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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 * 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.
10 *
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:
16 *
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):
20 * +-page_lock(page);
21 * +--spin_lock_irq(&b_dev_info->pages_lock);
22 * ... page->mapping updates here ...
23 *
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;
29 *
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)
34 *
35 * iv. isolation or dequeueing procedure must clear PagePrivate flag under
36 * page lock together with removing page from balloon device page list.
37 *
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.
42 *
43 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
44 */
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>
52#include <linux/fs.h>
53
54/*
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.
60 */
61struct 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);
67 struct inode *inode;
68};
69
70extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
71extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
72
73static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
74{
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;
80}
81
82#ifdef CONFIG_BALLOON_COMPACTION
83extern const struct address_space_operations balloon_aops;
84extern bool balloon_page_isolate(struct page *page,
85 isolate_mode_t mode);
86extern void balloon_page_putback(struct page *page);
87extern int balloon_page_migrate(struct address_space *mapping,
88 struct page *newpage,
89 struct page *page, enum migrate_mode mode);
90
91/*
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'
96 *
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.
99 */
100static inline void balloon_page_insert(struct balloon_dev_info *balloon,
101 struct page *page)
102{
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);
107}
108
109/*
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
113 *
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.
116 */
117static inline void balloon_page_delete(struct page *page)
118{
119 __ClearPageBalloon(page);
120 __ClearPageMovable(page);
121 set_page_private(page, 0);
122 /*
123 * No touch page.lru field once @page has been isolated
124 * because VM is using the field.
125 */
126 if (!PageIsolated(page))
127 list_del(&page->lru);
128}
129
130/*
131 * balloon_page_device - get the b_dev_info descriptor for the balloon device
132 * that enqueues the given page.
133 */
134static inline struct balloon_dev_info *balloon_page_device(struct page *page)
135{
136 return (struct balloon_dev_info *)page_private(page);
137}
138
139static inline gfp_t balloon_mapping_gfp_mask(void)
140{
141 return GFP_HIGHUSER_MOVABLE;
142}
143
144#else /* !CONFIG_BALLOON_COMPACTION */
145
146static inline void balloon_page_insert(struct balloon_dev_info *balloon,
147 struct page *page)
148{
149 __SetPageBalloon(page);
150 list_add(&page->lru, &balloon->pages);
151}
152
153static inline void balloon_page_delete(struct page *page)
154{
155 __ClearPageBalloon(page);
156 list_del(&page->lru);
157}
158
159static inline bool __is_movable_balloon_page(struct page *page)
160{
161 return false;
162}
163
164static inline bool balloon_page_movable(struct page *page)
165{
166 return false;
167}
168
169static inline bool isolated_balloon_page(struct page *page)
170{
171 return false;
172}
173
174static inline bool balloon_page_isolate(struct page *page)
175{
176 return false;
177}
178
179static inline void balloon_page_putback(struct page *page)
180{
181 return;
182}
183
184static inline int balloon_page_migrate(struct page *newpage,
185 struct page *page, enum migrate_mode mode)
186{
187 return 0;
188}
189
190static inline gfp_t balloon_mapping_gfp_mask(void)
191{
192 return GFP_HIGHUSER;
193}
194
195#endif /* CONFIG_BALLOON_COMPACTION */
196#endif /* _LINUX_BALLOON_COMPACTION_H */