Re: is hibernation usable?

On Fri, Feb 21, 2020 at 2:04 AM Rafael J. Wysocki [off-list ref] wrote:

My understanding of the problem is that the size of swap is
(theoretically) sufficient, but it is not used as expected during the
preallocation of image memory.

Right. I have no idea how locality of pages is determined in the swap
device. But if it's sufficiently fragmented such that contiguous free
space for a hibernation image is not sufficient, then hibernation
could fail.

It was stated in one of the previous messages (not in this thread,
cannot find it now) that swap (of the same size as RAM) was activated
(swapon) right before hibernation, so theoretically that should be
sufficient AFAICS.

I mentioned it as an idea floated by systemd developers. I'm not sure
if it's mentioned elsewhere. Some folks wonder if such functionality
could be prone to racing.
https://lore.kernel.org/linux-mm/CAJCQCtSx0FOX7q0p=9XgDLJ6O0+hF_vc-wU4KL=c9xoSGGkstA@mail.gmail.com/T/#m4d47d127da493f998b232d42d81621335358aee1 (local)

Another idea that's been suggested for a while is formally separating
hibernation and paging into separate files (or partitions).
a. Guarantees hibernation image has the necessary contiguous free space.
b. Might be easier to create (or even obviate) a sane interface for
hibernation images in swapfiles; that is, if it were a dedicated
hibernationfile rather than being inserted in a swapfile. Right now
that interface doesn't exist, so e.g. on Btrfs while it can support
swapfiles and hibernation images, the offset has to be figured out
manually so resume can succeed.
https://github.com/systemd/systemd/issues/11939#issuecomment-471684411





--
Chris Murphy