From: Pedro Alves <pedro@codesourcery.com>
To: Pavel Emelyanov <xemul@parallels.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Tejun Heo <tj@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Cyrill Gorcunov <gorcunov@openvz.org>,
James Bottomley <jbottomley@parallels.com>
Subject: Re: [RFC][PATCH 0/3] fork: Add the ability to create tasks with given pids
Date: Fri, 25 Nov 2011 22:36:39 +0000 [thread overview]
Message-ID: <201111252236.40246.pedro@codesourcery.com> (raw)
In-Reply-To: <4ECFCA5E.1020307@parallels.com>
On Friday 25 November 2011 17:03:26, Pavel Emelyanov wrote:
> On 11/25/2011 08:54 PM, Oleg Nesterov wrote:
> > How you can restore the multithread tracee?
>
> Don't know :) But if this approach sounds promising (I see, that now it's not, but...) I
> can think more on it.
>
> > You need to unreserve/reserve the previous pid, and we have the same problems again, no?
>
> With the existing patch - yes, but as I said above - we need to decide which direction to
> go and then I'll think further.
Thanks for thinking about all this. Being able to reserve pids would be
nice, but I won't pretend to know the kernel's internals enough to be able
to suggest a sane and acceptable way to do it. We'd have to be able
to restore multi-threaded tracees (which would also mean that there are
pids which leaders and others which are clones), and, we'd have to support
a single-threaded tracer debugging (and spawning) more than one process,
while not all tracees are involved in C/R. Maybe this (reservation) issue
should be be considered an orthogonal mechanism for now.
> By now your opinion is to better stay where we are ;) but if moving is unavoidable, then
> it's better to take the CLONE_CHILD_USEPIDS route. That's my position as well.
>From the perspective of a client that is
going to use this on a live system, CLONE_CHILD_USEPIDS seems a little better,
in that the pid race is only against another task reusing the same pid,
while with setting last_pid, you have a try/whoops-not-the-pid-I-want/kill/retry/rinse/repeat/
loop racing against all fork/clone's in the system, along with possibly
needing to first to do a kill(PID, 0) to check whether the PID is
available (unless setting last_pid already detects that).
BTW, it's not only GDB that would want this for live systems.
Check out Berkeley Lab's C/R (https://ftg.lbl.gov/projects/CheckpointRestart/),
where these guys use mixed kernel/userspace C/R in clusters for high-end
scientific computing to e.g., migrate tasks between nodes, and pause/resume
parallel MPI jobs (on live systems). (Apologies if everyone already knows
about this :-) .)
>From what I read from their papers, in their approach, from userspace, they
spawn new children as usual, with whatever pids the kernel wants, and then
afterwards (from userspace, but through a kernel module), magically change
the process and threads's pids to the pids they really want. They also fixup
the parent pids, and session ids after the fact, along the way.
--
Pedro Alves
next prev parent reply other threads:[~2011-11-25 22:36 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-17 11:41 [RFC][PATCH 0/3] fork: Add the ability to create tasks with given pids Pavel Emelyanov
2011-11-17 11:42 ` [PATCH 1/3] pids: Make alloc_pid return error Pavel Emelyanov
2011-11-17 11:42 ` [PATCH 2/3] pids: Split alloc_pidmap into parts Pavel Emelyanov
2011-11-17 11:43 ` [PATCH 3/3] pids: Make it possible to clone tasks with given pids Pavel Emelyanov
2011-11-17 15:32 ` Oleg Nesterov
2011-11-17 15:49 ` Pavel Emelyanov
2011-11-17 16:00 ` Oleg Nesterov
2011-11-17 17:28 ` Linus Torvalds
2011-11-17 19:04 ` Oleg Nesterov
2011-11-17 18:36 ` Oleg Nesterov
2011-11-18 10:05 ` Pavel Emelyanov
2011-11-17 15:49 ` [RFC][PATCH 0/3] fork: Add the ability to create " Oleg Nesterov
2011-11-17 16:01 ` Pavel Emelyanov
2011-11-17 16:02 ` Oleg Nesterov
2011-11-18 23:30 ` Tejun Heo
2011-11-21 9:15 ` Pavel Emelyanov
2011-11-21 22:50 ` Tejun Heo
2011-11-22 11:11 ` Pavel Emelyanov
2011-11-22 12:04 ` Pedro Alves
2011-11-22 15:33 ` Tejun Heo
2011-11-23 16:20 ` Pedro Alves
2011-11-23 16:24 ` Tejun Heo
2011-11-23 17:26 ` Oleg Nesterov
2011-11-23 17:37 ` Tejun Heo
2011-11-23 18:19 ` Pavel Emelyanov
2011-11-23 20:14 ` Pavel Emelyanov
2011-11-24 17:31 ` Oleg Nesterov
2011-11-25 10:14 ` Pavel Emelyanov
2011-11-25 16:22 ` Oleg Nesterov
2011-11-25 16:44 ` Pavel Emelyanov
2011-11-25 16:54 ` Oleg Nesterov
2011-11-25 17:03 ` Pavel Emelyanov
2011-11-25 22:36 ` Pedro Alves [this message]
2011-11-27 16:24 ` [RFC][PATCH 0/3] fork: Add the ability to create tasks with?given pids Oleg Nesterov
2011-11-27 9:41 ` [RFC][PATCH 0/3] fork: Add the ability to create tasks with given pids Konstantin Khlebnikov
2011-11-27 17:34 ` Oleg Nesterov
2011-11-27 18:47 ` Tejun Heo
2011-11-28 10:38 ` Pavel Emelyanov
2011-11-28 16:25 ` Tejun Heo
2011-11-22 15:23 ` Tejun Heo
2011-11-22 15:29 ` Tejun Heo
2011-11-22 16:30 ` Pavel Emelyanov
2011-11-22 16:44 ` Linus Torvalds
2011-11-22 19:29 ` Pavel Emelyanov
2012-01-26 23:28 ` Kay Sievers
2011-11-22 21:16 ` Oleg Nesterov
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