/* * 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_devinfo_alloc - allocates a balloon device information descriptor. * @balloon_dev_descriptor: pointer to reference the balloon device which * this struct balloon_dev_info will be servicing. * * Driver must call it to properly allocate and initialize an instance of * struct balloon_dev_info which will be used to reference a balloon device * as well as to keep track of the balloon device page list. */ struct balloon_dev_info *balloon_devinfo_alloc(void *balloon_dev_descriptor) { struct balloon_dev_info *b_dev_info; b_dev_info = kmalloc(sizeof(*b_dev_info), GFP_KERNEL); if (!b_dev_info) return ERR_PTR(-ENOMEM); b_dev_info->balloon_device = balloon_dev_descriptor; b_dev_info->mapping = NULL; b_dev_info->isolated_pages = 0; spin_lock_init(&b_dev_info->pages_lock); INIT_LIST_HEAD(&b_dev_info->pages); return b_dev_info; } EXPORT_SYMBOL_GPL(balloon_devinfo_alloc); /* * 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(page, b_dev_info->mapping, &b_dev_info->pages); 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)) { spin_lock_irqsave(&b_dev_info->pages_lock, flags); /* * Raise the page refcount here to prevent any wrong * attempt to isolate this page, in case of coliding * with balloon_page_isolate() just after we release * the page lock. * * balloon_page_free() will take care of dropping * this extra refcount later. */ get_page(page); balloon_page_delete(page); 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 /* * balloon_mapping_alloc - allocates a special ->mapping for ballooned pages. * @b_dev_info: holds the balloon device information descriptor. * @a_ops: balloon_mapping address_space_operations descriptor. * * Driver must call it to properly allocate and initialize an instance of * struct address_space which will be used as the special page->mapping for * balloon device enlisted page instances. */ struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info, const struct address_space_operations *a_ops) { struct address_space *mapping; mapping = kmalloc(sizeof(*mapping), GFP_KERNEL); if (!mapping) return ERR_PTR(-ENOMEM); /* * Give a clean 'zeroed' status to all elements of this special * balloon page->mapping struct address_space instance. */ address_space_init_once(mapping); /* * Set mapping->flags appropriately, to allow balloon pages * ->mapping identification. */ mapping_set_balloon(mapping); mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask()); /* balloon's page->mapping->a_ops callback descriptor */ mapping->a_ops = a_ops; /* * Establish a pointer reference back to the balloon device descriptor * this particular page->mapping will be servicing. * This is used by compaction / migration procedures to identify and * access the balloon device pageset while isolating / migrating pages. * * As some balloon drivers can register multiple balloon devices * for a single guest, this also helps compaction / migration to * properly deal with multiple balloon pagesets, when required. */ mapping->private_data = b_dev_info; b_dev_info->mapping = mapping; return mapping; } EXPORT_SYMBOL_GPL(balloon_mapping_alloc); static inline void __isolate_balloon_page(struct page *page) { struct balloon_dev_info *b_dev_info = page->mapping->private_data; unsigned long flags; spin_lock_irqsave(&b_dev_info->pages_lock, flags); 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 = page->mapping->private_data; unsigned long flags; spin_lock_irqsave(&b_dev_info->pages_lock, flags); list_add(&page->lru, &b_dev_info->pages); b_dev_info->isolated_pages--; spin_unlock_irqrestore(&b_dev_info->pages_lock, flags); } static inline int __migrate_balloon_page(struct address_space *mapping, struct page *newpage, struct page *page, enum migrate_mode mode) { return page->mapping->a_ops->migratepage(mapping, newpage, page, mode); } /* __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 just one refcount. * Prevent concurrent compaction threads from isolating * an already isolated balloon page by refcount check. */ if (__is_movable_balloon_page(page) && page_count(page) == 2) { __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); } 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 address_space *mapping; 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); unlock_page(newpage); return rc; } mapping = page->mapping; if (mapping) rc = __migrate_balloon_page(mapping, newpage, page, mode); unlock_page(newpage); return rc; } #endif /* CONFIG_BALLOON_COMPACTION */