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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#include <linux/list.h>
54
55/*
56 * Balloon device information descriptor.
57 * This struct is used to allow the common balloon compaction interface
58 * procedures to find the proper balloon device holding memory pages they'll
59 * have to cope for page compaction / migration, as well as it serves the
60 * balloon driver as a page book-keeper for its registered balloon devices.
61 */
62struct balloon_dev_info {
63 unsigned long isolated_pages; /* # of isolated pages for migration */
64 spinlock_t pages_lock; /* Protection to pages list */
65 struct list_head pages; /* Pages enqueued & handled to Host */
66 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
67 struct page *page, enum migrate_mode mode);
68 struct inode *inode;
69};
70
71extern struct page *balloon_page_alloc(void);
72extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
73 struct page *page);
74extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
75
76static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
77{
78 balloon->isolated_pages = 0;
79 spin_lock_init(&balloon->pages_lock);
80 INIT_LIST_HEAD(&balloon->pages);
81 balloon->migratepage = NULL;
82 balloon->inode = NULL;
83}
84
85#ifdef CONFIG_BALLOON_COMPACTION
86extern const struct address_space_operations balloon_aops;
87extern bool balloon_page_isolate(struct page *page,
88 isolate_mode_t mode);
89extern void balloon_page_putback(struct page *page);
90extern int balloon_page_migrate(struct address_space *mapping,
91 struct page *newpage,
92 struct page *page, enum migrate_mode mode);
93
94/*
95 * balloon_page_insert - insert a page into the balloon's page list and make
96 * the page->private assignment accordingly.
97 * @balloon : pointer to balloon device
98 * @page : page to be assigned as a 'balloon page'
99 *
100 * Caller must ensure the page is locked and the spin_lock protecting balloon
101 * pages list is held before inserting a page into the balloon device.
102 */
103static inline void balloon_page_insert(struct balloon_dev_info *balloon,
104 struct page *page)
105{
106 __SetPageBalloon(page);
107 __SetPageMovable(page, balloon->inode->i_mapping);
108 set_page_private(page, (unsigned long)balloon);
109 list_add(&page->lru, &balloon->pages);
110}
111
112/*
113 * balloon_page_delete - delete a page from balloon's page list and clear
114 * the page->private assignement accordingly.
115 * @page : page to be released from balloon's page list
116 *
117 * Caller must ensure the page is locked and the spin_lock protecting balloon
118 * pages list is held before deleting a page from the balloon device.
119 */
120static inline void balloon_page_delete(struct page *page)
121{
122 __ClearPageBalloon(page);
123 __ClearPageMovable(page);
124 set_page_private(page, 0);
125 /*
126 * No touch page.lru field once @page has been isolated
127 * because VM is using the field.
128 */
129 if (!PageIsolated(page))
130 list_del(&page->lru);
131}
132
133/*
134 * balloon_page_device - get the b_dev_info descriptor for the balloon device
135 * that enqueues the given page.
136 */
137static inline struct balloon_dev_info *balloon_page_device(struct page *page)
138{
139 return (struct balloon_dev_info *)page_private(page);
140}
141
142static inline gfp_t balloon_mapping_gfp_mask(void)
143{
144 return GFP_HIGHUSER_MOVABLE;
145}
146
147#else /* !CONFIG_BALLOON_COMPACTION */
148
149static inline void balloon_page_insert(struct balloon_dev_info *balloon,
150 struct page *page)
151{
152 __SetPageBalloon(page);
153 list_add(&page->lru, &balloon->pages);
154}
155
156static inline void balloon_page_delete(struct page *page)
157{
158 __ClearPageBalloon(page);
159 list_del(&page->lru);
160}
161
162static inline bool __is_movable_balloon_page(struct page *page)
163{
164 return false;
165}
166
167static inline bool balloon_page_movable(struct page *page)
168{
169 return false;
170}
171
172static inline bool isolated_balloon_page(struct page *page)
173{
174 return false;
175}
176
177static inline bool balloon_page_isolate(struct page *page)
178{
179 return false;
180}
181
182static inline void balloon_page_putback(struct page *page)
183{
184 return;
185}
186
187static inline int balloon_page_migrate(struct page *newpage,
188 struct page *page, enum migrate_mode mode)
189{
190 return 0;
191}
192
193static inline gfp_t balloon_mapping_gfp_mask(void)
194{
195 return GFP_HIGHUSER;
196}
197
198#endif /* CONFIG_BALLOON_COMPACTION */
199
200/*
201 * balloon_page_push - insert a page into a page list.
202 * @head : pointer to list
203 * @page : page to be added
204 *
205 * Caller must ensure the page is private and protect the list.
206 */
207static inline void balloon_page_push(struct list_head *pages, struct page *page)
208{
209 list_add(&page->lru, pages);
210}
211
212/*
213 * balloon_page_pop - remove a page from a page list.
214 * @head : pointer to list
215 * @page : page to be added
216 *
217 * Caller must ensure the page is private and protect the list.
218 */
219static inline struct page *balloon_page_pop(struct list_head *pages)
220{
221 struct page *page = list_first_entry_or_null(pages, struct page, lru);
222
223 if (!page)
224 return NULL;
225
226 list_del(&page->lru);
227 return page;
228}
229#endif /* _LINUX_BALLOON_COMPACTION_H */