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