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>

diff --git a/mm/ksm.c b/mm/ksm.c
index 46b4c52..ef89526 100644 (file)
--- 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);