patch-2.2.0-pre8 linux/mm/mmap_avl.c

• Lines: 375
• Date: Fri Jan 15 14:41:04 1999
• Orig file: v2.2.0-pre7/linux/mm/mmap_avl.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.2.0-pre7/linux/mm/mmap_avl.c linux/mm/mmap_avl.c
@@ -0,0 +1,374 @@
+/*
+ * Searching a VMA in the linear list task->mm->mmap is horribly slow.
+ * Use an AVL (Adelson-Velskii and Landis) tree to speed up this search
+ * from O(n) to O(log n), where n is the number of VMAs of the task
+ * n is typically around 6, but may reach 3000 in some cases: object-oriented
+ * databases, persistent store, generational garbage collection (Java, Lisp),
+ * ElectricFence.
+ * Written by Bruno Haible <haible@ma2s2.mathematik.uni-karlsruhe.de>.
+ */
+
+/* We keep the list and tree sorted by address. */
+#define vm_avl_key	vm_end
+#define vm_avl_key_t	unsigned long	/* typeof(vma->avl_key) */
+
+/*
+ * task->mm->mmap_avl is the AVL tree corresponding to task->mm->mmap
+ * or, more exactly, its root.
+ * A vm_area_struct has the following fields:
+ *   vm_avl_left     left son of a tree node
+ *   vm_avl_right    right son of a tree node
+ *   vm_avl_height   1+max(heightof(left),heightof(right))
+ * The empty tree is represented as NULL.
+ */
+
+/* Since the trees are balanced, their height will never be large. */
+#define avl_maxheight	41	/* why this? a small exercise */
+#define heightof(tree)	((tree) == vm_avl_empty ? 0 : (tree)->vm_avl_height)
+/*
+ * Consistency and balancing rules:
+ * 1. tree->vm_avl_height == 1+max(heightof(tree->vm_avl_left),heightof(tree->vm_avl_right))
+ * 2. abs( heightof(tree->vm_avl_left) - heightof(tree->vm_avl_right) ) <= 1
+ * 3. foreach node in tree->vm_avl_left: node->vm_avl_key <= tree->vm_avl_key,
+ *    foreach node in tree->vm_avl_right: node->vm_avl_key >= tree->vm_avl_key.
+ */
+
+#ifdef DEBUG_AVL
+
+/* Look up the nodes at the left and at the right of a given node. */
+static void avl_neighbours (struct vm_area_struct * node, struct vm_area_struct * tree, struct vm_area_struct ** to_the_left, struct vm_area_struct ** to_the_right)
+{
+	vm_avl_key_t key = node->vm_avl_key;
+
+	*to_the_left = *to_the_right = NULL;
+	for (;;) {
+		if (tree == vm_avl_empty) {
+			printk("avl_neighbours: node not found in the tree\n");
+			return;
+		}
+		if (key == tree->vm_avl_key)
+			break;
+		if (key < tree->vm_avl_key) {
+			*to_the_right = tree;
+			tree = tree->vm_avl_left;
+		} else {
+			*to_the_left = tree;
+			tree = tree->vm_avl_right;
+		}
+	}
+	if (tree != node) {
+		printk("avl_neighbours: node not exactly found in the tree\n");
+		return;
+	}
+	if (tree->vm_avl_left != vm_avl_empty) {
+		struct vm_area_struct * node;
+		for (node = tree->vm_avl_left; node->vm_avl_right != vm_avl_empty; node = node->vm_avl_right)
+			continue;
+		*to_the_left = node;
+	}
+	if (tree->vm_avl_right != vm_avl_empty) {
+		struct vm_area_struct * node;
+		for (node = tree->vm_avl_right; node->vm_avl_left != vm_avl_empty; node = node->vm_avl_left)
+			continue;
+		*to_the_right = node;
+	}
+	if ((*to_the_left && ((*to_the_left)->vm_next != node)) || (node->vm_next != *to_the_right))
+		printk("avl_neighbours: tree inconsistent with list\n");
+}
+
+#endif
+
+/*
+ * Rebalance a tree.
+ * After inserting or deleting a node of a tree we have a sequence of subtrees
+ * nodes[0]..nodes[k-1] such that
+ * nodes[0] is the root and nodes[i+1] = nodes[i]->{vm_avl_left|vm_avl_right}.
