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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 | ||
13 | /* | |
14 | * balloon_page_enqueue - allocates a new page and inserts it into the balloon | |
15 | * page list. | |
16 | * @b_dev_info: balloon device descriptor where we will insert a new page to | |
17 | * | |
18 | * Driver must call it to properly allocate a new enlisted balloon page | |
19 | * before definitively 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); | |
38 | balloon_page_insert(b_dev_info, page); | |
39 | __count_vm_event(BALLOON_INFLATE); | |
40 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
41 | unlock_page(page); | |
42 | return page; | |
43 | } | |
44 | EXPORT_SYMBOL_GPL(balloon_page_enqueue); | |
45 | ||
46 | /* | |
47 | * balloon_page_dequeue - removes a page from balloon's page list and returns | |
48 | * the its address to allow the driver release the page. | |
49 | * @b_dev_info: balloon device decriptor where we will grab a page from. | |
50 | * | |
51 | * Driver must call it to properly de-allocate a previous enlisted balloon page | |
52 | * before definetively releasing it back to the guest system. | |
53 | * This function returns the page address for the recently dequeued page or | |
54 | * NULL in the case we find balloon's page list temporarily empty due to | |
55 | * compaction isolated pages. | |
56 | */ | |
57 | struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) | |
58 | { | |
59 | struct page *page, *tmp; | |
60 | unsigned long flags; | |
61 | bool dequeued_page; | |
62 | ||
63 | dequeued_page = false; | |
64 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); | |
65 | list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) { | |
66 | /* | |
67 | * Block others from accessing the 'page' while we get around | |
68 | * establishing additional references and preparing the 'page' | |
69 | * to be released by the balloon driver. | |
70 | */ | |
71 | if (trylock_page(page)) { | |
72 | #ifdef CONFIG_BALLOON_COMPACTION | |
73 | if (PageIsolated(page)) { | |
74 | /* raced with isolation */ | |
75 | unlock_page(page); | |
76 | continue; | |
77 | } | |
78 | #endif | |
79 | balloon_page_delete(page); | |
80 | __count_vm_event(BALLOON_DEFLATE); | |
81 | unlock_page(page); | |
82 | dequeued_page = true; | |
83 | break; | |
84 | } | |
85 | } | |
86 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
87 | ||
88 | if (!dequeued_page) { | |
89 | /* | |
90 | * If we are unable to dequeue a balloon page because the page | |
91 | * list is empty and there is no isolated pages, then something | |
92 | * went out of track and some balloon pages are lost. | |
93 | * BUG() here, otherwise the balloon driver may get stuck into | |
94 | * an infinite loop while attempting to release all its pages. | |
95 | */ | |
96 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); | |
97 | if (unlikely(list_empty(&b_dev_info->pages) && | |
98 | !b_dev_info->isolated_pages)) | |
99 | BUG(); | |
100 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
101 | page = NULL; | |
102 | } | |
103 | return page; | |
104 | } | |
105 | EXPORT_SYMBOL_GPL(balloon_page_dequeue); | |
106 | ||
107 | #ifdef CONFIG_BALLOON_COMPACTION | |
108 | ||
109 | bool balloon_page_isolate(struct page *page, isolate_mode_t mode) | |
110 | ||
111 | { | |
112 | struct balloon_dev_info *b_dev_info = balloon_page_device(page); | |
113 | unsigned long flags; | |
114 | ||
115 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); | |
116 | list_del(&page->lru); | |
117 | b_dev_info->isolated_pages++; | |
118 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
119 | ||
120 | return true; | |
121 | } | |
122 | ||
123 | void balloon_page_putback(struct page *page) | |
124 | { | |
125 | struct balloon_dev_info *b_dev_info = balloon_page_device(page); | |
126 | unsigned long flags; | |
127 | ||
128 | spin_lock_irqsave(&b_dev_info->pages_lock, flags); | |
129 | list_add(&page->lru, &b_dev_info->pages); | |
130 | b_dev_info->isolated_pages--; | |
131 | spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); | |
132 | } | |
133 | ||
134 | ||
135 | /* move_to_new_page() counterpart for a ballooned page */ | |
136 | int balloon_page_migrate(struct address_space *mapping, | |
137 | struct page *newpage, struct page *page, | |
138 | enum migrate_mode mode) | |
139 | { | |
140 | struct balloon_dev_info *balloon = balloon_page_device(page); | |
141 | ||
142 | VM_BUG_ON_PAGE(!PageLocked(page), page); | |
143 | VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); | |
144 | ||
145 | return balloon->migratepage(balloon, newpage, page, mode); | |
146 | } | |
147 | ||
148 | const struct address_space_operations balloon_aops = { | |
149 | .migratepage = balloon_page_migrate, | |
150 | .isolate_page = balloon_page_isolate, | |
151 | .putback_page = balloon_page_putback, | |
152 | }; | |
153 | EXPORT_SYMBOL_GPL(balloon_aops); | |
154 | ||
155 | #endif /* CONFIG_BALLOON_COMPACTION */ |