LXR linux-old/mm/mmap

   1/*
   2 * Searching a VMA in the linear list task->mm->mmap is horribly slow.
   3 * Use an AVL (Adelson-Velskii and Landis) tree to speed up this search
   4 * from O(n) to O(log n), where n is the number of VMAs of the task
   5 * n is typically around 6, but may reach 3000 in some cases: object-oriented
   6 * databases, persistent store, generational garbage collection (Java, Lisp),
   7 * ElectricFence.
   8 * Written by Bruno Haible <haible@ma2s2.mathematik.uni-karlsruhe.de>.
   9 */
  10
  11/* We keep the list and tree sorted by address. */
  12#define vm_avl_key      vm_end
  13#define vm_avl_key_t    unsigned long   /* typeof(vma->avl_key) */
  14
  15/*
  16 * task->mm->mmap_avl is the AVL tree corresponding to task->mm->mmap
  17 * or, more exactly, its root.
  18 * A vm_area_struct has the following fields:
  19 *   vm_avl_left     left son of a tree node
  20 *   vm_avl_right    right son of a tree node
  21 *   vm_avl_height   1+max(heightof(left),heightof(right))
  22 * The empty tree is represented as NULL.
  23 */
  24
  25/* Since the trees are balanced, their height will never be large. */
  26#define avl_maxheight   41      /* why this? a small exercise */
  27#define heightof(tree)  ((tree) == vm_avl_empty ? 0 : (tree)->vm_avl_height)
  28/*
  29 * Consistency and balancing rules:
  30 * 1. tree->vm_avl_height == 1+max(heightof(tree->vm_avl_left),heightof(tree->vm_avl_right))
  31 * 2. abs( heightof(tree->vm_avl_left) - heightof(tree->vm_avl_right) ) <= 1
  32 * 3. foreach node in tree->vm_avl_left: node->vm_avl_key <= tree->vm_avl_key,
  33 *    foreach node in tree->vm_avl_right: node->vm_avl_key >= tree->vm_avl_key.
  34 */
  35
  36#ifdef DEBUG_AVL
  37
  38/* Look up the nodes at the left and at the right of a given node. */
  39static 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)
  40{
  41        vm_avl_key_t key = node->vm_avl_key;
  42
  43        *to_the_left = *to_the_right = NULL;
  44        for (;;) {
  45                if (tree == vm_avl_empty) {
  46                        printk("avl_neighbours: node not found in the tree\n");
  47                        return;
  48                }
  49                if (key == tree->vm_avl_key)
  50                        break;
  51                if (key < tree->vm_avl_key) {
  52                        *to_the_right = tree;
  53                        tree = tree->vm_avl_left;
  54                } else {
  55                        *to_the_left = tree;
  56                        tree = tree->vm_avl_right;
  57                }
  58        }
  59        if (tree != node) {
  60                printk("avl_neighbours: node not exactly found in the tree\n");
  61                return;
  62        }
  63        if (tree->vm_avl_left != vm_avl_empty) {
  64                struct vm_area_struct * node;
  65                for (node = tree->vm_avl_left; node->vm_avl_right != vm_avl_empty; node = node->vm_avl_right)
  66                        continue;
  67                *to_the_left = node;
  68        }
  69        if (tree->vm_avl_right != vm_avl_empty) {
  70                struct vm_area_struct * node;
  71                for (node = tree->vm_avl_right; node->vm_avl_left != vm_avl_empty; node = node->vm_avl_left)
  72                        continue;
  73                *to_the_right = node;
  74        }
  75        if ((*to_the_left && ((*to_the_left)->vm_next != node)) || (node->vm_next != *to_the_right))
  76                printk("avl_neighbours: tree inconsistent with list\n");
  77}
  78
  79#endif
  80
  81/*
  82 * Rebalance a tree.
  83 * After inserting or deleting a node of a tree we have a sequence of subtrees
  84 * nodes[0]..nodes[k-1] such that
  85 * nodes[0] is the root and nodes[i+1] = nodes[i]->{vm_avl_left|vm_avl_right}.
