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Rafael Aquini18468d92012-12-11 16:02:38 -08001/*
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_devinfo_alloc - allocates a balloon device information descriptor.
15 * @balloon_dev_descriptor: pointer to reference the balloon device which
16 * this struct balloon_dev_info will be servicing.
17 *
18 * Driver must call it to properly allocate and initialize an instance of
19 * struct balloon_dev_info which will be used to reference a balloon device
20 * as well as to keep track of the balloon device page list.
21 */
22struct balloon_dev_info *balloon_devinfo_alloc(void *balloon_dev_descriptor)
23{
24 struct balloon_dev_info *b_dev_info;
25 b_dev_info = kmalloc(sizeof(*b_dev_info), GFP_KERNEL);
26 if (!b_dev_info)
27 return ERR_PTR(-ENOMEM);
28
29 b_dev_info->balloon_device = balloon_dev_descriptor;
30 b_dev_info->mapping = NULL;
31 b_dev_info->isolated_pages = 0;
32 spin_lock_init(&b_dev_info->pages_lock);
33 INIT_LIST_HEAD(&b_dev_info->pages);
34
35 return b_dev_info;
36}
37EXPORT_SYMBOL_GPL(balloon_devinfo_alloc);
38
39/*
40 * balloon_page_enqueue - allocates a new page and inserts it into the balloon
41 * page list.
42 * @b_dev_info: balloon device decriptor where we will insert a new page to
43 *
44 * Driver must call it to properly allocate a new enlisted balloon page
45 * before definetively removing it from the guest system.
46 * This function returns the page address for the recently enqueued page or
47 * NULL in the case we fail to allocate a new page this turn.
48 */
49struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
50{
51 unsigned long flags;
52 struct page *page = alloc_page(balloon_mapping_gfp_mask() |
53 __GFP_NOMEMALLOC | __GFP_NORETRY);
54 if (!page)
55 return NULL;
56
57 /*
58 * Block others from accessing the 'page' when we get around to
59 * establishing additional references. We should be the only one
60 * holding a reference to the 'page' at this point.
61 */
62 BUG_ON(!trylock_page(page));
63 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
64 balloon_page_insert(page, b_dev_info->mapping, &b_dev_info->pages);
65 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
66 unlock_page(page);
67 return page;
68}
69EXPORT_SYMBOL_GPL(balloon_page_enqueue);
70
71/*
72 * balloon_page_dequeue - removes a page from balloon's page list and returns
73 * the its address to allow the driver release the page.
74 * @b_dev_info: balloon device decriptor where we will grab a page from.
75 *
76 * Driver must call it to properly de-allocate a previous enlisted balloon page
77 * before definetively releasing it back to the guest system.
78 * This function returns the page address for the recently dequeued page or
79 * NULL in the case we find balloon's page list temporarily empty due to
80 * compaction isolated pages.
81 */
82struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
83{
84 struct page *page, *tmp;
85 unsigned long flags;
86 bool dequeued_page;
87
88 dequeued_page = false;
89 list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
90 /*
91 * Block others from accessing the 'page' while we get around
92 * establishing additional references and preparing the 'page'
93 * to be released by the balloon driver.
94 */
95 if (trylock_page(page)) {
96 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
97 /*
98 * Raise the page refcount here to prevent any wrong
99 * attempt to isolate this page, in case of coliding
100 * with balloon_page_isolate() just after we release
101 * the page lock.
102 *
103 * balloon_page_free() will take care of dropping
104 * this extra refcount later.
105 */
106 get_page(page);
107 balloon_page_delete(page);
108 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
109 unlock_page(page);
110 dequeued_page = true;
111 break;
112 }
113 }
114
115 if (!dequeued_page) {
116 /*
117 * If we are unable to dequeue a balloon page because the page
118 * list is empty and there is no isolated pages, then something
119 * went out of track and some balloon pages are lost.
120 * BUG() here, otherwise the balloon driver may get stuck into
121 * an infinite loop while attempting to release all its pages.
122 */
123 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
124 if (unlikely(list_empty(&b_dev_info->pages) &&
125 !b_dev_info->isolated_pages))
126 BUG();
127 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
128 page = NULL;
129 }
130 return page;
131}
132EXPORT_SYMBOL_GPL(balloon_page_dequeue);
133
134#ifdef CONFIG_BALLOON_COMPACTION
135/*
136 * balloon_mapping_alloc - allocates a special ->mapping for ballooned pages.
137 * @b_dev_info: holds the balloon device information descriptor.
138 * @a_ops: balloon_mapping address_space_operations descriptor.
139 *
140 * Driver must call it to properly allocate and initialize an instance of
141 * struct address_space which will be used as the special page->mapping for
142 * balloon device enlisted page instances.
143 */
144struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
145 const struct address_space_operations *a_ops)
146{
147 struct address_space *mapping;
148
149 mapping = kmalloc(sizeof(*mapping), GFP_KERNEL);
150 if (!mapping)
151 return ERR_PTR(-ENOMEM);
152
153 /*
154 * Give a clean 'zeroed' status to all elements of this special
155 * balloon page->mapping struct address_space instance.
