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);
  67
  68static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
  69{
  70        balloon->isolated_pages = 0;
  71        spin_lock_init(&balloon->pages_lock);
  72        INIT_LIST_HEAD(&balloon->pages);
  73        balloon->migratepage = NULL;
  74        balloon->inode = NULL;
  75}
  76
  77#ifdef CONFIG_BALLOON_COMPACTION
  78extern const struct address_space_operations balloon_aops;
  79extern bool balloon_page_isolate(struct page *page,
  80                                isolate_mode_t mode);
  81extern void balloon_page_putback(struct page *page);
  82extern int balloon_page_migrate(struct address_space *mapping,
  83                                struct page *newpage,
  84                                struct page *page, enum migrate_mode mode);
  85
  86/*
  87 * balloon_page_insert - insert a page into the balloon's page list and make
  88 *                       the page->private assignment accordingly.
  89 * @balloon : pointer to balloon device
  90 * @page    : page to be assigned as a 'balloon page'
  91 *
  92 * Caller must ensure the page is locked and the spin_lock protecting balloon
  93 * pages list is held before inserting a page into the balloon device.
  94 */
  95static inline void balloon_page_insert(struct balloon_dev_info *balloon,
  96                                       struct page *page)
  97{
  98        __SetPageOffline(page);
  99        __SetPageMovable(page, balloon->inode->i_mapping);
 100        set_page_private(page, (unsigned long)balloon);
 101        list_add(&page->lru, &balloon->pages);
 102}
 103
 104/*
 105 * balloon_page_delete - delete a page from balloon's page list and clear
 106 *                       the page->private assignement accordingly.
 107 * @page    : page to be released from balloon's page list
 108 *
 109 * Caller must ensure the page is locked and the spin_lock protecting balloon
 110 * pages list is held before deleting a page from the balloon device.
 111 */
 112static inline void balloon_page_delete(struct page *page)
 113{
 114        __ClearPageOffline(page);
 115        __ClearPageMovable(page);
 116        set_page_private(page, 0);
 117        /*
 118         * No touch page.lru field once @page has been isolated
 119         * because VM is using the field.
 120         */
 121        if (!PageIsolated(page))
 122                list_del(&page->lru);
 123}
 124
 125/*
 126 * balloon_page_device - get the b_dev_info descriptor for the balloon device
 127 *                       that enqueues the given page.
 128 */
 129static inline struct balloon_dev_info *balloon_page_device(struct page *page)
 130{
 131        return (struct balloon_dev_info *)page_private(page);
 132}
 133
 134static inline gfp_t balloon_mapping_gfp_mask(void)
 135{
 136        return GFP_HIGHUSER_MOVABLE;
 137}
 138
 139#else /* !CONFIG_BALLOON_COMPACTION */
 140
 141static inline void balloon_page_insert(struct balloon_dev_info *balloon,
 142                                       struct page *page)
 143{
 144        __SetPageOffline(page);
 145        list_add(&page->lru, &balloon->pages);
 146}
 147
 148static inline void balloon_page_delete(struct page *page)
 149{
 150        __ClearPageOffline(page);
 151        list_del(&page->lru);
 152}
 153
 154static inline bool balloon_page_isolate(struct page *page)
 155{
 156        return false;
 157}
 158
 159static inline void balloon_page_putback(struct page *page)
 160{
 161        return;
 162}
 163
 164static inline int balloon_page_migrate(struct page *newpage,
 165                                struct page *page, enum migrate_mode mode)
 166{
 167        return 0;
 168}
 169
 170static inline gfp_t balloon_mapping_gfp_mask(void)
 171{
 172        return GFP_HIGHUSER;
 173}
 174
 175#endif /* CONFIG_BALLOON_COMPACTION */
 176
 177/*
 178 * balloon_page_push - insert a page into a page list.
 179 * @head : pointer to list
 180 * @page : page to be added
 181 *
 182 * Caller must ensure the page is private and protect the list.
 183 */
 184static inline void balloon_page_push(struct list_head *pages, struct page *page)
 185{
 186        list_add(&page->lru, pages);
 187}
 188
 189/*
 190 * balloon_page_pop - remove a page from a page list.
 191 * @head : pointer to list
 192 * @page : page to be added
 193 *
 194 * Caller must ensure the page is private and protect the list.
 195 */
 196static inline struct page *balloon_page_pop(struct list_head *pages)
 197{
 198        struct page *page = list_first_entry_or_null(pages, struct page, lru);
 199
 200        if (!page)
 201                return NULL;
 202
 203        list_del(&page->lru);
 204        return page;
 205}
 206#endif /* _LINUX_BALLOON_COMPACTION_H */
 207