Re: [RFC][2/3] Account and control virtual address space allocations

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Pavel Emelyanov wrote:
> Balbir Singh wrote:
>> Pavel Emelyanov wrote:
>>> [snip]
>>>
>>>> +int mem_cgroup_update_as(struct mm_struct *mm, long nr_pages)
>>>> +{
>>>> +	int ret = 0;
>>>> +	struct mem_cgroup *mem;
>>>> +	if (mem_cgroup_subsys.disabled)
>>>> +		return ret;
>>>> +
>>>> +	rcu_read_lock();
>>>> +	mem = rcu_dereference(mm->mem_cgroup);
>>>> +	css_get(&mem->css);
>>>> +	rcu_read_unlock();
>>>> +
>>>> +	if (nr_pages > 0) {
>>>> +		if (res_counter_charge(&mem->as_res, (nr_pages * PAGE_SIZE)))
>>>> +			ret = 1;
>>>> +	} else
>>>> +		res_counter_uncharge(&mem->as_res, (-nr_pages * PAGE_SIZE));
>>> No, please, no. Let's make two calls - mem_cgroup_charge_as and mem_cgroup_uncharge_as.
>>>
>>> [snip]
>>>
>> Yes, sure :)
> 
> Thanks :)
> 
>>>> @@ -1117,6 +1117,9 @@ munmap_back:
>>>>  		}
>>>>  	}
>>>>  
>>>> +	if (mem_cgroup_update_as(mm, len >> PAGE_SHIFT))
>>>> +		return -ENOMEM;
>>>> +
>>> Why not use existintg cap_vm_enough_memory and co?
>>>
>> I thought about it and almost used may_expand_vm(), but there is a slight catch
>> there. With cap_vm_enough_memory() or security_vm_enough_memory(), they are
>> called after total_vm has been calculated. In our case we need to keep the
>> cgroups equivalent of total_vm up to date, and we do this in mem_cgorup_update_as.
> 
> So? What prevents us from using these hooks? :)

1. We need to account total_vm usage of the task anyway. So why have two places,
   one for accounting and second for control?
2. These hooks are activated for conditionally invoked for vma's with VM_ACCOUNT
   set.


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL