linux-kernel - Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid at once

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Message-ID: <20090804140158.GA663@us.ibm.com>
Date:	Tue, 4 Aug 2009 09:01:58 -0500
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Benjamin Blum <bblum@...gle.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 6/6] Makes procs file writable to move all threads by
	tgid at once

Quoting Paul Menage (menage@...gle.com):
> On Mon, Aug 3, 2009 at 12:45 PM, Serge E. Hallyn<serue@...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
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