Root/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 */
76void 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
98void 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
114void 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 */
165struct 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}
209

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