1/* 2 * include/linux/balloon_compaction.h 3 * 4 * Common interface definitions for making balloon pages movable by compaction. 5 * 6 * Despite being perfectly possible to perform ballooned pages migration, they 7 * make a special corner case to compaction scans because balloon pages are not 8 * enlisted at any LRU list like the other pages we do compact / migrate. 9 * 10 * As the page isolation scanning step a compaction thread does is a lockless 11 * procedure (from a page standpoint), it might bring some racy situations while 12 * performing balloon page compaction. In order to sort out these racy scenarios 13 * and safely perform balloon's page compaction and migration we must, always, 14 * ensure following these three simple rules: 15 * 16 * i. when updating a balloon's page ->mapping element, strictly do it under 17 * the following lock order, independently of the far superior 18 * locking scheme (lru_lock, balloon_lock): 19 * +-page_lock(page); 20 * +--spin_lock_irq(&b_dev_info->pages_lock); 21 * ... page->mapping updates here ... 22 * 23 * ii. before isolating or dequeueing a balloon page from the balloon device 24 * pages list, the page reference counter must be raised by one and the 25 * extra refcount must be dropped when the page is enqueued back into 26 * the balloon device page list, thus a balloon page keeps its reference 27 * counter raised only while it is under our special handling; 28 * 29 * iii. after the lockless scan step have selected a potential balloon page for 30 * isolation, re-test the PageBalloon mark and the PagePrivate flag 31 * under the proper page lock, to ensure isolating a valid balloon page 32 * (not yet isolated, nor under release procedure) 33 * 34 * iv. isolation or dequeueing procedure must clear PagePrivate flag under 35 * page lock together with removing page from balloon device page list. 36 * 37 * The functions provided by this interface are placed to help on coping with 38 * the aforementioned balloon page corner case, as well as to ensure the simple 39 * set of exposed rules are satisfied while we are dealing with balloon pages 40 * compaction / migration. 41 * 42 * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com> 43 */ 44#ifndef _LINUX_BALLOON_COMPACTION_H 45#define _LINUX_BALLOON_COMPACTION_H 46#include <linux/pagemap.h> 47#include <linux/page-flags.h> 48#include <linux/migrate.h> 49#include <linux/gfp.h> 50#include <linux/err.h> 51 52/* 53 * Balloon device information descriptor. 54 * This struct is used to allow the common balloon compaction interface 55 * procedures to find the proper balloon device holding memory pages they'll 56 * have to cope for page compaction / migration, as well as it serves the 57 * balloon driver as a page book-keeper for its registered balloon devices. 58 */ 59struct balloon_dev_info { 60 unsigned long isolated_pages; /* # of isolated pages for migration */ 61 spinlock_t pages_lock; /* Protection to pages list */ 62 struct list_head pages; /* Pages enqueued & handled to Host */ 63 int (*migratepage)(struct balloon_dev_info *, struct page *newpage, 64 struct page *page, enum migrate_mode mode); 65}; 66 67extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info); 68extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info); 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(&balloon->pages); 75 balloon->migratepage = NULL; 76} 77 78#ifdef CONFIG_BALLOON_COMPACTION 79extern bool balloon_page_isolate(struct page *page); 80extern void balloon_page_putback(struct page *page); 81extern int balloon_page_migrate(struct page *newpage, 82 struct page *page, enum migrate_mode mode); 83 84/* 85 * __is_movable_balloon_page - helper to perform @page PageBalloon tests 86 */ 87static inline bool __is_movable_balloon_page(struct page *page) 88{ 89 return PageBalloon(page); 90} 91 92/* 93 * balloon_page_movable - test PageBalloon to identify balloon pages 94 * and PagePrivate to check that the page is not 95 * isolated and can be moved by compaction/migration. 96 * 97 * As we might return false positives in the case of a balloon page being just 98 * released under us, this need to be re-tested later, under the page lock. 99 */ 100static inline bool balloon_page_movable(struct page *page) 101{ 102 return PageBalloon(page) && PagePrivate(page); 103} 104 105/* 106 * isolated_balloon_page - identify an isolated balloon page on private 107 * compaction/migration page lists. 108 */ 109static inline bool isolated_balloon_page(struct page *page) 110{ 111 return PageBalloon(page); 112} 113 114/* 115 * balloon_page_insert - insert a page into the balloon's page list and make 116 * the page->private assignment accordingly. 117 * @balloon : pointer to balloon device 118 * @page : page to be assigned as a 'balloon page' 119 * 120 * Caller must ensure the page is locked and the spin_lock protecting balloon 121 * pages list is held before inserting a page into the balloon device. 122 */ 123static inline void balloon_page_insert(struct balloon_dev_info *balloon, 124 struct page *page) 125{ 126 __SetPageBalloon(page); 127 SetPagePrivate(page); 128 set_page_private(page, (unsigned long)balloon); 129 list_add(&page->lru, &balloon->pages); 130} 131 132/* 133 * balloon_page_delete - delete a page from balloon's page list and clear 134 * the page->private assignement accordingly. 135 * @page : page to be released from balloon's page list 136 * 137 * Caller must ensure the page is locked and the spin_lock protecting balloon 138 * pages list is held before deleting a page from the balloon device. 139 */ 140static inline void balloon_page_delete(struct page *page) 141{ 142 __ClearPageBalloon(page); 143 set_page_private(page, 0); 144 if (PagePrivate(page)) { 145 ClearPagePrivate(page); 146 list_del(&page->lru); 147 } 148} 149 150/* 151 * balloon_page_device - get the b_dev_info descriptor for the balloon device 152 * that enqueues the given page. 153 */ 154static inline struct balloon_dev_info *balloon_page_device(struct page *page) 155{ 156 return (struct balloon_dev_info *)page_private(page); 157} 158 159static inline gfp_t balloon_mapping_gfp_mask(void) 160{ 161 return GFP_HIGHUSER_MOVABLE; 162} 163 164#else /* !CONFIG_BALLOON_COMPACTION */ 165 166static inline void balloon_page_insert(struct balloon_dev_info *balloon, 167 struct page *page) 168{ 169 __SetPageBalloon(page); 170 list_add(&page->lru, &balloon->pages); 171} 172 173static inline void balloon_page_delete(struct page *page) 174{ 175 __ClearPageBalloon(page); 176 list_del(&page->lru); 177} 178 179static inline bool __is_movable_balloon_page(struct page *page) 180{ 181 return false; 182} 183 184static inline bool balloon_page_movable(struct page *page) 185{ 186 return false; 187} 188 189static inline bool isolated_balloon_page(struct page *page) 190{ 191 return false; 192} 193 194static inline bool balloon_page_isolate(struct page *page) 195{ 196 return false; 197} 198 199static inline void balloon_page_putback(struct page *page) 200{ 201 return; 202} 203 204static inline int balloon_page_migrate(struct page *newpage, 205 struct page *page, enum migrate_mode mode) 206{ 207 return 0; 208} 209 210static inline gfp_t balloon_mapping_gfp_mask(void) 211{ 212 return GFP_HIGHUSER; 213} 214 215#endif /* CONFIG_BALLOON_COMPACTION */ 216#endif /* _LINUX_BALLOON_COMPACTION_H */ 217