linux-kernel - Re: suspend2 merge (was Re: [Suspend2-devel] Re: CFS and suspend2: hang in atomic copy)

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Message-Id: <200704261648.25189.rjw@sisk.pl>
Date:	Thu, 26 Apr 2007 16:48:23 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Pekka Enberg" <penberg@...helsinki.fi>
Cc:	"Pavel Machek" <pavel@....cz>,
	"Dumitru Ciobarcianu" <Dumitru.Ciobarcianu@...s.ro>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Nigel Cunningham" <nigel@...el.suspend2.net>,
	"Christian Hesse" <mail@...thworm.de>,
	"Nick Piggin" <npiggin@...e.de>, "Mike Galbraith" <efault@....de>,
	linux-kernel@...r.kernel.org, "Con Kolivas" <kernel@...ivas.org>,
	suspend2-devel@...ts.suspend2.net,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Arjan van de Ven" <arjan@...radead.org>
Subject: Re: suspend2 merge (was Re: [Suspend2-devel] Re: CFS and suspend2: hang in atomic copy)

On Thursday, 26 April 2007 13:12, Pekka Enberg wrote:
> On 4/25/07, Pavel Machek <pavel@....cz> wrote:
> > > Please stop using FUD.
> > > Graphical progress it's not in the kernel, even with suspend2.
> >
> > It was ascii-art, but still 'graphical', last time I checked.
> 
> Suspend2 talks to an userspace client via netlink. While I find the
> name of the message ("redraw UI") rather appaling, there's nothing
> wrong in principle that userspace starts the suspend process and the
> kernel keeps feeding back progress information ("I froze all processes
> now") so it can display a graphical progress bar.
> 
> The real question here is what to do with compression and encryption.
> However, if you settle for one compression algorithm (such as LZF in
> the case of suspend2) and use the _existing_ in-kernel crypto API for
> encryption, suddenly the benefits of userspace suspend are not clear.
> 
> As you and Rafael seem to be mostly interested in uswsusp, why don't
> we replace the old in-kernel implementation with suspend2?

It has a lot of common code with uswsusp.  Practically, the saving of the image
is the only part of it that could be removed, but this is simple and _really_
helps with debugging.

In principle, we could add suspend2 as an alternative (in analogy with the I/O
schedulers, for example), but I think for this purpose it should be reviewed
properly.

There also is a real problem with how it uses the LRU pages.  It _seems_ to
work, but at least to me it seems to be potentially dangerous.

Greetings,
Rafael
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