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 }
208
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