[Devel] Re: [PATCH v3 04/13] kmem accounting basic infrastructure

[Glauber Costa]

On 09/26/2012 06:03 PM, Michal Hocko wrote:
> On Tue 18-09-12 18:04:01, Glauber Costa wrote:
>> This patch adds the basic infrastructure for the accounting of the slab
>> caches. To control that, the following files are created:
>>
>>  * memory.kmem.usage_in_bytes
>>  * memory.kmem.limit_in_bytes
>>  * memory.kmem.failcnt
>>  * memory.kmem.max_usage_in_bytes
>>
>> They have the same meaning of their user memory counterparts. They
>> reflect the state of the "kmem" res_counter.
> 
>> The code is not enabled until a limit is set. 
> 
> "Per cgroup slab memory accounting is not enabled until a limit is set
> for the group. Once the limit is set the accounting cannot be disabled
> such a group."
> 
> Better?
> 
>> This can be tested by the flag "kmem_accounted".
> 
> Sounds as if it could be done from userspace (because you were talking
> about an user interface) which it cannot and we do not see it in this
> patch because it is not used anywhere. So please be more specific.
> 
>> This means that after the patch is applied, no behavioral changes
>> exists for whoever is still using memcg to control their memory usage.
>>
>> We always account to both user and kernel resource_counters. 
> 
> This is in contradiction with your claim that there is no behavioral
> change for memcg users. Please clarify when we use u and when u+k
> accounting.
> "
> There is no behavioral change if the kmem accounting is turned off for
> memcg users but when there is a kmem.limit_in_bytes is set then the
> memory.usage_in_bytes will include both user and kmem memory.
> "
> 
>> This
>> effectively means that an independent kernel limit is in place when the
>> limit is set to a lower value than the user memory. A equal or higher
>> value means that the user limit will always hit first, meaning that kmem
>> is effectively unlimited.
>>
>> People who want to track kernel memory but not limit it, can set this
>> limit to a very high number (like RESOURCE_MAX - 1page - that no one
>> will ever hit, or equal to the user memory)
>>
>> Signed-off-by: Glauber Costa <glommer at parallels.com>
>> CC: Michal Hocko <mhocko at suse.cz>
>> CC: Johannes Weiner <hannes at cmpxchg.org>
>> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu at jp.fujitsu.com>
>> ---
>>  mm/memcontrol.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 63 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index d6ad138..f3fd354 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -265,6 +265,10 @@ struct mem_cgroup {
>>  	};
>>  
>>  	/*
>> +	 * the counter to account for kernel memory usage.
>> +	 */
>> +	struct res_counter kmem;
>> +	/*
>>  	 * Per cgroup active and inactive list, similar to the
>>  	 * per zone LRU lists.
>>  	 */
>> @@ -279,6 +283,7 @@ struct mem_cgroup {
>>  	 * Should the accounting and control be hierarchical, per subtree?
>>  	 */
>>  	bool use_hierarchy;
>> +	bool kmem_accounted;
>>  
>>  	bool		oom_lock;
>>  	atomic_t	under_oom;
>> @@ -389,6 +394,7 @@ enum res_type {
>>  	_MEM,
>>  	_MEMSWAP,
>>  	_OOM_TYPE,
>> +	_KMEM,
>>  };
>>  
>>  #define MEMFILE_PRIVATE(x, val)	((x) << 16 | (val))
>> @@ -1439,6 +1445,10 @@ done:
>>  		res_counter_read_u64(&memcg->memsw, RES_USAGE) >> 10,
>>  		res_counter_read_u64(&memcg->memsw, RES_LIMIT) >> 10,
>>  		res_counter_read_u64(&memcg->memsw, RES_FAILCNT));
>> +	printk(KERN_INFO "kmem: usage %llukB, limit %llukB, failcnt %llu\n",
>> +		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));
>>  }
>>  
>>  /*
>> @@ -3946,6 +3956,9 @@ static ssize_t mem_cgroup_read(struct cgroup *cont, struct cftype *cft,
>>  		else