  86 */
  87static void avl_rebalance (struct vm_area_struct *** nodeplaces_ptr, int count)
  88{
  89        for ( ; count > 0 ; count--) {
  90                struct vm_area_struct ** nodeplace = *--nodeplaces_ptr;
  91                struct vm_area_struct * node = *nodeplace;
  92                struct vm_area_struct * nodeleft = node->vm_avl_left;
  93                struct vm_area_struct * noderight = node->vm_avl_right;
  94                int heightleft = heightof(nodeleft);
  95                int heightright = heightof(noderight);
  96                if (heightright + 1 < heightleft) {
  97                        /*                                                      */
  98                        /*                            *                         */
  99                        /*                          /   \                       */
 100                        /*                       n+2      n                     */
 101                        /*                                                      */
 102                        struct vm_area_struct * nodeleftleft = nodeleft->vm_avl_left;
 103                        struct vm_area_struct * nodeleftright = nodeleft->vm_avl_right;
 104                        int heightleftright = heightof(nodeleftright);
 105                        if (heightof(nodeleftleft) >= heightleftright) {
 106                                /*                                                        */
 107                                /*                *                    n+2|n+3            */
 108                                /*              /   \                  /    \             */
 109                                /*           n+2      n      -->      /   n+1|n+2         */
 110                                /*           / \                      |    /    \         */
 111                                /*         n+1 n|n+1                 n+1  n|n+1  n        */
 112                                /*                                                        */
 113                                node->vm_avl_left = nodeleftright; nodeleft->vm_avl_right = node;
 114                                nodeleft->vm_avl_height = 1 + (node->vm_avl_height = 1 + heightleftright);
 115                                *nodeplace = nodeleft;
 116                        } else {
 117                                /*                                                        */
 118                                /*                *                     n+2               */
 119                                /*              /   \                 /     \             */
 120                                /*           n+2      n      -->    n+1     n+1           */
 121                                /*           / \                    / \     / \           */
 122                                /*          n  n+1                 n   L   R   n          */
 123                                /*             / \                                        */
 124                                /*            L   R                                       */
 125                                /*                                                        */
 126                                nodeleft->vm_avl_right = nodeleftright->vm_avl_left;
 127                                node->vm_avl_left = nodeleftright->vm_avl_right;
 128                                nodeleftright->vm_avl_left = nodeleft;
 129                                nodeleftright->vm_avl_right = node;
 130                                nodeleft->vm_avl_height = node->vm_avl_height = heightleftright;
 131                                nodeleftright->vm_avl_height = heightleft;
 132                                *nodeplace = nodeleftright;
 133                        }
 134                }
 135                else if (heightleft + 1 < heightright) {
 136                        /* similar to the above, just interchange 'left' <--> 'right' */
 137                        struct vm_area_struct * noderightright = noderight->vm_avl_right;
 138                        struct vm_area_struct * noderightleft = noderight->vm_avl_left;
 139                        int heightrightleft = heightof(noderightleft);
 140                        if (heightof(noderightright) >= heightrightleft) {
 141                                node->vm_avl_right = noderightleft; noderight->vm_avl_left = node;
 142                                noderight->vm_avl_height = 1 + (node->vm_avl_height = 1 + heightrightleft);
 143                                *nodeplace = noderight;
 144                        } else {
 145                                noderight->vm_avl_left = noderightleft->vm_avl_right;
 146                                node->vm_avl_right = noderightleft->vm_avl_left;
 147                                noderightleft->vm_avl_right = noderight;
 148                                noderightleft->vm_avl_left = node;
 149                                noderight->vm_avl_height = node->vm_avl_height = heightrightleft;
 150                                noderightleft->vm_avl_height = heightright;
 151                                *nodeplace = noderightleft;
 152                        }
 153                }
 154                else {
 155                        int height = (heightleft<heightright ? heightright : heightleft) + 1;
 156                        if (height == node->vm_avl_height)
 157                                break;
 158                        node->vm_avl_height = height;
 159                }
 160        }
 161}
 162
 163/* Insert a node into a tree. */
 164static inline void avl_insert (struct vm_area_struct * new_node, struct vm_area_struct ** ptree)
 165{
 166        vm_avl_key_t key = new_node->vm_avl_key;
 167        struct vm_area_struct ** nodeplace = ptree;
 168        struct vm_area_struct ** stack[avl_maxheight];
 169        int stack_count = 0;
 170        struct vm_area_struct *** stack_ptr = &stack[0]; /* = &stack[stackcount] */
 171        for (;;) {
 172                struct vm_area_struct * node = *nodeplace;
 173                if (node == vm_avl_empty)
 174                        break;
 175                *stack_ptr++ = nodeplace; stack_count++;
 176                if (key < node->vm_avl_key)
 177                        nodeplace = &node->vm_avl_left;
 178                else
 179                        nodeplace = &node->vm_avl_right;
 180        }
 181        new_node->vm_avl_left = vm_avl_empty;
 182        new_node->vm_avl_right = vm_avl_empty;
 183        new_node->vm_avl_height = 1;
 184        *nodeplace = new_node;
 185        avl_rebalance(stack_ptr,stack_count);
 186}
 187
 188/* Insert a node into a tree, and
 189 * return the node to the left of it and the node to the right of it.
