Re: [ckrm-tech] [PATCH 5/13] BC: user interface (syscalls)

[Balbir Singh <balbir@in.ibm.com>]

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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