1 /* SPDX-License-Identifier: GPL-2.0 */
3 * include/linux/balloon_compaction.h
5 * Common interface definitions for making balloon pages movable by compaction.
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.
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:
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):
21 * +--spin_lock_irq(&b_dev_info->pages_lock);
22 * ... page->mapping updates here ...
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;
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)
35 * iv. isolation or dequeueing procedure must clear PagePrivate flag under
36 * page lock together with removing page from balloon device page list.
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.
43 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
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>
55 * Balloon device information descriptor.
56 * This struct is used to allow the common balloon compaction interface
57 * procedures to find the proper balloon device holding memory pages they'll
58 * have to cope for page compaction / migration, as well as it serves the
59 * balloon driver as a page book-keeper for its registered balloon devices.
61 struct balloon_dev_info {
62 unsigned long isolated_pages; /* # of isolated pages for migration */
63 spinlock_t pages_lock; /* Protection to pages list */
64 struct list_head pages; /* Pages enqueued & handled to Host */
65 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
66 struct page *page, enum migrate_mode mode);
70 extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
71 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
73 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
75 balloon->isolated_pages = 0;
76 spin_lock_init(&balloon->pages_lock);
77 INIT_LIST_HEAD(&balloon->pages);
78 balloon->migratepage = NULL;
79 balloon->inode = NULL;
82 #ifdef CONFIG_BALLOON_COMPACTION
83 extern const struct address_space_operations balloon_aops;
84 extern bool balloon_page_isolate(struct page *page,
86 extern void balloon_page_putback(struct page *page);
87 extern int balloon_page_migrate(struct address_space *mapping,
89 struct page *page, enum migrate_mode mode);
92 * balloon_page_insert - insert a page into the balloon's page list and make
93 * the page->private assignment accordingly.
94 * @balloon : pointer to balloon device
95 * @page : page to be assigned as a 'balloon page'
97 * Caller must ensure the page is locked and the spin_lock protecting balloon
98 * pages list is held before inserting a page into the balloon device.
100 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
103 __SetPageBalloon(page);
104 __SetPageMovable(page, balloon->inode->i_mapping);
105 set_page_private(page, (unsigned long)balloon);
106 list_add(&page->lru, &balloon->pages);
110 * balloon_page_delete - delete a page from balloon's page list and clear
111 * the page->private assignement accordingly.
112 * @page : page to be released from balloon's page list
114 * Caller must ensure the page is locked and the spin_lock protecting balloon
115 * pages list is held before deleting a page from the balloon device.
117 static inline void balloon_page_delete(struct page *page)
119 __ClearPageBalloon(page);
120 __ClearPageMovable(page);
121 set_page_private(page, 0);
123 * No touch page.lru field once @page has been isolated
124 * because VM is using the field.
126 if (!PageIsolated(page))
127 list_del(&page->lru);
131 * balloon_page_device - get the b_dev_info descriptor for the balloon device
132 * that enqueues the given page.
134 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
136 return (struct balloon_dev_info *)page_private(page);
139 static inline gfp_t balloon_mapping_gfp_mask(void)
141 return GFP_HIGHUSER_MOVABLE;
144 #else /* !CONFIG_BALLOON_COMPACTION */
146 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
149 __SetPageBalloon(page);
150 list_add(&page->lru, &balloon->pages);
153 static inline void balloon_page_delete(struct page *page)
155 __ClearPageBalloon(page);
156 list_del(&page->lru);
159 static inline bool __is_movable_balloon_page(struct page *page)
164 static inline bool balloon_page_movable(struct page *page)
169 static inline bool isolated_balloon_page(struct page *page)
174 static inline bool balloon_page_isolate(struct page *page)
179 static inline void balloon_page_putback(struct page *page)
184 static inline int balloon_page_migrate(struct page *newpage,
185 struct page *page, enum migrate_mode mode)
190 static inline gfp_t balloon_mapping_gfp_mask(void)
195 #endif /* CONFIG_BALLOON_COMPACTION */
196 #endif /* _LINUX_BALLOON_COMPACTION_H */