Re: [RFC/PATCH 2/2] kernel: don't update load average during snapshot/shutdown

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Saturday, 28 April 2007 10:26, Pekka Enberg wrote:
> Nigel Cunningham wrote:
> > I therefore have to ask: Please. Go away. Hand the maintainership of
> > hibernation over to Rafael. Work on things you do care about and where
> > you do want to see a fully functional implementation. But stop being a
> > hindrance to us making Linux hibernation support everything that it
> > ought to be.
> 
> [snip]
> 
> Please. The load average is a problem and no the fix is not to make 
> kernel/timer.c worse for everybody but to snapshot the load averages 
> _before_ I/O and restore them after resume.

I'm having an impression that this problem is suspend2-specific.  With swsusp
we can have it only if the writing of snapshot fails.

Namely, with swsusp we have the pre-snapshot value of the load average in the
image and it should be, so to speak, "normal".  Then, once we've restored the
image, this "normal" value gets recovered and everything is fine.  If the writing
of image fails, we can have a "wrong" (i.e. too high) value of the load average
afterwards, but then this is an error condition anyway.  At least, as a user, I
can expect some glitches to happen after a failing hibernation.

With suspend2, in turn, the contents of LRU pages are saved before we create
the snapshot.  They can be compressed etc. in the process, so the load average
can grow quite substantially and this "unusual" load average is then
snapshotted.  Hence, the problem appears after the restore.  I think the
solution could be to save the post-tasks-freezing load average and restore it
right before snapshotting, but that's only needed for suspend2.

Greetings,
Rafael