Re: [linux-pm] Re: Hibernation considerations

Nigel Cunningham
2007-07-23T21:55:17Z

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Hi.

On Tuesday 24 July 2007 01:23:15 Alan Stern wrote:
> On Mon, 23 Jul 2007, Nigel Cunningham wrote:
>
> > Take a step back for a second.
> >
> > The problem we're facing now is that we're getting some userspace threads,
> > used in processing I/O, that are functioning as exceptions to the "freeze
> > userspace, then freezeable kernel threads" rule. They are only exceptions
> > because of that role in processing I/O - because they're de facto kernel
> > threads. So, if we orient our thinking more in terms of I/O processing and
> > less in terms of the userspace/kernelspace distinction, we'll have a
> > solution:
> >
> > 1) Freeze processes that aren't fs related (ie stop them generating I/O).
>
> The problem here is that with things like FUSE, _every_ process is
> potentially fs related. Nothing prevents a FUSE thread from doing IPC
> with any other thread.

Yes, but the fuse thread is going to know what other thread it's doing IPC
with, so it can get that thread flagged too.

> > 2) Flush pending I/O.
> > 3) Freeze filesystems in reverse order of dependency, the primary purpose
> > being to stop them generating further I/O on their metadata.
> >
> > Locks that are being held are only being held because work is being done.
If
> > we progressively focus on threads in terms of their create/process work
> > dependencies, we'll see that the problem isn't at all intractable.
>
> As has been mentioned before, keeping track of all that dependency
> information would be very fragile and time-consuming.

I disagree. It's at least going to be less fragile and time-consuming then
maintaining new/extra code for kexec.

Nigel

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