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1/*
2 * include/linux/balloon_compaction.h
3 *
4 * Common interface definitions for making balloon pages movable by compaction.
5 *
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.
9 *
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:
15 *
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):
19 * +-page_lock(page);
20 * +--spin_lock_irq(&b_dev_info->pages_lock);
21 * ... page->mapping updates here ...
22 *
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;
28 *
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)
33 *
34 * iv. isolation or dequeueing procedure must clear PagePrivate flag under
35 * page lock together with removing page from balloon device page list.
36 *
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.
41 *
42 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
43 */
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>
51#include <linux/fs.h>
52
53/*
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.
59 */
60struct 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);
66 struct inode *inode;
67};
68
69extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
70extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
71
72static 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 balloon->inode = NULL;
79}
80
81#ifdef CONFIG_BALLOON_COMPACTION
82extern const struct address_space_operations balloon_aops;
83extern bool balloon_page_isolate(struct page *page,
84 isolate_mode_t mode);
85extern void balloon_page_putback(struct page *page);
86extern int balloon_page_migrate(struct address_space *mapping,
87 struct page *newpage,
88 struct page *page, enum migrate_mode mode);
89
90/*
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'
95 *
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.
98 */
99static inline void balloon_page_insert(struct balloon_dev_info *balloon,
100 struct page *page)
101{
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);
106}
107
108/*
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
112 *
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.
115 */
116static inline void balloon_page_delete(struct page *page)
117{
118 __ClearPageBalloon(page);
119 __ClearPageMovable(page);
120 set_page_private(page, 0);
121 /*
122 * No touch page.lru field once @page has been isolated
123 * because VM is using the field.
124 */
125 if (!PageIsolated(page))
126 list_del(&page->lru);
127}
128
129/*
130 * balloon_page_device - get the b_dev_info descriptor for the balloon device
131 * that enqueues the given page.
132 */
133static inline struct balloon_dev_info *balloon_page_device(struct page *page)
134{
135 return (struct balloon_dev_info *)page_private(page);
136}
137
138static inline gfp_t balloon_mapping_gfp_mask(void)
139{
140 return GFP_HIGHUSER_MOVABLE;
141}
142
143#else /* !CONFIG_BALLOON_COMPACTION */
144
145static inline void balloon_page_insert(struct balloon_dev_info *balloon,
146 struct page *page)
147{
148 __SetPageBalloon(page);
149 list_add(&page->lru, &balloon->pages);
150}
151
152static inline void balloon_page_delete(struct page *page)
153{
154 __ClearPageBalloon(page);
155 list_del(&page->lru);
156}
157
158static inline bool __is_movable_balloon_page(struct page *page)
159{
160 return false;
161}
162
163static inline bool balloon_page_movable(struct page *page)
164{
165 return false;
166}
167
168static inline bool isolated_balloon_page(struct page *page)
169{
170 return false;
171}
172
173static inline bool balloon_page_isolate(struct page *page)
174{
175 return false;
176}
177
178static inline void balloon_page_putback(struct page *page)
179{
180 return;
181}
182
183static inline int balloon_page_migrate(struct page *newpage,
184 struct page *page, enum migrate_mode mode)
185{
186 return 0;
187}
188
189static inline gfp_t balloon_mapping_gfp_mask(void)
190{
191 return GFP_HIGHUSER;
192}
193
194#endif /* CONFIG_BALLOON_COMPACTION */
195#endif /* _LINUX_BALLOON_COMPACTION_H */