ksm: identify PageKsm pages

KSM will need to identify its kernel merged pages unambiguously, and
/proc/kpageflags will probably like to do so too.

Since KSM will only be substituting anonymous pages, statistics are best
preserved by making a PageKsm page a special PageAnon page: one with no
anon_vma.

But KSM then needs its own page_add_ksm_rmap() - keep it in ksm.h near
PageKsm; and do_wp_page() must COW them, unlike singly mapped PageAnons.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Izik Eidus <ieidus@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 2707c6c7a20f..2281c2cbfe2b 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -2,6 +2,7 @@
 #include <linux/compiler.h>
 #include <linux/fs.h>
 #include <linux/init.h>
+#include <linux/ksm.h>
 #include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/proc_fs.h>
@@ -95,6 +96,8 @@ static const struct file_operations proc_kpagecount_operations = {
 #define KPF_UNEVICTABLE         18
 #define KPF_NOPAGE              20
 
+#define KPF_KSM                 21
+
 /* kernel hacking assistances
  * WARNING: subject to change, never rely on them!
  */
@@ -137,6 +140,8 @@ static u64 get_uflags(struct page *page)
                 u |= 1 << KPF_MMAP;
         if (PageAnon(page))
                 u |= 1 << KPF_ANON;
+        if (PageKsm(page))
+                u |= 1 << KPF_KSM;
 
         /*
          * compound pages: export both head/tail info