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 * Balloon page migration makes use of the general "movable_ops page migration"
  8 * feature.
  9 *
 10 * page->private is used to reference the responsible balloon device.
 11 * That these pages have movable_ops, and which movable_ops apply,
 12 * is derived from the page type (PageOffline()) combined with the
 13 * PG_movable_ops flag (PageMovableOps()).
 14 *
 15 * As the page isolation scanning step a compaction thread does is a lockless
 16 * procedure (from a page standpoint), it might bring some racy situations while
 17 * performing balloon page compaction. In order to sort out these racy scenarios
 18 * and safely perform balloon's page compaction and migration we must, always,
 19 * ensure following these simple rules:
 20 *
 21 *   i. Setting the PG_movable_ops flag and page->private with the following
 22 *	lock order
 23 *	    +-page_lock(page);
 24 *	      +--spin_lock_irq(&b_dev_info->pages_lock);
 25 *
 26 *  ii. isolation or dequeueing procedure must remove the page from balloon
 27 *      device page list under b_dev_info->pages_lock.
 28 *
 29 * The functions provided by this interface are placed to help on coping with
 30 * the aforementioned balloon page corner case, as well as to ensure the simple
 31 * set of exposed rules are satisfied while we are dealing with balloon pages
 32 * compaction / migration.
 33 *
 34 * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com>
 35 */
 36#ifndef _LINUX_BALLOON_COMPACTION_H
 37#define _LINUX_BALLOON_COMPACTION_H
 38#include <linux/pagemap.h>
 39#include <linux/page-flags.h>
 40#include <linux/migrate.h>
 41#include <linux/gfp.h>
 42#include <linux/err.h>
 43#include <linux/fs.h>
 44#include <linux/list.h>
 45
 46/*
 47 * Balloon device information descriptor.
 48 * This struct is used to allow the common balloon compaction interface
 49 * procedures to find the proper balloon device holding memory pages they'll
 50 * have to cope for page compaction / migration, as well as it serves the
 51 * balloon driver as a page book-keeper for its registered balloon devices.
 52 */
 53struct balloon_dev_info {
 54	unsigned long isolated_pages;	/* # of isolated pages for migration */
 55	spinlock_t pages_lock;		/* Protection to pages list */
 56	struct list_head pages;		/* Pages enqueued & handled to Host */
 57	int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
 58			struct page *page, enum migrate_mode mode);
 59};
 60
 61extern struct page *balloon_page_alloc(void);
 62extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
 63				 struct page *page);
 64extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
 65extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
 66				      struct list_head *pages);
 67extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
 68				     struct list_head *pages, size_t n_req_pages);
 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 const struct movable_operations balloon_mops;
 80/*
 81 * balloon_page_device - get the b_dev_info descriptor for the balloon device
 82 *			 that enqueues the given page.
 83 */
 84static inline struct balloon_dev_info *balloon_page_device(struct page *page)
 85{
 86	return (struct balloon_dev_info *)page_private(page);
 87}
 88#endif /* CONFIG_BALLOON_COMPACTION */
 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	if (IS_ENABLED(CONFIG_BALLOON_COMPACTION)) {
104		SetPageMovableOps(page);
105		set_page_private(page, (unsigned long)balloon);
106	}
107	list_add(&page->lru, &balloon->pages);
108}
109
110static inline gfp_t balloon_mapping_gfp_mask(void)
111{
112	if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
113		return GFP_HIGHUSER_MOVABLE;
114	return GFP_HIGHUSER;
115}
116
117/*
118 * balloon_page_finalize - prepare a balloon page that was removed from the
119 *			   balloon list for release to the page allocator
120 * @page: page to be released to the page allocator
121 *
122 * Caller must ensure that the page is locked.
123 */
124static inline void balloon_page_finalize(struct page *page)
125{
126	if (IS_ENABLED(CONFIG_BALLOON_COMPACTION))
127		set_page_private(page, 0);
128	/* PageOffline is sticky until the page is freed to the buddy. */
129}
130
131/*
132 * balloon_page_push - insert a page into a page list.
133 * @head : pointer to list
134 * @page : page to be added
135 *
136 * Caller must ensure the page is private and protect the list.
137 */
138static inline void balloon_page_push(struct list_head *pages, struct page *page)
139{
140	list_add(&page->lru, pages);
141}
142
143/*
144 * balloon_page_pop - remove a page from a page list.
145 * @head : pointer to list
146 * @page : page to be added
147 *
148 * Caller must ensure the page is private and protect the list.
149 */
150static inline struct page *balloon_page_pop(struct list_head *pages)
151{
152	struct page *page = list_first_entry_or_null(pages, struct page, lru);
153
154	if (!page)
155		return NULL;
156
157	list_del(&page->lru);
158	return page;
159}
160#endif /* _LINUX_BALLOON_COMPACTION_H */