Add a new gfp flag

	__GFP_VFALLBACK

If specified during a higher order allocation then the system will fall
back to vmap if no physically contiguous pages can be found. This will
create a virtually contiguous area instead of a physically contiguous area.
In many cases the virtually contiguous area can stand in for the physically
contiguous area (with some loss of performance).

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 include/linux/gfp.h |    5 +
 mm/page_alloc.c     |  139 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 139 insertions(+), 5 deletions(-)

Index: linux-2.6/mm/page_alloc.c
===================================================================
--- linux-2.6.orig/mm/page_alloc.c	2007-10-03 19:44:07.000000000 -0700
+++ linux-2.6/mm/page_alloc.c	2007-10-03 19:44:08.000000000 -0700
@@ -60,6 +60,9 @@ long nr_swap_pages;
 int percpu_pagelist_fraction;
 
 static void __free_pages_ok(struct page *page, unsigned int order);
+static struct page *alloc_vcompound(gfp_t, int,
+					struct zonelist *, unsigned long);
+static void destroy_compound_page(struct page *page, unsigned long order);
 
 /*
  * results with 256, 32 in the lowmem_reserve sysctl:
@@ -260,9 +263,51 @@ static void bad_page(struct page *page)
  * This usage means that zero-order pages may not be compound.
  */
 
+static void __free_vcompound(void *addr)
+{
+	struct page **pages;
+	int i;
+	struct page *page = vmalloc_to_page(addr);
+	int order = compound_order(page);
+	int nr_pages = 1 << order;
+
+	if (!PageVcompound(page) || !PageHead(page)) {
+		bad_page(page);
+		return;
+	}
+	destroy_compound_page(page, order);
+	pages = vunmap(addr);
+	/*
+	 * First page will have zero refcount since it maintains state
+	 * for the compound and was decremented before we got here.
+	 */
+	set_page_address(page, NULL);
+	__ClearPageVcompound(page);
+	free_hot_page(page);
+
+	for (i = 1; i < nr_pages; i++) {
+		page = pages[i];
+		set_page_address(page, ...
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