mm/page_reporting.c - third_party/kernel - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 #include <linux/mm.h>
 #include <linux/mmzone.h>
 #include <linux/page_reporting.h>
 #include <linux/gfp.h>
 #include <linux/export.h>
 #include <linux/module.h>
 #include <linux/delay.h>
 #include <linux/scatterlist.h>

 #include "page_reporting.h"
 #include "internal.h"

 /* Initialize to an unsupported value */
 unsigned int page_reporting_order = -1;

 static int page_order_update_notify(const char *val, const struct kernel_param *kp)
 {
 	/*
 	 * If param is set beyond this limit, order is set to default
 	 * pageblock_order value
 	 */
 	return  param_set_uint_minmax(val, kp, 0, MAX_ORDER);
 }

 static const struct kernel_param_ops page_reporting_param_ops = {
 	.set = &page_order_update_notify,
 	/*
 	 * For the get op, use param_get_int instead of param_get_uint.
 	 * This is to make sure that when unset the initialized value of
 	 * -1 is shown correctly
 	 */
 	.get = &param_get_int,
 };

 module_param_cb(page_reporting_order, &page_reporting_param_ops,
 			&page_reporting_order, 0644);
 MODULE_PARM_DESC(page_reporting_order, "Set page reporting order");

 /*
  * This symbol is also a kernel parameter. Export the page_reporting_order
  * symbol so that other drivers can access it to control order values without
  * having to introduce another configurable parameter. Only one driver can
  * register with the page_reporting driver for the service, so we have just
  * one control parameter for the use case(which can be accessed in both
  * drivers)
  */
 EXPORT_SYMBOL_GPL(page_reporting_order);

 #define PAGE_REPORTING_DELAY	(2 * HZ)
 static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;

 enum {
 	PAGE_REPORTING_IDLE = 0,
 	PAGE_REPORTING_REQUESTED,
 	PAGE_REPORTING_ACTIVE
 };

 /* request page reporting */
 static void
 __page_reporting_request(struct page_reporting_dev_info *prdev)
 {
 	unsigned int state;

 	/* Check to see if we are in desired state */
 	state = atomic_read(&prdev->state);
 	if (state == PAGE_REPORTING_REQUESTED)
 		return;

 	/*
 	 * If reporting is already active there is nothing we need to do.
 	 * Test against 0 as that represents PAGE_REPORTING_IDLE.
 	 */
 	state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
 	if (state != PAGE_REPORTING_IDLE)
 		return;

 	/*
 	 * Delay the start of work to allow a sizable queue to build. For
 	 * now we are limiting this to running no more than once every
 	 * couple of seconds.
 	 */
 	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
 }

 /* notify prdev of free page reporting request */
 void __page_reporting_notify(void)
 {
 	struct page_reporting_dev_info *prdev;

 	/*
 	 * We use RCU to protect the pr_dev_info pointer. In almost all
 	 * cases this should be present, however in the unlikely case of
 	 * a shutdown this will be NULL and we should exit.
 	 */
 	rcu_read_lock();
 	prdev = rcu_dereference(pr_dev_info);
 	if (likely(prdev))
 		__page_reporting_request(prdev);

 	rcu_read_unlock();
 }

 static void
 page_reporting_drain(struct page_reporting_dev_info *prdev,
 		     struct scatterlist *sgl, unsigned int nents, bool reported)
 {
 	struct scatterlist *sg = sgl;

 	/*
 	 * Drain the now reported pages back into their respective
 	 * free lists/areas. We assume at least one page is populated.
 	 */
 	do {
 		struct page *page = sg_page(sg);
 		int mt = get_pageblock_migratetype(page);
 		unsigned int order = get_order(sg->length);

 		__putback_isolated_page(page, order, mt);

 		/* If the pages were not reported due to error skip flagging */
 		if (!reported)
 			continue;

 		/*
 		 * If page was not comingled with another page we can
 		 * consider the result to be "reported" since the page
 		 * hasn't been modified, otherwise we will need to
 		 * report on the new larger page when we make our way
 		 * up to that higher order.
 		 */
 		if (PageBuddy(page) && buddy_order(page) == order)
 			__SetPageReported(page);
 	} while ((sg = sg_next(sg)));

 	/* reinitialize scatterlist now that it is empty */
 	sg_init_table(sgl, nents);
 }

 /*
  * The page reporting cycle consists of 4 stages, fill, report, drain, and
  * idle. We will cycle through the first 3 stages until we cannot obtain a
  * full scatterlist of pages, in that case we will switch to idle.
  */
 static int
 page_reporting_cycle(struct page_reporting_dev_info *prdev, struct zone *zone,
 		     unsigned int order, unsigned int mt,
 		     struct scatterlist *sgl, unsigned int *offset)
 {
 	struct free_area *area = &zone->free_area[order];
 	struct list_head *list = &area->free_list[mt];
 	unsigned int page_len = PAGE_SIZE << order;
 	struct page *page, *next;
 	long budget;
 	int err = 0;

