Offering a potential alternative to the existing suspend and restore implementations in the Linux Kernel, Ying Huang posted a patch utilizing kexec, "kexec based hibernation has some potential advantages over uswsusp and suspend2. " He listed two such potential advantages, "the hibernation image size can exceed half of memory size easily," and, "the hibernation image can be written to and read from almost anywhere, such as a USB disk [or] NFS." He described the feature implemented by his patch as "jumping from a kexeced kernel to the original kernel", allowing someone to first boot from one kernel, then to kexec another crashdump kernel in reserved memory and run from it for a while, and finally to "jump back" to the original kernel.
Andrew Morton replied to the idea very positively, "this sounds awesome. Am I correct in expecting that ultimately the existing hibernation implementation just goes away and we reuse (and hence strengthen) the existing kexec (and kdump?) infrastructure? And that we get hibernation support almost for free on all kexec (and relocatable-kernel?) capable architectures? And that all the management of hibernation and resume happens in userspace?" He went on to ask, "how close do you think all this is to being a viable thing?" Ying replied, "the kexec jump is the first step, maybe the simplest step. There are many other issues to be resolved, at least the following ones," going on to list a series of steps that still have to be implemented before kexec based hibernation would be a viable option.
What started as the review of a bug report grew into an interesting debate as Linus Torvalds slammed the current suspend and resume [story] design in the Linux Kernel, "why the HELL cannot you realize that kernel threads are different? The right thing to do is AND HAS ALWAYS BEEN, to stop and start user threads only around the whole thing. Don't touch those kernel threads. Stop freezing them." Later in the discussion, Linus noted that he had no interest in Suspend to Disk (STD), and was only interested in a working Suspend to Ram (STR) implementation. He noted that complexity introduced by STD was infecting the STR logic, and that the two should be completely separated, "what irritates me is that STR really shouldn't have _had_ that bug at all. The only reason STR had the same bug as STD was exactly the fact that the two features are too closely inter-twined in the kernel. That irritates me hugely. We had a bug we should never had had! We had a bug because people are sharing code that shouldn't be shared! We had a bug because of code that makes no sense in the first place!" Linus noted that he doesn't use laptops much, but still likes STR on his desktop, "STR means they are quiet and don't waste energy when I don't use them, but they're instantly available when I care." He then went on to point to design flaws in the freezer:
"I actually don't think that processes should be frozen really at all. I agree that filesystems have to be frozen (and I think that checkpointing of the filesystem or block device is 'too clever'), but I just don't think that has anything to do with freezing processes. So I'd actually much prefer to freeze at the VFS (and socket layers, etc), and make sure that anybody who tries to write or do something else that we cannot do until resuming, will just be blocked (or perhaps just buffered)!"