mm/balloon_compaction: List interfaces

extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,

				 struct page *page);

extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);

extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,

				      struct list_head *pages);

extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,

				     struct list_head *pages, size_t n_req_pages);

static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)

{

#include <linux/export.h>

#include <linux/balloon_compaction.h>

static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,

				     struct page *page)

{

	/*

	 * 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. If we are not, then

	 * memory corruption is possible and we should stop execution.

	 */

	BUG_ON(!trylock_page(page));

	list_del(&page->lru);

	balloon_page_insert(b_dev_info, page);

	unlock_page(page);

	__count_vm_event(BALLOON_INFLATE);

}

/**

 * balloon_page_list_enqueue() - inserts a list of pages into the balloon page

 *				 list.

 * @b_dev_info: balloon device descriptor where we will insert a new page to

 * @pages: pages to enqueue - allocated using balloon_page_alloc.

 *

 * Driver must call it to properly enqueue a balloon pages before definitively

 * removing it from the guest system.

 *

 * Return: number of pages that were enqueued.

 */

size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,

				 struct list_head *pages)

{

	struct page *page, *tmp;

	unsigned long flags;

	size_t n_pages = 0;

	spin_lock_irqsave(&b_dev_info->pages_lock, flags);

	list_for_each_entry_safe(page, tmp, pages, lru) {

		balloon_page_enqueue_one(b_dev_info, page);

		n_pages++;

	}

	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

	return n_pages;

}

EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);

/**

 * balloon_page_list_dequeue() - removes pages from balloon's page list and

 *				 returns a list of the pages.

 * @b_dev_info: balloon device decriptor where we will grab a page from.

 * @pages: pointer to the list of pages that would be returned to the caller.

 * @n_req_pages: number of requested pages.

 *

 * Driver must call this function to properly de-allocate a previous enlisted

 * balloon pages before definetively releasing it back to the guest system.

 * This function tries to remove @n_req_pages from the ballooned pages and

 * return them to the caller in the @pages list.

 *

 * Note that this function may fail to dequeue some pages temporarily empty due

 * to compaction isolated pages.

 *

 * Return: number of pages that were added to the @pages list.

 */

size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,

				 struct list_head *pages, size_t n_req_pages)

{

	struct page *page, *tmp;

	unsigned long flags;

	size_t n_pages = 0;

	spin_lock_irqsave(&b_dev_info->pages_lock, flags);

	list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {

		if (n_pages == n_req_pages)

			break;

		/*

		 * Block others from accessing the 'page' while we get around to

		 * establishing additional references and preparing the 'page'

		 * to be released by the balloon driver.

		 */

		if (!trylock_page(page))

			continue;

		if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&

		    PageIsolated(page)) {

			/* raced with isolation */

			unlock_page(page);

			continue;

		}

		balloon_page_delete(page);

		__count_vm_event(BALLOON_DEFLATE);

		list_add(&page->lru, pages);

		unlock_page(page);

		n_pages++;

	}

	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

	return n_pages;

}

EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);

/*

 * balloon_page_alloc - allocates a new page for insertion into the balloon

 *			  page list.

{

	unsigned long flags;

	/*

	 * 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);

	balloon_page_enqueue_one(b_dev_info, page);

	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

	unlock_page(page);

}

EXPORT_SYMBOL_GPL(balloon_page_enqueue);

 */

struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)

{

	struct page *page, *tmp;

	unsigned long flags;

	bool dequeued_page;

	LIST_HEAD(pages);

	int n_pages;

	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);

	n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);

	if (!dequeued_page) {

	if (n_pages != 1) {

		/*

		 * If we are unable to dequeue a balloon page because the page

		 * list is empty and there is no isolated pages, then something

			     !b_dev_info->isolated_pages))

			BUG();

		spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);

		page = NULL;

		return NULL;

	}

	return page;

	return list_first_entry(&pages, struct page, lru);

}

EXPORT_SYMBOL_GPL(balloon_page_dequeue);