LXR linux/mm/prio

   1/*
   2 * mm/prio_tree.c - priority search tree for mapping->i_mmap
   3 *
   4 * Copyright (C) 2004, Rajesh Venkatasubramanian <vrajesh@umich.edu>
   5 *
   6 * This file is released under the GPL v2.
   7 *
   8 * Based on the radix priority search tree proposed by Edward M. McCreight
   9 * SIAM Journal of Computing, vol. 14, no.2, pages 257-276, May 1985
  10 *
  11 * 02Feb2004    Initial version
  12 */
  13
  14#include <linux/mm.h>
  15#include <linux/prio_tree.h>
  16
  17/*
  18 * See lib/prio_tree.c for details on the general radix priority search tree
  19 * code.
  20 */
  21
  22/*
  23 * The following #defines are mirrored from lib/prio_tree.c. They're only used
  24 * for debugging, and should be removed (along with the debugging code using
  25 * them) when switching also VMAs to the regular prio_tree code.
  26 */
  27
  28#define RADIX_INDEX(vma)  ((vma)->vm_pgoff)
  29#define VMA_SIZE(vma)     (((vma)->vm_end - (vma)->vm_start) >> PAGE_SHIFT)
  30/* avoid overflow */
  31#define HEAP_INDEX(vma)   ((vma)->vm_pgoff + (VMA_SIZE(vma) - 1))
  32
  33/*
  34 * Radix priority search tree for address_space->i_mmap
  35 *
  36 * For each vma that map a unique set of file pages i.e., unique [radix_index,
  37 * heap_index] value, we have a corresponding priority search tree node. If
  38 * multiple vmas have identical [radix_index, heap_index] value, then one of
  39 * them is used as a tree node and others are stored in a vm_set list. The tree
  40 * node points to the first vma (head) of the list using vm_set.head.
  41 *
  42 * prio_tree_root
  43 *      |
  44 *      A       vm_set.head
  45 *     / \      /
  46 *    L   R -> H-I-J-K-M-N-O-P-Q-S
  47 *    ^   ^    <-- vm_set.list -->
  48 *  tree nodes
  49 *
  50 * We need some way to identify whether a vma is a tree node, head of a vm_set
  51 * list, or just a member of a vm_set list. We cannot use vm_flags to store
  52 * such information. The reason is, in the above figure, it is possible that
  53 * vm_flags' of R and H are covered by the different mmap_sems. When R is
  54 * removed under R->mmap_sem, H replaces R as a tree node. Since we do not hold
  55 * H->mmap_sem, we cannot use H->vm_flags for marking that H is a tree node now.
  56 * That's why some trick involving shared.vm_set.parent is used for identifying
  57 * tree nodes and list head nodes.
  58 *
  59 * vma radix priority search tree node rules:
  60 *
  61 * vma->shared.vm_set.parent != NULL    ==> a tree node
  62 *      vma->shared.vm_set.head != NULL ==> list of others mapping same range
  63 *      vma->shared.vm_set.head == NULL ==> no others map the same range
  64 *
  65 * vma->shared.vm_set.parent == NULL
  66 *      vma->shared.vm_set.head != NULL ==> list head of vmas mapping same range
  67 *      vma->shared.vm_set.head == NULL ==> a list node
  68 */
  69
  70/*
  71 * Add a new vma known to map the same set of pages as the old vma:
  72 * useful for fork's dup_mmap as well as vma_prio_tree_insert below.
  73 * Note that it just happens to work correctly on i_mmap_nonlinear too.
