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Diffstat (limited to 'include/linux/balloon_compaction.h')
| -rw-r--r-- | include/linux/balloon_compaction.h | 216 |
1 files changed, 216 insertions, 0 deletions
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h new file mode 100644 index 000000000..9b0a15d06 --- /dev/null +++ b/include/linux/balloon_compaction.h @@ -0,0 +1,216 @@ +/* + * 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_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) +{ + __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 */ |