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Re: latest rawhide kernel 2.6.9-1.640 and suspend to disk



Just wondering: How much of suspend to disk it is possible to do fully
in userspace?

I mean, if the kernel boots normally, mounts the disks etc, and it then
is up to init (?) to detect some flag in some file, and load the ram
instead? But what would that do to things that use to be syncronized
between kernel and OS? Is there any such things?

tir, 26.10.2004 kl. 22.56 skrev Per Bjornsson:
> On Tue, 2004-10-26 at 11:10, Dave Jones wrote:
> 
> > My comments on swsusp are largely unprintable, but in short, this
> > kind of risk (where end-users can lose data) isn't justifiable.
> > Upstream, swsusp is still very much in flux, with a large out-of-tree
> > patchset to 'improve' upon it.
> 
> Is swsusp2 (I presume this is the "out-of-tree patchset" you mentioned)
> as ugly from a code point of view? I thought it might be a bit better.
> 
> By the way, what is the data loss scenario - pretty much just that
> whatever wasn't saved is is lost if the computer doesn't wake up
> (basically the same as hitting the hard reset button at a random
> moment), or random wreckage all over the hard disk? That makes a huge
> difference!
> 
> > I'm not optimistic we'll see this working reliably any time soon.
> > Read some of the comments from the upstream maintainer on linux-kernel.
> > There are numerous cases of swsusp failing where the end-user has
> > been given the brush-off "oh well, your hardware is crap".
> 
> Yes, looking at LKML it sure looks like some of the people involved
> sadly don't really care about how safe it is, as long as it kind of
> works with some luck.
> 
> My understanding was that Pat Mochel seemed to have a bit more of a
> grasp of the fundamentals involved, so I had some hope that the re-merge
> of swsusp and pmdisk would improve things a bit. That's not the case?
> 
> > Comments about swsusp code quality aside, there also exists a larger
> > problem -- lots of devices still don't handle wakeup from deepsleep state.
> > The code just isn't written, and a lot of maintainers of various device
> > drivers don't particularly care enough about suspend to make it work.
> > Unless someone who does care submits patches, those drivers remain
> > in the state they're in today.
> 
> Interesting; I thought that all the devices were actually turned off and
> the computer was completely booted from scratch with the current linux
> implementation of suspend-to-disk in any case. In that case, shouldn't
> all the devices just get initialized just as they would be in a regular
> boot sequence? On my dual-boot notebook I can run Windows, "hibernate"
> which is the Windows version of suspending to disk, turn it back on and
> boot into Linux, reboot and get back into the Windows session where I
> left off. That certainly indicates to me that at least the Windows
> suspend-to-disk state is in fact turned off, or at least the functional
> equivalent. I can't see how any state could be preserved across running
> another OS on the computer!
> 
> If this is the case, isn't it actually S3 (suspend to RAM) that would be
> the more difficult state to get devices back from? Coming back from that
> state it seems like lots of devices are not reinitialized by the BIOS,
> while they should be on boot. Or rather, Linux must know what to do with
> these devices on boot since they normally work!
> 
> > Still think this is something worth taking a risk for ?
> 
> Well, I've had a system hosed (massive filesystem corruption, lots of
> critical binaries had just disappeared so the system wouldn't even boot
> any longer - I needed it back so I just reinstalled, didn't have time to
> investigate further unfortunately) when I tried to get suspend-to-RAM
> working a few months ago, so it seems that the Red Hat kernels already
> do some things sleeping-wise that can be construed to be risky. Is
> non-functional suspend-to-disk more likely to corrupt data than
> non-functional suspend-to-RAM (which is to a great extent what we have
> now)? I guess the judgment call is yours to make, but I wouldn't be
> totally averse to seeing this turned on if the risk level is similar to
> that involved in S3 suspend.
> 
> If S3 suspend actually worked and was less risky, I wouldn't care
> particularly about S4/suspend to disk; however, I've certainly seen the
> sentiment that S3 is actually harder to do right (in terms of device
> initialization etc) than S4 so reliable S3 is unlikely to ever happen on
> a lot of hardware... Do you believe that reliable S3 suspend has a
> greater likelyhood of happening than reliable suspend-to-disk?
> 
> (My problem seems similar to
> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=122604 although I
> have a Fujitsu S2020, I'll try to investigate more when I have time to
> deal with potential file system corruption again. Of course, that report
> doesn't imply file system corruption; it might have been that I forgot
> to fsck between failed attempts though - but I am using ext3 so I
> thought journaling should help me a bit. I only saw it once though, I
> got too scared to continue after that.)
> 
> /Per
> 
> -- 
> Per Bjornsson <perbj stanford edu>
> Ph.D. Candidate, Department of Applied Physics, Stanford University


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