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 * Despite being perfectly possible to perform ballooned pages migration, they
8 * make a special corner case to compaction scans because balloon pages are not
9 * enlisted at any LRU list like the other pages we do compact / migrate.
10 *
11 * As the page isolation scanning step a compaction thread does is a lockless
12 * procedure (from a page standpoint), it might bring some racy situations while
13 * performing balloon page compaction. In order to sort out these racy scenarios
14 * and safely perform balloon's page compaction and migration we must, always,
15 * ensure following these three simple rules:
16 *
17 * i. when updating a balloon's page ->mapping element, strictly do it under
18 * the following lock order, independently of the far superior
19 * locking scheme (lru_lock, balloon_lock):
20 * +-page_lock(page);
21 * +--spin_lock_irq(&b_dev_info->pages_lock);
22 * ... page->mapping updates here ...
23 *
24 * ii. before isolating or dequeueing a balloon page from the balloon device
25 * pages list, the page reference counter must be raised by one and the
26 * extra refcount must be dropped when the page is enqueued back into
27 * the balloon device page list, thus a balloon page keeps its reference
28 * counter raised only while it is under our special handling;
29 *
30 * iii. after the lockless scan step have selected a potential balloon page for
31 * isolation, re-test the PageBalloon mark and the PagePrivate flag
32 * under the proper page lock, to ensure isolating a valid balloon page
33 * (not yet isolated, nor under release procedure)
34 *
35 * iv. isolation or dequeueing procedure must clear PagePrivate flag under
36 * page lock together with removing page from balloon device page list.
37 *
38 * The functions provided by this interface are placed to help on coping with
39 * the aforementioned balloon page corner case, as well as to ensure the simple
40 * set of exposed rules are satisfied while we are dealing with balloon pages
41 * compaction / migration.
42 *
43 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
44 */
45 #ifndef _LINUX_BALLOON_COMPACTION_H
46 #define _LINUX_BALLOON_COMPACTION_H
47 #include <linux/pagemap.h>
48 #include <linux/page-flags.h>
49 #include <linux/migrate.h>
50 #include <linux/gfp.h>
51 #include <linux/err.h>
52 #include <linux/fs.h>
53 #include <linux/list.h>
54
55 /*
56 * Balloon device information descriptor.
57 * This struct is used to allow the common balloon compaction interface
58 * procedures to find the proper balloon device holding memory pages they'll
59 * have to cope for page compaction / migration, as well as it serves the
60 * balloon driver as a page book-keeper for its registered balloon devices.
61 */
62 struct balloon_dev_info {
63 unsigned long isolated_pages; /* # of isolated pages for migration */
64 spinlock_t pages_lock; /* Protection to pages list */
65 struct list_head pages; /* Pages enqueued & handled to Host */
66 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
67 struct page *page, enum migrate_mode mode);
68 struct inode *inode;
69 };
70
71 extern struct page *balloon_page_alloc(void);
72 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
73 struct page *page);
74 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
75
balloon_devinfo_init(struct balloon_dev_info * balloon)76 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
77 {
78 balloon->isolated_pages = 0;
79 spin_lock_init(&balloon->pages_lock);
80 INIT_LIST_HEAD(&balloon->pages);
81 balloon->migratepage = NULL;
82 balloon->inode = NULL;
83 }
84
85 #ifdef CONFIG_BALLOON_COMPACTION
86 extern const struct address_space_operations balloon_aops;
87 extern bool balloon_page_isolate(struct page *page,
88 isolate_mode_t mode);
89 extern void balloon_page_putback(struct page *page);
90 extern int balloon_page_migrate(struct address_space *mapping,
91 struct page *newpage,
92 struct page *page, enum migrate_mode mode);
93
94 /*
95 * balloon_page_insert - insert a page into the balloon's page list and make
96 * the page->private assignment accordingly.
97 * @balloon : pointer to balloon device
98 * @page : page to be assigned as a 'balloon page'
99 *
100 * Caller must ensure the page is locked and the spin_lock protecting balloon
101 * pages list is held before inserting a page into the balloon device.
