ksm: three remove_rmap_item_from_tree cleanups

1. remove_rmap_item_from_tree() is called as a precaution from
   various places: don't dirty the rmap_item cacheline unnecessarily,
   just mask the flags out of the address when they have been set.

2. First get_next_rmap_item() removes an unstable rmap_item from its tree,
   then shortly afterwards cmp_and_merge_page() removes a stable rmap_item
   from its tree: it's easier just to do both at once (but definitely keep
   the BUG_ON(age > 1) which guards against a future omission).

3. When cmp_and_merge_page() moves an rmap_item from unstable to stable
   tree, it does its own rb_erase() and accounting: that's better
   expressed by remove_rmap_item_from_tree().

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: 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, 6 insertions, 11 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 5575f8628fef..133ea2ca8384 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -453,6 +453,7 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
                 }
 
                 rmap_item->next = NULL;
+                rmap_item->address &= PAGE_MASK;
 
         } else if (rmap_item->address & NODE_FLAG) {
                 unsigned char age;
@@ -467,11 +468,11 @@ static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
                 BUG_ON(age > 1);
                 if (!age)
                         rb_erase(&rmap_item->node, &root_unstable_tree);
+
                 ksm_pages_unshared--;
+                rmap_item->address &= PAGE_MASK;
         }
 
-        rmap_item->address &= PAGE_MASK;
-
         cond_resched();         /* we're called from many long loops */
 }
 
@@ -1086,8 +1087,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
         unsigned int checksum;
         int err;
 
-        if (in_stable_tree(rmap_item))
-                remove_rmap_item_from_tree(rmap_item);
+        remove_rmap_item_from_tree(rmap_item);
 
         /* We first start with searching the page inside the stable tree */
         tree_rmap_item = stable_tree_search(page, page2, rmap_item);
@@ -1143,9 +1143,7 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
                  * tree, and insert it instead as new node in the stable tree.
                  */
                 if (!err) {
-                        rb_erase(&tree_rmap_item->node, &root_unstable_tree);
-                        tree_rmap_item->address &= ~NODE_FLAG;
-                        ksm_pages_unshared--;
+                        remove_rmap_item_from_tree(tree_rmap_item);
 
                         /*
                          * If we fail to insert the page into the stable tree,
@@ -1174,11 +1172,8 @@ static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
 
         while (cur != &mm_slot->rmap_list) {
                 rmap_item = list_entry(cur, struct rmap_item, link);
-                if ((rmap_item->address & PAGE_MASK) == addr) {
-                        if (!in_stable_tree(rmap_item))
-                                remove_rmap_item_from_tree(rmap_item);
+                if ((rmap_item->address & PAGE_MASK) == addr)
                         return rmap_item;
-                }
                 if (rmap_item->address > addr)
                         break;
                 cur = cur->next;