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18468d93 RA |
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 | |
d6d86c0a | 30 | * isolation, re-test the PageBalloon mark and the PagePrivate flag |
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31 | * under the proper page lock, to ensure isolating a valid balloon page |
32 | * (not yet isolated, nor under release procedure) | |
33 | * | |
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34 | * iv. isolation or dequeueing procedure must clear PagePrivate flag under |
35 | * page lock together with removing page from balloon device page list. | |
36 | * | |
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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 | ||
52 | /* | |
53 | * Balloon device information descriptor. | |
54 | * This struct is used to allow the common balloon compaction interface | |
55 | * procedures to find the proper balloon device holding memory pages they'll | |
56 | * have to cope for page compaction / migration, as well as it serves the | |
57 | * balloon driver as a page book-keeper for its registered balloon devices. | |
58 | */ | |
59 | struct balloon_dev_info { | |
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60 | unsigned long isolated_pages; /* # of isolated pages for migration */ |
61 | spinlock_t pages_lock; /* Protection to pages list */ | |
62 | struct list_head pages; /* Pages enqueued & handled to Host */ | |
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63 | int (*migratepage)(struct balloon_dev_info *, struct page *newpage, |
64 | struct page *page, enum migrate_mode mode); | |
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65 | }; |
66 | ||
67 | extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info); | |
68 | extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info); | |
18468d93 | 69 | |
9d1ba805 | 70 | static inline void balloon_devinfo_init(struct balloon_dev_info *balloon) |
18468d93 | 71 | { |
9d1ba805 KK |
72 | balloon->isolated_pages = 0; |
73 | spin_lock_init(&balloon->pages_lock); | |
74 | INIT_LIST_HEAD(&balloon->pages); | |
75 | balloon->migratepage = NULL; | |
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76 | } |
77 | ||
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78 | #ifdef CONFIG_BALLOON_COMPACTION |
79 | extern bool balloon_page_isolate(struct page *page); | |
80 | extern void balloon_page_putback(struct page *page); | |
81 | extern int balloon_page_migrate(struct page *newpage, | |
82 | struct page *page, enum migrate_mode mode); | |
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83 | |
84 | /* | |
d6d86c0a | 85 | * __is_movable_balloon_page - helper to perform @page PageBalloon tests |
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86 | */ |
87 | static inline bool __is_movable_balloon_page(struct page *page) | |
88 | { | |
d6d86c0a | 89 | return PageBalloon(page); |
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90 | } |
91 | ||
92 | /* | |
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93 | * balloon_page_movable - test PageBalloon to identify balloon pages |
94 | * and PagePrivate to check that the page is not | |
95 | * isolated and can be moved by compaction/migration. | |
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96 | * |
97 | * As we might return false positives in the case of a balloon page being just | |
d6d86c0a | 98 | * released under us, this need to be re-tested later, under the page lock. |
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99 | */ |
100 | static inline bool balloon_page_movable(struct page *page) | |
101 | { | |
d6d86c0a | 102 | return PageBalloon(page) && PagePrivate(page); |
18468d93 RA |
103 | } |
104 | ||
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105 | /* |
106 | * isolated_balloon_page - identify an isolated balloon page on private | |
107 | * compaction/migration page lists. | |
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108 | */ |
109 | static inline bool isolated_balloon_page(struct page *page) | |
110 | { | |
d6d86c0a | 111 | return PageBalloon(page); |
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112 | } |
113 | ||
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114 | /* |
115 | * balloon_page_insert - insert a page into the balloon's page list and make | |
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116 | * the page->private assignment accordingly. |
117 | * @balloon : pointer to balloon device | |
18468d93 | 118 | * @page : page to be assigned as a 'balloon page' |
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119 | * |
120 | * Caller must ensure the page is locked and the spin_lock protecting balloon | |
121 | * pages list is held before inserting a page into the balloon device. | |
122 | */ | |
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123 | static inline void balloon_page_insert(struct balloon_dev_info *balloon, |
124 | struct page *page) | |
18468d93 | 125 | { |
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126 | __SetPageBalloon(page); |
127 | SetPagePrivate(page); | |
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128 | set_page_private(page, (unsigned long)balloon); |
129 | list_add(&page->lru, &balloon->pages); | |
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130 | } |
131 | ||
132 | /* | |
133 | * balloon_page_delete - delete a page from balloon's page list and clear | |
9d1ba805 | 134 | * the page->private assignement accordingly. |
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135 | * @page : page to be released from balloon's page list |
136 | * | |
137 | * Caller must ensure the page is locked and the spin_lock protecting balloon | |
138 | * pages list is held before deleting a page from the balloon device. | |
139 | */ | |
140 | static inline void balloon_page_delete(struct page *page) | |
141 | { | |
d6d86c0a | 142 | __ClearPageBalloon(page); |
9d1ba805 | 143 | set_page_private(page, 0); |
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144 | if (PagePrivate(page)) { |
145 | ClearPagePrivate(page); | |
146 | list_del(&page->lru); | |
147 | } | |
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148 | } |
149 | ||
150 | /* | |
151 | * balloon_page_device - get the b_dev_info descriptor for the balloon device | |
152 | * that enqueues the given page. | |
153 | */ | |
154 | static inline struct balloon_dev_info *balloon_page_device(struct page *page) | |
155 | { | |
9d1ba805 | 156 | return (struct balloon_dev_info *)page_private(page); |
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157 | } |
158 | ||
159 | static inline gfp_t balloon_mapping_gfp_mask(void) | |
160 | { | |
161 | return GFP_HIGHUSER_MOVABLE; | |
162 | } | |
163 | ||
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164 | #else /* !CONFIG_BALLOON_COMPACTION */ |
165 | ||
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166 | static inline void balloon_page_insert(struct balloon_dev_info *balloon, |
167 | struct page *page) | |
18468d93 | 168 | { |
09316c09 | 169 | __SetPageBalloon(page); |
9d1ba805 | 170 | list_add(&page->lru, &balloon->pages); |
18468d93 RA |
171 | } |
172 | ||
173 | static inline void balloon_page_delete(struct page *page) | |
174 | { | |
09316c09 | 175 | __ClearPageBalloon(page); |
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176 | list_del(&page->lru); |
177 | } | |
178 | ||
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179 | static inline bool __is_movable_balloon_page(struct page *page) |
180 | { | |
181 | return false; | |
182 | } | |
183 | ||
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184 | static inline bool balloon_page_movable(struct page *page) |
185 | { | |
186 | return false; | |
187 | } | |
188 | ||
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189 | static inline bool isolated_balloon_page(struct page *page) |
190 | { | |
191 | return false; | |
192 | } | |
193 | ||
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194 | static inline bool balloon_page_isolate(struct page *page) |
195 | { | |
196 | return false; | |
197 | } | |
198 | ||
199 | static inline void balloon_page_putback(struct page *page) | |
200 | { | |
201 | return; | |
202 | } | |
203 | ||
204 | static inline int balloon_page_migrate(struct page *newpage, | |
205 | struct page *page, enum migrate_mode mode) | |
206 | { | |
207 | return 0; | |
208 | } | |
209 | ||
210 | static inline gfp_t balloon_mapping_gfp_mask(void) | |
211 | { | |
212 | return GFP_HIGHUSER; | |
213 | } | |
214 | ||
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215 | #endif /* CONFIG_BALLOON_COMPACTION */ |
216 | #endif /* _LINUX_BALLOON_COMPACTION_H */ |