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18468d93 RA |
1 | /* |
2 | * mm/balloon_compaction.c | |
3 | * | |
4 | * Common interface for making balloon pages movable by compaction. | |
5 | * | |
6 | * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com> | |
7 | */ | |
8 | #include <linux/mm.h> | |
9 | #include <linux/slab.h> | |
10 | #include <linux/export.h> | |
11 | #include <linux/balloon_compaction.h> | |
12 | ||
18468d93 RA |
13 | /* |
14 | * balloon_page_enqueue - allocates a new page and inserts it into the balloon | |
15 | * page list. | |
16 | * @b_dev_info: balloon device decriptor where we will insert a new page to | |
17 | * | |
18 | * Driver must call it to properly allocate a new enlisted balloon page | |
19 | * before definetively removing it from the guest system. | |
20 | * This function returns the page address for the recently enqueued page or | |
21 | * NULL in the case we fail to allocate a new page this turn. | |
22 | */ | |
23 | struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info) | |
24 | { | |
25 | unsigned long flags; | |
26 | struct page *page = alloc_page(balloon_mapping_gfp_mask() | | |
27 | __GFP_NOMEMALLOC | __GFP_NORETRY); | |
28 | if (!page) | |
29 | return NULL; | |
30 | ||
31 | /* | |
32 | * Block others from accessing the 'page' when we get around to | |
33 | * establishing additional references. We should be the only one | |
34 | * holding a reference to the 'page' at this point. | |
35 | */ | |
36 | BUG_ON(!trylock_page(page)); | |
37 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); | |
9d1ba805 | 38 | balloon_page_insert(b_dev_info, page); |
18468d93 RA |
39 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); |
40 | unlock_page(page); | |
41 | return page; | |
42 | } | |
43 | EXPORT_SYMBOL_GPL(balloon_page_enqueue); | |
44 | ||
45 | /* | |
46 | * balloon_page_dequeue - removes a page from balloon's page list and returns | |
47 | * the its address to allow the driver release the page. | |
48 | * @b_dev_info: balloon device decriptor where we will grab a page from. | |
49 | * | |
50 | * Driver must call it to properly de-allocate a previous enlisted balloon page | |
51 | * before definetively releasing it back to the guest system. | |
52 | * This function returns the page address for the recently dequeued page or | |
53 | * NULL in the case we find balloon's page list temporarily empty due to | |
54 | * compaction isolated pages. | |
55 | */ | |
56 | struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) | |
57 | { | |
58 | struct page *page, *tmp; | |
59 | unsigned long flags; | |
60 | bool dequeued_page; | |
61 | ||
62 | dequeued_page = false; | |
63 | list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) { | |
64 | /* | |
65 | * Block others from accessing the 'page' while we get around | |
66 | * establishing additional references and preparing the 'page' | |
67 | * to be released by the balloon driver. | |
68 | */ | |
69 | if (trylock_page(page)) { | |
d6d86c0a KK |
70 | if (!PagePrivate(page)) { |
71 | /* raced with isolation */ | |
72 | unlock_page(page); | |
73 | continue; | |
74 | } | |
18468d93 | 75 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); |
18468d93 RA |
76 | balloon_page_delete(page); |
77 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
78 | unlock_page(page); | |
79 | dequeued_page = true; | |
80 | break; | |
81 | } | |
82 | } | |
83 | ||
84 | if (!dequeued_page) { | |
85 | /* | |
86 | * If we are unable to dequeue a balloon page because the page | |
87 | * list is empty and there is no isolated pages, then something | |
88 | * went out of track and some balloon pages are lost. | |
89 | * BUG() here, otherwise the balloon driver may get stuck into | |
90 | * an infinite loop while attempting to release all its pages. | |
91 | */ | |
92 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); | |
93 | if (unlikely(list_empty(&b_dev_info->pages) && | |
94 | !b_dev_info->isolated_pages)) | |
95 | BUG(); | |
96 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
97 | page = NULL; | |
98 | } | |
99 | return page; | |
100 | } | |
101 | EXPORT_SYMBOL_GPL(balloon_page_dequeue); | |
102 | ||
103 | #ifdef CONFIG_BALLOON_COMPACTION | |
18468d93 RA |
104 | |
105 | static inline void __isolate_balloon_page(struct page *page) | |
106 | { | |
9d1ba805 | 107 | struct balloon_dev_info *b_dev_info = balloon_page_device(page); |
18468d93 | 108 | unsigned long flags; |
