memcg: change memcg_oom_mutex to spinlock

memcg_oom_mutex is used to protect memcg OOM path and eventfd interface
for oom_control.  None of the critical sections which it protects sleep
(eventfd_signal works from atomic context and the rest are simple linked
list resp.  oom_lock atomic operations).

Mutex is also too heavyweight for those code paths because it triggers a
lot of scheduling.  It also makes makes convoying effects more visible
when we have a big number of oom killing because we take the lock
mutliple times during mem_cgroup_handle_oom so we have multiple places
where many processes can sleep.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 11 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 95d6c256b54c..c0b065ec1571 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1725,7 +1725,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
 /*
  * Check OOM-Killer is already running under our hierarchy.
  * If someone is running, return false.
- * Has to be called with memcg_oom_mutex
+ * Has to be called with memcg_oom_lock
  */
 static bool mem_cgroup_oom_lock(struct mem_cgroup *mem)
 {
@@ -1770,7 +1770,7 @@ done:
 }
 
 /*
- * Has to be called with memcg_oom_mutex
+ * Has to be called with memcg_oom_lock
  */
 static int mem_cgroup_oom_unlock(struct mem_cgroup *mem)
 {
@@ -1802,7 +1802,7 @@ static void mem_cgroup_unmark_under_oom(struct mem_cgroup *mem)
                 atomic_add_unless(&iter->under_oom, -1, 0);
 }
 
-static DEFINE_MUTEX(memcg_oom_mutex);
+static DEFINE_SPINLOCK(memcg_oom_lock);
 static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);
 
 struct oom_wait_info {
@@ -1864,7 +1864,7 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
         mem_cgroup_mark_under_oom(mem);
 
         /* At first, try to OOM lock hierarchy under mem.*/
-        mutex_lock(&memcg_oom_mutex);
+        spin_lock(&memcg_oom_lock);
         locked = mem_cgroup_oom_lock(mem);
         /*
          * Even if signal_pending(), we can't quit charge() loop without
@@ -1876,7 +1876,7 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
                 need_to_kill = false;
         if (locked)
                 mem_cgroup_oom_notify(mem);
-        mutex_unlock(&memcg_oom_mutex);
+        spin_unlock(&memcg_oom_lock);
 
         if (need_to_kill) {
                 finish_wait(&memcg_oom_waitq, &owait.wait);
@@ -1885,11 +1885,11 @@ bool mem_cgroup_handle_oom(struct mem_cgroup *mem, gfp_t mask)
                 schedule();
                 finish_wait(&memcg_oom_waitq, &owait.wait);
         }
-        mutex_lock(&memcg_oom_mutex);
+        spin_lock(&memcg_oom_lock);
         if (locked)
                 mem_cgroup_oom_unlock(mem);
         memcg_wakeup_oom(mem);
-        mutex_unlock(&memcg_oom_mutex);
+        spin_unlock(&memcg_oom_lock);
 
         mem_cgroup_unmark_under_oom(mem);
 
@@ -4553,7 +4553,7 @@ static int mem_cgroup_oom_register_event(struct cgroup *cgrp,
         if (!event)
                 return -ENOMEM;
 
-        mutex_lock(&memcg_oom_mutex);
+        spin_lock(&memcg_oom_lock);
 
         event->eventfd = eventfd;
         list_add(&event->list, &memcg->oom_notify);
@@ -4561,7 +4561,7 @@ static int mem_cgroup_oom_register_event(struct cgroup *cgrp,
         /* already in OOM ? */
         if (atomic_read(&memcg->under_oom))
                 eventfd_signal(eventfd, 1);
-        mutex_unlock(&memcg_oom_mutex);
+        spin_unlock(&memcg_oom_lock);
 
         return 0;
 }
@@ -4575,7 +4575,7 @@ static void mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
 
         BUG_ON(type != _OOM_TYPE);
 
-        mutex_lock(&memcg_oom_mutex);
+        spin_lock(&memcg_oom_lock);
 
         list_for_each_entry_safe(ev, tmp, &mem->oom_notify, list) {
                 if (ev->eventfd == eventfd) {
@@ -4584,7 +4584,7 @@ static void mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
                 }
         }
 
-        mutex_unlock(&memcg_oom_mutex);
+        spin_unlock(&memcg_oom_lock);
 }
 
 static int mem_cgroup_oom_control_read(struct cgroup *cgrp,