1 /*
2  * include/linux/balloon_compaction.h
3  *
4  * Common interface definitions for making balloon pages movable by compaction.
5  *
6  * Despite being perfectly possible to perform ballooned pages migration, they
7  * make a special corner case to compaction scans because balloon pages are not
8  * enlisted at any LRU list like the other pages we do compact / migrate.
9  *
10  * As the page isolation scanning step a compaction thread does is a lockless
11  * procedure (from a page standpoint), it might bring some racy situations while
12  * performing balloon page compaction. In order to sort out these racy scenarios
13  * and safely perform balloon's page compaction and migration we must, always,
14  * ensure following these three simple rules:
15  *
16  *   i. when updating a balloon's page ->mapping element, strictly do it under
17  *      the following lock order, independently of the far superior
18  *      locking scheme (lru_lock, balloon_lock):
19  *	    +-page_lock(page);
20  *	      +--spin_lock_irq(&b_dev_info->pages_lock);
21  *	            ... page->mapping updates here ...
22  *
23  *  ii. before isolating or dequeueing a balloon page from the balloon device
24  *      pages list, the page reference counter must be raised by one and the
25  *      extra refcount must be dropped when the page is enqueued back into
26  *      the balloon device page list, thus a balloon page keeps its reference
27  *      counter raised only while it is under our special handling;
28  *
29  * iii. after the lockless scan step have selected a potential balloon page for
30  *      isolation, re-test the PageBalloon mark and the PagePrivate flag
31  *      under the proper page lock, to ensure isolating a valid balloon page
32  *      (not yet isolated, nor under release procedure)
33  *
34  *  iv. isolation or dequeueing procedure must clear PagePrivate flag under
35  *      page lock together with removing page from balloon device page list.
36  *
37  * The functions provided by this interface are placed to help on coping with
38  * the aforementioned balloon page corner case, as well as to ensure the simple
39  * set of exposed rules are satisfied while we are dealing with balloon pages
40  * compaction / migration.
41  *
42  * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <[email protected]>
43  */
44 #ifndef _LINUX_BALLOON_COMPACTION_H
45 #define _LINUX_BALLOON_COMPACTION_H
46 #include <linux/pagemap.h>
47 #include <linux/page-flags.h>
48 #include <linux/migrate.h>
49 #include <linux/gfp.h>
50 #include <linux/err.h>
51 #include <linux/fs.h>
52 
53 /*
54  * Balloon device information descriptor.
55  * This struct is used to allow the common balloon compaction interface
56  * procedures to find the proper balloon device holding memory pages they'll
57  * have to cope for page compaction / migration, as well as it serves the
58  * balloon driver as a page book-keeper for its registered balloon devices.
59  */
60 struct balloon_dev_info {
61 	unsigned long isolated_pages;	/* # of isolated pages for migration */
62 	spinlock_t pages_lock;		/* Protection to pages list */
63 	struct list_head pages;		/* Pages enqueued & handled to Host */
64 	int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
65 			struct page *page, enum migrate_mode mode);
66 	struct inode *inode;
67 };
68 
69 extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
70 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
71 
72 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
73 {
74 	balloon->isolated_pages = 0;
75 	spin_lock_init(&balloon->pages_lock);
76 	INIT_LIST_HEAD(&balloon->pages);
77 	balloon->migratepage = NULL;
78 	balloon->inode = NULL;
79 }
80 
81 #ifdef CONFIG_BALLOON_COMPACTION
82 extern const struct address_space_operations balloon_aops;
83 extern bool balloon_page_isolate(struct page *page,
84 				isolate_mode_t mode);
85 extern void balloon_page_putback(struct page *page);
86 extern int balloon_page_migrate(struct address_space *mapping,
87 				struct page *newpage,
88 				struct page *page, enum migrate_mode mode);
89 
90 /*
91  * balloon_page_insert - insert a page into the balloon's page list and make
92  *			 the page->private assignment accordingly.
93  * @balloon : pointer to balloon device
94  * @page    : page to be assigned as a 'balloon page'
95  *
96  * Caller must ensure the page is locked and the spin_lock protecting balloon
97  * pages list is held before inserting a page into the balloon device.
98  */
99 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
100 				       struct page *page)
101 {
102 	__SetPageBalloon(page);
103 	__SetPageMovable(page, balloon->inode->i_mapping);
104 	set_page_private(page, (unsigned long)balloon);
105 	list_add(&page->lru, &balloon->pages);
106 }
107 
108 /*
109  * balloon_page_delete - delete a page from balloon's page list and clear
110  *			 the page->private assignement accordingly.
111  * @page    : page to be released from balloon's page list
112  *
113  * Caller must ensure the page is locked and the spin_lock protecting balloon
114  * pages list is held before deleting a page from the balloon device.
115  */
116 static inline void balloon_page_delete(struct page *page)
117 {
118 	__ClearPageBalloon(page);
119 	__ClearPageMovable(page);
120 	set_page_private(page, 0);
121 	/*
122 	 * No touch page.lru field once @page has been isolated
123 	 * because VM is using the field.
124 	 */
125 	if (!PageIsolated(page))
126 		list_del(&page->lru);
127 }
128 
129 /*
130  * balloon_page_device - get the b_dev_info descriptor for the balloon device
131  *			 that enqueues the given page.
132  */
133 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
134 {
135 	return (struct balloon_dev_info *)page_private(page);
136 }
137 
138 static inline gfp_t balloon_mapping_gfp_mask(void)
139 {
140 	return GFP_HIGHUSER_MOVABLE;
141 }
142 
143 #else /* !CONFIG_BALLOON_COMPACTION */
144 
145 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
146 				       struct page *page)
147 {
148 	__SetPageBalloon(page);
149 	list_add(&page->lru, &balloon->pages);
150 }
151 
152 static inline void balloon_page_delete(struct page *page)
153 {
154 	__ClearPageBalloon(page);
155 	list_del(&page->lru);
156 }
157 
158 static inline bool __is_movable_balloon_page(struct page *page)
159 {
160 	return false;
161 }
162 
163 static inline bool balloon_page_movable(struct page *page)
164 {
165 	return false;
166 }
167 
168 static inline bool isolated_balloon_page(struct page *page)
169 {
170 	return false;
171 }
172 
173 static inline bool balloon_page_isolate(struct page *page)
174 {
175 	return false;
176 }
177 
178 static inline void balloon_page_putback(struct page *page)
179 {
180 	return;
181 }
182 
183 static inline int balloon_page_migrate(struct page *newpage,
184 				struct page *page, enum migrate_mode mode)
185 {
186 	return 0;
187 }
188 
189 static inline gfp_t balloon_mapping_gfp_mask(void)
190 {
191 	return GFP_HIGHUSER;
192 }
193 
194 #endif /* CONFIG_BALLOON_COMPACTION */
195 #endif /* _LINUX_BALLOON_COMPACTION_H */
196