Edit File: balloon_compaction.h
/* * 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> #include <linux/list.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_alloc(void); extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info, struct page *page); 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_COMPACTION extern 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) { __SetPageOffline(page); list_add(&page->lru, &balloon->pages); } static inline void balloon_page_delete(struct page *page) { __ClearPageOffline(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 */ /* * balloon_page_push - insert a page into a page list. * @head : pointer to list * @page : page to be added * * Caller must ensure the page is private and protect the list. */ static inline void balloon_page_push(struct list_head *pages, struct page *page) { list_add(&page->lru, pages); } /* * balloon_page_pop - remove a page from a page list. * @head : pointer to list * @page : page to be added * * Caller must ensure the page is private and protect the list. */ static inline struct page *balloon_page_pop(struct list_head *pages) { struct page *page = list_first_entry_or_null(pages, struct page, lru); if (!page) return NULL; list_del(&page->lru); return page; } #endif /* _LINUX_BALLOON_COMPACTION_H */