1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3  * include/linux/balloon_compaction.h
4  *
5  * Common interface definitions for making balloon pages movable by compaction.
6  *
7  * Despite being perfectly possible to perform ballooned pages migration, they
8  * make a special corner case to compaction scans because balloon pages are not
9  * enlisted at any LRU list like the other pages we do compact / migrate.
10  *
11  * As the page isolation scanning step a compaction thread does is a lockless
12  * procedure (from a page standpoint), it might bring some racy situations while
13  * performing balloon page compaction. In order to sort out these racy scenarios
14  * and safely perform balloon's page compaction and migration we must, always,
15  * ensure following these three simple rules:
16  *
17  *   i. when updating a balloon's page ->mapping element, strictly do it under
18  *      the following lock order, independently of the far superior
19  *      locking scheme (lru_lock, balloon_lock):
20  *	    +-page_lock(page);
21  *	      +--spin_lock_irq(&b_dev_info->pages_lock);
22  *	            ... page->mapping updates here ...
23  *
24  *  ii. before isolating or dequeueing a balloon page from the balloon device
25  *      pages list, the page reference counter must be raised by one and the
26  *      extra refcount must be dropped when the page is enqueued back into
27  *      the balloon device page list, thus a balloon page keeps its reference
28  *      counter raised only while it is under our special handling;
29  *
30  * iii. after the lockless scan step have selected a potential balloon page for
31  *      isolation, re-test the PageBalloon mark and the PagePrivate flag
32  *      under the proper page lock, to ensure isolating a valid balloon page
33  *      (not yet isolated, nor under release procedure)
34  *
35  *  iv. isolation or dequeueing procedure must clear PagePrivate flag under
36  *      page lock together with removing page from balloon device page list.
37  *
38  * The functions provided by this interface are placed to help on coping with
39  * the aforementioned balloon page corner case, as well as to ensure the simple
40  * set of exposed rules are satisfied while we are dealing with balloon pages
41  * compaction / migration.
42  *
43  * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <[email protected]>
44  */
45 #ifndef _LINUX_BALLOON_COMPACTION_H
46 #define _LINUX_BALLOON_COMPACTION_H
47 #include <linux/pagemap.h>
48 #include <linux/page-flags.h>
49 #include <linux/migrate.h>
50 #include <linux/gfp.h>
51 #include <linux/err.h>
52 #include <linux/fs.h>
53 
54 /*
55  * Balloon device information descriptor.
56  * This struct is used to allow the common balloon compaction interface
57  * procedures to find the proper balloon device holding memory pages they'll
58  * have to cope for page compaction / migration, as well as it serves the
59  * balloon driver as a page book-keeper for its registered balloon devices.
60  */
61 struct balloon_dev_info {
62 	unsigned long isolated_pages;	/* # of isolated pages for migration */
63 	spinlock_t pages_lock;		/* Protection to pages list */
64 	struct list_head pages;		/* Pages enqueued & handled to Host */
65 	int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
66 			struct page *page, enum migrate_mode mode);
67 	struct inode *inode;
68 };
69 
70 extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
71 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
72 
73 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
74 {
75 	balloon->isolated_pages = 0;
76 	spin_lock_init(&balloon->pages_lock);
77 	INIT_LIST_HEAD(&balloon->pages);
78 	balloon->migratepage = NULL;
79 	balloon->inode = NULL;
80 }
81 
82 #ifdef CONFIG_BALLOON_COMPACTION
83 extern const struct address_space_operations balloon_aops;
84 extern bool balloon_page_isolate(struct page *page,
85 				isolate_mode_t mode);
86 extern void balloon_page_putback(struct page *page);
87 extern int balloon_page_migrate(struct address_space *mapping,
88 				struct page *newpage,
89 				struct page *page, enum migrate_mode mode);
90 
91 /*
92  * balloon_page_insert - insert a page into the balloon's page list and make
93  *			 the page->private assignment accordingly.
94  * @balloon : pointer to balloon device
95  * @page    : page to be assigned as a 'balloon page'
96  *
97  * Caller must ensure the page is locked and the spin_lock protecting balloon
98  * pages list is held before inserting a page into the balloon device.
99  */
100 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
101 				       struct page *page)
102 {
103 	__SetPageBalloon(page);
104 	__SetPageMovable(page, balloon->inode->i_mapping);
105 	set_page_private(page, (unsigned long)balloon);
106 	list_add(&page->lru, &balloon->pages);
107 }
108 
109 /*
110  * balloon_page_delete - delete a page from balloon's page list and clear
111  *			 the page->private assignement accordingly.
112  * @page    : page to be released from balloon's page list
113  *
114  * Caller must ensure the page is locked and the spin_lock protecting balloon
115  * pages list is held before deleting a page from the balloon device.
116  */
117 static inline void balloon_page_delete(struct page *page)
118 {
119 	__ClearPageBalloon(page);
120 	__ClearPageMovable(page);
121 	set_page_private(page, 0);
122 	/*
123 	 * No touch page.lru field once @page has been isolated
124 	 * because VM is using the field.
125 	 */
126 	if (!PageIsolated(page))
127 		list_del(&page->lru);
128 }
129 
130 /*
131  * balloon_page_device - get the b_dev_info descriptor for the balloon device
132  *			 that enqueues the given page.
133  */
134 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
135 {
136 	return (struct balloon_dev_info *)page_private(page);
137 }
138 
139 static inline gfp_t balloon_mapping_gfp_mask(void)
140 {
141 	return GFP_HIGHUSER_MOVABLE;
142 }
143 
144 #else /* !CONFIG_BALLOON_COMPACTION */
145 
146 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
147 				       struct page *page)
148 {
149 	__SetPageBalloon(page);
150 	list_add(&page->lru, &balloon->pages);
151 }
152 
153 static inline void balloon_page_delete(struct page *page)
154 {
155 	__ClearPageBalloon(page);
156 	list_del(&page->lru);
157 }
158 
159 static inline bool __is_movable_balloon_page(struct page *page)
160 {
161 	return false;
162 }
163 
164 static inline bool balloon_page_movable(struct page *page)
165 {
166 	return false;
167 }
168 
169 static inline bool isolated_balloon_page(struct page *page)
170 {
171 	return false;
172 }
173 
174 static inline bool balloon_page_isolate(struct page *page)
175 {
176 	return false;
177 }
178 
179 static inline void balloon_page_putback(struct page *page)
180 {
181 	return;
182 }
183 
184 static inline int balloon_page_migrate(struct page *newpage,
185 				struct page *page, enum migrate_mode mode)
186 {
187 	return 0;
188 }
189 
190 static inline gfp_t balloon_mapping_gfp_mask(void)
191 {
192 	return GFP_HIGHUSER;
193 }
194 
195 #endif /* CONFIG_BALLOON_COMPACTION */
196 #endif /* _LINUX_BALLOON_COMPACTION_H */
197