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

[Nigel Cunningham]

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@xxxxxxxxxxx>   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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