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 <[email protected]> 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 */ 62 struct 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 71 extern struct page *balloon_page_alloc(void); 72 extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, 73 struct page *page); 74 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info); 75 76 static 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 86 extern const struct address_space_operations balloon_aops; 87 extern bool balloon_page_isolate(struct page *page, 88 isolate_mode_t mode); 89 extern void balloon_page_putback(struct page *page); 90 extern 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 */ 103 static 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 */ 120 static 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 */ 137 static inline struct balloon_dev_info *balloon_page_device(struct page *page) 138 { 139 return (struct balloon_dev_info *)page_private(page); 140 } 141 142 static inline gfp_t balloon_mapping_gfp_mask(void) 143 { 144 return GFP_HIGHUSER_MOVABLE; 145 } 146 147 #else /* !CONFIG_BALLOON_COMPACTION */ 148 149 static 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 } 155 156 static inline void balloon_page_delete(struct page *page) 157 { 158 __ClearPageBalloon(page); 159 list_del(&page->lru); 160 } 161 162 static inline bool __is_movable_balloon_page(struct page *page) 163 { 164 return false; 165 } 166 167 static inline bool balloon_page_movable(struct page *page) 168 { 169 return false; 170 } 171 172 static inline bool isolated_balloon_page(struct page *page) 173 { 174 return false; 175 } 176 177 static inline bool balloon_page_isolate(struct page *page) 178 { 179 return false; 180 } 181 182 static inline void balloon_page_putback(struct page *page) 183 { 184 return; 185 } 186 187 static inline int balloon_page_migrate(struct page *newpage, 188 struct page *page, enum migrate_mode mode) 189 { 190 return 0; 191 } 192 193 static 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 */ 207 static 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 */ 219 static 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 */ 230