896MB address limit

[Cliff Wickman]

Hi Eric, and all,

On Mon, Sep 24, 2012 at 08:11:12PM -0700, Eric W. Biederman wrote:
> Cliff Wickman <cpw at sgi.com> writes:
> 
> > Gentlemen,
> >
> > In dumping very large memories we are running up against the 896MB 
> > limit in SLES11SP2 (3.0.38 kernel).
> 
> Odd.  That limit should be the maximum address in memory to load the
> crash kernel.  Tha limit should have nothing to do with the dump process
> itself.
> 
> Are you saying you need more that 512MiB reserved for the crash kernel
> to be able to dump all of the memory in your system?
> 
> Eric

As I noted to Eric privately, yes we need to bump up to crashkernel=1G
or more for some very large memories.

As an experiment I bumped
+++ linux/arch/x86/kernel/setup.c
@@ -528,7 +528,7 @@ static inline unsigned long long get_tot
 #ifdef CONFIG_X86_32
 # define CRASH_KERNEL_ADDR_MAX (512 << 20)
 #else
-# define CRASH_KERNEL_ADDR_MAX (896 << 20)
+# define CRASH_KERNEL_ADDR_MAX (1700 << 20)

And that seems to work.  i.e. I'm currently dumping a system where
crashkernel=1G and it seems to be working.

Am I just living dangerously? 

-Cliff
-- 
Cliff Wickman
SGI
cpw at sgi.com
(651) 683-3824