same time. Tthey are
+         * mutually exclusive by lock. (kill in 01 helps A.)
+         * When we use per memcg waitq, we have to wake up waiters on A and 02
+         * in addtion to waiters on 01. We use global waitq for avoiding mess.
+         * It will not be a big problem.
+         * (And a task may be moved to other groups while it's waiting for OOM.)
+         */
+        wake_up_all(&memcg_oom_waitq);
+        mutex_unlock(&memcg_oom_mutex);
+
+        if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))
+                return false;
+        /* Give chance to dying process */
+        schedule_timeout(1);
+        return true;
 }
 
 /*
@@ -1443,11 +1513,14 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
         struct res_counter *fail_res;
         int csize = CHARGE_SIZE;
 
-        if (unlikely(test_thread_flag(TIF_MEMDIE))) {
-                /* Don't account this! */
-                *memcg = NULL;
-                return 0;
-        }
+        /*
+         * Unlike gloval-vm's OOM-kill, we're not in memory shortage
+         * in system level. So, allow to go ahead dying process in addition to
+         * MEMDIE process.
+         */
+        if (unlikely(test_thread_flag(TIF_MEMDIE)
+                     || fatal_signal_pending(current)))
+                goto bypass;
 
         /*
          * We always charge the cgroup the mm_struct belongs to.
@@ -1560,11 +1633,15 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
                 }
 
                 if (!nr_retries--) {
-                        if (oom) {
-                                mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);
-                                record_last_oom(mem_over_limit);
+                        if (!oom)
+                                goto nomem;
+                        if (mem_cgroup_handle_oom(mem_over_limit, gfp_mask)) {
+                                nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+                                continue;
                         }
-                        goto nomem;
+                        /* When we reach here, current task is dying .*/
+                        css_put(&mem->css);
+                        goto bypass;
                 }
         }
         if (csize > PAGE_SIZE)
@@ -1574,6 +1651,9 @@ done:
 nomem:
         css_put(&mem->css);
         return -ENOMEM;
+bypass:
+        *memcg = NULL;
+        return 0;
 }
 
 /*
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 71d10bf52dc8..9b223af6a147 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -603,13 +603,6 @@ void pagefault_out_of_memory(void)
                 /* Got some memory back in the last second. */
                 return;
 
-        /*
-         * If this is from memcg, oom-killer is already invoked.
-         * and not worth to go system-wide-oom.
-         */
-        if (mem_cgroup_oom_called(current))
-                goto rest_and_return;
-
         if (sysctl_panic_on_oom)
                 panic("out of memory from page fault. panic_on_oom is selected.\n");
 
@@ -621,7 +614,6 @@ void pagefault_out_of_memory(void)
          * Give "p" a good chance of killing itself before we
          * retry to allocate memory.
          */
-rest_and_return:
         if (!test_thread_flag(TIF_MEMDIE))
                 schedule_timeout_uninterruptible(1);
 }