+ */
+static void avl_rebalance (struct vm_area_struct *** nodeplaces_ptr, int count)
+{
+	for ( ; count > 0 ; count--) {
+		struct vm_area_struct ** nodeplace = *--nodeplaces_ptr;
+		struct vm_area_struct * node = *nodeplace;
+		struct vm_area_struct * nodeleft = node->vm_avl_left;
+		struct vm_area_struct * noderight = node->vm_avl_right;
+		int heightleft = heightof(nodeleft);
+		int heightright = heightof(noderight);
+		if (heightright + 1 < heightleft) {
+			/*                                                      */
+			/*                            *                         */
+			/*                          /   \                       */
+			/*                       n+2      n                     */
+			/*                                                      */
+			struct vm_area_struct * nodeleftleft = nodeleft->vm_avl_left;
+			struct vm_area_struct * nodeleftright = nodeleft->vm_avl_right;
+			int heightleftright = heightof(nodeleftright);
+			if (heightof(nodeleftleft) >= heightleftright) {
+				/*                                                        */
+				/*                *                    n+2|n+3            */
+				/*              /   \                  /    \             */
+				/*           n+2      n      -->      /   n+1|n+2         */
+				/*           / \                      |    /    \         */
+				/*         n+1 n|n+1                 n+1  n|n+1  n        */
+				/*                                                        */
+				node->vm_avl_left = nodeleftright; nodeleft->vm_avl_right = node;
+				nodeleft->vm_avl_height = 1 + (node->vm_avl_height = 1 + heightleftright);
+				*nodeplace = nodeleft;
+			} else {
+				/*                                                        */
+				/*                *                     n+2               */
+				/*              /   \                 /     \             */
+				/*           n+2      n      -->    n+1     n+1           */
+				/*           / \                    / \     / \           */
+				/*          n  n+1                 n   L   R   n          */
+				/*             / \                                        */
+				/*            L   R                                       */
+				/*                                                        */
+				nodeleft->vm_avl_right = nodeleftright->vm_avl_left;
+				node->vm_avl_left = nodeleftright->vm_avl_right;
+				nodeleftright->vm_avl_left = nodeleft;
+				nodeleftright->vm_avl_right = node;
+				nodeleft->vm_avl_height = node->vm_avl_height = heightleftright;
+				nodeleftright->vm_avl_height = heightleft;
+				*nodeplace = nodeleftright;
+			}
+		}
+		else if (heightleft + 1 < heightright) {
+			/* similar to the above, just interchange 'left' <--> 'right' */
+			struct vm_area_struct * noderightright = noderight->vm_avl_right;
+			struct vm_area_struct * noderightleft = noderight->vm_avl_left;
+			int heightrightleft = heightof(noderightleft);
+			if (heightof(noderightright) >= heightrightleft) {
+				node->vm_avl_right = noderightleft; noderight->vm_avl_left = node;
+				noderight->vm_avl_height = 1 + (node->vm_avl_height = 1 + heightrightleft);
+				*nodeplace = noderight;
+			} else {
+				noderight->vm_avl_left = noderightleft->vm_avl_right;
+				node->vm_avl_right = noderightleft->vm_avl_left;
+				noderightleft->vm_avl_right = noderight;
+				noderightleft->vm_avl_left = node;
+				noderight->vm_avl_height = node->vm_avl_height = heightrightleft;
+				noderightleft->vm_avl_height = heightright;
+				*nodeplace = noderightleft;
+			}
+		}
+		else {
+			int height = (heightleft<heightright ? heightright : heightleft) + 1;
+			if (height == node->vm_avl_height)
+				break;
+			node->vm_avl_height = height;
+		}
+	}
+}
+
+/* Insert a node into a tree. */
+static inline void avl_insert (struct vm_area_struct * new_node, struct vm_area_struct ** ptree)
+{
+	vm_avl_key_t key = new_node->vm_avl_key;
+	struct vm_area_struct ** nodeplace = ptree;
+	struct vm_area_struct ** stack[avl_maxheight];
+	int stack_count = 0;
+	struct vm_area_struct *** stack_ptr = &stack[0]; /* = &stack[stackcount] */
+	for (;;) {
+		struct vm_area_struct * node = *nodeplace;
+		if (node == vm_avl_empty)
+			break;
+		*stack_ptr++ = nodeplace; stack_count++;
+		if (key < node->vm_avl_key)
+			nodeplace = &node->vm_avl_left;
+		else
+			nodeplace = &node->vm_avl_right;
+	}
+	new_node->vm_avl_left = vm_avl_empty;
+	new_node->vm_avl_right = vm_avl_empty;
+	new_node->vm_avl_height = 1;
+	*nodeplace = new_node;
+	avl_rebalance(stack_ptr,stack_count);
+}
+
+/* Insert a node into a tree, and
+ * return the node to the left of it and the node to the right of it.
