On Fri, 26 Sep 1997, Fabio Olive Leite wrote:
> Hi there,
>
> Just out of curiosity (nevertheless I'll shoot myself if it can't be
> done), I was wondering how it would be possible to implement a process
> migration facility on Linux, so that idle time can be put to better use
> on a net of Linux stations.
>
> The real fact is that I proposed just the above as my graduation project,
> so I gotta get it working somehow, and a couple of suggestions would be
> nice. I've been doing my homework (I obviously hadn't done it when I
> proposed such a gigantic work), and the more I study the Linux kernel more
> I get worried about not graduating :). But I can see a light at the end of
> the tunnel (maybe it's the train called _failure_).
>
> The model I'll use to attempt it will have some of the work done by the
> kernel, and some more by a user level daemon, that will comunicate with
> the kernel part in a kerneld fashion. The kernel will never take a strong
> part on the migration, like selecting processes for it (distributed
> scheduling would be a big bloat on a centralized system), or actually
> transfering the virtual memory of a process via the network.
>
> The idea is having a kernel that _supports_ process migration, _helps_ in
> the migration, but don't actually take any opinion on it's own, delegating
> that position to the user level daemon. I'm not concerned with speed,
> since it's gonna crawl anyway. I just want to get a process to actually
> get transfered to another machine and keep running (and you keep reading,
> I'm not crazy).
>
> Say we want to migrate process X. The daemon talks to the daemon at the
> target machine (I'm not concerned with a wonderfull selection of a target,
> as that's load _balancing_, not just load _sharing_), and the daemon at
> the target convinces the kernel to create a new process, which will have
> special needs, as all it's files _and_ code will be on another machine.
>
> I intend to alter all the f_ops, mm_ops, whetever_ops structures of this
> process, so that whenever it faults on a page, the routines on my kernel
> module get called, and so it talks to the daemon, which talks to the
> daemon on the source machine, which talks to the kernel on the source,
> which will find da damn page and send it back all the way through.
>
> File ops will have a similar treatment, but then there is some other
> concerns, like IPC. Rerouting signals is simple, and so are messages, but
> shared memory, for instance, would be a major pain in the ass, if not
> impossible at all. Simple tweaks like having all processes involved to
> fault on the shared page when it's accessed and then distribute the page
> (if someone faulted on it) to the other machine on the next schedule()
> would maybe work, but looks horrible.
>
> Anyway, I'm not terribly concerned with such "advanced" processes. If a
> simple RC5 cracker, which is CPU-bound, get to continue working, I'll
> consider it great. :)
>
> Another great job would have to be put to redirecting all syscalls which
> are not as simple as a getpid(). Maybe they can be redirected some way
> similar to the page faults. Also obvious is the fact that this migrated
> process will be in a state where it won't get on the run queue, or things
> will get funny. I don't know if it's better to create a new state, or use
> a similar one such as UNINTERRUPTIBLE.
>
> For the record, I was reading about process migration on Sprite when I
> decided to accomplish such beast. Maybe I went insane for some days, I
> don't know. The fact is that I have to do it.
>
> Now for the real thing: Does anyone consider this project so improbable
> as to not even a very simple "Hello World!" be able to migrate?
>
> I'm not on the list, as I can't cope with the traffic. Answers and
> suggestions directly (or CC'ed) to me, please!
>
> Now the sentence all mails to linux-kernel should have: Keep up the good
> work guys! Linux is the best thing since microwave popcorn!
>
> []!
> Fabio
> ( Fabio Olive Leite leitinho@akira.ucpel.tche.br )
> ( Computing Science Student http://akira.ucpel.tche.br/~leitinho/ )
> ( )
> ( LOADLIN.EXE: The best Windows95 application. [Debian GNU/Linux] )
>