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 
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 };
61 
62 extern struct page *balloon_page_alloc(void);
63 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
64 				 struct page *page);
65 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
66 extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
67 				      struct list_head *pages);
68 extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
69 				     struct list_head *pages, size_t n_req_pages);
70 
balloon_devinfo_init(struct balloon_dev_info * balloon)71 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
72 {
73 	balloon->isolated_pages = 0;
74 	spin_lock_init(&balloon->pages_lock);
75 	INIT_LIST_HEAD(&balloon->pages);
76 	balloon->migratepage = NULL;
77 }
78 
79 #ifdef CONFIG_BALLOON_COMPACTION
80 extern const struct movable_operations balloon_mops;
81 
82 /*
83  * balloon_page_insert - insert a page into the balloon's page list and make
84  *			 the page->private assignment accordingly.
85  * @balloon : pointer to balloon device
86  * @page    : page to be assigned as a 'balloon page'
87  *
88  * Caller must ensure the page is locked and the spin_lock protecting balloon
89  * pages list is held before inserting a page into the balloon device.
90  */
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)91 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
92 				       struct page *page)
93 {
94 	__SetPageOffline(page);
95 	__SetPageMovable(page, &balloon_mops);
96 	set_page_private(page, (unsigned long)balloon);
97 	list_add(&page->lru, &balloon->pages);
98 }
99 
100 /*
101  * balloon_page_delete - delete a page from balloon's page list and clear
102  *			 the page->private assignement accordingly.
103  * @page    : page to be released from balloon's page list
104  *
105  * Caller must ensure the page is locked and the spin_lock protecting balloon
106  * pages list is held before deleting a page from the balloon device.
107  */
balloon_page_delete(struct page * page)108 static inline void balloon_page_delete(struct page *page)
109 {
110 	__ClearPageOffline(page);
111 	__ClearPageMovable(page);
112 	set_page_private(page, 0);
113 	/*
114 	 * No touch page.lru field once @page has been isolated
115 	 * because VM is using the field.
116 	 */
117 	if (!PageIsolated(page))
118 		list_del(&page->lru);
119 }
120 
121 /*
122  * balloon_page_device - get the b_dev_info descriptor for the balloon device
123  *			 that enqueues the given page.
124  */
balloon_page_device(struct page * page)125 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
126 {
127 	return (struct balloon_dev_info *)page_private(page);
128 }
129 
balloon_mapping_gfp_mask(void)130 static inline gfp_t balloon_mapping_gfp_mask(void)
131 {
132 	return GFP_HIGHUSER_MOVABLE;
133 }
134 
135 #else /* !CONFIG_BALLOON_COMPACTION */
136 
balloon_page_insert(struct balloon_dev_info * balloon,struct page * page)137 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
138 				       struct page *page)
139 {
140 	__SetPageOffline(page);
141 	list_add(&page->lru, &balloon->pages);
142 }
143 
balloon_page_delete(struct page * page)144 static inline void balloon_page_delete(struct page *page)
145 {
146 	__ClearPageOffline(page);
147 	list_del(&page->lru);
148 }
149 
balloon_mapping_gfp_mask(void)150 static inline gfp_t balloon_mapping_gfp_mask(void)
151 {
152 	return GFP_HIGHUSER;
153 }
154 
155 #endif /* CONFIG_BALLOON_COMPACTION */
156 
157 /*
158  * balloon_page_push - insert a page into a page list.
159  * @head : pointer to list
160  * @page : page to be added
161  *
162  * Caller must ensure the page is private and protect the list.
163  */
balloon_page_push(struct list_head * pages,struct page * page)164 static inline void balloon_page_push(struct list_head *pages, struct page *page)
165 {
166 	list_add(&page->lru, pages);
167 }
168 
169 /*
170  * balloon_page_pop - remove a page from a page list.
171  * @head : pointer to list
172  * @page : page to be added
173  *
174  * Caller must ensure the page is private and protect the list.
175  */
balloon_page_pop(struct list_head * pages)176 static inline struct page *balloon_page_pop(struct list_head *pages)
177 {
178 	struct page *page = list_first_entry_or_null(pages, struct page, lru);
179 
180 	if (!page)
181 		return NULL;
182 
183 	list_del(&page->lru);
184 	return page;
185 }
186 #endif /* _LINUX_BALLOON_COMPACTION_H */
187