summaryrefslogtreecommitdiff
path: root/mm/balloon_compaction.c
blob: 3afdabdbc0a4668e4c7cbaa5e0cca27a98305059 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
/*
 * mm/balloon_compaction.c
 *
 * Common interface for making balloon pages movable by compaction.
 *
 * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com>
 */
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/export.h>
#include <linux/balloon_compaction.h>

/*
 * balloon_page_enqueue - allocates a new page and inserts it into the balloon
 *			  page list.
 * @b_dev_info: balloon device decriptor where we will insert a new page to
 *
 * Driver must call it to properly allocate a new enlisted balloon page
 * before definetively removing it from the guest system.
 * This function returns the page address for the recently enqueued page or
 * NULL in the case we fail to allocate a new page this turn.
 */
struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
{
	unsigned long flags;
	struct page *page = alloc_page(balloon_mapping_gfp_mask() |
					__GFP_NOMEMALLOC | __GFP_NORETRY);
	if (!page)
		return NULL;

	/*
	 * Block others from accessing the 'page' when we get around to
	 * establishing additional references. We should be the only one
	 * holding a reference to the 'page' at this point.
	 */
	BUG_ON(!trylock_page(page));
	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
	balloon_page_insert(b_dev_info, page);
	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
	unlock_page(page);
	return page;
}
EXPORT_SYMBOL_GPL(balloon_page_enqueue);

/*
 * balloon_page_dequeue - removes a page from balloon's page list and returns
 *			  the its address to allow the driver release the page.
 * @b_dev_info: balloon device decriptor where we will grab a page from.
 *
 * Driver must call it to properly de-allocate a previous enlisted balloon page
 * before definetively releasing it back to the guest system.
 * This function returns the page address for the recently dequeued page or
 * NULL in the case we find balloon's page list temporarily empty due to
 * compaction isolated pages.
 */
struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
{
	struct page *page, *tmp;
	unsigned long flags;
	bool dequeued_page;

	dequeued_page = false;
	list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
		/*
		 * Block others from accessing the 'page' while we get around
		 * establishing additional references and preparing the 'page'
		 * to be released by the balloon driver.
		 */
		if (trylock_page(page)) {
			if (!PagePrivate(page)) {
				/* raced with isolation */
				unlock_page(page);
				continue;
			}
			spin_lock_irqsave(&b_dev_info->pages_lock, flags);
			balloon_page_delete(page);
			spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
			unlock_page(page);
			dequeued_page = true;
			break;
		}
	}

	if (!dequeued_page) {
		/*
		 * If we are unable to dequeue a balloon page because the page
		 * list is empty and there is no isolated pages, then something
		 * went out of track and some balloon pages are lost.
		 * BUG() here, otherwise the balloon driver may get stuck into
		 * an infinite loop while attempting to release all its pages.
		 */
		spin_lock_irqsave(&b_dev_info->pages_lock, flags);
		if (unlikely(list_empty(&b_dev_info->pages) &&
			     !b_dev_info->isolated_pages))
			BUG();
		spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
		page = NULL;
	}
	return page;
}
EXPORT_SYMBOL_GPL(balloon_page_dequeue);

#ifdef CONFIG_BALLOON_COMPACTION

static inline void __isolate_balloon_page(struct page *page)
{
	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
	unsigned long flags;

	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
	ClearPagePrivate(page);
	list_del(&page->lru);
	b_dev_info->isolated_pages++;
	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
}

static inline void __putback_balloon_page(struct page *page)
{
	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
	unsigned long flags;

	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
	SetPagePrivate(page);
	list_add(&page->lru, &b_dev_info->pages);
	b_dev_info->isolated_pages--;
	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
}

/* __isolate_lru_page() counterpart for a ballooned page */
bool balloon_page_isolate(struct page *page)
{
	/*
	 * Avoid burning cycles with pages that are yet under __free_pages(),
	 * or just got freed under us.
	 *
	 * In case we 'win' a race for a balloon page being freed under us and
	 * raise its refcount preventing __free_pages() from doing its job
	 * the put_page() at the end of this block will take care of
	 * release this page, thus avoiding a nasty leakage.
	 */
	if (likely(get_page_unless_zero(page))) {
		/*
		 * As balloon pages are not isolated from LRU lists, concurrent
		 * compaction threads can race against page migration functions
		 * as well as race against the balloon driver releasing a page.
		 *
		 * In order to avoid having an already isolated balloon page
		 * being (wrongly) re-isolated while it is under migration,
		 * or to avoid attempting to isolate pages being released by
		 * the balloon driver, lets be sure we have the page lock
		 * before proceeding with the balloon page isolation steps.
		 */
		if (likely(trylock_page(page))) {
			/*
			 * A ballooned page, by default, has PagePrivate set.
			 * Prevent concurrent compaction threads from isolating
			 * an already isolated balloon page by clearing it.
			 */
			if (balloon_page_movable(page)) {
				__isolate_balloon_page(page);
				unlock_page(page);
				return true;
			}
			unlock_page(page);
		}
		put_page(page);
	}
	return false;
}

/* putback_lru_page() counterpart for a ballooned page */
void balloon_page_putback(struct page *page)
{
	/*
	 * 'lock_page()' stabilizes the page and prevents races against
	 * concurrent isolation threads attempting to re-isolate it.
	 */
	lock_page(page);

	if (__is_movable_balloon_page(page)) {
		__putback_balloon_page(page);
		/* drop the extra ref count taken for page isolation */
		put_page(page);
	} else {
		WARN_ON(1);
		dump_page(page, "not movable balloon page");
	}
	unlock_page(page);
}

/* move_to_new_page() counterpart for a ballooned page */
int balloon_page_migrate(struct page *newpage,
			 struct page *page, enum migrate_mode mode)
{
	struct balloon_dev_info *balloon = balloon_page_device(page);
	int rc = -EAGAIN;

	/*
	 * Block others from accessing the 'newpage' when we get around to
	 * establishing additional references. We should be the only one
	 * holding a reference to the 'newpage' at this point.
	 */
	BUG_ON(!trylock_page(newpage));

	if (WARN_ON(!__is_movable_balloon_page(page))) {
		dump_page(page, "not movable balloon page");
		unlock_page(newpage);
		return rc;
	}

	if (balloon && balloon->migratepage)
		rc = balloon->migratepage(balloon, newpage, page, mode);

	unlock_page(newpage);
	return rc;
}
#endif /* CONFIG_BALLOON_COMPACTION */