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 <aquini@redhat.com>
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 #include <linux/mem_relinquish.h>
47
48 /*
49 * Balloon device information descriptor.
50 * This struct is used to allow the common balloon compaction interface
51 * procedures to find the proper balloon device holding memory pages they'll
52 * have to cope for page compaction / migration, as well as it serves the
53 * balloon driver as a page book-keeper for its registered balloon devices.
54 */
55 struct balloon_dev_info {
56 unsigned long isolated_pages; /* # of isolated pages for migration */
57 spinlock_t pages_lock; /* Protection to pages list */
58 struct list_head pages; /* Pages enqueued & handled to Host */
59 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
60 struct page *page, enum migrate_mode mode);
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 extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
68 struct list_head *pages);
69 extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
70 struct list_head *pages, size_t n_req_pages);
71
balloon_devinfo_init(struct balloon_dev_info * balloon)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 }
79
80 #ifdef CONFIG_BALLOON_COMPACTION
81 extern const struct movable_operations balloon_mops;
82
83 /*
84 * balloon_page_insert - insert a page into the balloon's page list and make
85 * the page->private assignment accordingly.
86 * @balloon : pointer to balloon device
87 * @page : page to be assigned as a 'balloon page'
88 *
89 * Caller must ensure the page is locked and the spin_lock protecting balloon
90 * pages list is held before inserting a page into the balloon device.
91 */
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)92 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
93 struct page *page)
94 {
95 __SetPageOffline(page);
96 __SetPageMovable(page, &balloon_mops);
97 set_page_private(page, (unsigned long)balloon);
98 list_add(&page->lru, &balloon->pages);
99 page_relinquish(page);
100 }
101
102 /*
103 * balloon_page_delete - delete a page from balloon's page list and clear
104 * the page->private assignement accordingly.
105 * @page : page to be released from balloon's page list
106 *
107 * Caller must ensure the page is locked and the spin_lock protecting balloon
108 * pages list is held before deleting a page from the balloon device.
109 */
balloon_page_delete(struct page * page)110 static inline void balloon_page_delete(struct page *page)
111 {
112 __ClearPageOffline(page);
113 __ClearPageMovable(page);
114 set_page_private(page, 0);
115 /*
116 * No touch page.lru field once @page has been isolated
117 * because VM is using the field.
118 */
119 if (!PageIsolated(page))
120 list_del(&page->lru);
121 }
122
123 /*
124 * balloon_page_device - get the b_dev_info descriptor for the balloon device
125 * that enqueues the given page.
126 */
balloon_page_device(struct page * page)127 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
128 {
129 return (struct balloon_dev_info *)page_private(page);
130 }
131
balloon_mapping_gfp_mask(void)132 static inline gfp_t balloon_mapping_gfp_mask(void)
133 {
134 return GFP_HIGHUSER_MOVABLE;
135 }
136
137 #else /* !CONFIG_BALLOON_COMPACTION */
138
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)139 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
140 struct page *page)
141 {
142 __SetPageOffline(page);
143 list_add(&page->lru, &balloon->pages);
144 page_relinquish(page);
145 }
146
balloon_page_delete(struct page * page)147 static inline void balloon_page_delete(struct page *page)
148 {
149 __ClearPageOffline(page);
150 list_del(&page->lru);
151 }
152
balloon_mapping_gfp_mask(void)153 static inline gfp_t balloon_mapping_gfp_mask(void)
154 {
155 return GFP_HIGHUSER;
156 }
157
158 #endif /* CONFIG_BALLOON_COMPACTION */
159
160 /*
161 * balloon_page_push - insert a page into a page list.
162 * @head : pointer to list
163 * @page : page to be added
164 *
165 * Caller must ensure the page is private and protect the list.
166 */
balloon_page_push(struct list_head * pages,struct page * page)167 static inline void balloon_page_push(struct list_head *pages, struct page *page)
168 {
169 list_add(&page->lru, pages);
170 }
171
172 /*
173 * balloon_page_pop - remove a page from a page list.
174 * @head : pointer to list
175 * @page : page to be added
176 *
177 * Caller must ensure the page is private and protect the list.
178 */
balloon_page_pop(struct list_head * pages)179 static inline struct page *balloon_page_pop(struct list_head *pages)
180 {
181 struct page *page = list_first_entry_or_null(pages, struct page, lru);
182
183 if (!page)
184 return NULL;
185
186 list_del(&page->lru);
187 return page;
188 }
189 #endif /* _LINUX_BALLOON_COMPACTION_H */
190