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 heavy weight 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@xxxxxxx>
---
mm/memcontrol.c | 22 +++++++++++-----------
1 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index de1702c..f11f198 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1806,7 +1806,7 @@ 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)
{
@@ -1851,7 +1851,7 @@ 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)
{
@@ -1883,7 +1883,7 @@ 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 {
@@ -1945,7 +1945,7 @@ 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
@@ -1957,7 +1957,7 @@ 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);
@@ -1966,11 +1966,11 @@ 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);
@@ -4632,7 +4632,7 @@ 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);
@@ -4640,7 +4640,7 @@ 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;
}
@@ -4654,7 +4654,7 @@ 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) {
@@ -4663,7 +4663,7 @@ 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,
--
1.7.5.4
--
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