[rfc] allow to boot with >= 256GB physmem

[John Baldwin]

On Friday, January 21, 2011 11:09:10 am Sergey Kandaurov wrote:
> Hello.
> 
> Some time ago I faced with a problem booting with 400GB physmem.
> The problem is that vm.max_proc_mmap type overflows with
> such high value, and that results in a broken mmap() syscall.
> The max_proc_mmap value is a signed int and roughly calculated
> at vmmapentry_rsrc_init() as u_long vm_kmem_size quotient:
> vm_kmem_size / sizeof(struct vm_map_entry) / 100.
> 
> Although at the time it was introduced at svn r57263 the value
> was quite low (f.e. the related commit log stands:
> "The value defaults to around 9000 for a 128MB machine."),
> the problem is observed on amd64 where KVA space after
> r212784 is factually bound to the only physical memory size.
> 
> With INT_MAX here is 0x7fffffff, and sizeof(struct vm_map_entry)
> is 120, it's enough to have sligthly less than 256GB to be able
> to reproduce the problem.
> 
> I rewrote vmmapentry_rsrc_init() to set large enough limit for
> max_proc_mmap just to protect from integer type overflow.
> As it's also possible to live tune this value, I also added a
> simple anti-shoot constraint to its sysctl handler.
> I'm not sure though if it's worth to commit the second part.
> 
> As this patch may cause some bikeshedding,
> I'd like to hear your comments before I will commit it.
> 
> http://plukky.net/~pluknet/patches/max_proc_mmap.diff

Is there any reason we can't just make this variable and sysctl a long?

-- 
John Baldwin