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 */ 54 struct 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 63 extern struct page *balloon_page_alloc(void); 64 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, 65 struct page *page); 66 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info); 67 68 static 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 78 extern const struct address_space_operations balloon_aops; 79 extern bool balloon_page_isolate(struct page *page, 80 isolate_mode_t mode); 81 extern void balloon_page_putback(struct page *page); 82 extern 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 */ 95 static 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 */ 112 static 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 */ 129 static inline struct balloon_dev_info *balloon_page_device(struct page *page) 130 { 131 return (struct balloon_dev_info *)page_private(page); 132 } 133 134 static inline gfp_t balloon_mapping_gfp_mask(void) 135 { 136 return GFP_HIGHUSER_MOVABLE; 137 } 138 139 #else /* !CONFIG_BALLOON_COMPACTION */ 140 141 static 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 } 147 148 static inline void balloon_page_delete(struct page *page) 149 { 150 __ClearPageOffline(page); 151 list_del(&page->lru); 152 } 153 154 static inline bool balloon_page_isolate(struct page *page) 155 { 156 return false; 157 } 158 159 static inline void balloon_page_putback(struct page *page) 160 { 161 return; 162 } 163 164 static inline int balloon_page_migrate(struct page *newpage, 165 struct page *page, enum migrate_mode mode) 166 { 167 return 0; 168 } 169 170 static inline gfp_t balloon_mapping_gfp_mask(void) 171 { 172 return GFP_HIGHUSER; 173 } 174 175 #endif /* CONFIG_BALLOON_COMPACTION */ 176 177 /* 178 * balloon_page_push - insert a page into a page list. 179 * @head : pointer to list 180 * @page : page to be added 181 * 182 * Caller must ensure the page is private and protect the list. 183 */ 184 static inline void balloon_page_push(struct list_head *pages, struct page *page) 185 { 186 list_add(&page->lru, pages); 187 } 188 189 /* 190 * balloon_page_pop - remove a page from a page list. 191 * @head : pointer to list 192 * @page : page to be added 193 * 194 * Caller must ensure the page is private and protect the list. 195 */ 196 static inline struct page *balloon_page_pop(struct list_head *pages) 197 { 198 struct page *page = list_first_entry_or_null(pages, struct page, lru); 199 200 if (!page) 201 return NULL; 202 203 list_del(&page->lru); 204 return page; 205 } 206 #endif /* _LINUX_BALLOON_COMPACTION_H */ 207