 	/*
 	 * Perform early check, if free area is empty there is
 	 * nothing to process so we can skip this free_list.
 	 */
 	if (list_empty(list))
 		return err;

 	spin_lock_irq(&zone->lock);

 	/*
 	 * Limit how many calls we will be making to the page reporting
 	 * device for this list. By doing this we avoid processing any
 	 * given list for too long.
 	 *
 	 * The current value used allows us enough calls to process over a
 	 * sixteenth of the current list plus one additional call to handle
 	 * any pages that may have already been present from the previous
 	 * list processed. This should result in us reporting all pages on
 	 * an idle system in about 30 seconds.
 	 *
 	 * The division here should be cheap since PAGE_REPORTING_CAPACITY
 	 * should always be a power of 2.
 	 */
 	budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16);

 	/* loop through free list adding unreported pages to sg list */
 	list_for_each_entry_safe(page, next, list, lru) {
 		/* We are going to skip over the reported pages. */
 		if (PageReported(page))
 			continue;

 		/*
 		 * If we fully consumed our budget then update our
 		 * state to indicate that we are requesting additional
 		 * processing and exit this list.
 		 */
 		if (budget < 0) {
 			atomic_set(&prdev->state, PAGE_REPORTING_REQUESTED);
 			next = page;
 			break;
 		}

 		/* Attempt to pull page from list and place in scatterlist */
 		if (*offset) {
 			if (!__isolate_free_page(page, order)) {
 				next = page;
 				break;
 			}

 			/* Add page to scatter list */
 			--(*offset);
 			sg_set_page(&sgl[*offset], page, page_len, 0);

 			continue;
 		}

 		/*
 		 * Make the first non-reported page in the free list
 		 * the new head of the free list before we release the
 		 * zone lock.
 		 */
 		if (!list_is_first(&page->lru, list))
 			list_rotate_to_front(&page->lru, list);

 		/* release lock before waiting on report processing */
 		spin_unlock_irq(&zone->lock);

 		/* begin processing pages in local list */
 		err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);

 		/* reset offset since the full list was reported */
 		*offset = PAGE_REPORTING_CAPACITY;

 		/* update budget to reflect call to report function */
 		budget--;

 		/* reacquire zone lock and resume processing */
 		spin_lock_irq(&zone->lock);

 		/* flush reported pages from the sg list */
 		page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);

 		/*
 		 * Reset next to first entry, the old next isn't valid
 		 * since we dropped the lock to report the pages
 		 */
 		next = list_first_entry(list, struct page, lru);

 		/* exit on error */
 		if (err)
 			break;
 	}

 	/* Rotate any leftover pages to the head of the freelist */
 	if (!list_entry_is_head(next, list, lru) && !list_is_first(&next->lru, list))
 		list_rotate_to_front(&next->lru, list);

 	spin_unlock_irq(&zone->lock);

 	return err;
 }

 static int
 page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 			    struct scatterlist *sgl, struct zone *zone)
 {
 	unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY;
 	unsigned long watermark;
 	int err = 0;

 	/* Generate minimum watermark to be able to guarantee progress */
 	watermark = low_wmark_pages(zone) +
 		    (PAGE_REPORTING_CAPACITY << page_reporting_order);

 	/*
 	 * Cancel request if insufficient free memory or if we failed
 	 * to allocate page reporting statistics for the zone.
 	 */
 	if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
 		return err;

 	/* Process each free list starting from lowest order/mt */
 	for (order = page_reporting_order; order < NR_PAGE_ORDERS; order++) {
 		for (mt = 0; mt < MIGRATE_TYPES; mt++) {
 			/* We do not pull pages from the isolate free list */
 			if (is_migrate_isolate(mt))
 				continue;

 			err = page_reporting_cycle(prdev, zone, order, mt,
 						   sgl, &offset);
 			if (err)
 				return err;
 		}
 	}

 	/* report the leftover pages before going idle */
 	leftover = PAGE_REPORTING_CAPACITY - offset;
 	if (leftover) {
 		sgl = &sgl[offset];
 		err = prdev->report(prdev, sgl, leftover);

 		/* flush any remaining pages out from the last report */
 		spin_lock_irq(&zone->lock);
 		page_reporting_drain(prdev, sgl, leftover, !err);
 		spin_unlock_irq(&zone->lock);
 	}

 	return err;
 }

 static void page_reporting_process(struct work_struct *work)
 {
 	struct delayed_work *d_work = to_delayed_work(work);
 	struct page_reporting_dev_info *prdev =
 		container_of(d_work, struct page_reporting_dev_info, work);
 	int err = 0, state = PAGE_REPORTING_ACTIVE;
 	struct scatterlist *sgl;
 	struct zone *zone;

 	/*
 	 * Change the state to "Active" so that we can track if there is
 	 * anyone requests page reporting after we complete our pass. If
 	 * the state is not altered by the end of the pass we will switch
 	 * to idle and quit scheduling reporting runs.
 	 */
 	atomic_set(&prdev->state, state);

