Add support functions to allow the creation and destruction of virtual compound

pages. Virtual compound pages are similar to compound pages in that if

PageTail(page) is true then page->first points to the first page.
	vcompound_head_page(address)
(similar to virt_to_head_page) can be used to determine the head page from an

address.
Another similarity to compound pages is that page[1].lru.next contains the

order of the virtual compound page. However, the page structs of virtual

compound pages are not in order. So page[1] means the second page belonging

to the virtual compound mapping which is not necessarily the page following

the head page.
Freeing of virtual compound pages is support both from preemptible and

non preemptible context (freeing requires a preemptible context, we simply

defer free if we are not in a preemptible context).
However, allocation of virtual compound pages must at this stage be done from

preemptible contexts only (there are patches to implement allocations from

atomic context but those are unecessary at this early stage).
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---

 include/linux/vmalloc.h |   14 +++

 mm/vmalloc.c            |  197 ++++++++++++++++++++++++++++++++++++++++++++++++

 2 files changed, 211 insertions(+)
Index: linux-2.6.25-rc5-mm1/include/linux/vmalloc.h

===================================================================

--- linux-2.6.25-rc5-mm1.orig/include/linux/vmalloc.h	2008-03-20 23:03:14.600588151 -0700

+++ linux-2.6.25-rc5-mm1/include/linux/vmalloc.h	2008-03-20 23:03:14.612588010 -0700

@@ -86,6 +86,20 @@ extern struct vm_struct *alloc_vm_area(s

 extern void free_vm_area(struct vm_struct *area);
 /*

+ * Support for virtual compound pages.

+ *

+ * Calls to vcompound alloc will result in the allocation of normal compound

+ * pages unless memory is fragmented.  If insufficient physical linear memory

+ * is available then a virtually contiguous area of memory will be created

+ * using the vmalloc functi...
[ message continues ]

Hi
Hmm,

IMHO we need vcompound documentation more for the beginner in the Documentation/ directory.
may be, we need DocBook style comment at the head of these 4 functions.
--

Duh... alloc_vcompound is not used at this point. Typo. _alloc needs to be 
Ok.
--