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


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