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 <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index a485c14..1401a31 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -38,7 +38,8 @@
*/
static inline int PageKsm(struct page *page)
{
- return ((unsigned long)page->mapping == PAGE_MAPPING_ANON);
+ return ((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) ==
+ (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
}
/*
@@ -47,7 +48,7 @@
static inline void page_add_ksm_rmap(struct page *page)
{
if (atomic_inc_and_test(&page->_mapcount)) {
- page->mapping = (void *) PAGE_MAPPING_ANON;
+ page->mapping = (void *) (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
__inc_zone_page_state(page, NR_ANON_PAGES);
}
}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 24c3956..1202cd3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -620,13 +620,22 @@
/*
* On an anonymous page mapped into a user virtual memory area,
* page->mapping points to its anon_vma, not to a struct address_space;
- * with the PAGE_MAPPING_ANON bit set to distinguish it.
+ * with the PAGE_MAPPING_ANON bit set to distinguish it. See rmap.h.
+ *
+ * On an anonymous page in a VM_MERGEABLE area, if CONFIG_KSM is enabled,
+ * the PAGE_MAPPING_KSM bit may be set along with the PAGE_MAPPING_ANON bit;
+ * and then page->mapping points, not to an anon_vma, but to a private
+ * structure which KSM associates with that merged page. See ksm.h.
+ *
+ * PAGE_MAPPING_KSM without PAGE_MAPPING_ANON is currently never used.
*
* Please note that, confusingly, "page_mapping" refers to the inode
* address_space which maps the page from disk; whereas "page_mapped"
* refers to user virtual address space into which the page is mapped.
*/
#define PAGE_MAPPING_ANON 1
+#define PAGE_MAPPING_KSM 2
+#define PAGE_MAPPING_FLAGS (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM)
extern struct address_space swapper_space;
static inline struct address_space *page_mapping(struct page *page)
@@ -644,6 +653,12 @@
return mapping;
}
+/* Neutral page->mapping pointer to address_space or anon_vma or other */
+static inline void *page_rmapping(struct page *page)
+{
+ return (void *)((unsigned long)page->mapping & ~PAGE_MAPPING_FLAGS);
+}
+
static inline int PageAnon(struct page *page)
{
return ((unsigned long)page->mapping & PAGE_MAPPING_ANON) != 0;
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index cb0ba70..1f65af4 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -39,6 +39,14 @@
#ifdef CONFIG_MMU
+static inline struct anon_vma *page_anon_vma(struct page *page)
+{
+ if (((unsigned long)page->mapping & PAGE_MAPPING_FLAGS) !=
+ PAGE_MAPPING_ANON)
+ return NULL;
+ return page_rmapping(page);
+}
+
static inline void anon_vma_lock(struct vm_area_struct *vma)
{
struct anon_vma *anon_vma = vma->anon_vma;
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;