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  * Balloon page migration makes use of the general non-lru movable page
8  * feature.
9  *
10  * page->private is used to reference the responsible balloon device.
11  * page->mapping is used in context of non-lru page migration to reference
12  * the address space operations for page isolation/migration/compaction.
13  *
14  * As the page isolation scanning step a compaction thread does is a lockless
15  * procedure (from a page standpoint), it might bring some racy situations while
16  * performing balloon page compaction. In order to sort out these racy scenarios
17  * and safely perform balloon's page compaction and migration we must, always,
18  * ensure following these simple rules:
19  *
20  *   i. when updating a balloon's page ->mapping element, strictly do it under
21  *      the following lock order, independently of the far superior
22  *      locking scheme (lru_lock, balloon_lock):
23  *	    +-page_lock(page);
24  *	      +--spin_lock_irq(&b_dev_info->pages_lock);
25  *	            ... page->mapping updates here ...
26  *
27  *  ii. isolation or dequeueing procedure must remove the page from balloon
28  *      device page list under b_dev_info->pages_lock.
29  *
30  * The functions provided by this interface are placed to help on coping with
31  * the aforementioned balloon page corner case, as well as to ensure the simple
32  * set of exposed rules are satisfied while we are dealing with balloon pages
33  * compaction / migration.
34  *
35  * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <[email protected]>
36  */
37 #ifndef _LINUX_BALLOON_COMPACTION_H
38 #define _LINUX_BALLOON_COMPACTION_H
39 #include <linux/pagemap.h>
40 #include <linux/page-flags.h>
41 #include <linux/migrate.h>
42 #include <linux/gfp.h>
43 #include <linux/err.h>
44 #include <linux/fs.h>
45 #include <linux/list.h>
46 
47 /*
48  * Balloon device information descriptor.
49  * This struct is used to allow the common balloon compaction interface
50  * procedures to find the proper balloon device holding memory pages they'll
51  * have to cope for page compaction / migration, as well as it serves the
52  * balloon driver as a page book-keeper for its registered balloon devices.
53  */
54 struct balloon_dev_info {
55 	unsigned long isolated_pages;	/* # of isolated pages for migration */
56 	spinlock_t pages_lock;		/* Protection to pages list */
57 	struct list_head pages;		/* Pages enqueued & handled to Host */
58 	int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
59 			struct page *page, enum migrate_mode mode);
60 	struct inode *inode;
61 };
62 
63 extern struct page *balloon_page_alloc(void);
64 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
65 				 struct page *page);
66 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
67 
68 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
69 {
70 	balloon->isolated_pages = 0;
71 	spin_lock_init(&balloon->pages_lock);
72 	INIT_LIST_HEAD(&balloon->pages);
73 	balloon->migratepage = NULL;
74 	balloon->inode = NULL;
75 }
76 
77 #ifdef CONFIG_BALLOON_COMPACTION
78 extern const struct address_space_operations balloon_aops;
79 extern bool balloon_page_isolate(struct page *page,
80 				isolate_mode_t mode);
81 extern void balloon_page_putback(struct page *page);
82 extern int balloon_page_migrate(struct address_space *mapping,
83 				struct page *newpage,
84 				struct page *page, enum migrate_mode mode);
85 
86 /*
87  * balloon_page_insert - insert a page into the balloon's page list and make
88  *			 the page->private assignment accordingly.
89  * @balloon : pointer to balloon device
90  * @page    : page to be assigned as a 'balloon page'
91  *
92  * Caller must ensure the page is locked and the spin_lock protecting balloon
93  * pages list is held before inserting a page into the balloon device.
94  */
95 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
96 				       struct page *page)
97 {
98 	__SetPageOffline(page);
99 	__SetPageMovable(page, balloon->inode->i_mapping);
100 	set_page_private(page, (unsigned long)balloon);
101 	list_add(&page->lru, &balloon->pages);
102 }
103 
104 /*
105  * balloon_page_delete - delete a page from balloon's page list and clear
106  *			 the page->private assignement accordingly.
107  * @page    : page to be released from balloon's page list
108  *
109  * Caller must ensure the page is locked and the spin_lock protecting balloon
110  * pages list is held before deleting a page from the balloon device.
111  */
112 static inline void balloon_page_delete(struct page *page)
113 {
114 	__ClearPageOffline(page);
115 	__ClearPageMovable(page);
116 	set_page_private(page, 0);
117 	/*
118 	 * No touch page.lru field once @page has been isolated
119 	 * because VM is using the field.
120 	 */
121 	if (!PageIsolated(page))
122 		list_del(&page->lru);
123 }
124 
125 /*
126  * balloon_page_device - get the b_dev_info descriptor for the balloon device
127  *			 that enqueues the given page.
128  */
129 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
130 {
131 	return (struct balloon_dev_info *)page_private(page);
132 }
133 
134 static inline gfp_t balloon_mapping_gfp_mask(void)
135 {
136 	return GFP_HIGHUSER_MOVABLE;
137 }
138 
139 #else /* !CONFIG_BALLOON_COMPACTION */
140 
141 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
142 				       struct page *page)
143 {
144 	__SetPageOffline(page);
145 	list_add(&page->lru, &balloon->pages);
146 }
147 
148 static inline void balloon_page_delete(struct page *page)
149 {
150 	__ClearPageOffline(page);
151 	list_del(&page->lru);
152 }
153 
154 static inline bool __is_movable_balloon_page(struct page *page)
155 {
156 	return false;
157 }
158 
159 static inline bool balloon_page_movable(struct page *page)
160 {
161 	return false;
162 }
163 
164 static inline bool isolated_balloon_page(struct page *page)
165 {
166 	return false;
167 }
168 
169 static inline bool balloon_page_isolate(struct page *page)
170 {
171 	return false;
172 }
173 
174 static inline void balloon_page_putback(struct page *page)
175 {
176 	return;
177 }
178 
179 static inline int balloon_page_migrate(struct page *newpage,
180 				struct page *page, enum migrate_mode mode)
181 {
182 	return 0;
183 }
184 
185 static inline gfp_t balloon_mapping_gfp_mask(void)
186 {
187 	return GFP_HIGHUSER;
188 }
189 
190 #endif /* CONFIG_BALLOON_COMPACTION */
191 
192 /*
193  * balloon_page_push - insert a page into a page list.
194  * @head : pointer to list
195  * @page : page to be added
196  *
197  * Caller must ensure the page is private and protect the list.
198  */
199 static inline void balloon_page_push(struct list_head *pages, struct page *page)
200 {
201 	list_add(&page->lru, pages);
202 }
203 
204 /*
205  * balloon_page_pop - remove a page from a page list.
206  * @head : pointer to list
207  * @page : page to be added
208  *
209  * Caller must ensure the page is private and protect the list.
210  */
211 static inline struct page *balloon_page_pop(struct list_head *pages)
212 {
213 	struct page *page = list_first_entry_or_null(pages, struct page, lru);
214 
215 	if (!page)
216 		return NULL;
217 
218 	list_del(&page->lru);
219 	return page;
220 }
221 #endif /* _LINUX_BALLOON_COMPACTION_H */
222