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

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Message-ID: <4C09C662.2020705@crca.org.au>
Date:	Sat, 05 Jun 2010 13:37:06 +1000
From:	Nigel Cunningham <ncunningham@...a.org.au>
To:	Maxim Levitsky <maximlevitsky@...il.com>
CC:	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	TuxOnIce-devel <tuxonice-devel@...onice.net>
Subject: Re: [SUSPECTED SPAM] Re: [linux-pm] Proposal for a new algorithm
 for reading & writing a hibernation image.

Hi.

On 05/06/10 10:45, Maxim Levitsky wrote:
> On Sat, 2010-06-05 at 03:36 +0300, Maxim Levitsky wrote:
>> On Sat, 2010-06-05 at 09:58 +1000, Nigel Cunningham wrote:
>>> Hi Maxim.
>>>
>>> On 05/06/10 09:39, Maxim Levitsky wrote:
>>>> On Thu, 2010-06-03 at 16:50 +0200, Pavel Machek wrote:
>>>>>
>>>>> "Nigel Cunningham"<ncunningham@...a.org.au>   wrote:
>>>>>
>>>>>> Hi.
>>>>>>
>>>>>> On 30/05/10 15:25, Pavel Machek wrote:
>>>>>>> Hi!
>>>>>>>
>>>>>>>> 2. Prior to writing any of the image, also set up new 4k page tables
>>>>>>>> such that an attempt to make a change to any of the pages we're about to
>>>>>>>> write to disk will result in a page fault, giving us an opportunity to
>>>>>>>> flag the page as needing an atomic copy later. Once this is done, write
>>>>>>>> protection for the page can be disabled and the write that caused the
>>>>>>>> fault allowed to proceed.
>>>>>>>
>>>>>>> Tricky.
>>>>>>>
>>>>>>> page faulting code touches memory, too...
>>>>>>
>>>>>> Yeah. I realise we'd need to make the pages that are used to record the
>>>>>> faults be unprotected themselves. I'm imagining a bitmap for that.
>>>>>>
>>>>>> Do you see any reason that it could be inherently impossible? That's
>>>>>> what I really want to know before (potentially) wasting time trying it.
>>>>>
>>>>> I'm not sure it is impossible, but it certainly seems way too complex to be
>>>>> practical.
>>>>>
>>>>> 2mb pages will probably present a problem, as will bat mappings on powerpc.
>>>>
>>>>
>>>> Some time ago, after tuxonce caused medium fs corruption twice on my
>>>> root filesystem (superblock gone for example), I was thinking too about
>>>> how to make it safe to save whole memory.
>>>
>>> I'd be asking why you got the corruption. On the odd occasion where it
>>> has been reported, it's usually been because the person didn't set up
>>> their initramfs correctly (resumed after mounting filesystems). Is there
>>> any chance that you did that?
> I didn't use any initramfs.
> I did use kernel modesetting and nouveau.
> I used ext4.
> The corruption happened after normal suspend.

What's 'normal suspend'?

> I replaces swsusp with tuxonice.
>
> Anyway, some more or less verified method must be used to save memory
> because fs corruption is too scary thing to have.

Agreed.

> I can't say it scared me that much 'cause I had dealt with worse
> corruptions before, but being thrown to  "grub rescue>" on boot is not
> pleasant thing to see.

Oh, I agree and don't want anyone to ever experience corruption because 
of TuxOnIce. Unfortunately my wishes don't just happen :)

Nigel
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