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Subject[RFC][PATCH] memcg: page fault oom improvement
Nishimura-san, could you review and test your extreme test case with this ?

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

Now, because of page_fault_oom_kill, returning VM_FAULT_OOM means
random oom-killer should be called. Considering memcg, it handles
OOM-kill in its own logic, there was a problem as "oom-killer called
twice" problem.

By commit a636b327f731143ccc544b966cfd8de6cb6d72c6, I added a check
in pagefault_oom_killer shouldn't kill some (random) task if
memcg's oom-killer already killed anyone.
That was done by comapring current jiffies and last oom jiffies of memcg.

I thought that easy fix was enough, but Nishimura could write a test case
where checking jiffies is not enough. So, my fix was not enough.
This is a fix of above commit.

This new one does this.
* memcg's try_charge() never returns -ENOMEM if oom-killer is allowed.
* If someone is calling oom-killer, wait for it in try_charge().
* If TIF_MEMDIE is set as a result of try_charge(), return 0 and
allow process to make progress (and die.)
* removed hook in pagefault_out_of_memory.

By this, pagefult_out_of_memory will be never called if memcg's oom-killer
is called and scattered codes are now in memcg's charge logic again.

TODO:
If __GFP_WAIT is not specified in gfp_mask flag, VM_FAULT_OOM will return
anyway. We need to investigate it whether there is a case.

Cc: David Rientjes <rientjes@google.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 41 +++++++++++++++++++++++------------------
mm/oom_kill.c | 11 +++--------
2 files changed, 26 insertions(+), 26 deletions(-)
Index: mmotm-2.6.33-Feb11/mm/memcontrol.c
===================================================================
--- mmotm-2.6.33-Feb11.orig/mm/memcontrol.c
+++ mmotm-2.6.33-Feb11/mm/memcontrol.c
@@ -1234,21 +1234,12 @@ static int mem_cgroup_hierarchical_recla
return total;
}

-bool mem_cgroup_oom_called(struct task_struct *task)
+DEFINE_MUTEX(memcg_oom_mutex);
+bool mem_cgroup_oom_called(struct mem_cgroup *mem)
{
- bool ret = false;
- struct mem_cgroup *mem;
- struct mm_struct *mm;
-
- 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;
+ if (time_before(jiffies, mem->last_oom_jiffies + HZ/10))
+ return true;
+ return false;
}

static int record_last_oom_cb(struct mem_cgroup *mem, void *data)
@@ -1549,11 +1540,25 @@ static int __mem_cgroup_try_charge(struc
}

if (!nr_retries--) {
- if (oom) {
- mem_cgroup_out_of_memory(mem_over_limit, gfp_mask);
+ int oom_kill_called;
+ if (!oom)
+ goto nomem;
+ mutex_lock(&memcg_oom_mutex);
+ oom_kill_called = mem_cgroup_oom_called(mem_over_limit);
+ if (!oom_kill_called)
record_last_oom(mem_over_limit);
- }
- goto nomem;
+ mutex_unlock(&memcg_oom_mutex);
+ if (!oom_kill_called)
+ mem_cgroup_out_of_memory(mem_over_limit,
+ gfp_mask);
+ else /* give a chance to die for other tasks */
+ schedule_timeout(1);
+ nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+ /* Killed myself ? */
+ if (!test_thread_flag(TIF_MEMDIE))
+ continue;
+ /* For smooth oom-kill of current, return 0 */
+ return 0;
}
}
if (csize > PAGE_SIZE)
Index: mmotm-2.6.33-Feb11/mm/oom_kill.c
===================================================================
--- mmotm-2.6.33-Feb11.orig/mm/oom_kill.c
+++ mmotm-2.6.33-Feb11/mm/oom_kill.c
@@ -487,6 +487,9 @@ retry:
goto retry;
out:
read_unlock(&tasklist_lock);
+ /* give a chance to die for selected process */
+ if (test_thread_flag(TIF_MEMDIE))
+ schedule_timeout_uninterruptible(1);
}
#endif

@@ -601,13 +604,6 @@ 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");

@@ -619,7 +615,6 @@ 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);
}


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