+ */
+static inline void avl_insert_neighbours (struct vm_area_struct * new_node, struct vm_area_struct ** ptree,
+	struct vm_area_struct ** to_the_left, struct vm_area_struct ** to_the_right)
+{
+	vm_avl_key_t key = new_node->vm_avl_key;
+	struct vm_area_struct ** nodeplace = ptree;
+	struct vm_area_struct ** stack[avl_maxheight];
+	int stack_count = 0;
+	struct vm_area_struct *** stack_ptr = &stack[0]; /* = &stack[stackcount] */
+	*to_the_left = *to_the_right = NULL;
+	for (;;) {
+		struct vm_area_struct * node = *nodeplace;
+		if (node == vm_avl_empty)
+			break;
+		*stack_ptr++ = nodeplace; stack_count++;
+		if (key < node->vm_avl_key) {
+			*to_the_right = node;
+			nodeplace = &node->vm_avl_left;
+		} else {
+			*to_the_left = node;
+			nodeplace = &node->vm_avl_right;
+		}
+	}
+	new_node->vm_avl_left = vm_avl_empty;
+	new_node->vm_avl_right = vm_avl_empty;
+	new_node->vm_avl_height = 1;
+	*nodeplace = new_node;
+	avl_rebalance(stack_ptr,stack_count);
+}
+
+/* Removes a node out of a tree. */
+static void avl_remove (struct vm_area_struct * node_to_delete, struct vm_area_struct ** ptree)
+{
+	vm_avl_key_t key = node_to_delete->vm_avl_key;
+	struct vm_area_struct ** nodeplace = ptree;
+	struct vm_area_struct ** stack[avl_maxheight];
+	int stack_count = 0;
+	struct vm_area_struct *** stack_ptr = &stack[0]; /* = &stack[stackcount] */
+	struct vm_area_struct ** nodeplace_to_delete;
+	for (;;) {
+		struct vm_area_struct * node = *nodeplace;
+#ifdef DEBUG_AVL
+		if (node == vm_avl_empty) {
+			/* what? node_to_delete not found in tree? */
+			printk("avl_remove: node to delete not found in tree\n");
+			return;
+		}
+#endif
+		*stack_ptr++ = nodeplace; stack_count++;
+		if (key == node->vm_avl_key)
+			break;
+		if (key < node->vm_avl_key)
+			nodeplace = &node->vm_avl_left;
+		else
+			nodeplace = &node->vm_avl_right;
+	}
+	nodeplace_to_delete = nodeplace;
+	/* Have to remove node_to_delete = *nodeplace_to_delete. */
+	if (node_to_delete->vm_avl_left == vm_avl_empty) {
+		*nodeplace_to_delete = node_to_delete->vm_avl_right;
+		stack_ptr--; stack_count--;
+	} else {
+		struct vm_area_struct *** stack_ptr_to_delete = stack_ptr;
+		struct vm_area_struct ** nodeplace = &node_to_delete->vm_avl_left;
+		struct vm_area_struct * node;
+		for (;;) {
+			node = *nodeplace;
+			if (node->vm_avl_right == vm_avl_empty)
+				break;
+			*stack_ptr++ = nodeplace; stack_count++;
+			nodeplace = &node->vm_avl_right;
+		}
+		*nodeplace = node->vm_avl_left;
+		/* node replaces node_to_delete */
+		node->vm_avl_left = node_to_delete->vm_avl_left;
+		node->vm_avl_right = node_to_delete->vm_avl_right;
+		node->vm_avl_height = node_to_delete->vm_avl_height;
+		*nodeplace_to_delete = node; /* replace node_to_delete */
+		*stack_ptr_to_delete = &node->vm_avl_left; /* replace &node_to_delete->vm_avl_left */
+	}
+	avl_rebalance(stack_ptr,stack_count);
