[PATCH 6/6] Makes procs file writable to move all threads by tgid at once

[Serge E. Hallyn]

Quoting Paul Menage (menage at google.com):
> On Mon, Aug 3, 2009 at 12:45 PM, Serge E. Hallyn<serue at us.ibm.com> wrote:
> >
> > This is probably a stupid idea, but...  what about having zero
> > overhead at clone(), and instead, at cgroup_task_migrate(),
> > dequeue_task()ing all of the affected threads for the duration of
> > the migrate?
> 
> That doesn't sound too unreasonable, actually - it would certainly
> simplify things a fair bit. Is there a standard API for doing that?
> dequeue_task() itself doesn't really look like a public API. I guess
> that the task freezer would be one way to accomplish this?

Actually if we wanted to try to avoid -EINTRs for the tasks, which
they get with the freezer, we might want to code our own helpers
in sched.c based on dequeue_task().  Instead of interrupting ongoing
system calls, we'll want to set a flag saying if the syscall exits
(before we unset the flag) then dequeue it real quick.

> I can imagine that the set of people who'd complain about the latency
> hit when migrating with your solution would be smaller than the people
> who'd complain about the increased overhead in the normal clone case.
> 
> Paul