Re: [PATCH 2.6.11-rc4-mm1] end-of-proces handling for acct-csa

[Jay Lan]

Hi Andrew,

You asked:
>
> In other words: given that ELSA can do its thing via existing accounting
> interfaces and a fork notifier, why does CSA need to add lots more kernel
> code?

And i explained:
> Here are some codes from do_exit() starting line 813 (based on
> 2.6.11-rc4-mm1):
>
> 813        acct_update_integrals(tsk);
> 814        update_mem_hiwater(tsk);
> 815        group_dead = atomic_dec_and_test(&tsk->signal->live);
> 816        if (group_dead) {
> 817                del_timer_sync(&tsk->signal->real_timer);
> 818                acct_process(code);
> 819        }
> 820        exit_mm(tsk);
>
> The acct_process() is called to save off BSD accounting data at
> line 818. The next statement at 820, tsk->mm is disposed and all
> data saved at tsk->mm is gone, including memory hiwater marks
> information saved at line 814. The complete tsk is disposed
> before exit of do_exit() routine.

I was hoping Guilluame could jump in himself...
But, in a separate discussion thread, he wrote:
>> (Jay asked)
>> I spent some time trying to understand how ELSA save the per-process
>> accounting data before the task_struct data structure gets disposed,
>> but failed to find anything. My assumption would be that ELSA does
>> not collection those data in the kernel itself? Instead, it would
>> read the pacct file created by either BSD or CSA?
>
> Yes you're right, ELSA reads accounting file created by BSD or CSA. We
> don't make accounting. I think that the communication problem is here

Guilluame's reply should answer your question. ELSA does not collect
accounting data in the kernel as BSD/CSA does. It uses accounting
data collected by BSD/CSA.

The exit hook is essential for CSA to save off data before the data
is gone, A netlink type of thing does not help. BSD is in the same
situation. You can not replace the acct_process() call with a netlink.
If ELSA is to use the enhanced accounting data, it needs the CSA
eop handling at exit as well.

Thanks,
 - jay


Guillaume Thouvenin wrote:
> On Thu, 2005-02-24 at 20:46 -0800, Andrew Morton wrote:
>
> > Jay Lan <jlan@xxxxxxx> wrote:
> >
> > > Since my idea of providing an accounting framework was considered
> > > 'overkill', here i submit a tiny patch just to allow CSA to
> > > handle end-of-process (eop) situation by saving off accounting
> > > data before a task_struct is disposed.
> > >
> > > This patch is to modify the acct_process() in acct.c, which is
> > > invoked from do_exit() to handle eop for BSD accounting. Now
> > > the acct_process() wrapper will also take care of CSA, if it has
> > > been loaded. If the CSA module has been loaded, a CSA routine
> > > will be invoked to construct a CSA job record and to write the
> > > record to the CSA accounting file.
> >
> > I really don't want to have to (and shouldn't need to) become an accounting
> > person, but as there seems to be a communication problem somewhere..
> >
> > Please, you guys are the subject matter experts.  Put your heads together
> > and come up with something.
>
>
> I completely agree with that and we will continue this conversation in
> private with Jay and all people involved to come up with an appropriate
> solution.
>
> Guillaume

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