mm/balloon_compaction.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * 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>

 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));
 	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 this function to properly enqueue balloon pages before
  * definitively removing them 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) {
 		list_del(&page->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 descriptor 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 definitively 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 even if the balloon
  * isn't empty - since the page list can be temporarily empty due to compaction
  * of 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.
  *
  * Driver must call this function to properly allocate a new balloon page.
  * Driver must call balloon_page_enqueue before definitively removing the page
  * from the guest system.
  *
  * Return: struct page for the allocated page or NULL on allocation failure.
  */
 struct page *balloon_page_alloc(void)
 {
 	struct page *page = alloc_page(balloon_mapping_gfp_mask() |
 				       __GFP_NOMEMALLOC | __GFP_NORETRY |
 				       __GFP_NOWARN);
 	return page;
 }
 EXPORT_SYMBOL_GPL(balloon_page_alloc);

 /*
  * balloon_page_enqueue - inserts a new page into the balloon page list.
  *
  * @b_dev_info: balloon device descriptor where we will insert a new page
  * @page: new page to enqueue - allocated using balloon_page_alloc.
  *
  * Drivers must call this function to properly enqueue a new allocated balloon
  * page before definitively removing the page from the guest system.
  *
  * Drivers must not call balloon_page_enqueue on pages that have been pushed to
  * a list with balloon_page_push before removing them with balloon_page_pop. To
  * enqueue a list of pages, use balloon_page_list_enqueue instead.
  */
 void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
 			  struct page *page)
 {
 	unsigned long flags;

 	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
 	balloon_page_enqueue_one(b_dev_info, page);
 	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
 }
 EXPORT_SYMBOL_GPL(balloon_page_enqueue);

 /*
  * balloon_page_dequeue - removes a page from balloon's page list and returns
  *			  its address to allow the driver to release the page.
  * @b_dev_info: balloon device descriptor where we will grab a page from.
  *
  * Driver must call this function to properly dequeue a previously enqueued page
  * before definitively releasing it back to the guest system.
  *
  * Caller must perform its own accounting to ensure that this
  * function is called only if some pages are actually enqueued.
  *
  * Note that this function may fail to dequeue some pages even if there are
  * some enqueued pages - since the page list can be temporarily empty due to
  * the compaction of isolated pages.
  *
  * TODO: remove the caller accounting requirements, and allow caller to wait
  * until all pages can be dequeued.
  *
  * Return: struct page for the dequeued page, or NULL if no page was dequeued.
  */
 struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
 {
 	unsigned long flags;
 	LIST_HEAD(pages);
 	int n_pages;

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

 	if (n_pages != 1) {
 		/*
 		 * If we are unable to dequeue a balloon page because the page
 		 * list is empty and there are no isolated pages, then something
 		 * went out of track and some balloon pages are lost.
 		 * BUG() here, otherwise the balloon driver may get stuck in
 		 * 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);
 		return NULL;
 	}
 	return list_first_entry(&pages, struct page, lru);
 }
 EXPORT_SYMBOL_GPL(balloon_page_dequeue);

 #ifdef CONFIG_BALLOON_COMPACTION

 static 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;
 }

 static 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 */
 static 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);

 	/*
 	 * We can not easily support the no copy case here so ignore it as it
 	 * is unlikely to be used with balloon pages. See include/linux/hmm.h
 	 * for a user of the MIGRATE_SYNC_NO_COPY mode.
 	 */
 	if (mode == MIGRATE_SYNC_NO_COPY)
 		return -EINVAL;

 	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 */
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* 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>

	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));
	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 this function to properly enqueue balloon pages before
	* definitively removing them 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) {
	list_del(&page->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 descriptor 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 definitively 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 even if the balloon
	* isn't empty - since the page list can be temporarily empty due to compaction
	* of 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.
	*
	* Driver must call this function to properly allocate a new balloon page.
	* Driver must call balloon_page_enqueue before definitively removing the page
	* from the guest system.
	*
	* Return: struct page for the allocated page or NULL on allocation failure.
	*/
	struct page *balloon_page_alloc(void)
	{
	struct page *page = alloc_page(balloon_mapping_gfp_mask() \|
	__GFP_NOMEMALLOC \| __GFP_NORETRY \|
	__GFP_NOWARN);
	return page;
	}
	EXPORT_SYMBOL_GPL(balloon_page_alloc);

	/*
	* balloon_page_enqueue - inserts a new page into the balloon page list.
	*
	* @b_dev_info: balloon device descriptor where we will insert a new page
	* @page: new page to enqueue - allocated using balloon_page_alloc.
	*
	* Drivers must call this function to properly enqueue a new allocated balloon
	* page before definitively removing the page from the guest system.
	*
	* Drivers must not call balloon_page_enqueue on pages that have been pushed to
	* a list with balloon_page_push before removing them with balloon_page_pop. To
	* enqueue a list of pages, use balloon_page_list_enqueue instead.
	*/
	void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
	struct page *page)
	{
	unsigned long flags;

	spin_lock_irqsave(&b_dev_info->pages_lock, flags);
	balloon_page_enqueue_one(b_dev_info, page);
	spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
	}
	EXPORT_SYMBOL_GPL(balloon_page_enqueue);

	/*
	* balloon_page_dequeue - removes a page from balloon's page list and returns
	* its address to allow the driver to release the page.
	* @b_dev_info: balloon device descriptor where we will grab a page from.
	*
	* Driver must call this function to properly dequeue a previously enqueued page
	* before definitively releasing it back to the guest system.
	*
	* Caller must perform its own accounting to ensure that this
	* function is called only if some pages are actually enqueued.
	*
	* Note that this function may fail to dequeue some pages even if there are
	* some enqueued pages - since the page list can be temporarily empty due to
	* the compaction of isolated pages.
	*
	* TODO: remove the caller accounting requirements, and allow caller to wait
	* until all pages can be dequeued.
	*
	* Return: struct page for the dequeued page, or NULL if no page was dequeued.
	*/
	struct page balloon_page_dequeue(struct balloon_dev_info b_dev_info)
	{
	unsigned long flags;
	LIST_HEAD(pages);
	int n_pages;

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

	if (n_pages != 1) {
	/*
	* If we are unable to dequeue a balloon page because the page
	* list is empty and there are no isolated pages, then something
	* went out of track and some balloon pages are lost.
	* BUG() here, otherwise the balloon driver may get stuck in
	* 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);
	return NULL;
	}
	return list_first_entry(&pages, struct page, lru);
	}
	EXPORT_SYMBOL_GPL(balloon_page_dequeue);

	#ifdef CONFIG_BALLOON_COMPACTION

	static 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;
	}

	static 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 */
	static 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);

	/*
	* We can not easily support the no copy case here so ignore it as it
	* is unlikely to be used with balloon pages. See include/linux/hmm.h
	* for a user of the MIGRATE_SYNC_NO_COPY mode.
	*/
	if (mode == MIGRATE_SYNC_NO_COPY)
	return -EINVAL;

	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 */