Re: [linux-pm] Re: Hibernation considerations

[david@lang.hm]

On Fri, 20 Jul 2007, Huang, Ying wrote:

> On Fri, 2007-07-20 at 09:01 -0500, Milton Miller wrote:
> > Simplifying kjump: the proposal for v3.
> >
> > The current code is trying to use crash dump area as a safe, reserved
> > area to run the second kernel.   However, that means that the kernel
> > has to be linked specially to run in the reserved area.   I think we
> > need to finish separating kexec_jump from the other code paths.
> >
> > (1) add a new command line argument that specifies the kexec_jump
> > target area (or just size?)
> >
> > (2) add a kjump flag to the flags parameter, used by kexec_load.   When
> > loading a jump kernel, it is loaded like a normal kernel, however,
> > additional control pages are allocated to (a) save this kenrel's use of
> > the kexec_jump target area (b) save the backed up region that is used
> > by all kernels like crash dump, and (c) space for invoking
> > relocate_new_kernel that will get its args from the execution entry
> > point and will restore the kernel then call resume and suspend.
>
> Backuping target memory before kexec and restoring it after kexec is
> planed feature for kexec jump. But I will work on image writing/reading
> first.

if we can get a list of what memory is safe to backup/restore then the 
reading/writing of the image should be able to be done in userspace.

> > (3) replace jump_huf_pfn with two command line addresses that specify
> > the (a) return point for after resume, and (b) the return point for
> > after image save.   Actually these can be done in userspace; the second
> > restore kernel can just specify the null copy list and the entry points
> > supplied by the suspended kernel.  To do resume we also need (c) where
> > to store resume address for the save kernel.
>
> There is many free spaces in jump_buf_pfn page now. I think passing the
> needed information through jump_buf_pfn is more convenient than through
> kernel command line. That is, the jump_buf_pfn can be seen as a meta
> interface, which is passed to kexeced kernel though command line, while
> other information can be passed though jmp_buf_pfn.



> > The seperation should be whoever builds a scatter copy list builds the
> > inverse list.  This is why I propose simple jump entry points.  I
> > expect just a few instructions to establish arguments for the call to
> > the exstinging relocate_new_kernel code.
>
> If the "scatter copy" is replaced by "scatter swap", we need not the
> inverse list, and the state of kexeced kernel can be backuped too. There
> are "scatter copy" support in normal kexec implementation in
> "relocate_kernel".

what do you mean by "scatter swap"?

David Lang
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