Re: [PATCH] ia64, kexec: allow base of crashkernel to be

[Zou Nan hai <nanhai.zou@intel.com>]

On Thu, 2006-06-29 at 09:44, Horms wrote:
> On Thu, Jun 29, 2006 at 06:38:22AM +0800, Zou Nan hai wrote:
> > On Wed, 2006-06-28 at 19:00, Horms wrote:
> > > The crashkernel command line parameter accepts a size and base address for
> > > the memory region that is reserved to be used as the memory space for a
> > > crash kernel. At this time, on some architectures, notably i386 and x86_64,
> > > the base address of the crash kernel needs to be modified at compile time
> > > to match the base address passed to crashkernel. However, on ia64 the
> > > crash kernel does not need to be relocated at compile time, thus
> > > there the base address of the crashkernel region does not need to be fixed.
> > > 
> > > This patch allows the base address of crashkernel to be determined at boot
> > > time if the base address passed on the command line is 0. Otherwise
> > > the specified base address will be used, as is currently the case.
> > > 
> > > The advantage is that the region layout may vary from machine to machine,
> > > and finding a place for the crashkernel is a manual process. This eliminates
> > > that manual work, and I expect will make life slightly easier for distros.
> > > 
> > > I would like to note that currently it will try and place the crashkernel
> > > region inside the first "System RAM" region that has space. I am not
> > > sure if there should be a lower or upper bond on the crashkernel base address,
> > > but it will be trivial to add to the arguments passed to allocate_region()
> > > if necessary.
> > > 
> >   I think there is no upper and lower limit of crash kernel base
> > address, but the base address should be aligned to 64M.
> > 
> > which is max(max possible IA64_GRANULE_SIZE, KERNEL_TR_PAGE_SIZE)
> 
> Ok, thanks. That should be an easy enough change. Can someone confirm that it
> is necessary? Anecdotally, on my system the region ended up at 48f0000
> (~72Mb) and kdump does seem to work.

  That only works by accident. 
  kernel will pin mapping 64M PAGE to kernel data and code at the  
beginning. T
hat is ALIGN(0x48f0000, 64M) = 0x4000000to 0x8000000, 
if the total kernel segment size is less than 0x8000000 - 0x48f0000, you
get the entire data and code segment pin mapped in TLB. 
  However if the start address is very near to 0x8000000, say 0x7FF0000,
you will get most of kernel segment out of TR mapping.
  Also it is wrong to put TLB map of RAM that does not exist together
with kernel text and data.

Thanks
Zou Nan hai