 190 */
 191static inline void avl_insert_neighbours (struct vm_area_struct * new_node, struct vm_area_struct ** ptree,
 192        struct vm_area_struct ** to_the_left, struct vm_area_struct ** to_the_right)
 193{
 194        vm_avl_key_t key = new_node->vm_avl_key;
 195        struct vm_area_struct ** nodeplace = ptree;
 196        struct vm_area_struct ** stack[avl_maxheight];
 197        int stack_count = 0;
 198        struct vm_area_struct *** stack_ptr = &stack[0]; /* = &stack[stackcount] */
 199        *to_the_left = *to_the_right = NULL;
 200        for (;;) {
 201                struct vm_area_struct * node = *nodeplace;
 202                if (node == vm_avl_empty)
 203                        break;
 204                *stack_ptr++ = nodeplace; stack_count++;
 205                if (key < node->vm_avl_key) {
 206                        *to_the_right = node;
 207                        nodeplace = &node->vm_avl_left;
 208                } else {
 209                        *to_the_left = node;
 210                        nodeplace = &node->vm_avl_right;
 211                }
 212        }
 213        new_node->vm_avl_left = vm_avl_empty;
 214        new_node->vm_avl_right = vm_avl_empty;
 215        new_node->vm_avl_height = 1;
 216        *nodeplace = new_node;
 217        avl_rebalance(stack_ptr,stack_count);
 218}
 219
 220/* Removes a node out of a tree. */
 221static void avl_remove (struct vm_area_struct * node_to_delete, struct vm_area_struct ** ptree)
 222{
 223        vm_avl_key_t key = node_to_delete->vm_avl_key;
 224        struct vm_area_struct ** nodeplace = ptree;
 225        struct vm_area_struct ** stack[avl_maxheight];
 226        int stack_count = 0;
 227        struct vm_area_struct *** stack_ptr = &stack[0]; /* = &stack[stackcount] */
 228        struct vm_area_struct ** nodeplace_to_delete;
 229        for (;;) {
 230                struct vm_area_struct * node = *nodeplace;
 231#ifdef DEBUG_AVL
 232                if (node == vm_avl_empty) {
 233                        /* what? node_to_delete not found in tree? */
 234                        printk("avl_remove: node to delete not found in tree\n");
 235                        return;
 236                }
 237#endif
 238                *stack_ptr++ = nodeplace; stack_count++;
 239                if (key == node->vm_avl_key)
 240                        break;
 241                if (key < node->vm_avl_key)
 242                        nodeplace = &node->vm_avl_left;
 243                else
 244                        nodeplace = &node->vm_avl_right;
 245        }
 246        nodeplace_to_delete = nodeplace;
 247        /* Have to remove node_to_delete = *nodeplace_to_delete. */
 248        if (node_to_delete->vm_avl_left == vm_avl_empty) {
 249                *nodeplace_to_delete = node_to_delete->vm_avl_right;
 250                stack_ptr--; stack_count--;
 251        } else {
 252                struct vm_area_struct *** stack_ptr_to_delete = stack_ptr;
 253                struct vm_area_struct ** nodeplace = &node_to_delete->vm_avl_left;
 254                struct vm_area_struct * node;
 255                for (;;) {
 256                        node = *nodeplace;
 257                        if (node->vm_avl_right == vm_avl_empty)
 258                                break;
 259                        *stack_ptr++ = nodeplace; stack_count++;
 260                        nodeplace = &node->vm_avl_right;
 261                }
 262                *nodeplace = node->vm_avl_left;
 263                /* node replaces node_to_delete */
 264                node->vm_avl_left = node_to_delete->vm_avl_left;
 265                node->vm_avl_right = node_to_delete->vm_avl_right;
 266                node->vm_avl_height = node_to_delete->vm_avl_height;
 267                *nodeplace_to_delete = node; /* replace node_to_delete */
 268                *stack_ptr_to_delete = &node->vm_avl_left; /* replace &node_to_delete->vm_avl_left */
