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 "movable_ops page migration"
8 * feature.
9 *
10 * page->private is used to reference the responsible balloon device.
11 * That these pages have movable_ops, and which movable_ops apply,
12 * is derived from the page type (PageOffline()) combined with the
13 * PG_movable_ops flag (PageMovableOps()).
14 *
15 * As the page isolation scanning step a compaction thread does is a lockless
16 * procedure (from a page standpoint), it might bring some racy situations while
17 * performing balloon page compaction. In order to sort out these racy scenarios
18 * and safely perform balloon's page compaction and migration we must, always,
19 * ensure following these simple rules:
20 *
21 * i. Setting the PG_movable_ops flag and page->private with the following
22 * lock order
23 * +-page_lock(page);
24 * +--spin_lock_irq(&b_dev_info->pages_lock);
25 *
26 * ii. isolation or dequeueing procedure must remove the page from balloon
27 * device page list under b_dev_info->pages_lock.
28 *
29 * The functions provided by this interface are placed to help on coping with
30 * the aforementioned balloon page corner case, as well as to ensure the simple
31 * set of exposed rules are satisfied while we are dealing with balloon pages
32 * compaction / migration.
33 *
34 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com>
35 */
36#ifndef _LINUX_BALLOON_COMPACTION_H
37#define _LINUX_BALLOON_COMPACTION_H
38#include <linux/pagemap.h>
39#include <linux/page-flags.h>
40#include <linux/migrate.h>
41#include <linux/gfp.h>
42#include <linux/err.h>
43#include <linux/fs.h>
44#include <linux/list.h>
45
46/*
47 * Balloon device information descriptor.
48 * This struct is used to allow the common balloon compaction interface
49 * procedures to find the proper balloon device holding memory pages they'll
50 * have to cope for page compaction / migration, as well as it serves the
51 * balloon driver as a page book-keeper for its registered balloon devices.
52 */
53struct balloon_dev_info {
54 unsigned long isolated_pages; /* # of isolated pages for migration */
55 spinlock_t pages_lock; /* Protection to pages list */
56 struct list_head pages; /* Pages enqueued & handled to Host */
57 int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
58 struct page *page, enum migrate_mode mode);
59};
60
61extern struct page *balloon_page_alloc(void);
62extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
63 struct page *page);
64extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
65extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
66 struct list_head *pages);
67extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
68 struct list_head *pages, size_t n_req_pages);
69
70static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
71{
72 balloon->isolated_pages = 0;
73 spin_lock_init(&balloon->pages_lock);
74 INIT_LIST_HEAD(list: &balloon->pages);
75 balloon->migratepage = NULL;
76}
77
78#ifdef CONFIG_BALLOON_COMPACTION
79extern const struct movable_operations balloon_mops;
80/*
81 * balloon_page_device - get the b_dev_info descriptor for the balloon device
82 * that enqueues the given page.
83 */
84static inline struct balloon_dev_info *balloon_page_device(struct page *page)
85{
86 return (struct balloon_dev_info *)page_private(page);
87}
88#endif /* CONFIG_BALLOON_COMPACTION */
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 __SetPageOffline(page);
103 if (IS_ENABLED(CONFIG_BALLOON_COMPACTION)) {
104 SetPageMovableOps(page);
105 set_page_private(page, private: (unsigned long)balloon);
106 }
107 list_add(new: &page->lru, head: &balloon->pages);
108}
109
110static inline gfp_t balloon_mapping_gfp_mask(void)
111{
112 if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
113 return GFP_HIGHUSER_MOVABLE;
114 return GFP_HIGHUSER;
115}
116
117/*
118 * balloon_page_finalize - prepare a balloon page that was removed from the
119 * balloon list for release to the page allocator
120 * @page: page to be released to the page allocator
121 *
122 * Caller must ensure that the page is locked.
123 */
124static inline void balloon_page_finalize(struct page *page)
125{
126 if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
127 set_page_private(page, private: 0);
128 /* PageOffline is sticky until the page is freed to the buddy. */
129}
130
131/*
132 * balloon_page_push - insert a page into a page list.
133 * @head : pointer to list
134 * @page : page to be added
135 *
136 * Caller must ensure the page is private and protect the list.
137 */
138static inline void balloon_page_push(struct list_head *pages, struct page *page)
139{
140 list_add(new: &page->lru, head: pages);
141}
142
143/*
144 * balloon_page_pop - remove a page from a page list.
145 * @head : pointer to list
146 * @page : page to be added
147 *
148 * Caller must ensure the page is private and protect the list.
149 */
150static inline struct page *balloon_page_pop(struct list_head *pages)
151{
152 struct page *page = list_first_entry_or_null(pages, struct page, lru);
153
154 if (!page)
155 return NULL;
156
157 list_del(entry: &page->lru);
158 return page;
159}
160#endif /* _LINUX_BALLOON_COMPACTION_H */
161

source code of linux/include/linux/balloon_compaction.h