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 <aquini@redhat.com>
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 #include <linux/list.h>
54 
55 /*
56  * Balloon device information descriptor.
57  * This struct is used to allow the common balloon compaction interface
58  * procedures to find the proper balloon device holding memory pages they'll
59  * have to cope for page compaction / migration, as well as it serves the
60  * balloon driver as a page book-keeper for its registered balloon devices.
61  */
62 struct balloon_dev_info {
63 	unsigned long isolated_pages;	/* # of isolated pages for migration */
64 	spinlock_t pages_lock;		/* Protection to pages list */
65 	struct list_head pages;		/* Pages enqueued & handled to Host */
66 	int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
67 			struct page *page, enum migrate_mode mode);
68 	struct inode *inode;
69 };
70 
71 extern struct page *balloon_page_alloc(void);
72 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
73 				 struct page *page);
74 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
75 
balloon_devinfo_init(struct balloon_dev_info * balloon)76 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
77 {
78 	balloon->isolated_pages = 0;
79 	spin_lock_init(&balloon->pages_lock);
80 	INIT_LIST_HEAD(&balloon->pages);
81 	balloon->migratepage = NULL;
82 	balloon->inode = NULL;
83 }
84 
85 #ifdef CONFIG_BALLOON_COMPACTION
86 extern const struct address_space_operations balloon_aops;
87 extern bool balloon_page_isolate(struct page *page,
88 				isolate_mode_t mode);
89 extern void balloon_page_putback(struct page *page);
90 extern int balloon_page_migrate(struct address_space *mapping,
91 				struct page *newpage,
92 				struct page *page, enum migrate_mode mode);
93 
94 /*
95  * balloon_page_insert - insert a page into the balloon's page list and make
96  *			 the page->private assignment accordingly.
97  * @balloon : pointer to balloon device
98  * @page    : page to be assigned as a 'balloon page'
99  *
100  * Caller must ensure the page is locked and the spin_lock protecting balloon
101  * pages list is held before inserting a page into the balloon device.
102  */
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)103 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
104 				       struct page *page)
105 {
106 	__SetPageBalloon(page);
107 	__SetPageMovable(page, balloon->inode->i_mapping);
108 	set_page_private(page, (unsigned long)balloon);
109 	list_add(&page->lru, &balloon->pages);
110 }
111 
112 /*
113  * balloon_page_delete - delete a page from balloon's page list and clear
114  *			 the page->private assignement accordingly.
115  * @page    : page to be released from balloon's page list
116  *
117  * Caller must ensure the page is locked and the spin_lock protecting balloon
118  * pages list is held before deleting a page from the balloon device.
119  */
balloon_page_delete(struct page * page)120 static inline void balloon_page_delete(struct page *page)
121 {
122 	__ClearPageBalloon(page);
123 	__ClearPageMovable(page);
124 	set_page_private(page, 0);
125 	/*
126 	 * No touch page.lru field once @page has been isolated
127 	 * because VM is using the field.
128 	 */
129 	if (!PageIsolated(page))
130 		list_del(&page->lru);
131 }
132 
133 /*
134  * balloon_page_device - get the b_dev_info descriptor for the balloon device
135  *			 that enqueues the given page.
136  */
balloon_page_device(struct page * page)137 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
138 {
139 	return (struct balloon_dev_info *)page_private(page);
140 }
141 
balloon_mapping_gfp_mask(void)142 static inline gfp_t balloon_mapping_gfp_mask(void)
143 {
144 	return GFP_HIGHUSER_MOVABLE;
145 }
146 
147 #else /* !CONFIG_BALLOON_COMPACTION */
148 
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)149 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
150 				       struct page *page)
151 {
152 	__SetPageBalloon(page);
153 	list_add(&page->lru, &balloon->pages);
154 }
155 
balloon_page_delete(struct page * page)156 static inline void balloon_page_delete(struct page *page)
157 {
158 	__ClearPageBalloon(page);
159 	list_del(&page->lru);
160 }
161 
__is_movable_balloon_page(struct page * page)162 static inline bool __is_movable_balloon_page(struct page *page)
163 {
164 	return false;
165 }
166 
balloon_page_movable(struct page * page)167 static inline bool balloon_page_movable(struct page *page)
168 {
169 	return false;
170 }
171 
isolated_balloon_page(struct page * page)172 static inline bool isolated_balloon_page(struct page *page)
173 {
174 	return false;
175 }
176 
balloon_page_isolate(struct page * page)177 static inline bool balloon_page_isolate(struct page *page)
178 {
179 	return false;
180 }
181 
balloon_page_putback(struct page * page)182 static inline void balloon_page_putback(struct page *page)
183 {
184 	return;
185 }
186 
balloon_page_migrate(struct page * newpage,struct page * page,enum migrate_mode mode)187 static inline int balloon_page_migrate(struct page *newpage,
188 				struct page *page, enum migrate_mode mode)
189 {
190 	return 0;
191 }
192 
balloon_mapping_gfp_mask(void)193 static inline gfp_t balloon_mapping_gfp_mask(void)
194 {
195 	return GFP_HIGHUSER;
196 }
197 
198 #endif /* CONFIG_BALLOON_COMPACTION */
199 
200 /*
201  * balloon_page_push - insert a page into a page list.
202  * @head : pointer to list
203  * @page : page to be added
204  *
205  * Caller must ensure the page is private and protect the list.
206  */
balloon_page_push(struct list_head * pages,struct page * page)207 static inline void balloon_page_push(struct list_head *pages, struct page *page)
208 {
209 	list_add(&page->lru, pages);
210 }
211 
212 /*
213  * balloon_page_pop - remove a page from a page list.
214  * @head : pointer to list
215  * @page : page to be added
216  *
217  * Caller must ensure the page is private and protect the list.
218  */
balloon_page_pop(struct list_head * pages)219 static inline struct page *balloon_page_pop(struct list_head *pages)
220 {
221 	struct page *page = list_first_entry_or_null(pages, struct page, lru);
222 
223 	if (!page)
224 		return NULL;
225 
226 	list_del(&page->lru);
227 	return page;
228 }
229 #endif /* _LINUX_BALLOON_COMPACTION_H */
230