2 * include/linux/balloon_compaction.h
4 * Common interface definitions for making balloon pages movable by compaction.
6 * Despite being perfectly possible to perform ballooned pages migration, they
7 * make a special corner case to compaction scans because balloon pages are not
8 * enlisted at any LRU list like the other pages we do compact / migrate.
10 * As the page isolation scanning step a compaction thread does is a lockless
11 * procedure (from a page standpoint), it might bring some racy situations while
12 * performing balloon page compaction. In order to sort out these racy scenarios
13 * and safely perform balloon's page compaction and migration we must, always,
14 * ensure following these three simple rules:
16 * i. when updating a balloon's page ->mapping element, strictly do it under
17 * the following lock order, independently of the far superior
18 * locking scheme (lru_lock, balloon_lock):
20 * +--spin_lock_irq(&b_dev_info->pages_lock);
21 * ... page->mapping updates here ...
23 * ii. before isolating or dequeueing a balloon page from the balloon device
24 * pages list, the page reference counter must be raised by one and the
25 * extra refcount must be dropped when the page is enqueued back into
26 * the balloon device page list, thus a balloon page keeps its reference
27 * counter raised only while it is under our special handling;
29 * iii. after the lockless scan step have selected a potential balloon page for
30 * isolation, re-test the PageBalloon mark and the PagePrivate flag
31 * under the proper page lock, to ensure isolating a valid balloon page
32 * (not yet isolated, nor under release procedure)
34 * iv. isolation or dequeueing procedure must clear PagePrivate flag under
35 * page lock together with removing page from balloon device page list.
37 * The functions provided by this interface are placed to help on coping with
38 * the aforementioned balloon page corner case, as well as to ensure the simple
39 * set of exposed rules are satisfied while we are dealing with balloon pages
40 * compaction / migration.
42 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
44 #ifndef _LINUX_BALLOON_COMPACTION_H
45 #define _LINUX_BALLOON_COMPACTION_H
46 #include <linux/pagemap.h>
47 #include <linux/page-flags.h>
48 #include <linux/migrate.h>
49 #include <linux/gfp.h>
50 #include <linux/err.h>
54 * Balloon device information descriptor.
55 * This struct is used to allow the common balloon compaction interface
56 * procedures to find the proper balloon device holding memory pages they'll
57 * have to cope for page compaction / migration, as well as it serves the
58 * balloon driver as a page book-keeper for its registered balloon devices.
60 struct balloon_dev_info
{
61 unsigned long isolated_pages
; /* # of isolated pages for migration */
62 spinlock_t pages_lock
; /* Protection to pages list */
63 struct list_head pages
; /* Pages enqueued & handled to Host */
64 int (*migratepage
)(struct balloon_dev_info
*, struct page
*newpage
,
65 struct page
*page
, enum migrate_mode mode
);
69 extern struct page
*balloon_page_enqueue(struct balloon_dev_info
*b_dev_info
);
70 extern struct page
*balloon_page_dequeue(struct balloon_dev_info
*b_dev_info
);
72 static inline void balloon_devinfo_init(struct balloon_dev_info
*balloon
)
74 balloon
->isolated_pages
= 0;
75 spin_lock_init(&balloon
->pages_lock
);
76 INIT_LIST_HEAD(&balloon
->pages
);
77 balloon
->migratepage
= NULL
;
78 balloon
->inode
= NULL
;
81 #ifdef CONFIG_BALLOON_COMPACTION
82 extern const struct address_space_operations balloon_aops
;
83 extern bool balloon_page_isolate(struct page
*page
,
85 extern void balloon_page_putback(struct page
*page
);
86 extern int balloon_page_migrate(struct address_space
*mapping
,
88 struct page
*page
, enum migrate_mode mode
);
91 * balloon_page_insert - insert a page into the balloon's page list and make
92 * the page->private assignment accordingly.
93 * @balloon : pointer to balloon device
94 * @page : page to be assigned as a 'balloon page'
96 * Caller must ensure the page is locked and the spin_lock protecting balloon
97 * pages list is held before inserting a page into the balloon device.
99 static inline void balloon_page_insert(struct balloon_dev_info
*balloon
,
102 __SetPageBalloon(page
);
103 __SetPageMovable(page
, balloon
->inode
->i_mapping
);
104 set_page_private(page
, (unsigned long)balloon
);
105 list_add(&page
->lru
, &balloon
->pages
);
109 * balloon_page_delete - delete a page from balloon's page list and clear
110 * the page->private assignement accordingly.
111 * @page : page to be released from balloon's page list
113 * Caller must ensure the page is locked and the spin_lock protecting balloon
114 * pages list is held before deleting a page from the balloon device.
116 static inline void balloon_page_delete(struct page
*page
)
118 __ClearPageBalloon(page
);
119 __ClearPageMovable(page
);
120 set_page_private(page
, 0);
122 * No touch page.lru field once @page has been isolated
123 * because VM is using the field.
125 if (!PageIsolated(page
))
126 list_del(&page
->lru
);
130 * balloon_page_device - get the b_dev_info descriptor for the balloon device
131 * that enqueues the given page.
133 static inline struct balloon_dev_info
*balloon_page_device(struct page
*page
)
135 return (struct balloon_dev_info
*)page_private(page
);
138 static inline gfp_t
balloon_mapping_gfp_mask(void)
140 return GFP_HIGHUSER_MOVABLE
;
143 #else /* !CONFIG_BALLOON_COMPACTION */
145 static inline void balloon_page_insert(struct balloon_dev_info
*balloon
,
148 __SetPageBalloon(page
);
149 list_add(&page
->lru
, &balloon
->pages
);
152 static inline void balloon_page_delete(struct page
*page
)
154 __ClearPageBalloon(page
);
155 list_del(&page
->lru
);
158 static inline bool __is_movable_balloon_page(struct page
*page
)
163 static inline bool balloon_page_movable(struct page
*page
)
168 static inline bool isolated_balloon_page(struct page
*page
)
173 static inline bool balloon_page_isolate(struct page
*page
)
178 static inline void balloon_page_putback(struct page
*page
)
183 static inline int balloon_page_migrate(struct page
*newpage
,
184 struct page
*page
, enum migrate_mode mode
)
189 static inline gfp_t
balloon_mapping_gfp_mask(void)
194 #endif /* CONFIG_BALLOON_COMPACTION */
195 #endif /* _LINUX_BALLOON_COMPACTION_H */