include/linux/balloon_compaction.h

   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 <aquini@redhat.com>
  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 */