Re: Memory consumption difference between in-kernel and userspace hibernation

Pavel Machek
2009-11-21T09:29:12Z

On Fri 2009-11-13 21:05:07, Rafael J. Wysocki wrote:
> On Thursday 12 November 2009, Thomas Petazzoni wrote:
> > Hello,
> >
> > Thanks for your feedback.
> >
> > Le Thu, 12 Nov 2009 21:52:02 +0100,
> > "Rafael J. Wysocki" <rjw@sisk.pl> a ??crit :
> >
> > > The userspace interface doesn't really allow you to write to a file.
> > > You can write into the area the file occupies on the partition, but
> > > you can't use the filesystem code for the actual writing. At least
> > > you shouldn't do that.
> >
> > Ah. But it seems to work fairly nicely. Why can't the filesystem code
> > could be used to store the resume image ? Note that my file is stored
> > in a separate partition, fully dedicated to storing the resume file and
> > mounted only at very specific points in the system lifetime.
>
> That doesn't really matter.
>
> The problem is that the image is likely to contain filesystem data (eg.
> superblocks etc.) that correspond to the state before the image has been
> created. Now, your using the filesystem code for writing the image modifies
> the on-disk metadata which become inconsistent with the filesystem data in
> the image. This inconsistencies may very well result in an unfixable
> corruption of the file system after the resume (that actually happened to
> a number of people, so it's not just pure theory).
>
> That really depends on the fileystem used, though.

But based on his description... if fs is only mounted after atomic
snapshot... it actually should be safe.
Pavel
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