Checkpoint/restart in user space [LWN.net]

Checkpoint/restart in user space

Posted Oct 30, 2013 18:41 UTC (Wed) by nix (subscriber, #2304)
Parent article: Checkpoint/restart in user space

Yeah. I imagine it would be problematic if you checkpointed something using a network connection and the far end timed it out while it was checkpointed. (e.g., what happens if you checkpoint an X client? The X server will presume it dead after a fairly short time...)

The 'checkpoint everything, kexec, and uncheckpoint' mechanism looks awesome. The sooner it works fully, the happier I'll be. It's a big hammer, unlike, say, ksplice, but it should work well enough. (Kernel modesetting probably helps here, since it is at least possible to checkpoint things like an X server, where before KMS that was a hopeless dream.)

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Checkpoint/restart in user space

Posted Oct 30, 2013 19:44 UTC (Wed) by raven667 (guest, #5198) [Link] (7 responses)

I was thinking about that and it seems a simple solution to just let the TCP connection be immediately reset by the remote side, the application should have some way of handling that in any case, checkpointing or not.

Checkpoint/restart in user space

Posted Oct 30, 2013 19:48 UTC (Wed) by dlang (guest, #313) [Link] (6 responses)

the thing is that if the process isn't asleep for very long, and the IP moves with the process, the TCP connection may be able to recover.

Checkpoint/restart in user space

Posted Oct 30, 2013 21:33 UTC (Wed) by raven667 (guest, #5198) [Link] (5 responses)

I should have been more clear what I meant by the "remote side", I meant the remote end of the TCP connection. If TCP can't recover it's no real loss because the network stack and application can handle dropped TCP connections without trouble. You see the same thing when devices suspend and resume on another network segment.

Checkpoint/restart in user space

Posted Nov 1, 2013 22:24 UTC (Fri) by nix (subscriber, #2304) [Link] (4 responses)

the network stack and application can handle dropped TCP connections without trouble

My X server disagrees -- or rather its connected clients do. X connection drops, oops you're dead.

For some sorts of TCP-connected application what you say is true -- but not for all, by any means.

Checkpoint/restart in user space

Posted Nov 2, 2013 17:59 UTC (Sat) by Oddscurity (guest, #46851) [Link] (1 responses)

Is there something like tmux or screen for X, where you can pick up a session after a disconnection?

Checkpoint/restart in user space

Posted Nov 2, 2013 21:04 UTC (Sat) by mmorrow (guest, #83845) [Link]

http://xpra.org/

Checkpoint/restart in user space

Posted Nov 2, 2013 19:23 UTC (Sat) by raven667 (guest, #5198) [Link] (1 responses)

I understand. What I meant to say is that a dropped tcp connection is a common error with expected behavior, as opposed to having some sort of obscure error in the middle of you application in some operation that normally doesn't fail and no one handles errors for.

Checkpoint/restart in user space

Posted Nov 3, 2013 19:59 UTC (Sun) by nix (subscriber, #2304) [Link]

Oh, agreed, it's better than a sudden bus error or whatever.

Checkpoint/restart in user space

Posted Nov 26, 2013 21:23 UTC (Tue) by scientes (guest, #83068) [Link]

But unlike ksplice you can upgrade your kernel.