taskstats interface for accounting

[Jay Lan <jlan@sgi.com>]

Hi Balbir and Shailabh,

I finally have time to think about implementation details of CSA over
taskstats interface. I took another look at the taskstats interface
proposal and was a little bit nervous.

Do you remember i suggested to use #ifdef to cut down traffic and i
was told a generic netlink header would serve the purpose?
What i see now at Documentation/accounting/taskstats.txt saying
NETLINK_GENERIC family is used for unicast query/reply mode. The
NETLINK_GENERIC family provides great flexsibility on what to receive. 
However, CSA only uses the multicast mode to receive from kernel
whenever tasks are existing. I guess i would need to read the netlink
documentation more carefully to see whether my understanding is
correct.

Another thing i overlooked when i did the review was that taskstats
interface is designed to provide _BOTH_ per task _AND_ per thread
accounting data EVERY TIME a task exists. A thread is an aggregate
of (per-pid) tasks. Since this type of aggregation is not used in
CSA, half of data traffic would be useless. Can we add a way to
configure to not send per-thread data to the socket?

Regards,
jay