linux-kernel - Re: [linux-pm] [SUSPECTED SPAM] Re: Proposal for a new algorithm for reading & writing a hibernation image.

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Date:	Sun, 6 Jun 2010 15:57:20 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	Nigel Cunningham <ncunningham@...a.org.au>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"TuxOnIce-devel" <tuxonice-devel@...onice.net>
Subject: Re: [linux-pm] [SUSPECTED SPAM] Re: Proposal for a new algorithm 
 for	reading & writing a hibernation image.

On Sunday 06 June 2010, Maxim Levitsky wrote:
> On Sat, 2010-06-05 at 21:21 +0200, Rafael J. Wysocki wrote: 
> > On Saturday 05 June 2010, Maxim Levitsky wrote:
> > > On Sat, 2010-06-05 at 20:45 +0200, Rafael J. Wysocki wrote: 
> > > > On Saturday 05 June 2010, Nigel Cunningham wrote:
> > > > > Hi again.
> > > > > 
> > > > > As I think about this more, I reckon we could run into problems at 
> > > > > resume time with reloading the image. Even if some bits aren't modified 
> > > > > as we're writing the image, they still might need to be atomically 
> > > > > restored. If we make the atomic restore part too small, we might not be 
> > > > > able to do that.
> > > > > 
> > > > > So perhaps the best thing would be to stick with the way TuxOnIce splits 
> > > > > the image at the moment (page cache / process pages vs 'rest'), but 
> > > > > using this faulting mechanism to ensure we do get all the pages that are 
> > > > > changed while writing the first part of the image.
> > > > 
> > > > I still don't quite understand why you insist on saving the page cache data
> > > > upfront and re-using the memory occupied by them for another purpose.  If you
> > > > dropped that requirement, I'd really have much less of a problem with the
> > > > TuxOnIce's approach.
> > > Because its the biggest advantage?
> > 
> > It isn't in fact.
> > 
> > > Really saving whole memory makes huge difference.
> > 
> > You don't have to save the _whole_ memory to get the same speed (you don't
> > do that anyway, but the amount of data you don't put into the image with
> > TuxOnIce is smaller).  Something like 80% would be just sufficient IMO and
> > then (a) the level of complications involved would drop significantly and (2)
> > you'd be able to use the image-reading code already in the kernel without
> > any modifications.  It really looks like a win-win to me, doesn't it?
> 
> 
> Well, in fact on modern systems its not possible to save 100% of ram
> even if we save it all because of video memory.
> Look I got 256MB of video ram, and when compiz is used I say most of it
> is used, and its isn't going to be magically preserved during suspend.
> So system still has to free about 256MB of memory before suspend (which
> means around 80% percent of ram is saved in best case :-) )

So how TuxOnIce helps here?

Rafael
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