Re: [RFC][PATCH] memcg: page fault oom improvement

[Daisuke Nishimura]

On Tue, 23 Feb 2010 12:03:15 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> Nishimura-san, could you review and test your extreme test case with this ?
> 
Thank you for your patch.
I don't know why, but the problem seems not so easy to cause in mmotm as in 2.6.32.8,
but I'll try more anyway.

A few comments are inlined.

> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Cc: Balbir Singh <balbir@xxxxxxxxxx>
> Cc: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
>  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);
it can be static.

> +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
>  
I think it should be "if (!test_thread_flag(TIF_MEMDIE))".


Thanks,
Daisuke Nishimura.

> @@ -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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