/*
   * 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 descriptor where we will insert a new page to

   *
   * Driver must call it to properly allocate a new enlisted balloon page

   * before definitively 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;

  	spin_lock_irqsave(&b_dev_info->pages_lock, flags);

  	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 (PageIsolated(page)) {

  				/* raced with isolation */
  				unlock_page(page);
  				continue;
  			}

  #endif

  			balloon_page_delete(page);

  			__count_vm_event(BALLOON_DEFLATE);

  			unlock_page(page);
  			dequeued_page = true;
  			break;
  		}
  	}

  	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

  
  	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

  bool balloon_page_isolate(struct page *page, isolate_mode_t mode)

  {

  	struct balloon_dev_info *b_dev_info = balloon_page_device(page);

  	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);

  
  	return true;

  }

  void balloon_page_putback(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);
  	list_add(&page->lru, &b_dev_info->pages);
  	b_dev_info->isolated_pages--;
  	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
  }

  
  /* move_to_new_page() counterpart for a ballooned page */

  int balloon_page_migrate(struct address_space *mapping,
  		struct page *newpage, struct page *page,
  		enum migrate_mode mode)

  {

  	struct balloon_dev_info *balloon = balloon_page_device(page);

  	VM_BUG_ON_PAGE(!PageLocked(page), page);
  	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);

  	return balloon->migratepage(balloon, newpage, page, mode);
  }

  const struct address_space_operations balloon_aops = {
  	.migratepage = balloon_page_migrate,
  	.isolate_page = balloon_page_isolate,
  	.putback_page = balloon_page_putback,
  };
  EXPORT_SYMBOL_GPL(balloon_aops);

  #endif /* CONFIG_BALLOON_COMPACTION */