  74 */
  75void vma_prio_tree_add(struct vm_area_struct *vma, struct vm_area_struct *old)
  76{
  77        /* Leave these BUG_ONs till prio_tree patch stabilizes */
  78        BUG_ON(RADIX_INDEX(vma) != RADIX_INDEX(old));
  79        BUG_ON(HEAP_INDEX(vma) != HEAP_INDEX(old));
  80
  81        vma->shared.vm_set.head = NULL;
  82        vma->shared.vm_set.parent = NULL;
  83
  84        if (!old->shared.vm_set.parent)
  85                list_add(&vma->shared.vm_set.list,
  86                                &old->shared.vm_set.list);
  87        else if (old->shared.vm_set.head)
  88                list_add_tail(&vma->shared.vm_set.list,
  89                                &old->shared.vm_set.head->shared.vm_set.list);
  90        else {
  91                INIT_LIST_HEAD(&vma->shared.vm_set.list);
  92                vma->shared.vm_set.head = old;
  93                old->shared.vm_set.head = vma;
  94        }
  95}
  96
  97void vma_prio_tree_insert(struct vm_area_struct *vma,
  98                          struct prio_tree_root *root)
  99{
 100        struct prio_tree_node *ptr;
 101        struct vm_area_struct *old;
 102
 103        vma->shared.vm_set.head = NULL;
 104
 105        ptr = raw_prio_tree_insert(root, &vma->shared.prio_tree_node);
 106        if (ptr != (struct prio_tree_node *) &vma->shared.prio_tree_node) {
 107                old = prio_tree_entry(ptr, struct vm_area_struct,
 108                                        shared.prio_tree_node);
 109                vma_prio_tree_add(vma, old);
 110        }
 111}
 112
 113void vma_prio_tree_remove(struct vm_area_struct *vma,
 114                          struct prio_tree_root *root)
 115{
 116        struct vm_area_struct *node, *head, *new_head;
 117
 118        if (!vma->shared.vm_set.head) {
 119                if (!vma->shared.vm_set.parent)
 120                        list_del_init(&vma->shared.vm_set.list);
 121                else
 122                        raw_prio_tree_remove(root, &vma->shared.prio_tree_node);
 123        } else {
 124                /* Leave this BUG_ON till prio_tree patch stabilizes */
 125                BUG_ON(vma->shared.vm_set.head->shared.vm_set.head != vma);
 126                if (vma->shared.vm_set.parent) {
 127                        head = vma->shared.vm_set.head;
 128                        if (!list_empty(&head->shared.vm_set.list)) {
 129                                new_head = list_entry(
 130                                        head->shared.vm_set.list.next,
 131                                        struct vm_area_struct,
 132                                        shared.vm_set.list);
 133                                list_del_init(&head->shared.vm_set.list);
 134                        } else
 135                                new_head = NULL;
 136
 137                        raw_prio_tree_replace(root, &vma->shared.prio_tree_node,
 138                                        &head->shared.prio_tree_node);
 139                        head->shared.vm_set.head = new_head;
 140                        if (new_head)
 141                                new_head->shared.vm_set.head = head;
 142
 143                } else {
 144                        node = vma->shared.vm_set.head;
 145                        if (!list_empty(&vma->shared.vm_set.list)) {
 146                                new_head = list_entry(
 147                                        vma->shared.vm_set.list.next,
 148                                        struct vm_area_struct,
 149                                        shared.vm_set.list);
 150                                list_del_init(&vma->shared.vm_set.list);
 151                                node->shared.vm_set.head = new_head;
 152                                new_head->shared.vm_set.head = node;
 153                        } else
 154                                node->shared.vm_set.head = NULL;
 155                }
 156        }
 157}
 158
 159/*
 160 * Helper function to enumerate vmas that map a given file page or a set of
 161 * contiguous file pages. The function returns vmas that at least map a single
 162 * page in the given range of contiguous file pages.
 163 */
 164struct vm_area_struct *vma_prio_tree_next(struct vm_area_struct *vma,
 165                                        struct prio_tree_iter *iter)
 166{
 167        struct prio_tree_node *ptr;
 168        struct vm_area_struct *next;
 169
 170        if (!vma) {
 171                /*
 172                 * First call is with NULL vma
 173                 */
 174                ptr = prio_tree_next(iter);
 175                if (ptr) {
 176                        next = prio_tree_entry(ptr, struct vm_area_struct,
 177                                                shared.prio_tree_node);
 178                        prefetch(next->shared.vm_set.head);
 179                        return next;
 180                } else
 181                        return NULL;
 182        }
 183
 184        if (vma->shared.vm_set.parent) {
 185                if (vma->shared.vm_set.head) {
 186                        next = vma->shared.vm_set.head;
 187                        prefetch(next->shared.vm_set.list.next);
 188                        return next;
 189                }
 190        } else {
 191                next = list_entry(vma->shared.vm_set.list.next,
 192                                struct vm_area_struct, shared.vm_set.list);
 193                if (!next->shared.vm_set.head) {
 194                        prefetch(next->shared.vm_set.list.next);
 195                        return next;
 196                }
 197        }
 198
 199        ptr = prio_tree_next(iter);
 200        if (ptr) {
 201                next = prio_tree_entry(ptr, struct vm_area_struct,
 202                                        shared.prio_tree_node);
 203                prefetch(next->shared.vm_set.head);
 204                return next;
 205        } else
 206                return NULL;
 207}
 208