Re: [PATCH 2/2] Make res_counter hierarchical

[Pavel Emelyanov <xemul@openvz.org>]

Balbir Singh wrote:
> Pavel Emelyanov wrote:
>> This allows us two things basically:
>>
>> 1. If the subgroup has the limit higher than its parent has
>>    then the one will get more memory than allowed.
> 
> But should we allow such configuration? I suspect that we should catch such
> things at the time of writing the limit.

We cannot catch this at the limit-set-time. See, if you have a cgroup A
with a 1GB limit and the usage is 999Mb, then creating a subgroup B with
even 500MB limit will cause the A group consume 1.5GB of memory
effectively.

>> 2. When we will need to account for a resource in more than
>>    one place, we'll be able to use this technics.
>>
>>    Look, consider we have a memory limit and swap limit. The
>>    memory limit is the limit for the sum of RSS, page cache
>>    and swap usage. To account for this gracefuly, we'll set
>>    two counters:
>>
>> 	   res_counter mem_counter;
>> 	   res_counter swap_counter;
>>
>>    attach mm to the swap one
>>
>> 	   mm->mem_cnt = &swap_counter;
>>
>>    and make the swap_counter be mem's child. That's it. If we
>>    want hierarchical support, then the tree will look like this:
>>
>>    mem_counter_top
>>     swap_counter_top <- mm_struct living at top
>>      mem_counter_sub
>>       swap_counter_sub <- mm_struct living at sub
>>
> 
> Hmm... not sure about this one. What I want to see is a resource counter
> hierarchy to mimic the container hierarchy. Then ensure that all limits are set
> sanely. I am planning to implement shares support on to of resource counters.
> 
> 
>> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
>>
>> ---
>>  include/linux/res_counter.h |   11 ++++++++++-
>>  kernel/res_counter.c        |   36 +++++++++++++++++++++++++++++-------
>>  mm/memcontrol.c             |    9 ++++++---
>>  3 files changed, 45 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
>> index 2c4deb5..a27105e 100644
>> --- a/include/linux/res_counter.h
>> +++ b/include/linux/res_counter.h
>> @@ -41,6 +41,10 @@ struct res_counter {
>>  	 * the routines below consider this to be IRQ-safe
>>  	 */
>>  	spinlock_t lock;
>> +	/*
>> +	 * the parent counter. used for hierarchical resource accounting
>> +	 */
>> +	struct res_counter *parent;
>>  };
>>
>>  /**
>> @@ -80,7 +84,12 @@ enum {
>>   * helpers for accounting
>>   */
>>
>> -void res_counter_init(struct res_counter *counter);
>> +/*
>> + * the parent pointer is set only once - during the counter
>> + * initialization. caller then must itself provide that this
>> + * pointer is valid during the new counter lifetime
>> + */
>> +void res_counter_init(struct res_counter *counter, struct res_counter *parent);
>>
>>  /*
>>   * charge - try to consume more resource.
>> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
>> index f1f20c2..046f6f4 100644
>> --- a/kernel/res_counter.c
>> +++ b/kernel/res_counter.c
>> @@ -13,10 +13,11 @@
>>  #include <linux/res_counter.h>
>>  #include <linux/uaccess.h>
>>
>> -void res_counter_init(struct res_counter *counter)
>> +void res_counter_init(struct res_counter *counter, struct res_counter *parent)
>>  {
>>  	spin_lock_init(&counter->lock);
>>  	counter->limit = (unsigned long long)LLONG_MAX;
>> +	counter->parent = parent;
>>  }
>>
>>  int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
>> @@ -36,10 +37,26 @@ int res_counter_charge(struct res_counter *counter, unsigned long val)
>>  {
>>  	int ret;
>>  	unsigned long flags;
>> +	struct res_counter *c, *unroll_c;
>> +
>> +	local_irq_save(flags);
>> +	for (c = counter; c != NULL; c = c->parent) {
>> +		spin_lock(&c->lock);
>> +		ret = res_counter_charge_locked(c, val);
>> +		spin_unlock(&c->lock);
>> +		if (ret < 0)
>> +			goto unroll;
> 
> We'd like to know which resource counter failed to allow charging, so that we
> can reclaim from that mem_res_cgroup.
> 
>> +	}
>> +	local_irq_restore(flags);
>> +	return 0;
>>
>> -	spin_lock_irqsave(&counter->lock, flags);
>> -	ret = res_counter_charge_locked(counter, val);
>> -	spin_unlock_irqrestore(&counter->lock, flags);
>> +unroll:
>> +	for (unroll_c = counter; unroll_c != c; unroll_c = unroll_c->parent) {
>> +		spin_lock(&unroll_c->lock);
>> +		res_counter_uncharge_locked(unroll_c, val);
>> +		spin_unlock(&unroll_c->lock);
>> +	}
>> +	local_irq_restore(flags);
>>  	return ret;
>>  }
>>
>> @@ -54,10 +71,15 @@ void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
>>  void res_counter_uncharge(struct res_counter *counter, unsigned long val)
>>  {
>>  	unsigned long flags;
>> +	struct res_counter *c;
>>
>> -	spin_lock_irqsave(&counter->lock, flags);
>> -	res_counter_uncharge_locked(counter, val);
>> -	spin_unlock_irqrestore(&counter->lock, flags);
>> +	local_irq_save(flags);
>> +	for (c = counter; c != NULL; c = c->parent) {
>> +		spin_lock(&c->lock);
>> +		res_counter_uncharge_locked(c, val);
>> +		spin_unlock(&c->lock);
>> +	}
>> +	local_irq_restore(flags);
>>  }
>>
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index e5c741a..61db79c 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -976,19 +976,22 @@ static void free_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
>>  static struct cgroup_subsys_state *
>>  mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
>>  {
>> -	struct mem_cgroup *mem;
>> +	struct mem_cgroup *mem, *parent;
>>  	int node;
>>
>>  	if (unlikely((cont->parent) == NULL)) {
>>  		mem = &init_mem_cgroup;
>>  		init_mm.mem_cgroup = mem;
>> -	} else
>> +		parent = NULL;
>> +	} else {
>>  		mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
>> +		parent = mem_cgroup_from_cont(cont->parent);
>> +	}
>>
>>  	if (mem == NULL)
>>  		return ERR_PTR(-ENOMEM);
>>
>> -	res_counter_init(&mem->res);
>> +	res_counter_init(&mem->res, parent ? &parent->res : NULL);
>>
>>  	memset(&mem->info, 0, sizeof(mem->info));
>>
> 
> 

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