ksm: move pages_sharing updates

The pages_shared count is incremented and decremented when adding a node
to and removing a node from the stable tree: easy to understand.  But the
pages_sharing count was hard to follow, being adjusted in various places:
increment and decrement it when adding to and removing from the stable tree.

And the pages_sharing variable used to include the pages_shared, then those
were subtracted when shown in the pages_sharing sysfs file: now keep it as
an exclusive count of leaves hanging off the stable tree nodes, throughout.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Acked-by: Izik Eidus <ieidus@redhat.com>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 15 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 46b4c522ea4f..ef89526fb862 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -152,7 +152,7 @@ static struct kmem_cache *mm_slot_cache;
 /* The number of nodes in the stable tree */
 static unsigned long ksm_pages_shared;
 
-/* The number of page slots sharing those nodes */
+/* The number of page slots additionally sharing those nodes */
 static unsigned long ksm_pages_sharing;
 
 /* Limit on the number of unswappable pages used */
@@ -382,6 +382,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
                                                 &next_item->node,
                                                 &root_stable_tree);
                                 next_item->address |= NODE_FLAG;
+                                ksm_pages_sharing--;
                         } else {
                                 rb_erase(&rmap_item->node, &root_stable_tree);
                                 ksm_pages_shared--;
@@ -395,10 +396,10 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
                                 BUG_ON(next_item->prev != rmap_item);
                                 next_item->prev = rmap_item->prev;
                         }
+                        ksm_pages_sharing--;
                 }
 
                 rmap_item->next = NULL;
-                ksm_pages_sharing--;
 
         } else if (rmap_item->address & NODE_FLAG) {
                 unsigned char age;
@@ -786,8 +787,6 @@ static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
                  */
                 if (err)
                         break_cow(mm1, addr1);
-                else
-                        ksm_pages_sharing += 2;
         }
 
         put_page(kpage);
@@ -816,9 +815,6 @@ static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
         err = try_to_merge_one_page(vma, page1, kpage);
         up_read(&mm1->mmap_sem);
 
-        if (!err)
-                ksm_pages_sharing++;
-
         return err;
 }
 
@@ -928,13 +924,12 @@ static struct rmap_item *stable_tree_insert(struct page *page,
                 }
         }
 
-        ksm_pages_shared++;
-
         rmap_item->address |= NODE_FLAG | STABLE_FLAG;
         rmap_item->next = NULL;
         rb_link_node(&rmap_item->node, parent, new);
         rb_insert_color(&rmap_item->node, &root_stable_tree);
 
+        ksm_pages_shared++;
         return rmap_item;
 }
 
@@ -1019,6 +1014,8 @@ static void stable_tree_append(struct rmap_item *rmap_item,
 
         tree_rmap_item->next = rmap_item;
         rmap_item->address |= STABLE_FLAG;
+
+        ksm_pages_sharing++;
 }
 
 /*
@@ -1043,10 +1040,9 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
         /* We first start with searching the page inside the stable tree */
         tree_rmap_item = stable_tree_search(page, page2, rmap_item);
         if (tree_rmap_item) {
-                if (page == page2[0]) {                 /* forked */
-                        ksm_pages_sharing++;
+                if (page == page2[0])                   /* forked */
                         err = 0;
-                } else
+                else
                         err = try_to_merge_with_ksm_page(rmap_item->mm,
                                                          rmap_item->address,
                                                          page, page2[0]);
@@ -1107,7 +1103,6 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                                 break_cow(tree_rmap_item->mm,
                                                 tree_rmap_item->address);
                                 break_cow(rmap_item->mm, rmap_item->address);
-                                ksm_pages_sharing -= 2;
                         }
                 }
 
@@ -1475,8 +1470,7 @@ KSM_ATTR_RO(pages_shared);
 static ssize_t pages_sharing_show(struct kobject *kobj,
                                   struct kobj_attribute *attr, char *buf)
 {
-        return sprintf(buf, "%lu\n",
-                        ksm_pages_sharing - ksm_pages_shared);
+        return sprintf(buf, "%lu\n", ksm_pages_sharing);
 }
 KSM_ATTR_RO(pages_sharing);