linux-kernel - Re: Hibernation Redesign

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Date:	Wed, 11 Jul 2007 14:19:10 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	a1426z@...ab.com, jeremy@...p.org, jbms@....edu, pavel@....cz,
	nickpiggin@...oo.com.au, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: Hibernation Redesign

On Wednesday, 11 July 2007 13:54, Miklos Szeredi wrote:
> > > > 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.
> > 
> > First, please list those problems for completness.  Moreover, I think they
> > should be documented if they haven't been yet.
> 
> Suspend failing due to ordering requirements from fuse, I think you
> documented this one.
> 
> Suspend failing due to malicious/buggy fuse filesystem.
> 
> Suspend failing if network filesystem is mounted, and network or
> server is down.  This is one of those "we can live with it" things
> that only happen rarely, and it's annoying then, but soon forgotten.

All of the above boil down to the freezer limitation regarding uninterruptible
tasks.  And yes, I think it should be explicitly documented.

> Freezing of tasks is slowing down suspend.  Don't know how serious
> this is, suspend is pretty fast, but could possibly be even faster.

Hmm, I don't know either.  I'm not seeing this in my tests, but well, more
data will be appreciated.

The sync probably slows down more than the freezing itself ...

> Don't know what the OLPC guys do to make suspending extremely quick,
> are they freezing any tasks?

They used to, but I'm not sure if they do.

> > Second, there were many more problems with the freezer in the past and we
> > were able to eliminate them over time.  It sometimes is difficult to invent a
> > viable solution on demand ...
> 
> OK, if you elimitate all of the above problems with the freezer, I'll
> say no more against it.

I think the ordering issue may be eliminated, to some extent.  I have a patch
for that, but you were CCed on that patch series, so you should know. ;-)

The other ones are more difficult, so time will tell.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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