Re: [Suspend2][ 0/9] Extents support.

Nigel Cunningham
2006-06-28T23:27:08Z

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Hi.

On Thursday 29 June 2006 08:35, Rafael J. Wysocki wrote:
> On Wednesday 28 June 2006 01:47, Nigel Cunningham wrote:
> > On Wednesday 28 June 2006 08:19, Rafael J. Wysocki wrote:
> > > On Tuesday 27 June 2006 11:35, Nigel Cunningham wrote:
> > > > On Tuesday 27 June 2006 19:26, Rafael J. Wysocki wrote:
> > > > > > > Now I haven't followed the suspend2 vs swsusp debate very
> > > > > > > closely, but it seems to me that your biggest problem with
> > > > > > > getting this merged is getting consensus on where exactly this
> > > > > > > is going. Nobody wants two different suspend modules in the
> > > > > > > kernel. So there are two options - suspend2 is deemed the way
> > > > > > > to go, and it gets merged and replaces swsusp. Or the other way
> > > > > > > around - people like swsusp more, and you are doomed to
> > > > > > > maintain suspend2 outside the tree.
> > > > > >
> > > > > > Generally, I agree, although my understanding of Rafael and
> > > > > > Pavel's mindset is that swsusp is a dead dog and uswsusp is the
> > > > > > way they want to see things go. swsusp is only staying for
> > > > > > backwards compatability. If that's the case, perhaps we can just
> > > > > > replace swsusp with Suspend2 and let them have their existing
> > > > > > interface for uswsusp. Still not ideal, I agree, but it would be
> > > > > > progress.
> > > > >
> > > > > Well, ususpend needs some core functionality to be provided by the
> > > > > kernel, like freezing/thawing processes (this is also used by the
> > > > > STR), snapshotting the system memory. These should be shared with
> > > > > the in-kernel suspend, be it swsusp or suspend2.
> > > >
> > > > If I modify suspend2 so that from now on it replaces swsusp, using
> > > > noresume, resume= and echo disk > /sys/power/state in a way that's
> > > > backward compatible with swsusp and doesn't interfere with uswsusp
> > > > support, would you be happy? IIRC, Pavel has said in the past he
> > > > wishes I'd just do that, but he's not you of course.
> > >
> > > That depends on how it's done. For sure, I wouldn't like it to be done
> > > in the "everything at once" manner.
> >
> > I'm not sure I get what you're saying. Do you mean you'd prefer them to
> > coexist for a time in mainline? If so, I'd point out that suspend2 uses
> > different parameters at the moment precisely so they can coexist, so that
> > wouldn't be any change.
>
> No, I'd like it to be done in small steps. Actually as small as possible,
> so that it's always clear what we are going to do and why.
>
> If you want to start right now, please submit a bdevs freezing patch
> without any non-essential additions.

Well, I admit that I'd far prefer to work with you than Pavel, but aren't we
still just going to reach a point where you say "But that should be done in
userspace" and I say "But I disagree that userspace is the right place for
suspend to disk" and we stalemate? What then? It seems that I've already
wasted a lot of effort listening to requests to split Suspend2 up into
digestable chunks for review, only to find that they're not the digestable
chunks people wanted to digest. I don't want to spent my time slicing and
dicing in another way, only to find that the customer doesn't like that meal
presentation either.

Can't we instead do what we started to do with the pageflags support? That is,
look at the files one at a time, beginning with those that implement the more
primitive functions, such as pageflags and extents and the like, verifying
that they're implemented ok. Then progress to the higher level functions and
check that they combine the primitives together okay, and so on. Or (if you
prefer), do the reverse, beginning with suspend.c and progressing down into
the details?

I guess the other question is, at the end of this, do you have to understand
perfectly and completely how Suspend2 works? If not, are there things I could
do to help? (Straight off, it occurs to me that I should get around to
completing and updating the Documentation - it might help you a lot).

Regards,

Nigel
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