Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=c0bc9875b701c588e448302d41181995c21e8040
Commit:     c0bc9875b701c588e448302d41181995c21e8040
Parent:     b55ed816235cf41c29159d22a4cdeec7deb5821c
Author:     Nick Piggin <[EMAIL PROTECTED]>
AuthorDate: Tue Oct 16 01:24:42 2007 -0700
Committer:  Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Tue Oct 16 09:42:53 2007 -0700

    radix-tree: use indirect bit
    
    Rather than sign direct radix-tree pointers with a special bit, sign the
    indirect one that hangs off the root.  This means that, given a lookup_slot
    operation, the invalid result will be differentiated from the valid
    (previously, valid results could have the bit either set or clear).
    
    This does not affect slot lookups which occur under lock -- they can never
    return an invalid result.  Is needed in future for lockless pagecache.
    
    Signed-off-by: Nick Piggin <[EMAIL PROTECTED]>
    Acked-by: Peter Zijlstra <[EMAIL PROTECTED]>
    Cc: Hugh Dickins <[EMAIL PROTECTED]>
    Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
    Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
 include/linux/radix-tree.h |   38 +++++++++++++-----------
 lib/radix-tree.c           |   69 +++++++++++++++++++++++++++----------------
 2 files changed, 64 insertions(+), 43 deletions(-)

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 430e4a8..b6116b4 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -26,28 +26,31 @@
 #include <linux/rcupdate.h>
 
 /*
- * A direct pointer (root->rnode pointing directly to a data item,
- * rather than another radix_tree_node) is signalled by the low bit
- * set in the root->rnode pointer.
+ * An indirect pointer (root->rnode pointing to a radix_tree_node, rather
+ * than a data item) is signalled by the low bit set in the root->rnode
+ * pointer.
  *
- * In this case root->height is also NULL, but the direct pointer tests are
- * needed for RCU lookups when root->height is unreliable.
+ * In this case root->height is > 0, but the indirect pointer tests are
+ * needed for RCU lookups (because root->height is unreliable). The only
+ * time callers need worry about this is when doing a lookup_slot under
+ * RCU.
  */
-#define RADIX_TREE_DIRECT_PTR  1
+#define RADIX_TREE_INDIRECT_PTR        1
+#define RADIX_TREE_RETRY ((void *)-1UL)
 
-static inline void *radix_tree_ptr_to_direct(void *ptr)
+static inline void *radix_tree_ptr_to_indirect(void *ptr)
 {
-       return (void *)((unsigned long)ptr | RADIX_TREE_DIRECT_PTR);
+       return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
 }
 
-static inline void *radix_tree_direct_to_ptr(void *ptr)
+static inline void *radix_tree_indirect_to_ptr(void *ptr)
 {
-       return (void *)((unsigned long)ptr & ~RADIX_TREE_DIRECT_PTR);
+       return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
 }
 
-static inline int radix_tree_is_direct_ptr(void *ptr)
+static inline int radix_tree_is_indirect_ptr(void *ptr)
 {
-       return (int)((unsigned long)ptr & RADIX_TREE_DIRECT_PTR);
+       return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
 }
 
 /*** radix-tree API starts here ***/
@@ -130,7 +133,10 @@ do {                                                       
                \
  */
 static inline void *radix_tree_deref_slot(void **pslot)
 {
-       return radix_tree_direct_to_ptr(*pslot);
+       void *ret = *pslot;
+       if (unlikely(radix_tree_is_indirect_ptr(ret)))
+               ret = RADIX_TREE_RETRY;
+       return ret;
 }
 /**
  * radix_tree_replace_slot     - replace item in a slot
@@ -142,10 +148,8 @@ static inline void *radix_tree_deref_slot(void **pslot)
  */
 static inline void radix_tree_replace_slot(void **pslot, void *item)
 {
-       BUG_ON(radix_tree_is_direct_ptr(item));
-       rcu_assign_pointer(*pslot,
-               (void *)((unsigned long)item |
-                       ((unsigned long)*pslot & RADIX_TREE_DIRECT_PTR)));
+       BUG_ON(radix_tree_is_indirect_ptr(item));
+       rcu_assign_pointer(*pslot, item);
 }
 
