Re: [Xen-devel] 2.6.32 pv_ops and sparse/flat memory

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Nov 23, 2010 at 10:01:21PM +0300, Vasiliy G Tolstov wrote:
> On Tue, 2010-11-23 at 19:06 +0100, Daniel Kiper wrote:
> > Hello,
> > 
> > On Mon, Nov 22, 2010 at 01:22:30PM +0300, Vasiliy G Tolstov wrote:
> > > On Mon, 2010-11-22 at 11:09 +0100, Daniel Kiper wrote:
> > > > Hello,
> > > >
> > > > On Fri, Nov 19, 2010 at 04:44:17PM +0300, Vasiliy G Tolstov wrote:
> > > > > Hello. I'm try to compile 32 bit pae kernel from xen git repo. If i
> > > > > check sparse memory - i get error
> > > >
> > > > Please send me full address of Xen repository which you are using
> > > > its head
> > >
> > > git clone git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen
> > > git checkout -b xen/stable-2.6.32.x origin/xen/stable-2.6.32.x
> > >
> > > > and contents of your config file.
> > > in attach, modify flat memory to sparse mem and compile under i686 arch
> > 
> > As I find out it is normal behavior when CONFIG_XEN is enabled in this
> > kernel version. Unlike mainline kernel this version establish new PG_foreign
> > page flag which with CONFIG_SPARSEMEM_MANUAL and CONFIG_HIGHMEM64G
> > enabled overflow page flags field which is - surprise - 32-bit long in
> > i386 (for more details read include/linux/page-flags.h file).
> > 
> > Solution:
> >   - enable CONFIG_HIGHMEM4G,
> >   - disable CONFIG_XEN (I am not sure that it
> >     is good one for you :-))) ).
> > 
> > Daniel
> 
> Thank You Daniel! But i need to able to run vm with 56Gb memory size and
> highmem 4g not usable =). My question is - can i use memory about 56Gb
> and use memory hotplug, what you write?  (using flat memory config)
> 

You could enable 64GB mem support.. 

But running a 32bit kernel with 56GB of memory is not good..
you'll probably run into all kinds of problems, since page structs
will eat *most* of your lowmem and thus make your whole system
pretty much unusable..

You really need 64bit kernel for that big amount of memory.
(Note that you can still run 32bit userspace if you need to).

-- Pasi


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