diff options
Diffstat (limited to 'kernel/mm/balloon_compaction.c')
| -rw-r--r-- | kernel/mm/balloon_compaction.c | 221 |
1 files changed, 221 insertions, 0 deletions
diff --git a/kernel/mm/balloon_compaction.c b/kernel/mm/balloon_compaction.c new file mode 100644 index 000000000..fcad8322e --- /dev/null +++ b/kernel/mm/balloon_compaction.c @@ -0,0 +1,221 @@ +/* + * mm/balloon_compaction.c + * + * Common interface for making balloon pages movable by compaction. + * + * Copyright (C) 2012, Red Hat, Inc. Rafael Aquini <aquini@redhat.com> + */ +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/export.h> +#include <linux/balloon_compaction.h> + +/* + * balloon_page_enqueue - allocates a new page and inserts it into the balloon + * page list. + * @b_dev_info: balloon device decriptor where we will insert a new page to + * + * Driver must call it to properly allocate a new enlisted balloon page + * before definetively removing it from the guest system. + * This function returns the page address for the recently enqueued page or + * NULL in the case we fail to allocate a new page this turn. + */ +struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info) +{ + unsigned long flags; + struct page *page = alloc_page(balloon_mapping_gfp_mask() | + __GFP_NOMEMALLOC | __GFP_NORETRY); + if (!page) + return NULL; + + /* + * Block others from accessing the 'page' when we get around to + * establishing additional references. We should be the only one + * holding a reference to the 'page' at this point. + */ + BUG_ON(!trylock_page(page)); + spin_lock_irqsave(&b_dev_info->pages_lock, flags); + balloon_page_insert(b_dev_info, page); + __count_vm_event(BALLOON_INFLATE); + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); + unlock_page(page); + return page; +} +EXPORT_SYMBOL_GPL(balloon_page_enqueue); + +/* + * balloon_page_dequeue - removes a page from balloon's page list and returns + * the its address to allow the driver release the page. + * @b_dev_info: balloon device decriptor where we will grab a page from. + * + * Driver must call it to properly de-allocate a previous enlisted balloon page + * before definetively releasing it back to the guest system. + * This function returns the page address for the recently dequeued page or + * NULL in the case we find balloon's page list temporarily empty due to + * compaction isolated pages. + */ +struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info) +{ + struct page *page, *tmp; + unsigned long flags; + bool dequeued_page; + + dequeued_page = false; + list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) { + /* + * Block others from accessing the 'page' while we get around + * establishing additional references and preparing the 'page' + * to be released by the balloon driver. + */ + if (trylock_page(page)) { +#ifdef CONFIG_BALLOON_COMPACTION + if (!PagePrivate(page)) { + /* raced with isolation */ + unlock_page(page); + continue; + } +#endif + spin_lock_irqsave(&b_dev_info->pages_lock, flags); + balloon_page_delete(page); + __count_vm_event(BALLOON_DEFLATE); + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); + unlock_page(page); + dequeued_page = true; + break; + } + } + + if (!dequeued_page) { + /* + * If we are unable to dequeue a balloon page because the page + * list is empty and there is no isolated pages, then something + * went out of track and some balloon pages are lost. + * BUG() here, otherwise the balloon driver may get stuck into + * an infinite loop while attempting to release all its pages. + */ + spin_lock_irqsave(&b_dev_info->pages_lock, flags); + if (unlikely(list_empty(&b_dev_info->pages) && + !b_dev_info->isolated_pages)) + BUG(); + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); + page = NULL; + } + return page; +} +EXPORT_SYMBOL_GPL(balloon_page_dequeue); + +#ifdef CONFIG_BALLOON_COMPACTION + +static inline void __isolate_balloon_page(struct page *page) +{ + struct balloon_dev_info *b_dev_info = balloon_page_device(page); + unsigned long flags; + + spin_lock_irqsave(&b_dev_info->pages_lock, flags); + ClearPagePrivate(page); + list_del(&page->lru); + b_dev_info->isolated_pages++; + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); +} + +static inline void __putback_balloon_page(struct page *page) +{ + struct balloon_dev_info *b_dev_info = balloon_page_device(page); + unsigned long flags; + + spin_lock_irqsave(&b_dev_info->pages_lock, flags); + SetPagePrivate(page); + list_add(&page->lru, &b_dev_info->pages); + b_dev_info->isolated_pages--; + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); +} + +/* __isolate_lru_page() counterpart for a ballooned page */ +bool balloon_page_isolate(struct page *page) +{ + /* + * Avoid burning cycles with pages that are yet under __free_pages(), + * or just got freed under us. + * + * In case we 'win' a race for a balloon page being freed under us and + * raise its refcount preventing __free_pages() from doing its job + * the put_page() at the end of this block will take care of + * release this page, thus avoiding a nasty leakage. + */ + if (likely(get_page_unless_zero(page))) { + /* + * As balloon pages are not isolated from LRU lists, concurrent + * compaction threads can race against page migration functions + * as well as race against the balloon driver releasing a page. + * + * In order to avoid having an already isolated balloon page + * being (wrongly) re-isolated while it is under migration, + * or to avoid attempting to isolate pages being released by + * the balloon driver, lets be sure we have the page lock + * before proceeding with the balloon page isolation steps. + */ + if (likely(trylock_page(page))) { + /* + * A ballooned page, by default, has PagePrivate set. + * Prevent concurrent compaction threads from isolating + * an already isolated balloon page by clearing it. + */ + if (balloon_page_movable(page)) { + __isolate_balloon_page(page); + unlock_page(page); + return true; + } + unlock_page(page); + } + put_page(page); + } + return false; +} + +/* putback_lru_page() counterpart for a ballooned page */ +void balloon_page_putback(struct page *page) +{ + /* + * 'lock_page()' stabilizes the page and prevents races against + * concurrent isolation threads attempting to re-isolate it. + */ + lock_page(page); + + if (__is_movable_balloon_page(page)) { + __putback_balloon_page(page); + /* drop the extra ref count taken for page isolation */ + put_page(page); + } else { + WARN_ON(1); + dump_page(page, "not movable balloon page"); + } + unlock_page(page); +} + +/* move_to_new_page() counterpart for a ballooned page */ +int balloon_page_migrate(struct page *newpage, + struct page *page, enum migrate_mode mode) +{ + struct balloon_dev_info *balloon = balloon_page_device(page); + int rc = -EAGAIN; + + /* + * Block others from accessing the 'newpage' when we get around to + * establishing additional references. We should be the only one + * holding a reference to the 'newpage' at this point. + */ + BUG_ON(!trylock_page(newpage)); + + if (WARN_ON(!__is_movable_balloon_page(page))) { + dump_page(page, "not movable balloon page"); + unlock_page(newpage); + return rc; + } + + if (balloon && balloon->migratepage) + rc = balloon->migratepage(balloon, newpage, page, mode); + + unlock_page(newpage); + return rc; +} +#endif /* CONFIG_BALLOON_COMPACTION */ |