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 corresponing 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  */
  75 void 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
  97 void 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
 113 void 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  */
 164 struct 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 }