rbtree: Undo augmented trees performance damage and regression

Reimplement augmented RB-trees without sprinkling extra branches
all over the RB-tree code (which lives in the scheduler hot path).

This approach is 'borrowed' from Fabio's BFQ implementation and
relies on traversing the rebalance path after the RB-tree-op to
correct the heap property for insertion/removal and make up for
the damage done by the tree rotations.

For insertion the rebalance path is trivially that from the new
node upwards to the root, for removal it is that from the deepest
node in the path from the to be removed node that will still
be around after the removal.

[ This patch also fixes a video driver regression reported by
  Ali Gholami Rudi - the memtype->subtree_max_end was updated
  incorrectly. ]

Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Ali Gholami Rudi <ali@rudi.ir>
Cc: Fabio Checconi <fabio@gandalf.sssup.it>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <1275414172.27810.27961.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 28 deletions

diff --git a/arch/x86/mm/pat_rbtree.c b/arch/x86/mm/pat_rbtree.c
index f20eeec85a86..8acaddd0fb21 100644
--- a/arch/x86/mm/pat_rbtree.c
+++ b/arch/x86/mm/pat_rbtree.c
@@ -34,8 +34,7 @@
  * memtype_lock protects the rbtree.
  */
 
-static void memtype_rb_augment_cb(struct rb_node *node);
-static struct rb_root memtype_rbroot = RB_AUGMENT_ROOT(&memtype_rb_augment_cb);
+static struct rb_root memtype_rbroot = RB_ROOT;
 
 static int is_node_overlap(struct memtype *node, u64 start, u64 end)
 {
@@ -56,7 +55,7 @@ static u64 get_subtree_max_end(struct rb_node *node)
 }
 
 /* Update 'subtree_max_end' for a node, based on node and its children */
-static void update_node_max_end(struct rb_node *node)
+static void memtype_rb_augment_cb(struct rb_node *node, void *__unused)
 {
         struct memtype *data;
         u64 max_end, child_max_end;
@@ -78,25 +77,6 @@ static void update_node_max_end(struct rb_node *node)
         data->subtree_max_end = max_end;
 }
 
-/* Update 'subtree_max_end' for a node and all its ancestors */
-static void update_path_max_end(struct rb_node *node)
-{
-        u64 old_max_end, new_max_end;
-
-        while (node) {
-                struct memtype *data = container_of(node, struct memtype, rb);
-
-                old_max_end = data->subtree_max_end;
-                update_node_max_end(node);
-                new_max_end = data->subtree_max_end;
-
-                if (new_max_end == old_max_end)
-                        break;
-
-                node = rb_parent(node);
-        }
-}
-
 /* Find the first (lowest start addr) overlapping range from rb tree */
 static struct memtype *memtype_rb_lowest_match(struct rb_root *root,
                                 u64 start, u64 end)
@@ -190,12 +170,6 @@ failure:
         return -EBUSY;
 }
 
-static void memtype_rb_augment_cb(struct rb_node *node)
-{
-        if (node)
-                update_path_max_end(node);
-}
-
 static void memtype_rb_insert(struct rb_root *root, struct memtype *newdata)
 {
         struct rb_node **node = &(root->rb_node);
@@ -213,6 +187,7 @@ static void memtype_rb_insert(struct rb_root *root, struct memtype *newdata)
 
         rb_link_node(&newdata->rb, parent, node);
         rb_insert_color(&newdata->rb, root);
+        rb_augment_insert(&newdata->rb, memtype_rb_augment_cb, NULL);
 }
 
 int rbt_memtype_check_insert(struct memtype *new, unsigned long *ret_type)
@@ -234,13 +209,16 @@ int rbt_memtype_check_insert(struct memtype *new, unsigned long *ret_type)
 
 struct memtype *rbt_memtype_erase(u64 start, u64 end)
 {
+        struct rb_node *deepest;
         struct memtype *data;
 
         data = memtype_rb_exact_match(&memtype_rbroot, start, end);
         if (!data)
                 goto out;
 
+        deepest = rb_augment_erase_begin(&data->rb);
         rb_erase(&data->rb, &memtype_rbroot);
+        rb_augment_erase_end(deepest, memtype_rb_augment_cb, NULL);
 out:
         return data;
 }