1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * include/linux/balloon_compaction.h
4 *
5 * Common interface definitions for making balloon pages movable by compaction.
6 *
7 * Balloon page migration makes use of the general non-lru movable page
8 * feature.
9 *
10 * page->private is used to reference the responsible balloon device.
11 * page->mapping is used in context of non-lru page migration to reference
12 * the address space operations for page isolation/migration/compaction.
13 *
14 * As the page isolation scanning step a compaction thread does is a lockless
15 * procedure (from a page standpoint), it might bring some racy situations while
16 * performing balloon page compaction. In order to sort out these racy scenarios
17 * and safely perform balloon's page compaction and migration we must, always,
18 * ensure following these simple rules:
19 *
20 * i. when updating a balloon's page ->mapping element, strictly do it under
21 * the following lock order, independently of the far superior
22 * locking scheme (lru_lock, balloon_lock):
23 * +-page_lock(page);
24 * +--spin_lock_irq(&b_dev_info->pages_lock);
25 * ... page->mapping updates here ...
26 *
27 * ii. isolation or dequeueing procedure must remove the page from balloon
28 * device page list under b_dev_info->pages_lock.
29 *
30 * The functions provided by this interface are placed to help on coping with
31 * the aforementioned balloon page corner case, as well as to ensure the simple
32 * set of exposed rules are satisfied while we are dealing with balloon pages
33 * compaction / migration.
34 *
35 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
36 */
37 #ifndef _LINUX_BALLOON_COMPACTION_H
38 #define _LINUX_BALLOON_COMPACTION_H
39 #include <linux/pagemap.h>
40 #include <linux/page-flags.h>
41 #include <linux/migrate.h>
42 #include <linux/gfp.h>
43 #include <linux/err.h>
44 #include <linux/fs.h>
45 #include <linux/list.h>
46
47 /*
48 * Balloon device information descriptor.
49 * This struct is used to allow the common balloon compaction interface
50 * procedures to find the proper balloon device holding memory pages they'll
51 * have to cope for page compaction / migration, as well as it serves the
52 * balloon driver as a page book-keeper for its registered balloon devices.
53 */
54 struct balloon_dev_info {
55 unsigned long isolated_pages; /* # of isolated pages for migration */
56 spinlock_t pages_lock; /* Protection to pages list */
57 struct list_head pages; /* Pages enqueued & handled to Host */
58 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
59 struct page *page, enum migrate_mode mode);
60 struct inode *inode;
61 };
62
63 extern struct page *balloon_page_alloc(void);
64 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
65 struct page *page);
66 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
67 extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
68 struct list_head *pages);
69 extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
70 struct list_head *pages, size_t n_req_pages);
71
72 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
73 {
74 balloon->isolated_pages = 0;
75 spin_lock_init(&balloon->pages_lock);
76 INIT_LIST_HEAD(&balloon->pages);
77 balloon->migratepage = NULL;
78 balloon->inode = NULL;
79 }
80
81 #ifdef CONFIG_BALLOON_COMPACTION
82 extern const struct address_space_operations balloon_aops;
83 extern bool balloon_page_isolate(struct page *page,
84 isolate_mode_t mode);
85 extern void balloon_page_putback(struct page *page);
86 extern int balloon_page_migrate(struct address_space *mapping,
87 struct page *newpage,
88 struct page *page, enum migrate_mode mode);
89
90 /*
91 * balloon_page_insert - insert a page into the balloon's page list and make
92 * the page->private assignment accordingly.
93 * @balloon : pointer to balloon device
94 * @page : page to be assigned as a 'balloon page'
95 *
96 * Caller must ensure the page is locked and the spin_lock protecting balloon
97 * pages list is held before inserting a page into the balloon device.
98 */
99 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
100 struct page *page)
101 {
102 __SetPageOffline(page);
103 __SetPageMovable(page, balloon->inode->i_mapping);
104 set_page_private(page, (unsigned long)balloon);
105 list_add(&page->lru, &balloon->pages);
106 }
107
108 /*
109 * balloon_page_delete - delete a page from balloon's page list and clear
110 * the page->private assignement accordingly.
111 * @page : page to be released from balloon's page list
112 *
113 * Caller must ensure the page is locked and the spin_lock protecting balloon
114 * pages list is held before deleting a page from the balloon device.
115 */
116 static inline void balloon_page_delete(struct page *page)
117 {
118 __ClearPageOffline(page);
119 __ClearPageMovable(page);
120 set_page_private(page, 0);
121 /*
122 * No touch page.lru field once @page has been isolated
123 * because VM is using the field.
124 */
125 if (!PageIsolated(page))
126 list_del(&page->lru);
127 }
128
129 /*
130 * balloon_page_device - get the b_dev_info descriptor for the balloon device
131 * that enqueues the given page.
132 */
133 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
134 {
135 return (struct balloon_dev_info *)page_private(page);
136 }
137
138 static inline gfp_t balloon_mapping_gfp_mask(void)
139 {
140 return GFP_HIGHUSER_MOVABLE;
141 }
142
143 #else /* !CONFIG_BALLOON_COMPACTION */
144
145 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
146 struct page *page)
147 {
148 __SetPageOffline(page);
149 list_add(&page->lru, &balloon->pages);
150 }
151
152 static inline void balloon_page_delete(struct page *page)
153 {
154 __ClearPageOffline(page);
155 list_del(&page->lru);
156 }
157
158 static inline bool balloon_page_isolate(struct page *page)
159 {
160 return false;
161 }
162
163 static inline void balloon_page_putback(struct page *page)
164 {
165 return;
166 }
167
168 static inline int balloon_page_migrate(struct page *newpage,
169 struct page *page, enum migrate_mode mode)
170 {
171 return 0;
172 }
173
174 static inline gfp_t balloon_mapping_gfp_mask(void)
175 {
176 return GFP_HIGHUSER;
177 }
178
179 #endif /* CONFIG_BALLOON_COMPACTION */
180
181 /*
182 * balloon_page_push - insert a page into a page list.
183 * @head : pointer to list
184 * @page : page to be added
185 *
186 * Caller must ensure the page is private and protect the list.
187 */
188 static inline void balloon_page_push(struct list_head *pages, struct page *page)
189 {
190 list_add(&page->lru, pages);
191 }
192
193 /*
194 * balloon_page_pop - remove a page from a page list.
195 * @head : pointer to list
196 * @page : page to be added
197 *
198 * Caller must ensure the page is private and protect the list.
199 */
200 static inline struct page *balloon_page_pop(struct list_head *pages)
201 {
202 struct page *page = list_first_entry_or_null(pages, struct page, lru);
203
204 if (!page)
205 return NULL;
206
207 list_del(&page->lru);
208 return page;
209 }
210 #endif /* _LINUX_BALLOON_COMPACTION_H */