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 extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info, 68 struct list_head *pages); 69 extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info, 70 struct list_head *pages, size_t n_req_pages); 71 72 static inline void balloon_devinfo_init(struct balloon_dev_info *balloon) 73 { 74 balloon->isolated_pages = 0; 75 spin_lock_init(&balloon->pages_lock); 76 INIT_LIST_HEAD(&balloon->pages); 77 balloon->migratepage = NULL; 78 balloon->inode = NULL; 79 } 80 81 #ifdef CONFIG_BALLOON_COMPACTION 82 extern const struct address_space_operations balloon_aops; 83 84 /* 85 * balloon_page_insert - insert a page into the balloon's page list and make 86 * the page->private assignment accordingly. 87 * @balloon : pointer to balloon device 88 * @page : page to be assigned as a 'balloon page' 89 * 90 * Caller must ensure the page is locked and the spin_lock protecting balloon 91 * pages list is held before inserting a page into the balloon device. 92 */ 93 static inline void balloon_page_insert(struct balloon_dev_info *balloon, 94 struct page *page) 95 { 96 __SetPageOffline(page); 97 __SetPageMovable(page, balloon->inode->i_mapping); 98 set_page_private(page, (unsigned long)balloon); 99 list_add(&page->lru, &balloon->pages); 100 } 101 102 /* 103 * balloon_page_delete - delete a page from balloon's page list and clear 104 * the page->private assignement accordingly. 105 * @page : page to be released from balloon's page list 106 * 107 * Caller must ensure the page is locked and the spin_lock protecting balloon 108 * pages list is held before deleting a page from the balloon device. 109 */ 110 static inline void balloon_page_delete(struct page *page) 111 { 112 __ClearPageOffline(page); 113 __ClearPageMovable(page); 114 set_page_private(page, 0); 115 /* 116 * No touch page.lru field once @page has been isolated 117 * because VM is using the field. 118 */ 119 if (!PageIsolated(page)) 120 list_del(&page->lru); 121 } 122 123 /* 124 * balloon_page_device - get the b_dev_info descriptor for the balloon device 125 * that enqueues the given page. 126 */ 127 static inline struct balloon_dev_info *balloon_page_device(struct page *page) 128 { 129 return (struct balloon_dev_info *)page_private(page); 130 } 131 132 static inline gfp_t balloon_mapping_gfp_mask(void) 133 { 134 return GFP_HIGHUSER_MOVABLE; 135 } 136 137 #else /* !CONFIG_BALLOON_COMPACTION */ 138 139 static inline void balloon_page_insert(struct balloon_dev_info *balloon, 140 struct page *page) 141 { 142 __SetPageOffline(page); 143 list_add(&page->lru, &balloon->pages); 144 } 145 146 static inline void balloon_page_delete(struct page *page) 147 { 148 __ClearPageOffline(page); 149 list_del(&page->lru); 150 } 151 152 static inline gfp_t balloon_mapping_gfp_mask(void) 153 { 154 return GFP_HIGHUSER; 155 } 156 157 #endif /* CONFIG_BALLOON_COMPACTION */ 158 159 /* 160 * balloon_page_push - insert a page into a page list. 161 * @head : pointer to list 162 * @page : page to be added 163 * 164 * Caller must ensure the page is private and protect the list. 165 */ 166 static inline void balloon_page_push(struct list_head *pages, struct page *page) 167 { 168 list_add(&page->lru, pages); 169 } 170 171 /* 172 * balloon_page_pop - remove a page from a page list. 173 * @head : pointer to list 174 * @page : page to be added 175 * 176 * Caller must ensure the page is private and protect the list. 177 */ 178 static inline struct page *balloon_page_pop(struct list_head *pages) 179 { 180 struct page *page = list_first_entry_or_null(pages, struct page, lru); 181 182 if (!page) 183 return NULL; 184 185 list_del(&page->lru); 186 return page; 187 } 188 #endif /* _LINUX_BALLOON_COMPACTION_H */ 189