Andrew Morton wrote:
On Wed, 11 Jul 2007 15:30:31 +0000
"Huang, Ying" <ying.huang@xxxxxxxxx> wrote:
1. Boot a kernel A
2. Work under kernel A
3. Kexec another kernel B in kernel A
4. Work under kernel B
5. Jump from kernel B to kernel A
6. Continue work under kernel A
This is the first step to implement kexec based hibernation. If the
memory image of kernel A is written to or read from a permanent media
in step 4, a preliminary version of kexec based hibernation can be
implemented.
The kernel B is run as a crashdump kernel in reserved memory
region. This is the biggest constrains of the patch. It is planed to
be eliminated in the next version. That is, instead of reserving memory
region previously, the needed memory region is backuped before kexec
and restored after jumping back.
Another constrains of the patch is that the CONFIG_ACPI must be turned
off to make kexec jump work. Because ACPI will put devices into low
power state, the kexeced kernel can not be booted properly under
it. This constrains can be eliminated by separating the suspend method
and hibernation method of the devices as proposed earlier in the LKML.
The kexec jump is implemented in the framework of software suspend. In
fact, the kexec based hibernation can be seen as just implementing the
image writing and reading method of software suspend with a kexeced
Linux kernel.
I guess I'm (still) confused by the terminology here. Do you mean that
it fits into suspend-to-disk as a disk-writing mechanism, or in
suspend-to-ram as a way of going to sleep?
Now, only the i386 architecture is supported. The patch is based on
Linux kernel 2.6.22, and has been tested on my IBM T42.
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?
I didn't understand the ACPI problem. Does this mean that CONFIG_ACPI must
be disabled in the to-be-hibernated kernel, or in the little transient
kexec kernel?
I think the point is that if kernel A says "I'm suspending" and calls
the suspend method on all its devices, then kernel B finds that it has
no powered on devices to work with. But then couldn't it turn on the
ones it wants anyway? And don't you want to suspend them, to make sure
they're not still DMAing memory while B is trying to shuffle everything
off to disk?
It does sound pretty cool.
J
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