Re: kernel upgrade on the fly

From: Pavel Machek (
Date: Sat Jun 22 2002 - 03:34:11 EST


> Nothing is impossible for anyone impervious to reason, and you might suprise
> us (it'd make a heck of a graduate project). Hot migration isn't IMPOSSIBLE,
> it's just a flipping pain in the ass. But the issue's a bit threadbare in
> these parts (somewhere between "are we there yet mommy?" and "can I buy a
> pony?").

Actually, getting a pony is easy compared to *this* ;-).

> The SANE answer always has been to just schedule some down time for the box.
> The insane answer involves giving an awful lot of money to Sun or IBM or some
> such for hot-pluggable backplanes. (How do you swap out THE BACKPLANE?
> That's an answer nobody seems to have...)

You have two back backplanes and you use the other one during the switch?

> Clusters. Migrating tasks in the cluster, potentially similar problem. Look
> at mosix and the NUMA stuff as well, if you're actually serious
> about this.
> You have to reduce a process to its vital data, once all the resources you
> can peel away from it have been peeled away, swapped out, freed, etc. If you
> can suspend and save an individual running process to a disk image (just a
> file in the filesystem), in such a way that it can be individually re-loaded
> later (by the same kernel), you're halfway there. No, it's not as easy as it
> sounds. :)

Actually, if you can select few "important" processes, and only care
about them, it can be done from userspace. Martin Mares did something
like that, involving ptrace() and lots of limitations.

> > I can see the advantage of such a thing when a server can have the kernel
> > upgraded (major or minor upgrade) without disrupting the ongoing services
> > (ok, maybe a small few-seconds delay). Another instance would be to
> > switch between different kernels in the /boot/ directory (for testing
> > purposes, etc.) without rebooting the machine.
> See "belling the cat". Yeah, it's a great idea. The implementation's the
> tricky bit.

My dictionary is too weak for this.

(about SSSCA) "I don't say this lightly.  However, I really think that the U.S.
no longer is classifiable as a democracy, but rather as a plutocracy." --hpa
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

This archive was generated by hypermail 2b29 : Sun Jun 30 2002 - 22:00:07 EST