d6d86c0a | 109 | |
18468d93 | 110 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); |
d6d86c0a | 111 | ClearPagePrivate(page); |
18468d93 RA |
112 | list_del(&page->lru); |
113 | b_dev_info->isolated_pages++; | |
114 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
115 | } | |
116 | ||
117 | static inline void __putback_balloon_page(struct page *page) | |
118 | { | |
9d1ba805 | 119 | struct balloon_dev_info *b_dev_info = balloon_page_device(page); |
18468d93 | 120 | unsigned long flags; |
d6d86c0a | 121 | |
18468d93 | 122 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); |
d6d86c0a | 123 | SetPagePrivate(page); |
18468d93 RA |
124 | list_add(&page->lru, &b_dev_info->pages); |
125 | b_dev_info->isolated_pages--; | |
126 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
127 | } | |
128 | ||
18468d93 RA |
129 | /* __isolate_lru_page() counterpart for a ballooned page */ |
130 | bool balloon_page_isolate(struct page *page) | |
131 | { | |
132 | /* | |
133 | * Avoid burning cycles with pages that are yet under __free_pages(), | |
134 | * or just got freed under us. | |
135 | * | |
136 | * In case we 'win' a race for a balloon page being freed under us and | |
137 | * raise its refcount preventing __free_pages() from doing its job | |
138 | * the put_page() at the end of this block will take care of | |
139 | * release this page, thus avoiding a nasty leakage. | |
140 | */ | |
141 | if (likely(get_page_unless_zero(page))) { | |
142 | /* | |
143 | * As balloon pages are not isolated from LRU lists, concurrent | |
144 | * compaction threads can race against page migration functions | |
145 | * as well as race against the balloon driver releasing a page. | |
146 | * | |
147 | * In order to avoid having an already isolated balloon page | |
148 | * being (wrongly) re-isolated while it is under migration, | |
149 | * or to avoid attempting to isolate pages being released by | |
150 | * the balloon driver, lets be sure we have the page lock | |
151 | * before proceeding with the balloon page isolation steps. | |
152 | */ | |
153 | if (likely(trylock_page(page))) { | |
154 | /* | |
d6d86c0a | 155 | * A ballooned page, by default, has PagePrivate set. |
18468d93 | 156 | * Prevent concurrent compaction threads from isolating |
d6d86c0a | 157 | * an already isolated balloon page by clearing it. |
18468d93 | 158 | */ |
d6d86c0a | 159 | if (balloon_page_movable(page)) { |
18468d93 RA |
160 | __isolate_balloon_page(page); |
161 | unlock_page(page); | |
162 | return true; | |
163 | } | |
164 | unlock_page(page); | |
165 | } | |
166 | put_page(page); | |
167 | } | |
168 | return false; | |
169 | } | |
170 | ||
171 | /* putback_lru_page() counterpart for a ballooned page */ | |
172 | void balloon_page_putback(struct page *page) | |
173 | { | |
174 | /* | |
175 | * 'lock_page()' stabilizes the page and prevents races against | |
176 | * concurrent isolation threads attempting to re-isolate it. | |
177 | */ | |
178 | lock_page(page); | |
179 | ||
180 | if (__is_movable_balloon_page(page)) { | |
181 | __putback_balloon_page(page); | |
182 | /* drop the extra ref count taken for page isolation */ | |
183 | put_page(page); | |
184 | } else { | |
185 | WARN_ON(1); | |
f0b791a3 | 186 | dump_page(page, "not movable balloon page"); |
18468d93 RA |
187 | } |
188 | unlock_page(page); | |
189 | } | |
190 | ||
191 | /* move_to_new_page() counterpart for a ballooned page */ | |
192 | int balloon_page_migrate(struct page *newpage, | |
193 | struct page *page, enum migrate_mode mode) | |
194 | { | |
9d1ba805 | 195 | struct balloon_dev_info *balloon = balloon_page_device(page); |
18468d93 RA |
196 | int rc = -EAGAIN; |
197 | ||
198 | /* | |
199 | * Block others from accessing the 'newpage' when we get around to | |
200 | * establishing additional references. We should be the only one | |
201 | * holding a reference to the 'newpage' at this point. | |
202 | */ | |
203 | BUG_ON(!trylock_page(newpage)); | |
204 | ||
205 | if (WARN_ON(!__is_movable_balloon_page(page))) { | |
f0b791a3 | 206 | dump_page(page, "not movable balloon page"); |
18468d93 RA |
207 | unlock_page(newpage); |
208 | return rc; | |
209 | } | |
210 | ||
9d1ba805 KK |
211 | if (balloon && balloon->migratepage) |
212 | rc = balloon->migratepage(balloon, newpage, page, mode); | |
18468d93 RA |
213 | |
214 | unlock_page(newpage); | |
215 | return rc; | |
216 | } | |
217 | #endif /* CONFIG_BALLOON_COMPACTION */ |