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 * Balloon page migration makes use of the general non-lru movable page
8 * feature.
9 *
10 * page->private is used to reference the responsible balloon device.
11 * page->mapping is used in context of non-lru page migration to reference
12 * the address space operations for page isolation/migration/compaction.
13 *
14 * As the page isolation scanning step a compaction thread does is a lockless
15 * procedure (from a page standpoint), it might bring some racy situations while
16 * performing balloon page compaction. In order to sort out these racy scenarios
17 * and safely perform balloon's page compaction and migration we must, always,
18 * ensure following these simple rules:
19 *
20 * i. when updating a balloon's page ->mapping element, strictly do it under
21 * the following lock order, independently of the far superior
22 * locking scheme (lru_lock, balloon_lock):
23 * +-page_lock(page);
24 * +--spin_lock_irq(&b_dev_info->pages_lock);
25 * ... page->mapping updates here ...
26 *
27 * ii. isolation or dequeueing procedure must remove the page from balloon
28 * device page list under b_dev_info->pages_lock.
29 *
30 * The functions provided by this interface are placed to help on coping with
31 * the aforementioned balloon page corner case, as well as to ensure the simple
32 * set of exposed rules are satisfied while we are dealing with balloon pages
33 * compaction / migration.
34 *
35 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
36 */
37#ifndef _LINUX_BALLOON_COMPACTION_H
38#define _LINUX_BALLOON_COMPACTION_H
39#include <linux/pagemap.h>
40#include <linux/page-flags.h>
41#include <linux/migrate.h>
42#include <linux/gfp.h>
43#include <linux/err.h>
44#include <linux/fs.h>
45#include <linux/list.h>
46
47/*
48 * Balloon device information descriptor.
49 * This struct is used to allow the common balloon compaction interface
50 * procedures to find the proper balloon device holding memory pages they'll
51 * have to cope for page compaction / migration, as well as it serves the
52 * balloon driver as a page book-keeper for its registered balloon devices.
53 */
54struct balloon_dev_info {
55 unsigned long isolated_pages; /* # of isolated pages for migration */
56 spinlock_t pages_lock; /* Protection to pages list */
57 struct list_head pages; /* Pages enqueued & handled to Host */
58 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
59 struct page *page, enum migrate_mode mode);
60 struct inode *inode;
61};
62
63extern struct page *balloon_page_alloc(void);
64extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
65 struct page *page);
66extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
67
68static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
69{
70 balloon->isolated_pages = 0;
71 spin_lock_init(&balloon->pages_lock);
72 INIT_LIST_HEAD(&balloon->pages);
73 balloon->migratepage = NULL;
74 balloon->inode = NULL;
75}
76
77#ifdef CONFIG_BALLOON_COMPACTION
78extern const struct address_space_operations balloon_aops;
79extern bool balloon_page_isolate(struct page *page,
80 isolate_mode_t mode);
81extern void balloon_page_putback(struct page *page);
82extern int balloon_page_migrate(struct address_space *mapping,
83 struct page *newpage,
84 struct page *page, enum migrate_mode mode);
85
86/*
87 * balloon_page_insert - insert a page into the balloon's page list and make
88 * the page->private assignment accordingly.
89 * @balloon : pointer to balloon device
90 * @page : page to be assigned as a 'balloon page'
91 *
92 * Caller must ensure the page is locked and the spin_lock protecting balloon
93 * pages list is held before inserting a page into the balloon device.
94 */
95static inline void balloon_page_insert(struct balloon_dev_info *balloon,
96 struct page *page)
97{
98 __SetPageOffline(page);
99 __SetPageMovable(page, balloon->inode->i_mapping);
100 set_page_private(page, (unsigned long)balloon);
101 list_add(&page->lru, &balloon->pages);
102}
103
104/*
105 * balloon_page_delete - delete a page from balloon's page list and clear
106 * the page->private assignement accordingly.
107 * @page : page to be released from balloon's page list
108 *
109 * Caller must ensure the page is locked and the spin_lock protecting balloon
110 * pages list is held before deleting a page from the balloon device.
111 */
112static inline void balloon_page_delete(struct page *page)
113{
114 __ClearPageOffline(page);
115 __ClearPageMovable(page);
116 set_page_private(page, 0);
117 /*
118 * No touch page.lru field once @page has been isolated
119 * because VM is using the field.
120 */
121 if (!PageIsolated(page))
122 list_del(&page->lru);
123}
124
125/*
126 * balloon_page_device - get the b_dev_info descriptor for the balloon device
127 * that enqueues the given page.
128 */
129static inline struct balloon_dev_info *balloon_page_device(struct page *page)
130{
131 return (struct balloon_dev_info *)page_private(page);
132}
133
134static inline gfp_t balloon_mapping_gfp_mask(void)
135{
136 return GFP_HIGHUSER_MOVABLE;
137}
138
139#else /* !CONFIG_BALLOON_COMPACTION */
140
141static inline void balloon_page_insert(struct balloon_dev_info *balloon,
142 struct page *page)
143{
144 __SetPageOffline(page);
145 list_add(&page->lru, &balloon->pages);
146}
147
148static inline void balloon_page_delete(struct page *page)
149{
150 __ClearPageOffline(page);
151 list_del(&page->lru);
152}
153
154static inline bool __is_movable_balloon_page(struct page *page)
155{
156 return false;
157}
158
159static inline bool balloon_page_movable(struct page *page)
160{
161 return false;
162}
163
164static inline bool isolated_balloon_page(struct page *page)
165{
166 return false;
167}
168
169static inline bool balloon_page_isolate(struct page *page)
170{
171 return false;
172}
173
174static inline void balloon_page_putback(struct page *page)
175{
176 return;
177}
178
179static inline int balloon_page_migrate(struct page *newpage,
180 struct page *page, enum migrate_mode mode)
181{
182 return 0;
183}
184
185static inline gfp_t balloon_mapping_gfp_mask(void)
186{
187 return GFP_HIGHUSER;
188}
189
190#endif /* CONFIG_BALLOON_COMPACTION */
191
192/*
193 * balloon_page_push - insert a page into a page list.
194 * @head : pointer to list
195 * @page : page to be added
196 *
197 * Caller must ensure the page is private and protect the list.
198 */
199static inline void balloon_page_push(struct list_head *pages, struct page *page)
200{
201 list_add(&page->lru, pages);
202}
203
204/*
205 * balloon_page_pop - remove a page from a page list.
206 * @head : pointer to list
207 * @page : page to be added
208 *
209 * Caller must ensure the page is private and protect the list.
210 */
211static inline struct page *balloon_page_pop(struct list_head *pages)
212{
213 struct page *page = list_first_entry_or_null(pages, struct page, lru);
214
215 if (!page)
216 return NULL;
217
218 list_del(&page->lru);
219 return page;
220}
221#endif /* _LINUX_BALLOON_COMPACTION_H */
222