Re: Hibernation Redesign

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On Wed, 11 Jul 2007, Nigel Cunningham wrote:

Hi.

On Wednesday 11 July 2007 21:11:34 Miklos Szeredi wrote:
Anyway, to implement the kexec approach we must separate the
hibernation from the suspend at the drivers level, which I'm still
going to do, but I need to take part in endless discussions

Discussions are good.  We understand the problem better.  Now I still
think we don't understand every aspect completely, so continuing the
discussion makes sense.

regarding the freezer, how it is bad and how we should drop it,
because it breaks things (which NB is not true, because it doesn't).

This thread started out from a bug, that seemed to be caused by the
freezer (we still don't exactly know what it was caused by), and the
discussion uncovered various problems _with_ the freezer, that up to
now no other _proper_ solutions have been propsed than to remove the
freezer.

No other _proper_ solutions have been proposed. Everyone who suggests removing
the freezer also suggests implementing it all over again. It might be sending
SIGSTOP to everything. It might be shifting the desk chairs around and
creating a completely new kernel context, but they always have the same
goal - stopping the existing activity, and they all come with their own
issues (even if they're not obvious yet because the alternatives are
currently vapourware to one extent or another).

I think the big problem with the existing freezer is that you want to stop everything, except X, except Y, except Z.....

the advantage of the new approaches being proposed is that they don't require _anything_ from the origional system continue to run so you avoid all the exceptions.

freezing everything is easy, figuring out what you don't want to freeze is where everyone is seeing problems.

IMHO, the real solution is to go back to the original issue and fix it
properly. Make fuse filesystems play nicely with the existing freezer. I've
just gone back and looked at the point where you started talking
about "malicious filesystems". You talk about fuse imposing certain ordering
in the userspace tasks being frozen. Please, say more. What ordering issues?
Why? How can such ordering be determined programmatically?

I think most people just see this as a symptom of the problem, not the core problem itself.

David Lang
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