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 #include <linux/mem_relinquish.h>
47
48 /*
49 * Balloon device information descriptor.
50 * This struct is used to allow the common balloon compaction interface
51 * procedures to find the proper balloon device holding memory pages they'll
52 * have to cope for page compaction / migration, as well as it serves the
53 * balloon driver as a page book-keeper for its registered balloon devices.
54 */
55 struct balloon_dev_info {
56 unsigned long isolated_pages; /* # of isolated pages for migration */
57 spinlock_t pages_lock; /* Protection to pages list */
58 struct list_head pages; /* Pages enqueued & handled to Host */
59 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
60 struct page *page, enum migrate_mode mode);
61 struct inode *inode;
62 };
63
64 extern struct page *balloon_page_alloc(void);
65 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
66 struct page *page);
67 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
68 extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
69 struct list_head *pages);
70 extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
71 struct list_head *pages, size_t n_req_pages);
72
balloon_devinfo_init(struct balloon_dev_info * balloon)73 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
74 {
75 balloon->isolated_pages = 0;
76 spin_lock_init(&balloon->pages_lock);
77 INIT_LIST_HEAD(&balloon->pages);
78 balloon->migratepage = NULL;
79 balloon->inode = NULL;
80 }
81
82 #ifdef CONFIG_BALLOON_COMPACTION
83 extern const struct address_space_operations balloon_aops;
84 extern bool balloon_page_isolate(struct page *page,
85 isolate_mode_t mode);
86 extern void balloon_page_putback(struct page *page);
87 extern int balloon_page_migrate(struct address_space *mapping,
88 struct page *newpage,
89 struct page *page, enum migrate_mode mode);
90
91 /*
92 * balloon_page_insert - insert a page into the balloon's page list and make
93 * the page->private assignment accordingly.
94 * @balloon : pointer to balloon device
95 * @page : page to be assigned as a 'balloon page'
96 *
97 * Caller must ensure the page is locked and the spin_lock protecting balloon
98 * pages list is held before inserting a page into the balloon device.
99 */
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)100 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
101 struct page *page)
102 {
103 __SetPageOffline(page);
104 __SetPageMovable(page, balloon->inode->i_mapping);
105 set_page_private(page, (unsigned long)balloon);
106 list_add(&page->lru, &balloon->pages);
107 page_relinquish(page);
108 }
109
110 /*
111 * balloon_page_delete - delete a page from balloon's page list and clear
112 * the page->private assignement accordingly.
113 * @page : page to be released from balloon's page list
114 *
115 * Caller must ensure the page is locked and the spin_lock protecting balloon
116 * pages list is held before deleting a page from the balloon device.
117 */
balloon_page_delete(struct page * page)118 static inline void balloon_page_delete(struct page *page)
119 {
120 __ClearPageOffline(page);
121 __ClearPageMovable(page);
122 set_page_private(page, 0);
123 /*
124 * No touch page.lru field once @page has been isolated
125 * because VM is using the field.
126 */
127 if (!PageIsolated(page))
128 list_del(&page->lru);
129 }
130
131 /*
132 * balloon_page_device - get the b_dev_info descriptor for the balloon device
133 * that enqueues the given page.
134 */
balloon_page_device(struct page * page)135 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
136 {
137 return (struct balloon_dev_info *)page_private(page);
138 }
139
balloon_mapping_gfp_mask(void)140 static inline gfp_t balloon_mapping_gfp_mask(void)
141 {
142 return GFP_HIGHUSER_MOVABLE;
143 }
144
145 #else /* !CONFIG_BALLOON_COMPACTION */
146
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)147 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
148 struct page *page)
149 {
150 __SetPageOffline(page);
151 list_add(&page->lru, &balloon->pages);
152 page_relinquish(page);
153 }
154
balloon_page_delete(struct page * page)155 static inline void balloon_page_delete(struct page *page)
156 {
157 __ClearPageOffline(page);
158 list_del(&page->lru);
159 }
160
balloon_page_isolate(struct page * page)161 static inline bool balloon_page_isolate(struct page *page)
162 {
163 return false;
164 }
165
balloon_page_putback(struct page * page)166 static inline void balloon_page_putback(struct page *page)
167 {
168 return;
169 }
170
balloon_page_migrate(struct page * newpage,struct page * page,enum migrate_mode mode)171 static inline int balloon_page_migrate(struct page *newpage,
172 struct page *page, enum migrate_mode mode)
173 {
174 return 0;
175 }
176
balloon_mapping_gfp_mask(void)177 static inline gfp_t balloon_mapping_gfp_mask(void)
178 {
179 return GFP_HIGHUSER;
180 }
181
182 #endif /* CONFIG_BALLOON_COMPACTION */
183
184 /*
185 * balloon_page_push - insert a page into a page list.
186 * @head : pointer to list
187 * @page : page to be added
188 *
189 * Caller must ensure the page is private and protect the list.
190 */
balloon_page_push(struct list_head * pages,struct page * page)191 static inline void balloon_page_push(struct list_head *pages, struct page *page)
192 {
193 list_add(&page->lru, pages);
194 }
195
196 /*
197 * balloon_page_pop - remove a page from a page list.
198 * @head : pointer to list
199 * @page : page to be added
200 *
201 * Caller must ensure the page is private and protect the list.
202 */
balloon_page_pop(struct list_head * pages)203 static inline struct page *balloon_page_pop(struct list_head *pages)
204 {
205 struct page *page = list_first_entry_or_null(pages, struct page, lru);
206
207 if (!page)
208 return NULL;
209
210 list_del(&page->lru);
211 return page;
212 }
213 #endif /* _LINUX_BALLOON_COMPACTION_H */
214