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SubjectRe: [ckrm-tech] [PATCH 5/13] BC: user interface (syscalls)
Pavel Emelianov wrote:
> Balbir Singh wrote:
>> Pavel Emelianov wrote:
>>> Balbir Singh wrote:
>>>>> +
>>>>> +asmlinkage long sys_set_bcid(bcid_t id)
>>>>> +{
>>>>> + int error;
>>>>> + struct beancounter *bc;
>>>>> + struct task_beancounter *task_bc;
>>>>> +
>>>>> + task_bc = &current->task_bc;
>>>> I was playing around with the bc patches and found that to make
>>>> use of bc's, I had to actually call set_bcid() and then exec() a
>>>> task/shell so that the id would stick around. Would you consider
>>> That sounds very strange as sys_set_bcid() actually changes current's
>>> exec_bc.
>>> One note is about mm's bc - mm obtains new bc only after fork or exec -
>>> that's
>>> true. But kmemsize starts charging right after the sys_set_bcid.
>> I was playing around only with kmemsize. I think the reason for my
>> observation
>> is this
>> bash --> (my utility) --> set_bcid()
>> Since bash spawns my utility in a separate process, it creates and
>> assigns
>> a bean counter to it and then my utility exits. Unless it
>> spawns/exec()'s a
>> new shell, the beancounter is freed when the task exits (my utility).
> Well, beancounter is not "inherited" by parent task :)
> After setting bcid you need to spawn/exec a new shell.
> But seeting limits and getting stats is possible from the old shell
> as well as from the new one.

That's what I suspected. I suggest changing the system call to allow adding any
task to a particular id (not necessarily only the current one). It would help us
group tasks to a particular id. It would also solve my problem of spawning a
shell each time I decide to use a task with a beancounter and limits.

>>>> changing sys_set_bcid to sys_set_task_bcid() or adding a new
>>>> system call sys_set_task_bcid()? We could pass the pid that we
>>>> intend to associate with the new id. This also means we'll need
>>>> locking around to protect task->task_bc.


Balbir Singh,
Linux Technology Center,
IBM Software Labs
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