mm/prio_tree.c

   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 static void dump_vma(struct vm_area_struct *vma)
  71 {
  72         void **ptr = (void **) vma;
  73         int i;
  74
  75         printk("vm_area_struct at %p:", ptr);
  76         for (i = 0; i < sizeof(*vma)/sizeof(*ptr); i++, ptr++) {
  77                 if (!(i & 3))
  78                         printk("\n");
  79                 printk(" %p", *ptr);
  80         }
  81         printk("\n");
  82 }
  83
  84 /*
  85  * Add a new vma known to map the same set of pages as the old vma:
  86  * useful for fork's dup_mmap as well as vma_prio_tree_insert below.
  87  * Note that it just happens to work correctly on i_mmap_nonlinear too.
  88  */
  89 void vma_prio_tree_add(struct vm_area_struct *vma, struct vm_area_struct *old)
  90 {
  91         vma->shared.vm_set.head = NULL;
  92         vma->shared.vm_set.parent = NULL;
  93
  94         if (WARN_ON(RADIX_INDEX(vma) != RADIX_INDEX(old) ||
  95                     HEAP_INDEX(vma)  != HEAP_INDEX(old))) {
  96                 /*
  97                  * This should never happen, yet it has been seen a few times:
  98                  * we cannot say much about it without seeing the vma contents.
  99                  */
 100                 dump_vma(vma);
 101                 dump_vma(old);
 102                 /*
 103                  * Don't try to link this (corrupt?) vma into the (corrupt?)
 104                  * prio_tree, but arrange for its removal to succeed later.
 105                  */
 106                 INIT_LIST_HEAD(&vma->shared.vm_set.list);
 107         } else if (!old->shared.vm_set.parent)
 108                 list_add(&vma->shared.vm_set.list,
 109                                 &old->shared.vm_set.list);
 110         else if (old->shared.vm_set.head)
 111                 list_add_tail(&vma->shared.vm_set.list,
 112                                 &old->shared.vm_set.head->shared.vm_set.list);
 113         else {
 114                 INIT_LIST_HEAD(&vma->shared.vm_set.list);
 115                 vma->shared.vm_set.head = old;
 116                 old->shared.vm_set.head = vma;
 117         }
 118 }
 119
 120 void vma_prio_tree_insert(struct vm_area_struct *vma,
 121                           struct prio_tree_root *root)
 122 {
 123         struct prio_tree_node *ptr;
 124         struct vm_area_struct *old;
 125
 126         vma->shared.vm_set.head = NULL;
 127
 128         ptr = raw_prio_tree_insert(root, &vma->shared.prio_tree_node);
 129         if (ptr != (struct prio_tree_node *) &vma->shared.prio_tree_node) {
 130                 old = prio_tree_entry(ptr, struct vm_area_struct,
 131                                         shared.prio_tree_node);
 132                 vma_prio_tree_add(vma, old);
 133         }
 134 }
 135
 136 void vma_prio_tree_remove(struct vm_area_struct *vma,
 137                           struct prio_tree_root *root)
 138 {
 139         struct vm_area_struct *node, *head, *new_head;
 140
 141         if (!vma->shared.vm_set.head) {
 142                 if (!vma->shared.vm_set.parent)
 143                         list_del_init(&vma->shared.vm_set.list);
 144                 else
 145                         raw_prio_tree_remove(root, &vma->shared.prio_tree_node);
 146         } else {
 147                 /* Leave this BUG_ON till prio_tree patch stabilizes */
 148                 BUG_ON(vma->shared.vm_set.head->shared.vm_set.head != vma);
 149                 if (vma->shared.vm_set.parent) {
 150                         head = vma->shared.vm_set.head;
 151                         if (!list_empty(&head->shared.vm_set.list)) {
 152                                 new_head = list_entry(
 153                                         head->shared.vm_set.list.next,
 154                                         struct vm_area_struct,
 155                                         shared.vm_set.list);
 156                                 list_del_init(&head->shared.vm_set.list);
 157                         } else
 158                                 new_head = NULL;
 159
 160                         raw_prio_tree_replace(root, &vma->shared.prio_tree_node,
 161                                         &head->shared.prio_tree_node);
 162                         head->shared.vm_set.head = new_head;
 163                         if (new_head)
 164                                 new_head->shared.vm_set.head = head;
 165
 166                 } else {
 167                         node = vma->shared.vm_set.head;
 168                         if (!list_empty(&vma->shared.vm_set.list)) {
 169                                 new_head = list_entry(
 170                                         vma->shared.vm_set.list.next,
 171                                         struct vm_area_struct,
 172                                         shared.vm_set.list);
 173                                 list_del_init(&vma->shared.vm_set.list);
 174                                 node->shared.vm_set.head = new_head;
 175                                 new_head->shared.vm_set.head = node;
 176                         } else
 177                                 node->shared.vm_set.head = NULL;
 178                 }
 179         }
 180 }
 181
 182 /*
 183  * Helper function to enumerate vmas that map a given file page or a set of
 184  * contiguous file pages. The function returns vmas that at least map a single
 185  * page in the given range of contiguous file pages.
 186  */
 187 struct vm_area_struct *vma_prio_tree_next(struct vm_area_struct *vma,
 188                                         struct prio_tree_iter *iter)
 189 {
 190         struct prio_tree_node *ptr;
 191         struct vm_area_struct *next;
 192
 193         if (!vma) {
 194                 /*
 195                  * First call is with NULL vma
 196                  */
 197                 ptr = prio_tree_next(iter);
 198                 if (ptr) {
 199                         next = prio_tree_entry(ptr, struct vm_area_struct,
 200                                                 shared.prio_tree_node);
 201                         prefetch(next->shared.vm_set.head);
 202                         return next;
 203                 } else
 204                         return NULL;
 205         }
 206
 207         if (vma->shared.vm_set.parent) {
 208                 if (vma->shared.vm_set.head) {
 209                         next = vma->shared.vm_set.head;
 210                         prefetch(next->shared.vm_set.list.next);
 211                         return next;
 212                 }
 213         } else {
 214                 next = list_entry(vma->shared.vm_set.list.next,
 215                                 struct vm_area_struct, shared.vm_set.list);
 216                 if (!next->shared.vm_set.head) {
 217                         prefetch(next->shared.vm_set.list.next);
 218                         return next;
 219                 }
 220         }
 221
 222         ptr = prio_tree_next(iter);
 223         if (ptr) {
 224                 next = prio_tree_entry(ptr, struct vm_area_struct,
 225                                         shared.prio_tree_node);
 226                 prefetch(next->shared.vm_set.head);
 227                 return next;
 228         } else
 229                 return NULL;
 230 }