Re: [Xen-ia64-devel] Virtual mem map

[Alex Williamson <alex.williamson@xxxxxx>]

On Mon, 2006-01-09 at 11:49 +0100, Tristan Gingold wrote:
> Le Vendredi 06 Janvier 2006 22:40, Magenheimer, Dan (HP Labs Fort Collins) a 
> écrit :
> > I spent a lot of time recently digging through the physical
> > memory management code of Linux/ia64.  It is very messy because
> > it has to support a wide variety of physical memory layouts.
> > And it makes surprising choices that throw away huge chunks of
> > physical memory (anything that doesn't fit conveniently in
> > a "granule").
> Yes, this is very surprising.  At least 16MB of memory are lost!  Maybe Xen 
> can use this memory for itself ?

   Careful, there's a reason for the madness.  We throw away those big
chunks of memory to avoid address aliasing.  We can't supports granules
that contain both cacheable and uncacheable memory regions.  You'll get
into trouble if you maintain granule size mappings, but ignore their
access attributes.  The first granule is usually thrown away because VGA
has some uncacheable memory regions below 1MB.

        Alex

-- 
Alex Williamson                             HP Linux & Open Source Lab


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