 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 7af368a..0eee402 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -104,7 +104,7 @@ radix_tree_node_alloc(struct radix_tree_root *root)
                        rtp->nr--;
                }
        }
-       BUG_ON(radix_tree_is_direct_ptr(ret));
+       BUG_ON(radix_tree_is_indirect_ptr(ret));
        return ret;
 }
 
@@ -240,7 +240,7 @@ static int radix_tree_extend(struct radix_tree_root *root, 
unsigned long index)
                        return -ENOMEM;
 
                /* Increase the height.  */
-               node->slots[0] = radix_tree_direct_to_ptr(root->rnode);
+               node->slots[0] = radix_tree_indirect_to_ptr(root->rnode);
 
                /* Propagate the aggregated tag info into the new root */
                for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
@@ -251,6 +251,7 @@ static int radix_tree_extend(struct radix_tree_root *root, 
unsigned long index)
                newheight = root->height+1;
                node->height = newheight;
                node->count = 1;
+               node = radix_tree_ptr_to_indirect(node);
                rcu_assign_pointer(root->rnode, node);
                root->height = newheight;
        } while (height > root->height);
@@ -274,7 +275,7 @@ int radix_tree_insert(struct radix_tree_root *root,
        int offset;
        int error;
 
-       BUG_ON(radix_tree_is_direct_ptr(item));
+       BUG_ON(radix_tree_is_indirect_ptr(item));
 
        /* Make sure the tree is high enough.  */
        if (index > radix_tree_maxindex(root->height)) {
@@ -283,7 +284,8 @@ int radix_tree_insert(struct radix_tree_root *root,
                        return error;
        }
 
-       slot = root->rnode;
+       slot = radix_tree_indirect_to_ptr(root->rnode);
+
        height = root->height;
        shift = (height-1) * RADIX_TREE_MAP_SHIFT;
 
@@ -298,7 +300,8 @@ int radix_tree_insert(struct radix_tree_root *root,
                                rcu_assign_pointer(node->slots[offset], slot);
                                node->count++;
                        } else
-                               rcu_assign_pointer(root->rnode, slot);
+                               rcu_assign_pointer(root->rnode,
+                                       radix_tree_ptr_to_indirect(slot));
                }
 
                /* Go a level down */
@@ -318,7 +321,7 @@ int radix_tree_insert(struct radix_tree_root *root,
                BUG_ON(tag_get(node, 0, offset));
                BUG_ON(tag_get(node, 1, offset));
        } else {
-               rcu_assign_pointer(root->rnode, radix_tree_ptr_to_direct(item));
+               rcu_assign_pointer(root->rnode, item);
                BUG_ON(root_tag_get(root, 0));
                BUG_ON(root_tag_get(root, 1));
        }
@@ -350,11 +353,12 @@ void **radix_tree_lookup_slot(struct radix_tree_root 
*root, unsigned long index)
        if (node == NULL)
                return NULL;
 
-       if (radix_tree_is_direct_ptr(node)) {
+       if (!radix_tree_is_indirect_ptr(node)) {
                if (index > 0)
                        return NULL;
                return (void **)&root->rnode;
        }
+       node = radix_tree_indirect_to_ptr(node);
 
        height = node->height;
        if (index > radix_tree_maxindex(height))
@@ -398,11 +402,12 @@ void *radix_tree_lookup(struct radix_tree_root *root, 
unsigned long index)
        if (node == NULL)
                return NULL;
 
-       if (radix_tree_is_direct_ptr(node)) {
+       if (!radix_tree_is_indirect_ptr(node)) {
                if (index > 0)
                        return NULL;
-               return radix_tree_direct_to_ptr(node);
+               return node;
        }
+       node = radix_tree_indirect_to_ptr(node);
 
        height = node->height;
        if (index > radix_tree_maxindex(height))
@@ -447,7 +452,7 @@ void *radix_tree_tag_set(struct radix_tree_root *root,
        height = root->height;
        BUG_ON(index > radix_tree_maxindex(height));
 