102 */
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)103 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
104 struct page *page)
105 {
106 __SetPageBalloon(page);
107 __SetPageMovable(page, balloon->inode->i_mapping);
108 set_page_private(page, (unsigned long)balloon);
109 list_add(&page->lru, &balloon->pages);
110 }
111
112 /*
113 * balloon_page_delete - delete a page from balloon's page list and clear
114 * the page->private assignement accordingly.
115 * @page : page to be released from balloon's page list
116 *
117 * Caller must ensure the page is locked and the spin_lock protecting balloon
118 * pages list is held before deleting a page from the balloon device.
119 */
balloon_page_delete(struct page * page)120 static inline void balloon_page_delete(struct page *page)
121 {
122 __ClearPageBalloon(page);
123 __ClearPageMovable(page);
124 set_page_private(page, 0);
125 /*
126 * No touch page.lru field once @page has been isolated
127 * because VM is using the field.
128 */
129 if (!PageIsolated(page))
130 list_del(&page->lru);
131 }
132
133 /*
134 * balloon_page_device - get the b_dev_info descriptor for the balloon device
135 * that enqueues the given page.
136 */
balloon_page_device(struct page * page)137 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
138 {
139 return (struct balloon_dev_info *)page_private(page);
140 }
141
balloon_mapping_gfp_mask(void)142 static inline gfp_t balloon_mapping_gfp_mask(void)
143 {
144 return GFP_HIGHUSER_MOVABLE;
145 }
146
147 #else /* !CONFIG_BALLOON_COMPACTION */
148
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)149 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
150 struct page *page)
151 {
152 __SetPageBalloon(page);
153 list_add(&page->lru, &balloon->pages);
154 }
155
balloon_page_delete(struct page * page)156 static inline void balloon_page_delete(struct page *page)
157 {
158 __ClearPageBalloon(page);
159 list_del(&page->lru);
160 }
161
__is_movable_balloon_page(struct page * page)162 static inline bool __is_movable_balloon_page(struct page *page)
163 {
164 return false;
165 }
166
balloon_page_movable(struct page * page)167 static inline bool balloon_page_movable(struct page *page)
168 {
169 return false;
170 }
171
isolated_balloon_page(struct page * page)172 static inline bool isolated_balloon_page(struct page *page)
173 {
174 return false;
175 }
176
balloon_page_isolate(struct page * page)177 static inline bool balloon_page_isolate(struct page *page)
178 {
179 return false;
180 }
181
balloon_page_putback(struct page * page)182 static inline void balloon_page_putback(struct page *page)
183 {
184 return;
185 }
186
balloon_page_migrate(struct page * newpage,struct page * page,enum migrate_mode mode)187 static inline int balloon_page_migrate(struct page *newpage,
188 struct page *page, enum migrate_mode mode)
189 {
190 return 0;
191 }
192
balloon_mapping_gfp_mask(void)193 static inline gfp_t balloon_mapping_gfp_mask(void)
194 {
195 return GFP_HIGHUSER;
196 }
197
198 #endif /* CONFIG_BALLOON_COMPACTION */
199
200 /*
201 * balloon_page_push - insert a page into a page list.
202 * @head : pointer to list
203 * @page : page to be added
204 *
205 * Caller must ensure the page is private and protect the list.
206 */
balloon_page_push(struct list_head * pages,struct page * page)207 static inline void balloon_page_push(struct list_head *pages, struct page *page)
208 {
209 list_add(&page->lru, pages);
210 }
211
212 /*
213 * balloon_page_pop - remove a page from a page list.
214 * @head : pointer to list
215 * @page : page to be added
216 *
217 * Caller must ensure the page is private and protect the list.
218 */
balloon_page_pop(struct list_head * pages)219 static inline struct page *balloon_page_pop(struct list_head *pages)
220 {
221 struct page *page = list_first_entry_or_null(pages, struct page, lru);
222
223 if (!page)
224 return NULL;
225
226 list_del(&page->lru);
227 return page;
228 }
229 #endif /* _LINUX_BALLOON_COMPACTION_H */
230