Re: [linux-pm] Re: Hibernation considerations

Alan Stern
2007-07-23T15:23:24Z

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.

> 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.

Alan Stern