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Subject: Re: [linux-pm] [SUSPECTED SPAM] Re: Proposal for a new algorithm 
 for	reading & writing a hibernation image.
From: Maxim Levitsky <maximlevitsky@gmail.com>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Nigel Cunningham <ncunningham@crca.org.au>,
       pm list <linux-pm@lists.linux-foundation.org>,
       LKML <linux-kernel@vger.kernel.org>,
       TuxOnIce-devel <tuxonice-devel@tuxonice.net>
In-Reply-To: <201006061557.20482.rjw@sisk.pl>
References: <9rpccea67yy402c975fqru8r.1275576653521@email.android.com>
	 <201006052121.45816.rjw@sisk.pl> <1275784828.17835.4.camel@maxim-laptop>
	 <201006061557.20482.rjw@sisk.pl>
Content-Type: text/plain; charset="UTF-8"
Date: Sun, 06 Jun 2010 18:54:10 +0300
Message-ID: <1275839650.5331.2.camel@maxim-laptop>
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On Sun, 2010-06-06 at 15:57 +0200, Rafael J. Wysocki wrote: 
> 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?
Very simple.

With swsusp, I can save 750MB (memory) + 250 Vram (vram)
With full memory save I can save (1750 MB of memory) + 250 MB of
vram....

Of course save of vram sure can be made non atomic....


Best regards,
Maxim Levitsky

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