[Devel] Re: [PATCH 2/2] Make res_counter hierarchical

[Pavel Emelyanov]

Balbir Singh wrote:
> Pavel Emelyanov wrote:
>> 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.
>>
> 
> No... If you propagate the charge of the child up to the parent, then it won't.
> If each page charged to a child is also charged to the parent, this cannot
> happen. The code you have below does that right?

Yup! What you described is available with this patch only.

>>>> 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 at 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.
>>>
> 
> This is also important, so that we can reclaim from the nodes that go over their
> limit.

Agree. I'll think over how to provide this facility.

>>>> +	}
>>>> +	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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> 
> 

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