include/linux/balloon_compaction.h

   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 #include <linux/fs.h>
  52
  53 /*
  54  * Balloon device information descriptor.
  55  * This struct is used to allow the common balloon compaction interface
  56  * procedures to find the proper balloon device holding memory pages they'll
  57  * have to cope for page compaction / migration, as well as it serves the
  58  * balloon driver as a page book-keeper for its registered balloon devices.
  59  */
  60 struct balloon_dev_info {
  61         unsigned long isolated_pages;   /* # of isolated pages for migration */
  62         spinlock_t pages_lock;          /* Protection to pages list */
  63         struct list_head pages;         /* Pages enqueued & handled to Host */
  64         int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
  65                         struct page *page, enum migrate_mode mode);
  66         struct inode *inode;
  67 };
  68
  69 extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
  70 extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
  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 extern bool balloon_page_isolate(struct page *page,
  84                                 isolate_mode_t mode);
  85 extern void balloon_page_putback(struct page *page);
  86 extern int balloon_page_migrate(struct address_space *mapping,
  87                                 struct page *newpage,
  88                                 struct page *page, enum migrate_mode mode);
  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  */
  99 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 100                                        struct page *page)
 101 {
 102         __SetPageBalloon(page);
 103         __SetPageMovable(page, balloon->inode->i_mapping);
 104         set_page_private(page, (unsigned long)balloon);
 105         list_add(&page->lru, &balloon->pages);
 106 }
 107
 108 /*
 109  * balloon_page_delete - delete a page from balloon's page list and clear
 110  *                       the page->private assignement accordingly.
 111  * @page    : page to be released from balloon's page list
 112  *
 113  * Caller must ensure the page is locked and the spin_lock protecting balloon
 114  * pages list is held before deleting a page from the balloon device.
 115  */
 116 static inline void balloon_page_delete(struct page *page)
 117 {
 118         __ClearPageBalloon(page);
 119         __ClearPageMovable(page);
 120         set_page_private(page, 0);
 121         /*
 122          * No touch page.lru field once @page has been isolated
 123          * because VM is using the field.
 124          */
 125         if (!PageIsolated(page))
 126                 list_del(&page->lru);
 127 }
 128
 129 /*
 130  * balloon_page_device - get the b_dev_info descriptor for the balloon device
 131  *                       that enqueues the given page.
 132  */
 133 static inline struct balloon_dev_info *balloon_page_device(struct page *page)
 134 {
 135         return (struct balloon_dev_info *)page_private(page);
 136 }
 137
 138 static inline gfp_t balloon_mapping_gfp_mask(void)
 139 {
 140         return GFP_HIGHUSER_MOVABLE;
 141 }
 142
 143 #else /* !CONFIG_BALLOON_COMPACTION */
 144
 145 static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 146                                        struct page *page)
 147 {
 148         __SetPageBalloon(page);
 149         list_add(&page->lru, &balloon->pages);
 150 }
 151
 152 static inline void balloon_page_delete(struct page *page)
 153 {
 154         __ClearPageBalloon(page);
 155         list_del(&page->lru);
 156 }
 157
 158 static inline bool __is_movable_balloon_page(struct page *page)
 159 {
 160         return false;
 161 }
 162
 163 static inline bool balloon_page_movable(struct page *page)
 164 {
 165         return false;
 166 }
 167
 168 static inline bool isolated_balloon_page(struct page *page)
 169 {
 170         return false;
 171 }
 172
 173 static inline bool balloon_page_isolate(struct page *page)
 174 {
 175         return false;
 176 }
 177
 178 static inline void balloon_page_putback(struct page *page)
 179 {
 180         return;
 181 }
 182
 183 static inline int balloon_page_migrate(struct page *newpage,
 184                                 struct page *page, enum migrate_mode mode)
 185 {
 186         return 0;
 187 }
 188
 189 static inline gfp_t balloon_mapping_gfp_mask(void)
 190 {
 191         return GFP_HIGHUSER;
 192 }
 193
 194 #endif /* CONFIG_BALLOON_COMPACTION */
 195 #endif /* _LINUX_BALLOON_COMPACTION_H */