+}
+
+#ifdef DEBUG_AVL
+
+/* print a list */
+static void printk_list (struct vm_area_struct * vma)
+{
+	printk("[");
+	while (vma) {
+		printk("%08lX-%08lX", vma->vm_start, vma->vm_end);
+		vma = vma->vm_next;
+		if (!vma)
+			break;
+		printk(" ");
+	}
+	printk("]");
+}
+
+/* print a tree */
+static void printk_avl (struct vm_area_struct * tree)
+{
+	if (tree != vm_avl_empty) {
+		printk("(");
+		if (tree->vm_avl_left != vm_avl_empty) {
+			printk_avl(tree->vm_avl_left);
+			printk("<");
+		}
+		printk("%08lX-%08lX", tree->vm_start, tree->vm_end);
+		if (tree->vm_avl_right != vm_avl_empty) {
+			printk(">");
+			printk_avl(tree->vm_avl_right);
+		}
+		printk(")");
+	}
+}
+
+static char *avl_check_point = "somewhere";
+
+/* check a tree's consistency and balancing */
+static void avl_checkheights (struct vm_area_struct * tree)
+{
+	int h, hl, hr;
+
+	if (tree == vm_avl_empty)
+		return;
+	avl_checkheights(tree->vm_avl_left);
+	avl_checkheights(tree->vm_avl_right);
+	h = tree->vm_avl_height;
+	hl = heightof(tree->vm_avl_left);
+	hr = heightof(tree->vm_avl_right);
+	if ((h == hl+1) && (hr <= hl) && (hl <= hr+1))
+		return;
+	if ((h == hr+1) && (hl <= hr) && (hr <= hl+1))
+		return;
+	printk("%s: avl_checkheights: heights inconsistent\n",avl_check_point);
+}
+
+/* check that all values stored in a tree are < key */
+static void avl_checkleft (struct vm_area_struct * tree, vm_avl_key_t key)
+{
+	if (tree == vm_avl_empty)
+		return;
+	avl_checkleft(tree->vm_avl_left,key);
+	avl_checkleft(tree->vm_avl_right,key);
+	if (tree->vm_avl_key < key)
+		return;
+	printk("%s: avl_checkleft: left key %lu >= top key %lu\n",avl_check_point,tree->vm_avl_key,key);
+}
+
+/* check that all values stored in a tree are > key */
+static void avl_checkright (struct vm_area_struct * tree, vm_avl_key_t key)
+{
+	if (tree == vm_avl_empty)
+		return;
+	avl_checkright(tree->vm_avl_left,key);
+	avl_checkright(tree->vm_avl_right,key);
+	if (tree->vm_avl_key > key)
+		return;
+	printk("%s: avl_checkright: right key %lu <= top key %lu\n",avl_check_point,tree->vm_avl_key,key);
+}
+
+/* check that all values are properly increasing */
+static void avl_checkorder (struct vm_area_struct * tree)
+{
+	if (tree == vm_avl_empty)
+		return;
+	avl_checkorder(tree->vm_avl_left);
+	avl_checkorder(tree->vm_avl_right);
+	avl_checkleft(tree->vm_avl_left,tree->vm_avl_key);
+	avl_checkright(tree->vm_avl_right,tree->vm_avl_key);
+}
+
+/* all checks */
+static void avl_check (struct task_struct * task, char *caller)
+{
+	avl_check_point = caller;
+/*	printk("task \"%s\", %s\n",task->comm,caller); */
+/*	printk("task \"%s\" list: ",task->comm); printk_list(task->mm->mmap); printk("\n"); */
+/*	printk("task \"%s\" tree: ",task->comm); printk_avl(task->mm->mmap_avl); printk("\n"); */
+	avl_checkheights(task->mm->mmap_avl);
+	avl_checkorder(task->mm->mmap_avl);
+}
+
+#endif