From af1500db46b4700ac61a120e88b8e9e359cc17a9 Mon Sep 17 00:00:00 2001
From: Christoph Lameter <clameter@sgi.com>
Date: Wed, 3 Oct 2007 20:42:43 -0700
Subject: [PATCH] vcompound: vmalloc_to_head page

The determination of a page struct for an address in a compound page
will need some more smarts in order to deal with (possibly) vmalloc
addresses.

We need to use the evil constants VMALLOC_START and VMALLOC_END for this
and they are notoriously for referencing various arch header files or may
even be variables. Uninline the function to avoid trouble.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
---
 include/linux/mm.h |    8 ++++++++
 mm/page_alloc.c    |   23 +++++++++++++++++++++++
 2 files changed, 31 insertions(+)

Index: linux-2.6.25-rc5-mm1/include/linux/mm.h
===================================================================
--- linux-2.6.25-rc5-mm1.orig/include/linux/mm.h	2008-03-19 18:21:23.675437663 -0700
+++ linux-2.6.25-rc5-mm1/include/linux/mm.h	2008-03-19 18:25:11.881378660 -0700
@@ -262,6 +262,9 @@ static inline void get_page(struct page 
 	atomic_inc(&page->_count);
 }
 
+/*
+ * Determine head page for a given address (cannot be a vmalloc address).
+ */
 static inline struct page *virt_to_head_page(const void *x)
 {
 	struct page *page = virt_to_page(x);
@@ -269,6 +272,11 @@ static inline struct page *virt_to_head_
 }
 
 /*
+ * Determine head page of a (possibly mapped via vmalloc) compound page.
+ */
+struct page *vmalloc_to_head_page(const void *x);
+
+/*
  * Setup the page count before being freed into the page allocator for
  * the first time (boot or memory hotplug)
  */
Index: linux-2.6.25-rc5-mm1/mm/page_alloc.c
===================================================================
--- linux-2.6.25-rc5-mm1.orig/mm/page_alloc.c	2008-03-18 12:20:10.779827793 -0700
+++ linux-2.6.25-rc5-mm1/mm/page_alloc.c	2008-03-19 18:25:53.065717434 -0700
@@ -174,6 +174,29 @@ static void set_pageblock_migratetype(st
 					PB_migrate, PB_migrate_end);
 }
 
+/*
+ * Determine the appropriate page struct given a virtual address
+ * (including vmalloced areas).
+ *
+ * Return the head page if this is a compound page.
+ *
+ * Cannot be inlined since VMALLOC_START and VMALLOC_END may contain
+ * complex calculations that depend on multiple arch includes or
+ * even variables.
+ */
+struct page *vmalloc_to_head_page(const void *x)
+{
+	unsigned long addr = (unsigned long)x;
+	struct page *page;
+
+	if (unlikely(addr >= VMALLOC_START && addr < VMALLOC_END))
+		page = vmalloc_to_page((void *)addr);
+	else
+		page = virt_to_page(addr);
+
+	return compound_head(page);
+}
+
 #ifdef CONFIG_DEBUG_VM
 static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
 {