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Subject[PATCH 1/3] memcg: oom wakeup filter
This patch is my answer to a concern for 
memcg-fix-oom-kill-behavior-v4.patch
in mmotm. The concern was that patch uses system-wide waitq.

For handling hierarchy, per-mm waitq is not useful...this patch adds
filter at wake-up. Works well on my test.

==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

memcg's oom waitqueue is a system-wide wait_queue (for handling hierarchy.)
So, it's better to add custom wake function and do flitering in wake up path.

This patch adds a filtering feature for waking up oom-waiters.
Hierarchy is properly handled.

Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 61 ++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 44 insertions(+), 17 deletions(-)

Index: mmotm-2.6.34-Mar9/mm/memcontrol.c
===================================================================
--- mmotm-2.6.34-Mar9.orig/mm/memcontrol.c
+++ mmotm-2.6.34-Mar9/mm/memcontrol.c
@@ -1293,14 +1293,54 @@ static void mem_cgroup_oom_unlock(struct
static DEFINE_MUTEX(memcg_oom_mutex);
static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);

+struct oom_wait_info {
+ struct mem_cgroup *mem;
+ wait_queue_t wait;
+};
+
+static int memcg_oom_wake_function(wait_queue_t *wait,
+ unsigned mode, int sync, void *arg)
+{
+ struct mem_cgroup *wake_mem = (struct mem_cgroup *)arg;
+ struct oom_wait_info *oom_wait_info;
+
+ /* both of oom_wait_info->mem and wake_mem are stable under us */
+ oom_wait_info = container_of(wait, struct oom_wait_info, wait);
+
+ if (oom_wait_info->mem == wake_mem)
+ goto wakeup;
+ /* if no hierarchy, no match */
+ if (!oom_wait_info->mem->use_hierarchy || !wake_mem->use_hierarchy)
+ return 0;
+ /* check hierarchy */
+ if (!css_is_ancestor(&oom_wait_info->mem->css, &wake_mem->css) &&
+ !css_is_ancestor(&wake_mem->css, &oom_wait_info->mem->css))
+ return 0;
+
+wakeup:
+ return autoremove_wake_function(wait, mode, sync, arg);
+}
+
+static void memcg_wakeup_oom(struct mem_cgroup *mem)
+{
+ /* for filtering, pass "mem" as argument. */
+ __wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, mem);
+}
+
/*
* 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);
+ struct oom_wait_info owait;
bool locked;

+ owait.mem = mem;
+ owait.wait.flags = 0;
+ owait.wait.func = memcg_oom_wake_function;
+ owait.wait.private = current;
+ INIT_LIST_HEAD(&owait.wait.task_list);
+
/* At first, try to OOM lock hierarchy under mem.*/
mutex_lock(&memcg_oom_mutex);
locked = mem_cgroup_oom_lock(mem);
@@ -1310,31 +1350,18 @@ bool mem_cgroup_handle_oom(struct mem_cg
* under OOM is always welcomed, use TASK_KILLABLE here.
*/
if (!locked)
- prepare_to_wait(&memcg_oom_waitq, &wait, TASK_KILLABLE);
+ prepare_to_wait(&memcg_oom_waitq, &owait.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);
+ finish_wait(&memcg_oom_waitq, &owait.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);
+ memcg_wakeup_oom(mem);
mutex_unlock(&memcg_oom_mutex);

if (test_thread_flag(TIF_MEMDIE) || fatal_signal_pending(current))


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