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 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 */
23struct 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}
44EXPORT_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 */
57struct 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 (!PagePrivate(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}
105EXPORT_SYMBOL_GPL(balloon_page_dequeue);
106
107#ifdef CONFIG_BALLOON_COMPACTION
108
109static inline void __isolate_balloon_page(struct page *page)
110{
111	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
112	unsigned long flags;
113
114	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
115	ClearPagePrivate(page);
116	list_del(&page->lru);
117	b_dev_info->isolated_pages++;
118	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
119}
120
121static inline void __putback_balloon_page(struct page *page)
122{
123	struct balloon_dev_info *b_dev_info = balloon_page_device(page);
124	unsigned long flags;
125
126	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
127	SetPagePrivate(page);
128	list_add(&page->lru, &b_dev_info->pages);
129	b_dev_info->isolated_pages--;
130	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
131}
132
133/* __isolate_lru_page() counterpart for a ballooned page */
134bool balloon_page_isolate(struct page *page)
135{
136	/*
137	 * Avoid burning cycles with pages that are yet under __free_pages(),
138	 * or just got freed under us.
139	 *
140	 * In case we 'win' a race for a balloon page being freed under us and
141	 * raise its refcount preventing __free_pages() from doing its job
142	 * the put_page() at the end of this block will take care of
143	 * release this page, thus avoiding a nasty leakage.
144	 */
145	if (likely(get_page_unless_zero(page))) {
146		/*
147		 * As balloon pages are not isolated from LRU lists, concurrent
148		 * compaction threads can race against page migration functions
149		 * as well as race against the balloon driver releasing a page.
150		 *
151		 * In order to avoid having an already isolated balloon page
152		 * being (wrongly) re-isolated while it is under migration,
153		 * or to avoid attempting to isolate pages being released by
154		 * the balloon driver, lets be sure we have the page lock
155		 * before proceeding with the balloon page isolation steps.
156		 */
157		if (likely(trylock_page(page))) {
158			/*
159			 * A ballooned page, by default, has PagePrivate set.
160			 * Prevent concurrent compaction threads from isolating
161			 * an already isolated balloon page by clearing it.
162			 */
163			if (balloon_page_movable(page)) {
164				__isolate_balloon_page(page);
165				unlock_page(page);
166				return true;
167			}
168			unlock_page(page);
169		}
170		put_page(page);
171	}
172	return false;
173}
174
175/* putback_lru_page() counterpart for a ballooned page */
176void balloon_page_putback(struct page *page)
177{
178	/*
179	 * 'lock_page()' stabilizes the page and prevents races against
180	 * concurrent isolation threads attempting to re-isolate it.
181	 */
182	lock_page(page);
183
184	if (__is_movable_balloon_page(page)) {
185		__putback_balloon_page(page);
186		/* drop the extra ref count taken for page isolation */
187		put_page(page);
188	} else {
189		WARN_ON(1);
190		dump_page(page, "not movable balloon page");
191	}
192	unlock_page(page);
193}
194
195/* move_to_new_page() counterpart for a ballooned page */
196int balloon_page_migrate(struct page *newpage,
197			 struct page *page, enum migrate_mode mode)
198{
199	struct balloon_dev_info *balloon = balloon_page_device(page);
200	int rc = -EAGAIN;
201
202	/*
203	 * Block others from accessing the 'newpage' when we get around to
204	 * establishing additional references. We should be the only one
205	 * holding a reference to the 'newpage' at this point.
206	 */
207	BUG_ON(!trylock_page(newpage));
208
209	if (WARN_ON(!__is_movable_balloon_page(page))) {
210		dump_page(page, "not movable balloon page");
211		unlock_page(newpage);
212		return rc;
213	}
214
215	if (balloon && balloon->migratepage)
216		rc = balloon->migratepage(balloon, newpage, page, mode);
217
218	unlock_page(newpage);
219	return rc;
220}
221#endif /* CONFIG_BALLOON_COMPACTION */
222