Re: [gentoo-user] Suspend to swap on a diskless host

[Hans-Werner Hilse]

Hi,

On Sun, 27 May 2007 16:21:03 +0200 "Michal 'vorner' Vaner"
<vorner@×××.cz> wrote:

> First: You need to load the kernel from the swap, in the time it
> loads, you have no running kernel (well, there is a little part, but
> that one has no clue about network).

No, that's not entirely true. Userspace suspend and resume is in the
kernel since 2.6.17. See my other post in this thread for a pointer (I
think it was http://suspend.sf.net/). So for this way it really happens
all in userspace, with a fully working kernel available. When the image
is loaded into RAM, the resume utility makes a syscall to have the
kernel automatically copy & switch over.

See /usr/src/linux/Documentation/power/*suspend* for all the details.

> Second: You do not want swap on nfs, since it is terribly slow, buggy,
> nfs can allocate memory to transfer data and you get a circular
> problem
> - to get a memory, you need to get a memory. And, what if your cat
> steps on the ethernet cable?

Resume aborts, checksum error. But that's it. But true, I wouldn't
trust NFS too much, either. But then, there are nbd's (network block
devices) which would probably work a treat. But userspace resume from a
file on NFS should work reliably, too.

You're right, however, regarding the slowlyness. Suspending a 4Gig-RAM
machine via NFS is probably a bad idea.

> Third: the suspend does not use swap as a swap, but as a part of a
> disc.

Doesn't matter at all for userspace resume.

> You might try suspend to ram, thought. It should work on diskless
> machine as well as on any other.

...cough, cough... yeah, /as/ well as on any other. So this probably
means: It won't work until you switch off ACPI and resort to APM... But
of course, that will depend.

-hwh
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