include/linux/balloon_compaction.h - kernel/msm-4.9 - Gitiles

 /*
  * 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 */
	/*
	* 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 */