diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/balloon_compaction.h | 272 | ||||
| -rw-r--r-- | include/linux/migrate.h | 10 | ||||
| -rw-r--r-- | include/linux/pagemap.h | 16 |
3 files changed, 298 insertions, 0 deletions
diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h new file mode 100644 index 000000000000..f7f1d7169b11 --- /dev/null +++ b/include/linux/balloon_compaction.h @@ -0,0 +1,272 @@ +/* + * 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 page->mapping flags and the page ref counter + * under the proper page lock, to ensure isolating a valid balloon page + * (not yet isolated, nor under release procedure) + * + * 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 { + void *balloon_device; /* balloon device descriptor */ + struct address_space *mapping; /* balloon special page->mapping */ + 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 */ +}; + +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); +extern struct balloon_dev_info *balloon_devinfo_alloc( + void *balloon_dev_descriptor); + +static inline void balloon_devinfo_free(struct balloon_dev_info *b_dev_info) +{ + kfree(b_dev_info); +} + +/* + * balloon_page_free - release a balloon page back to the page free lists + * @page: ballooned page to be set free + * + * This function must be used to properly set free an isolated/dequeued balloon + * page at the end of a sucessful page migration, or at the balloon driver's + * page release procedure. + */ +static inline void balloon_page_free(struct page *page) +{ + /* + * Balloon pages always get an extra refcount before being isolated + * and before being dequeued to help on sorting out fortuite colisions + * between a thread attempting to isolate and another thread attempting + * to release the very same balloon page. + * + * Before we handle the page back to Buddy, lets drop its extra refcnt. + */ + put_page(page); + __free_page(page); +} + +#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); +extern struct address_space +*balloon_mapping_alloc(struct balloon_dev_info *b_dev_info, + const struct address_space_operations *a_ops); + +static inline void balloon_mapping_free(struct address_space *balloon_mapping) +{ + kfree(balloon_mapping); +} + +/* + * page_flags_cleared - helper to perform balloon @page ->flags tests. + * + * As balloon pages are obtained from buddy and we do not play with page->flags + * at driver level (exception made when we get the page lock for compaction), + * we can safely identify a ballooned page by checking if the + * PAGE_FLAGS_CHECK_AT_PREP page->flags are all cleared. This approach also + * helps us skip ballooned pages that are locked for compaction or release, thus + * mitigating their racy check at balloon_page_movable() + */ +static inline bool page_flags_cleared(struct page *page) +{ + return !(page->flags & PAGE_FLAGS_CHECK_AT_PREP); +} + +/* + * __is_movable_balloon_page - helper to perform @page mapping->flags tests + */ +static inline bool __is_movable_balloon_page(struct page *page) +{ + struct address_space *mapping = page->mapping; + return mapping_balloon(mapping); +} + +/* + * balloon_page_movable - test page->mapping->flags to identify balloon pages + * that can be moved by compaction/migration. + * + * This function is used at core compaction's page isolation scheme, therefore + * most pages exposed to it are not enlisted as balloon pages and so, to avoid + * undesired side effects like racing against __free_pages(), we cannot afford + * holding the page locked while testing page->mapping->flags here. + * + * As we might return false positives in the case of a balloon page being just + * released under us, the page->mapping->flags need to be re-tested later, + * under the proper page lock, at the functions that will be coping with the + * balloon page case. + */ +static inline bool balloon_page_movable(struct page *page) +{ + /* + * Before dereferencing and testing mapping->flags, let's make sure + * this is not a page that uses ->mapping in a different way + */ + if (page_flags_cleared(page) && !page_mapped(page) && + page_count(page) == 1) + return __is_movable_balloon_page(page); + + return false; +} + +/* + * balloon_page_insert - insert a page into the balloon's page list and make + * the page->mapping assignment accordingly. + * @page : page to be assigned as a 'balloon page' + * @mapping : allocated special 'balloon_mapping' + * @head : balloon's device page list head + * + * 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 page *page, + struct address_space *mapping, + struct list_head *head) +{ + page->mapping = mapping; + list_add(&page->lru, head); +} + +/* + * balloon_page_delete - delete a page from balloon's page list and clear + * the page->mapping 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) +{ + page->mapping = NULL; + 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) +{ + struct address_space *mapping = page->mapping; + if (likely(mapping)) + return mapping->private_data; + + return NULL; +} + +static inline gfp_t balloon_mapping_gfp_mask(void) +{ + return GFP_HIGHUSER_MOVABLE; +} + +static inline bool balloon_compaction_check(void) +{ + return true; +} + +#else /* !CONFIG_BALLOON_COMPACTION */ + +static inline void *balloon_mapping_alloc(void *balloon_device, + const struct address_space_operations *a_ops) +{ + return ERR_PTR(-EOPNOTSUPP); +} + +static inline void balloon_mapping_free(struct address_space *balloon_mapping) +{ + return; +} + +static inline void balloon_page_insert(struct page *page, + struct address_space *mapping, + struct list_head *head) +{ + list_add(&page->lru, head); +} + +static inline void balloon_page_delete(struct page *page) +{ + list_del(&page->lru); +} + +static inline bool balloon_page_movable(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; +} + +static inline bool balloon_compaction_check(void) +{ + return false; +} +#endif /* CONFIG_BALLOON_COMPACTION */ +#endif /* _LINUX_BALLOON_COMPACTION_H */ diff --git a/include/linux/migrate.h b/include/linux/migrate.h index a4e886d17f87..ce42847ed35f 100644 --- a/include/linux/migrate.h +++ b/include/linux/migrate.h @@ -11,8 +11,18 @@ typedef struct page *new_page_t(struct page *, unsigned long private, int **); * Return values from addresss_space_operations.migratepage(): * - negative errno on page migration failure; * - zero on page migration success; + * + * The balloon page migration introduces this special case where a 'distinct' + * return code is used to flag a successful page migration to unmap_and_move(). + * This approach is necessary because page migration can race against balloon + * deflation procedure, and for such case we could introduce a nasty page leak + * if a successfully migrated balloon page gets released concurrently with + * migration's unmap_and_move() wrap-up steps. */ #define MIGRATEPAGE_SUCCESS 0 +#define MIGRATEPAGE_BALLOON_SUCCESS 1 /* special ret code for balloon page + * sucessful migration case. + */ #ifdef CONFIG_MIGRATION diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index e42c762f0dc7..6da609d14c15 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -24,6 +24,7 @@ enum mapping_flags { AS_ENOSPC = __GFP_BITS_SHIFT + 1, /* ENOSPC on async write */ AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */ AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */ + AS_BALLOON_MAP = __GFP_BITS_SHIFT + 4, /* balloon page special map */ }; static inline void mapping_set_error(struct address_space *mapping, int error) @@ -53,6 +54,21 @@ static inline int mapping_unevictable(struct address_space *mapping) return !!mapping; } +static inline void mapping_set_balloon(struct address_space *mapping) +{ + set_bit(AS_BALLOON_MAP, &mapping->flags); +} + +static inline void mapping_clear_balloon(struct address_space *mapping) +{ + clear_bit(AS_BALLOON_MAP, &mapping->flags); +} + +static inline int mapping_balloon(struct address_space *mapping) +{ + return mapping && test_bit(AS_BALLOON_MAP, &mapping->flags); +} + static inline gfp_t mapping_gfp_mask(struct address_space * mapping) { return (__force gfp_t)mapping->flags & __GFP_BITS_MASK; |