156 */
157 address_space_init_once(mapping);
158
159 /*
160 * Set mapping->flags appropriately, to allow balloon pages
161 * ->mapping identification.
162 */
163 mapping_set_balloon(mapping);
164 mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask());
165
166 /* balloon's page->mapping->a_ops callback descriptor */
167 mapping->a_ops = a_ops;
168
169 /*
170 * Establish a pointer reference back to the balloon device descriptor
171 * this particular page->mapping will be servicing.
172 * This is used by compaction / migration procedures to identify and
173 * access the balloon device pageset while isolating / migrating pages.
174 *
175 * As some balloon drivers can register multiple balloon devices
176 * for a single guest, this also helps compaction / migration to
177 * properly deal with multiple balloon pagesets, when required.
178 */
179 mapping->private_data = b_dev_info;
180 b_dev_info->mapping = mapping;
181
182 return mapping;
183}
184EXPORT_SYMBOL_GPL(balloon_mapping_alloc);
185
186static inline void __isolate_balloon_page(struct page *page)
187{
188 struct balloon_dev_info *b_dev_info = page->mapping->private_data;
189 unsigned long flags;
190 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
191 list_del(&page->lru);
192 b_dev_info->isolated_pages++;
193 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
194}
195
196static inline void __putback_balloon_page(struct page *page)
197{
198 struct balloon_dev_info *b_dev_info = page->mapping->private_data;
199 unsigned long flags;
200 spin_lock_irqsave(&b_dev_info->pages_lock, flags);
201 list_add(&page->lru, &b_dev_info->pages);
202 b_dev_info->isolated_pages--;
203 spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
204}
205
206static inline int __migrate_balloon_page(struct address_space *mapping,
207 struct page *newpage, struct page *page, enum migrate_mode mode)
208{
209 return page->mapping->a_ops->migratepage(mapping, newpage, page, mode);
210}
211
212/* __isolate_lru_page() counterpart for a ballooned page */
213bool balloon_page_isolate(struct page *page)
214{
215 /*
216 * Avoid burning cycles with pages that are yet under __free_pages(),
217 * or just got freed under us.
218 *
219 * In case we 'win' a race for a balloon page being freed under us and
220 * raise its refcount preventing __free_pages() from doing its job
221 * the put_page() at the end of this block will take care of
222 * release this page, thus avoiding a nasty leakage.
223 */
224 if (likely(get_page_unless_zero(page))) {
225 /*
226 * As balloon pages are not isolated from LRU lists, concurrent
227 * compaction threads can race against page migration functions
228 * as well as race against the balloon driver releasing a page.
229 *
230 * In order to avoid having an already isolated balloon page
231 * being (wrongly) re-isolated while it is under migration,
232 * or to avoid attempting to isolate pages being released by
233 * the balloon driver, lets be sure we have the page lock
234 * before proceeding with the balloon page isolation steps.
235 */
236 if (likely(trylock_page(page))) {
237 /*
238 * A ballooned page, by default, has just one refcount.
239 * Prevent concurrent compaction threads from isolating
240 * an already isolated balloon page by refcount check.
241 */
242 if (__is_movable_balloon_page(page) &&
243 page_count(page) == 2) {
244 __isolate_balloon_page(page);
245 unlock_page(page);
246 return true;
247 }
248 unlock_page(page);
249 }
250 put_page(page);
251 }
252 return false;
253}
254
255/* putback_lru_page() counterpart for a ballooned page */
256void balloon_page_putback(struct page *page)
257{
258 /*
259 * 'lock_page()' stabilizes the page and prevents races against
260 * concurrent isolation threads attempting to re-isolate it.
261 */
262 lock_page(page);
263
264 if (__is_movable_balloon_page(page)) {
265 __putback_balloon_page(page);
266 /* drop the extra ref count taken for page isolation */
267 put_page(page);
268 } else {
269 WARN_ON(1);
Dave Hansenf0b791a2014-01-23 15:52:49 -0800270 dump_page(page, "not movable balloon page");
Rafael Aquini18468d92012-12-11 16:02:38 -0800271 }
272 unlock_page(page);
273}
274
275/* move_to_new_page() counterpart for a ballooned page */
276int balloon_page_migrate(struct page *newpage,
277 struct page *page, enum migrate_mode mode)
278{
279 struct address_space *mapping;
280 int rc = -EAGAIN;
281
282 /*
283 * Block others from accessing the 'newpage' when we get around to
284 * establishing additional references. We should be the only one
285 * holding a reference to the 'newpage' at this point.
286 */
287 BUG_ON(!trylock_page(newpage));
288
289 if (WARN_ON(!__is_movable_balloon_page(page))) {
Dave Hansenf0b791a2014-01-23 15:52:49 -0800290 dump_page(page, "not movable balloon page");
Rafael Aquini18468d92012-12-11 16:02:38 -0800291 unlock_page(newpage);
292 return rc;
293 }
294
295 mapping = page->mapping;
296 if (mapping)
297 rc = __migrate_balloon_page(mapping, newpage, page, mode);
298
299 unlock_page(newpage);
300 return rc;
301}
302#endif /* CONFIG_BALLOON_COMPACTION */