>>  			val = res_counter_read_u64(&memcg->memsw, name);
>>  		break;
>> +	case _KMEM:
>> +		val = res_counter_read_u64(&memcg->kmem, name);
>> +		break;
>>  	default:
>>  		BUG();
>>  	}
>> @@ -3984,8 +3997,18 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
>>  			break;
>>  		if (type == _MEM)
>>  			ret = mem_cgroup_resize_limit(memcg, val);
>> -		else
>> +		else if (type == _MEMSWAP)
>>  			ret = mem_cgroup_resize_memsw_limit(memcg, val);
>> +		else if (type == _KMEM) {
>> +			ret = res_counter_set_limit(&memcg->kmem, val);
>> +			if (ret)
>> +				break;
>> +
>> +			/* For simplicity, we won't allow this to be disabled */
>> +			if (!memcg->kmem_accounted && val != RESOURCE_MAX)
>> +				memcg->kmem_accounted = true;
>> +		} else
>> +			return -EINVAL;
>>  		break;
>>  	case RES_SOFT_LIMIT:
>>  		ret = res_counter_memparse_write_strategy(buffer, &val);
>> @@ -4051,12 +4074,16 @@ static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
>>  	case RES_MAX_USAGE:
>>  		if (type == _MEM)
>>  			res_counter_reset_max(&memcg->res);
>> +		else if (type == _KMEM)
>> +			res_counter_reset_max(&memcg->kmem);
>>  		else
>>  			res_counter_reset_max(&memcg->memsw);
>>  		break;
>>  	case RES_FAILCNT:
>>  		if (type == _MEM)
>>  			res_counter_reset_failcnt(&memcg->res);
>> +		else if (type == _KMEM)
>> +			res_counter_reset_failcnt(&memcg->kmem);
>>  		else
>>  			res_counter_reset_failcnt(&memcg->memsw);
>>  		break;
>> @@ -4618,6 +4645,33 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
>>  }
>>  
>>  #ifdef CONFIG_MEMCG_KMEM
> 
> Some things are guarded CONFIG_MEMCG_KMEM but some are not (e.g. struct
> mem_cgroup.kmem). I do understand you want to keep ifdefs on the leash
> but we should clean this up one day.
> 
>> +static struct cftype kmem_cgroup_files[] = {
>> +	{
>> +		.name = "kmem.limit_in_bytes",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
>> +		.write_string = mem_cgroup_write,
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{
>> +		.name = "kmem.usage_in_bytes",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{
>> +		.name = "kmem.failcnt",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
>> +		.trigger = mem_cgroup_reset,
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{
>> +		.name = "kmem.max_usage_in_bytes",
>> +		.private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
>> +		.trigger = mem_cgroup_reset,
>> +		.read = mem_cgroup_read,
>> +	},
>> +	{},
>> +};
>> +
>>  static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>>  {
>>  	return mem_cgroup_sockets_init(memcg, ss);
>> @@ -4961,6 +5015,12 @@ mem_cgroup_create(struct cgroup *cont)
>>  		int cpu;
>>  		enable_swap_cgroup();
>>  		parent = NULL;
>> +
>> +#ifdef CONFIG_MEMCG_KMEM
>> +		WARN_ON(cgroup_add_cftypes(&mem_cgroup_subsys,
>> +					   kmem_cgroup_files));
>> +#endif
>> +
>>  		if (mem_cgroup_soft_limit_tree_init())
>>  			goto free_out;
>>  		root_mem_cgroup = memcg;
>> @@ -4979,6 +5039,7 @@ mem_cgroup_create(struct cgroup *cont)
>>  	if (parent && parent->use_hierarchy) {
>>  		res_counter_init(&memcg->res, &parent->res);
>>  		res_counter_init(&memcg->memsw, &parent->memsw);
>> +		res_counter_init(&memcg->kmem, &parent->kmem);
> 
> Haven't we already discussed that a new memcg should inherit kmem_accounted
> from its parent for use_hierarchy?
> Say we have
> root
> |
> A (kmem_accounted = 1, use_hierachy = 1)
>  \
>   B (kmem_accounted = 0)
>    \
>     C (kmem_accounted = 1)
> 
> B find's itself in an awkward situation becuase it doesn't want to
> account u+k but it ends up doing so becuase C.
> 

Ok, I haven't updated it here. But that should be taken care of in the
lifecycle patch.