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