LXR linux/include/linux/balloon

   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 */
  54struct 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
  63extern struct page *balloon_page_alloc(void);
  64extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
  65                                 struct page *page);
  66extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
  67extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
  68                                      struct list_head *pages);
  69extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
  70                                     struct list_head *pages, size_t n_req_pages);
  71
  72static 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
  82extern const struct address_space_operations balloon_aops;
  83extern bool balloon_page_isolate(struct page *page,
  84                                isolate_mode_t mode);
  85extern void balloon_page_putback(struct page *page);
  86extern 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 */
  99static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 100                                       struct page *page)
 101{
 102        __SetPageOffline(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 */
 116static inline void balloon_page_delete(struct page *page)
 117{
 118        __ClearPageOffline(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 */
 133static inline struct balloon_dev_info *balloon_page_device(struct page *page)
 134{
 135        return (struct balloon_dev_info *)page_private(page);
 136}
 137
 138static inline gfp_t balloon_mapping_gfp_mask(void)
 139{
 140        return GFP_HIGHUSER_MOVABLE;
 141}
 142
 143#else /* !CONFIG_BALLOON_COMPACTION */
 144
 145static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 146                                       struct page *page)
 147{
 148        __SetPageOffline(page);
 149        list_add(&page->lru, &balloon->pages);
 150}
 151
 152static inline void balloon_page_delete(struct page *page)
 153{
 154        __ClearPageOffline(page);
 155        list_del(&page->lru);
 156}
 157
 158static inline bool balloon_page_isolate(struct page *page)
 159{
 160        return false;
 161}
 162
 163static inline void balloon_page_putback(struct page *page)
 164{
 165        return;
 166}
 167
 168static inline int balloon_page_migrate(struct page *newpage,
 169                                struct page *page, enum migrate_mode mode)
 170{
 171        return 0;
 172}
 173
 174static inline gfp_t balloon_mapping_gfp_mask(void)
 175{
 176        return GFP_HIGHUSER;
 177}
 178
 179#endif /* CONFIG_BALLOON_COMPACTION */
 180
 181/*
 182 * balloon_page_push - insert a page into a page list.
 183 * @head : pointer to list
 184 * @page : page to be added
 185 *
 186 * Caller must ensure the page is private and protect the list.
 187 */
 188static inline void balloon_page_push(struct list_head *pages, struct page *page)
 189{
 190        list_add(&page->lru, pages);
 191}
 192
 193/*
 194 * balloon_page_pop - remove a page from a page list.
 195 * @head : pointer to list
 196 * @page : page to be added
 197 *
 198 * Caller must ensure the page is private and protect the list.
 199 */
 200static inline struct page *balloon_page_pop(struct list_head *pages)
 201{
 202        struct page *page = list_first_entry_or_null(pages, struct page, lru);
 203
 204        if (!page)
 205                return NULL;
 206
 207        list_del(&page->lru);
 208        return page;
 209}
 210#endif /* _LINUX_BALLOON_COMPACTION_H */
 211