> Date: Fri, 13 Jul 2007 01:42:48 -0400
> On Thu, Jul 12, 2007 at 08:06:43PM -0700,
david@lang.hm wrote:
>> On Thu, 12 Jul 2007, Rafael J. Wysocki wrote:
>
>>> Plus we need to figure out how to avoid corrupting filesystems and
>>> swap in use by the "old" kernel and its processes (hint: a separate
>>> "hibernation partition" is a no-go).
>>
>> I thought the existing hibernation wrote to the swap partition as it's
>> dedicated space?
>>
>> I didn't know that anyone was suggesting writing the hibernation image to
>> a filesystem that the kernel was activly accessing.
>
> I'm suggesting a dedicated, preallocated hibernation *file*, right
> now. There's no way around it, if hibernation is to be reliable --
> otherwise hibernation can fail if the system has used enough of its
> swap space, so that there isn't enough room to write the hibernate
> image.
>
> Even if it's desirable to allow hibernation to fail if the system is
> too deep into swap, it's a moot point.
>
> Consider how the need to ensure that there is enough space to write
> the hibernate image is dealt with now: by making a big honking swap
> space, so big that enough of it is all but guaranteed to be free,
> except under the heaviest of memory usage. So the space is already
> reserved -- and now that it's commingled with actual swap, you have the
> need to pass the swap data structures between the two kernels.
>
> Consider instead, you set up two swap spaces, one regular, and one
> for hibernation. You don't touch the "hibernation swap" unless the
> other is full -- I think just setting a lower priority on the swap
> space is enough for this. Before you jump to the hibernate kernel,
> you swapoff that hibernate swap.
>
> If you can't swapoff the hibernate swap, hibernate fails right there.
>
> If you can, you have your space for writing the image, free and clear
> of any of the original kernel's internal state. There isn't any need
> to treat that space as swap any more at all -- the only reason to do
> so would be to reuse the existing code.
>
> Setting aside two partitions for swap is obviously undesireable, but
> thankfully, Linux supports swap *files*.
