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1 | /* | |
2 | * include/linux/balloon_compaction.h | |
3 | * | |
4 | * Common interface definitions for making balloon pages movable by compaction. | |
5 | * | |
6 | * Despite being perfectly possible to perform ballooned pages migration, they | |
7 | * make a special corner case to compaction scans because balloon pages are not | |
8 | * enlisted at any LRU list like the other pages we do compact / migrate. | |
9 | * | |
10 | * As the page isolation scanning step a compaction thread does is a lockless | |
11 | * procedure (from a page standpoint), it might bring some racy situations while | |
12 | * performing balloon page compaction. In order to sort out these racy scenarios | |
13 | * and safely perform balloon's page compaction and migration we must, always, | |
14 | * ensure following these three simple rules: | |
15 | * | |
16 | * i. when updating a balloon's page ->mapping element, strictly do it under | |
17 | * the following lock order, independently of the far superior | |
18 | * locking scheme (lru_lock, balloon_lock): | |
19 | * +-page_lock(page); | |
20 | * +--spin_lock_irq(&b_dev_info->pages_lock); | |
21 | * ... page->mapping updates here ... | |
22 | * | |
23 | * ii. before isolating or dequeueing a balloon page from the balloon device | |
24 | * pages list, the page reference counter must be raised by one and the | |
25 | * extra refcount must be dropped when the page is enqueued back into | |
26 | * the balloon device page list, thus a balloon page keeps its reference | |
27 | * counter raised only while it is under our special handling; | |
28 | * | |
29 | * iii. after the lockless scan step have selected a potential balloon page for | |
30 | * isolation, re-test the PageBalloon mark and the PagePrivate flag | |
31 | * under the proper page lock, to ensure isolating a valid balloon page | |
32 | * (not yet isolated, nor under release procedure) | |
33 | * | |
34 | * iv. isolation or dequeueing procedure must clear PagePrivate flag under | |
35 | * page lock together with removing page from balloon device page list. | |
36 | * | |
37 | * The functions provided by this interface are placed to help on coping with | |
38 | * the aforementioned balloon page corner case, as well as to ensure the simple | |
39 | * set of exposed rules are satisfied while we are dealing with balloon pages | |
40 | * compaction / migration. | |
41 | * | |
42 | * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com> | |
43 | */ | |
44 | #ifndef _LINUX_BALLOON_COMPACTION_H | |
45 | #define _LINUX_BALLOON_COMPACTION_H | |
46 | #include <linux/pagemap.h> | |
47 | #include <linux/page-flags.h> | |
48 | #include <linux/migrate.h> | |
49 | #include <linux/gfp.h> | |
50 | #include <linux/err.h> | |
51 | #include <linux/fs.h> | |
52 | ||
53 | /* | |
54 | * Balloon device information descriptor. | |
55 | * This struct is used to allow the common balloon compaction interface | |
56 | * procedures to find the proper balloon device holding memory pages they'll | |
57 | * have to cope for page compaction / migration, as well as it serves the | |
58 | * balloon driver as a page book-keeper for its registered balloon devices. | |
59 | */ | |
60 | struct balloon_dev_info { | |
61 | unsigned long isolated_pages; /* # of isolated pages for migration */ | |
62 | spinlock_t pages_lock; /* Protection to pages list */ | |
63 | struct list_head pages; /* Pages enqueued & handled to Host */ | |
64 | int (*migratepage)(struct balloon_dev_info *, struct page *newpage, | |
65 | struct page *page, enum migrate_mode mode); | |
66 | struct inode *inode; | |
67 | }; | |
68 | ||
69 | extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info); | |
70 | extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info); | |
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 | __SetPageBalloon(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 | __ClearPageBalloon(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 | __SetPageBalloon(page); | |
149 | list_add(&page->lru, &balloon->pages); | |
150 | } | |
151 | ||
152 | static inline void balloon_page_delete(struct page *page) | |
153 | { | |
154 | __ClearPageBalloon(page); | |
155 | list_del(&page->lru); | |
156 | } | |
157 | ||
158 | static inline bool __is_movable_balloon_page(struct page *page) | |
159 | { | |
160 | return false; | |
161 | } | |
162 | ||
163 | static inline bool balloon_page_movable(struct page *page) | |
164 | { | |
165 | return false; | |
166 | } | |
167 | ||
168 | static inline bool isolated_balloon_page(struct page *page) | |
169 | { | |
170 | return false; | |
171 | } | |
172 | ||
173 | static inline bool balloon_page_isolate(struct page *page) | |
174 | { | |
175 | return false; | |
176 | } | |
177 | ||
178 | static inline void balloon_page_putback(struct page *page) | |
179 | { | |
180 | return; | |
181 | } | |
182 | ||
183 | static inline int balloon_page_migrate(struct page *newpage, | |
184 | struct page *page, enum migrate_mode mode) | |
185 | { | |
186 | return 0; | |
187 | } | |
188 | ||
189 | static inline gfp_t balloon_mapping_gfp_mask(void) | |
190 | { | |
191 | return GFP_HIGHUSER; | |
192 | } | |
193 | ||
194 | #endif /* CONFIG_BALLOON_COMPACTION */ | |
195 | #endif /* _LINUX_BALLOON_COMPACTION_H */ |