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