[PATCH] Fix small vmalloc per allocation limit

The vmap vmalloc rework in 2.5 had a unintended side effect.  vmalloc uses
kmalloc now to allocate an array with a list of pages.  kmalloc has a 128K
maximum.  This limits the vmalloc maximum size to 64MB on a 64bit system
with 4K pages.  That limit causes problems with other subsystems, e.g.
iptables relies on allocating large vmallocs for its rule sets.

This is a bug IMHO - on 64bit platforms there shouldn't be such a low limit
on the vmalloc size.  And even on 32bit it's too small for custom kernels
with enlarged vmalloc area.

Another problem is that this makes vmalloc unreliable.  After the system
has been running for some time it is unlikely that kmalloc will be able to
allocate >order 2 pages due to memory fragmentation.

This patch takes the easy way out for fixing this by just allocating this
array with vmalloc when it is larger than a page.  While more complicated
and intrusive solutions would be possible they didn't use vmalloc
recursively they didn't seem it worth to handle this very infrequent case.

Please note that the vmalloc recursion is strictly bounded because each
nested allocation will generate a much smaller stack frame.  Also the
kernel stack can handle even a few recursion steps easily because vmalloc
has only a small stack frame.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/vmalloc.c

@@ -378,7 +378,10 @@ void __vunmap(void *addr, int deallocate_pages)
 			__free_page(area->pages[i]);
 		}
 
-		kfree(area->pages);
+		if (area->nr_pages > PAGE_SIZE/sizeof(struct page *))
+			vfree(area->pages);
+		else
+			kfree(area->pages);
 	}
 
 	kfree(area);
@@ -482,7 +485,12 @@ void *__vmalloc(unsigned long size, int gfp_mask, pgprot_t prot)
 	array_size = (nr_pages * sizeof(struct page *));
 
 	area->nr_pages = nr_pages;
-	area->pages = pages = kmalloc(array_size, (gfp_mask & ~__GFP_HIGHMEM));
+	/* Please note that the recursion is strictly bounded. */
+	if (array_size > PAGE_SIZE)
+		pages = __vmalloc(array_size, gfp_mask, PAGE_KERNEL);
+	else
+		pages = kmalloc(array_size, (gfp_mask & ~__GFP_HIGHMEM));
+	area->pages = pages;
 	if (!area->pages) {
 		remove_vm_area(area->addr);
 		kfree(area);