/* * include/linux/balloon_compaction.h * * Common interface definitions for making balloon pages movable by compaction. * * Despite being perfectly possible to perform ballooned pages migration, they * make a special corner case to compaction scans because balloon pages are not * enlisted at any LRU list like the other pages we do compact / migrate. * * As the page isolation scanning step a compaction thread does is a lockless * procedure (from a page standpoint), it might bring some racy situations while * performing balloon page compaction. In order to sort out these racy scenarios * and safely perform balloon's page compaction and migration we must, always, * ensure following these three simple rules: * *   i. when updating a balloon's page ->mapping element, strictly do it under *      the following lock order, independently of the far superior *      locking scheme (lru_lock, balloon_lock): *	    +-page_lock(page); *	      +--spin_lock_irq(&b_dev_info->pages_lock); *	            ... page->mapping updates here ... * *  ii. before isolating or dequeueing a balloon page from the balloon device *      pages list, the page reference counter must be raised by one and the *      extra refcount must be dropped when the page is enqueued back into *      the balloon device page list, thus a balloon page keeps its reference *      counter raised only while it is under our special handling; * * iii. after the lockless scan step have selected a potential balloon page for *      isolation, re-test the PageBalloon mark and the PagePrivate flag *      under the proper page lock, to ensure isolating a valid balloon page *      (not yet isolated, nor under release procedure) * *  iv. isolation or dequeueing procedure must clear PagePrivate flag under *      page lock together with removing page from balloon device page list. * * The functions provided by this interface are placed to help on coping with * the aforementioned balloon page corner case, as well as to ensure the simple * set of exposed rules are satisfied while we are dealing with balloon pages * compaction / migration. * * Copyright (C) 2012, Red Hat, Inc.  Rafael Aquini <aquini@redhat.com> */#ifndef _LINUX_BALLOON_COMPACTION_H#define _LINUX_BALLOON_COMPACTION_H#include <linux/pagemap.h>#include <linux/page-flags.h>#include <linux/migrate.h>#include <linux/gfp.h>#include <linux/err.h> /* * Balloon device information descriptor. * This struct is used to allow the common balloon compaction interface * procedures to find the proper balloon device holding memory pages they'll * have to cope for page compaction / migration, as well as it serves the * balloon driver as a page book-keeper for its registered balloon devices. */struct balloon_dev_info {	unsigned long isolated_pages;	/* # of isolated pages for migration */	spinlock_t pages_lock;		/* Protection to pages list */	struct list_head pages;		/* Pages enqueued & handled to Host */	int (*migratepage)(struct balloon_dev_info *, struct page *newpage,			struct page *page, enum migrate_mode mode);}; extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info); static inline void balloon_devinfo_init(struct balloon_dev_info *balloon){	balloon->isolated_pages = 0;	spin_lock_init(&balloon->pages_lock);	INIT_LIST_HEAD(&balloon->pages);	balloon->migratepage = NULL;} #ifdef CONFIG_BALLOON_COMPACTIONextern bool balloon_page_isolate(struct page *page);extern void balloon_page_putback(struct page *page);extern int balloon_page_migrate(struct page *newpage,				struct page *page, enum migrate_mode mode); /* * __is_movable_balloon_page - helper to perform @page PageBalloon tests */static inline bool __is_movable_balloon_page(struct page *page){	return PageBalloon(page);} /* * balloon_page_movable - test PageBalloon to identify balloon pages *			  and PagePrivate to check that the page is not *			  isolated and can be moved by compaction/migration. * * As we might return false positives in the case of a balloon page being just * released under us, this need to be re-tested later, under the page lock. */static inline bool balloon_page_movable(struct page *page){	return PageBalloon(page) && PagePrivate(page);} /* * isolated_balloon_page - identify an isolated balloon page on private *			   compaction/migration page lists. */static inline bool isolated_balloon_page(struct page *page){	return PageBalloon(page);} /* * balloon_page_insert - insert a page into the balloon's page list and make *			 the page->private assignment accordingly. * @balloon : pointer to balloon device * @page    : page to be assigned as a 'balloon page' * * Caller must ensure the page is locked and the spin_lock protecting balloon * pages list is held before inserting a page into the balloon device. */static inline void balloon_page_insert(struct balloon_dev_info *balloon,				       struct page *page){	__SetPageBalloon(page);	SetPagePrivate(page);	set_page_private(page, (unsigned long)balloon);	list_add(&page->lru, &balloon->pages);} /* * balloon_page_delete - delete a page from balloon's page list and clear *			 the page->private assignement accordingly. * @page    : page to be released from balloon's page list * * Caller must ensure the page is locked and the spin_lock protecting balloon * pages list is held before deleting a page from the balloon device. */static inline void balloon_page_delete(struct page *page){	__ClearPageBalloon(page);	set_page_private(page, 0);	if (PagePrivate(page)) {		ClearPagePrivate(page);		list_del(&page->lru);	}} /* * balloon_page_device - get the b_dev_info descriptor for the balloon device *			 that enqueues the given page. */static inline struct balloon_dev_info *balloon_page_device(struct page *page){	return (struct balloon_dev_info *)page_private(page);} static inline gfp_t balloon_mapping_gfp_mask(void){	return GFP_HIGHUSER_MOVABLE;} #else /* !CONFIG_BALLOON_COMPACTION */ static inline void balloon_page_insert(struct balloon_dev_info *balloon,				       struct page *page){	__SetPageBalloon(page);	list_add(&page->lru, &balloon->pages);} static inline void balloon_page_delete(struct page *page){	__ClearPageBalloon(page);	list_del(&page->lru);} static inline bool __is_movable_balloon_page(struct page *page){	return false;} static inline bool balloon_page_movable(struct page *page){	return false;} static inline bool isolated_balloon_page(struct page *page){	return false;} static inline bool balloon_page_isolate(struct page *page){	return false;} static inline void balloon_page_putback(struct page *page){	return;} static inline int balloon_page_migrate(struct page *newpage,				struct page *page, enum migrate_mode mode){	return 0;} static inline gfp_t balloon_mapping_gfp_mask(void){	return GFP_HIGHUSER;} #endif /* CONFIG_BALLOON_COMPACTION */#endif /* _LINUX_BALLOON_COMPACTION_H */