mm: define PAGE_MAPPING_FLAGS At present we define PageAnon(page) by the low PAGE_MAPPING_ANON bit set in page->mapping, with the higher bits a pointer to the anon_vma; and have defined PageKsm(page) as that with NULL anon_vma. But KSM swapping will need to store a pointer there: so in preparation for that, now define PAGE_MAPPING_FLAGS as the low two bits, including PAGE_MAPPING_KSM (always set along with PAGE_MAPPING_ANON, until some other use for the bit emerges). Declare page_rmapping(page) to return the pointer part of page->mapping, and page_anon_vma(page) to return the anon_vma pointer when that's what it is. Use these in a few appropriate places: notably, unuse_vma() has been testing page->mapping, but is better to be testing page_anon_vma() (cases may be added in which flag bits are set without any pointer). Signed-off-by: Hugh Dickins <[email protected]> Cc: Izik Eidus <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Nick Piggin <[email protected]> Cc: KOSAKI Motohiro <[email protected]> Reviewed-by: Rik van Riel <[email protected]> Cc: Lee Schermerhorn <[email protected]> Cc: Andi Kleen <[email protected]> Cc: KAMEZAWA Hiroyuki <[email protected]> Cc: Wu Fengguang <[email protected]> Cc: Minchan Kim <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/migrate.c b/mm/migrate.c
index 576c25ee..367272d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c

@@ -172,17 +172,14 @@
 {
 	struct anon_vma *anon_vma;
 	struct vm_area_struct *vma;
-	unsigned long mapping;
-
-	mapping = (unsigned long)new->mapping;
-
-	if (!mapping || (mapping & PAGE_MAPPING_ANON) == 0)
-		return;
 
 	/*
 	 * We hold the mmap_sem lock. So no need to call page_lock_anon_vma.
 	 */
-	anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
+	anon_vma = page_anon_vma(new);
+	if (!anon_vma)
+		return;
+
 	spin_lock(&anon_vma->lock);
 
 	list_for_each_entry(vma, &anon_vma->head, anon_vma_node)

diff --git a/mm/rmap.c b/mm/rmap.c
index 1a0ee6e..f06cee4 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c

@@ -203,7 +203,7 @@
 
 	rcu_read_lock();
 	anon_mapping = (unsigned long) page->mapping;
-	if (!(anon_mapping & PAGE_MAPPING_ANON))
+	if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
 		goto out;
 	if (!page_mapped(page))
 		goto out;
@@ -248,8 +248,7 @@
 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 {
 	if (PageAnon(page)) {
-		if ((void *)vma->anon_vma !=
-		    (void *)page->mapping - PAGE_MAPPING_ANON)
+		if (vma->anon_vma != page_anon_vma(page))
 			return -EFAULT;
 	} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
 		if (!vma->vm_file ||
@@ -513,7 +512,7 @@
 		referenced++;
 
 	*vm_flags = 0;
-	if (page_mapped(page) && page->mapping) {
+	if (page_mapped(page) && page_rmapping(page)) {
 		if (PageAnon(page))
 			referenced += page_referenced_anon(page, mem_cont,
 								vm_flags);

diff --git a/mm/swapfile.c b/mm/swapfile.c
index d5eb2e8..e74112e 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c

@@ -938,7 +938,7 @@
 	unsigned long addr, end, next;
 	int ret;
 
-	if (page->mapping) {
+	if (page_anon_vma(page)) {
 		addr = page_address_in_vma(page, vma);
 		if (addr == -EFAULT)
 			return 0;