Re: [PATCH V3] memcg, oom: provide more precise dump info while memcg oom happening

[Sha Zhengju <handai.szj@gmail.com>]

On 11/09/2012 12:25 AM, Michal Hocko wrote:
> On Thu 08-11-12 23:52:47, Sha Zhengju wrote:
> [...]
>> (2) After change
>> [  269.225628] mal invoked oom-killer: gfp_mask=0xd0, order=0, oom_score_adj=0
>> [  269.225633] mal cpuset=/ mems_allowed=0-1
>> [  269.225636] Pid: 4616, comm: mal Not tainted 3.6.0+ #25
>> [  269.225637] Call Trace:
>> [  269.225647]  [<ffffffff8111b9c4>] dump_header+0x84/0xd0
>> [  269.225650]  [<ffffffff8111c691>] oom_kill_process+0x331/0x350
>> [  269.225710]  .......(call trace)
>> [  269.225713]  [<ffffffff81517325>] page_fault+0x25/0x30
>> [  269.225716] Task in /1/2 killed as a result of limit of /1
>> [  269.225718] memory: usage 511732kB, limit 512000kB, failcnt 5071
>> [  269.225720] memory+swap: usage 563200kB, limit 563200kB, failcnt 57
>> [  269.225721] kmem: usage 0kB, limit 9007199254740991kB, failcnt 0
>> [  269.225722] Memory cgroup stats:cache:8KB rss:511724KB mapped_file:4KB swap:51468KB inactive_anon:265864KB active_anon:245832KB inactive_file:0KB active_file:0KB unevictable:0KB
>> [  269.225741] [ pid ]   uid  tgid total_vm      rss nr_ptes swapents oom_score_adj name
>> [  269.225757] [ 4554]     0  4554    16626      473      17       25             0 bash
>> [  269.225759] [ 4611]     0  4611   103328    90231     208    12260             0 mal
>> [  269.225762] [ 4616]     0  4616   103328    32799      88     7562             0 mal
>> [  269.225764] Memory cgroup out of memory: Kill process 4611 (mal) score 699 or sacrifice child
>> [  269.225766] Killed process 4611 (mal) total-vm:413312kB, anon-rss:360632kB, file-rss:292kB
>>
>> This version provides more pointed info for memcg in "Memory cgroup stats" section.
> Looks much better!
>
>> Change log:
>> v3<--- v2
>> 	1. fix towards hierarchy
>> 	2. undo rework dump_tasks
>> v2<--- v1
>> 	1. some modification towards hierarchy
>> 	2. rework dump_tasks
>> 	3. rebased on Michal's mm tree since-3.6
>>
>> Signed-off-by: Sha Zhengju<handai.szj@taobao.com>
>> ---
>>   mm/memcontrol.c |   41 +++++++++++++++++++++++++++++++----------
>>   mm/oom_kill.c   |    6 ++++--
>>   2 files changed, 35 insertions(+), 12 deletions(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 0eab7d5..17317fa 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
> [...]
>> @@ -1501,8 +1509,8 @@ static void move_unlock_mem_cgroup(struct mem_cgroup *memcg,
>>   	spin_unlock_irqrestore(&memcg->move_lock, *flags);
>>   }
>>
>> +#define K(x) ((x)<<  (PAGE_SHIFT-10))
>>   /**
>> - * mem_cgroup_print_oom_info: Called from OOM with tasklist_lock held in read mode.
> No need to remove this just fix it:
>   * mem_cgroup_print_oom_info: Print OOM information relevant to memory controller.
>
>>    * @memcg: The memory cgroup that went over limit
>>    * @p: Task that is going to be killed
>>    *
>> @@ -1520,8 +1528,10 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
>>   	 */
>>   	static char memcg_name[PATH_MAX];
>>   	int ret;
>> +	struct mem_cgroup *mi;
>> +	unsigned int i;
>>
>> -	if (!memcg || !p)
>> +	if (!p)
>>   		return;
>>
>>   	rcu_read_lock();
>> @@ -1569,6 +1579,25 @@ done:
>>   		res_counter_read_u64(&memcg->kmem, RES_USAGE)>>  10,
>>   		res_counter_read_u64(&memcg->kmem, RES_LIMIT)>>  10,
>>   		res_counter_read_u64(&memcg->kmem, RES_FAILCNT));
>> +
>> +	printk(KERN_INFO "Memory cgroup stats:");
> "Memory cgroup hierarchy stats" is probably a better fit with the
> current implementation.
>
>> +	for (i = 0; i<  MEM_CGROUP_STAT_NSTATS; i++) {
>> +		long long val = 0;
>> +		if (i == MEM_CGROUP_STAT_SWAP&&  !do_swap_account)
>> +			continue;
>> +		for_each_mem_cgroup_tree(mi, memcg)
>> +			val += mem_cgroup_read_stat(mi, i);
>> +		printk(KERN_CONT "%s:%lldKB ", mem_cgroup_stat_names[i], K(val));
>> +	}
>> +
>> +	for (i = 0; i<  NR_LRU_LISTS; i++) {
>> +		unsigned long long val = 0;
>> +
>> +		for_each_mem_cgroup_tree(mi, memcg)
>> +			val += mem_cgroup_nr_lru_pages(mi, BIT(i));
>> +		printk(KERN_CONT "%s:%lluKB ", mem_cgroup_lru_names[i], K(val));
>> +	}
>> +	printk(KERN_CONT "\n");
> This is nice and simple I am just thinking whether it is enough. Say
> that you have a deeper hierarchy and the there is a safety limit in the
> its root
>          A (limit)
>         /|\
>        B C D
>            |\
> 	  E F
>
> and we trigger an OOM on the A's limit. Now we know that something blew
> up but what it was we do not know. Wouldn't it be better to swap the for
> and for_each_mem_cgroup_tree loops? Then we would see the whole
> hierarchy and can potentially point at the group which doesn't behave.
> Memory cgroup stats for A/: ...
> Memory cgroup stats for A/B/: ...
> Memory cgroup stats for A/C/: ...
> Memory cgroup stats for A/D/: ...
> Memory cgroup stats for A/D/E/: ...
> Memory cgroup stats for A/D/F/: ...
>
> Would it still fit in with your use case?
> [...]

We haven't used those complicate hierarchy yet, but it sounds a good 
suggestion. :)
Hierarchy is a little complex to use from our experience, and the three 
cgroups involved in memcg oom can be different: memcg of invoker, killed 
task, memcg of going over limit.Suppose a process in B triggers oom and 
a victim in root A is selected to be killed, we may as well want to know 
memcg stats just local in A cgroup(excludes BCD). So besides hierarchy 
info, does it acceptable to also print the local root node stats which 
as I did in the V1 version(https://lkml.org/lkml/2012/7/30/179).

Another one I'm hesitating is numa stats, it seems the output is 
beginning to get more and more....


Thanks,
Sha

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