 269        }
 270        avl_rebalance(stack_ptr,stack_count);
 271}
 272
 273#ifdef DEBUG_AVL
 274
 275/* print a list */
 276static void printk_list (struct vm_area_struct * vma)
 277{
 278        printk("[");
 279        while (vma) {
 280                printk("%08lX-%08lX", vma->vm_start, vma->vm_end);
 281                vma = vma->vm_next;
 282                if (!vma)
 283                        break;
 284                printk(" ");
 285        }
 286        printk("]");
 287}
 288
 289/* print a tree */
 290static void printk_avl (struct vm_area_struct * tree)
 291{
 292        if (tree != vm_avl_empty) {
 293                printk("(");
 294                if (tree->vm_avl_left != vm_avl_empty) {
 295                        printk_avl(tree->vm_avl_left);
 296                        printk("<");
 297                }
 298                printk("%08lX-%08lX", tree->vm_start, tree->vm_end);
 299                if (tree->vm_avl_right != vm_avl_empty) {
 300                        printk(">");
 301                        printk_avl(tree->vm_avl_right);
 302                }
 303                printk(")");
 304        }
 305}
 306
 307static char *avl_check_point = "somewhere";
 308
 309/* check a tree's consistency and balancing */
 310static void avl_checkheights (struct vm_area_struct * tree)
 311{
 312        int h, hl, hr;
 313
 314        if (tree == vm_avl_empty)
 315                return;
 316        avl_checkheights(tree->vm_avl_left);
 317        avl_checkheights(tree->vm_avl_right);
 318        h = tree->vm_avl_height;
 319        hl = heightof(tree->vm_avl_left);
 320        hr = heightof(tree->vm_avl_right);
 321        if ((h == hl+1) && (hr <= hl) && (hl <= hr+1))
 322                return;
 323        if ((h == hr+1) && (hl <= hr) && (hr <= hl+1))
 324                return;
 325        printk("%s: avl_checkheights: heights inconsistent\n",avl_check_point);
 326}
 327
 328/* check that all values stored in a tree are < key */
 329static void avl_checkleft (struct vm_area_struct * tree, vm_avl_key_t key)
 330{
 331        if (tree == vm_avl_empty)
 332                return;
 333        avl_checkleft(tree->vm_avl_left,key);
 334        avl_checkleft(tree->vm_avl_right,key);
 335        if (tree->vm_avl_key < key)
 336                return;
 337        printk("%s: avl_checkleft: left key %lu >= top key %lu\n",avl_check_point,tree->vm_avl_key,key);
 338}
 339
 340/* check that all values stored in a tree are > key */
 341static void avl_checkright (struct vm_area_struct * tree, vm_avl_key_t key)
 342{
 343        if (tree == vm_avl_empty)
 344                return;
 345        avl_checkright(tree->vm_avl_left,key);
 346        avl_checkright(tree->vm_avl_right,key);
 347        if (tree->vm_avl_key > key)
 348                return;
 349        printk("%s: avl_checkright: right key %lu <= top key %lu\n",avl_check_point,tree->vm_avl_key,key);
 350}
 351
 352/* check that all values are properly increasing */
 353static void avl_checkorder (struct vm_area_struct * tree)
 354{
 355        if (tree == vm_avl_empty)
 356                return;
 357        avl_checkorder(tree->vm_avl_left);
 358        avl_checkorder(tree->vm_avl_right);
 359        avl_checkleft(tree->vm_avl_left,tree->vm_avl_key);
 360        avl_checkright(tree->vm_avl_right,tree->vm_avl_key);
 361}
 362
 363/* all checks */
 364static void avl_check (struct task_struct * task, char *caller)
 365{
 366        avl_check_point = caller;
 367/*      printk("task \"%s\", %s\n",task->comm,caller); */
 368/*      printk("task \"%s\" list: ",task->comm); printk_list(task->mm->mmap); printk("\n"); */
 369/*      printk("task \"%s\" tree: ",task->comm); printk_avl(task->mm->mmap_avl); printk("\n"); */
 370        avl_checkheights(task->mm->mmap_avl);
 371        avl_checkorder(task->mm->mmap_avl);
 372}
 373
 374#endif
 375