-       slot = root->rnode;
+       slot = radix_tree_indirect_to_ptr(root->rnode);
        shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
 
        while (height > 0) {
@@ -497,7 +502,7 @@ void *radix_tree_tag_clear(struct radix_tree_root *root,
 
        shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
        pathp->node = NULL;
-       slot = root->rnode;
+       slot = radix_tree_indirect_to_ptr(root->rnode);
 
        while (height > 0) {
                int offset;
@@ -562,8 +567,9 @@ int radix_tree_tag_get(struct radix_tree_root *root,
        if (node == NULL)
                return 0;
 
-       if (radix_tree_is_direct_ptr(node))
+       if (!radix_tree_is_indirect_ptr(node))
                return (index == 0);
+       node = radix_tree_indirect_to_ptr(node);
 
        height = node->height;
        if (index > radix_tree_maxindex(height))
@@ -716,13 +722,13 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void 
**results,
        if (!node)
                return 0;
 
-       if (radix_tree_is_direct_ptr(node)) {
+       if (!radix_tree_is_indirect_ptr(node)) {
                if (first_index > 0)
                        return 0;
-               node = radix_tree_direct_to_ptr(node);
-               results[0] = rcu_dereference(node);
+               results[0] = node;
                return 1;
        }
+       node = radix_tree_indirect_to_ptr(node);
 
        max_index = radix_tree_maxindex(node->height);
 
@@ -844,13 +850,13 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, 
void **results,
        if (!node)
                return 0;
 
-       if (radix_tree_is_direct_ptr(node)) {
+       if (!radix_tree_is_indirect_ptr(node)) {
                if (first_index > 0)
                        return 0;
-               node = radix_tree_direct_to_ptr(node);
-               results[0] = rcu_dereference(node);
+               results[0] = node;
                return 1;
        }
+       node = radix_tree_indirect_to_ptr(node);
 
        max_index = radix_tree_maxindex(node->height);
 
@@ -880,12 +886,22 @@ EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
 static inline void radix_tree_shrink(struct radix_tree_root *root)
 {
        /* try to shrink tree height */
-       while (root->height > 0 &&
-                       root->rnode->count == 1 &&
-                       root->rnode->slots[0]) {
+       while (root->height > 0) {
                struct radix_tree_node *to_free = root->rnode;
                void *newptr;
 
+               BUG_ON(!radix_tree_is_indirect_ptr(to_free));
+               to_free = radix_tree_indirect_to_ptr(to_free);
+
+               /*
+                * The candidate node has more than one child, or its child
+                * is not at the leftmost slot, we cannot shrink.
+                */
+               if (to_free->count != 1)
+                       break;
+               if (!to_free->slots[0])
+                       break;
+
                /*
                 * We don't need rcu_assign_pointer(), since we are simply
                 * moving the node from one part of the tree to another. If
@@ -894,8 +910,8 @@ static inline void radix_tree_shrink(struct radix_tree_root 
*root)
                 * one (root->rnode).
                 */
                newptr = to_free->slots[0];
-               if (root->height == 1)
-                       newptr = radix_tree_ptr_to_direct(newptr);
+               if (root->height > 1)
+                       newptr = radix_tree_ptr_to_indirect(newptr);
                root->rnode = newptr;
                root->height--;
                /* must only free zeroed nodes into the slab */
@@ -930,12 +946,12 @@ void *radix_tree_delete(struct radix_tree_root *root, 
unsigned long index)
                goto out;
 
        slot = root->rnode;
-       if (height == 0 && root->rnode) {
-               slot = radix_tree_direct_to_ptr(slot);
+       if (height == 0) {
                root_tag_clear_all(root);
                root->rnode = NULL;
                goto out;
        }
+       slot = radix_tree_indirect_to_ptr(slot);
 
        shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
        pathp->node = NULL;
@@ -977,7 +993,8 @@ void *radix_tree_delete(struct radix_tree_root *root, 
unsigned long index)
                        radix_tree_node_free(to_free);
 
                if (pathp->node->count) {
-                       if (pathp->node == root->rnode)
+                       if (pathp->node ==
+                                       radix_tree_indirect_to_ptr(root->rnode))
                                radix_tree_shrink(root);
                        goto out;
                }
-
To unsubscribe from this list: send the line "unsubscribe git-commits-head" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to