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

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Message-ID: <4C0C8386.1040209@crca.org.au>
Date:	Mon, 07 Jun 2010 15:28:38 +1000
From:	Nigel Cunningham <ncunningham@...a.org.au>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Maxim Levitsky <maximlevitsky@...il.com>,
	TuxOnIce-devel <tuxonice-devel@...onice.net>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] [SUSPECTED SPAM] Re: Proposal for a new algorithm
 for reading & writing a hibernation image.

Hi.

On 06/06/10 23:57, 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?

The 256MB of video ram is irrelevant, unless it's 'stolen', in which 
case it will be saved.
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