 	/* allocate scatterlist to store pages being reported on */
 	sgl = kmalloc_array(PAGE_REPORTING_CAPACITY, sizeof(*sgl), GFP_KERNEL);
 	if (!sgl)
 		goto err_out;

 	sg_init_table(sgl, PAGE_REPORTING_CAPACITY);

 	for_each_zone(zone) {
 		err = page_reporting_process_zone(prdev, sgl, zone);
 		if (err)
 			break;
 	}

 	kfree(sgl);
 err_out:
 	/*
 	 * If the state has reverted back to requested then there may be
 	 * additional pages to be processed. We will defer for 2s to allow
 	 * more pages to accumulate.
 	 */
 	state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE);
 	if (state == PAGE_REPORTING_REQUESTED)
 		schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
 }

 static DEFINE_MUTEX(page_reporting_mutex);
 DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);

 int page_reporting_register(struct page_reporting_dev_info *prdev)
 {
 	int err = 0;

 	mutex_lock(&page_reporting_mutex);

 	/* nothing to do if already in use */
 	if (rcu_dereference_protected(pr_dev_info,
 				lockdep_is_held(&page_reporting_mutex))) {
 		err = -EBUSY;
 		goto err_out;
 	}

 	/*
 	 * If the page_reporting_order value is not set, we check if
 	 * an order is provided from the driver that is performing the
 	 * registration. If that is not provided either, we default to
 	 * pageblock_order.
 	 */

 	if (page_reporting_order == -1) {
 		if (prdev->order > 0 && prdev->order <= MAX_ORDER)
 			page_reporting_order = prdev->order;
 		else
 			page_reporting_order = pageblock_order;
 	}

 	/* initialize state and work structures */
 	atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
 	INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);

 	/* Begin initial flush of zones */
 	__page_reporting_request(prdev);

 	/* Assign device to allow notifications */
 	rcu_assign_pointer(pr_dev_info, prdev);

 	/* enable page reporting notification */
 	if (!static_key_enabled(&page_reporting_enabled)) {
 		static_branch_enable(&page_reporting_enabled);
 		pr_info("Free page reporting enabled\n");
 	}
 err_out:
 	mutex_unlock(&page_reporting_mutex);

 	return err;
 }
 EXPORT_SYMBOL_GPL(page_reporting_register);

 void page_reporting_unregister(struct page_reporting_dev_info *prdev)
 {
 	mutex_lock(&page_reporting_mutex);

 	if (prdev == rcu_dereference_protected(pr_dev_info,
 				lockdep_is_held(&page_reporting_mutex))) {
 		/* Disable page reporting notification */
 		RCU_INIT_POINTER(pr_dev_info, NULL);
 		synchronize_rcu();

 		/* Flush any existing work, and lock it out */
 		cancel_delayed_work_sync(&prdev->work);
 	}

 	mutex_unlock(&page_reporting_mutex);
 }
 EXPORT_SYMBOL_GPL(page_reporting_unregister);
	// SPDX-License-Identifier: GPL-2.0
	#include <linux/mm.h>
	#include <linux/mmzone.h>
	#include <linux/page_reporting.h>
	#include <linux/gfp.h>
	#include <linux/export.h>
	#include <linux/module.h>
	#include <linux/delay.h>
	#include <linux/scatterlist.h>

	#include "page_reporting.h"
	#include "internal.h"

	/* Initialize to an unsupported value */
	unsigned int page_reporting_order = -1;

	static int page_order_update_notify(const char val, const struct kernel_param kp)
	{
	/*
	* If param is set beyond this limit, order is set to default
	* pageblock_order value
	*/
	return param_set_uint_minmax(val, kp, 0, MAX_ORDER);
	}

	static const struct kernel_param_ops page_reporting_param_ops = {
	.set = &page_order_update_notify,
	/*
	* For the get op, use param_get_int instead of param_get_uint.
	* This is to make sure that when unset the initialized value of
	* -1 is shown correctly
	*/
	.get = &param_get_int,
	};

	module_param_cb(page_reporting_order, &page_reporting_param_ops,
	&page_reporting_order, 0644);
	MODULE_PARM_DESC(page_reporting_order, "Set page reporting order");

	/*
	* This symbol is also a kernel parameter. Export the page_reporting_order
	* symbol so that other drivers can access it to control order values without
	* having to introduce another configurable parameter. Only one driver can
	* register with the page_reporting driver for the service, so we have just
	* one control parameter for the use case(which can be accessed in both
	* drivers)
	*/
	EXPORT_SYMBOL_GPL(page_reporting_order);

	#define PAGE_REPORTING_DELAY (2 * HZ)
	static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;

	enum {
	PAGE_REPORTING_IDLE = 0,
	PAGE_REPORTING_REQUESTED,
	PAGE_REPORTING_ACTIVE
	};

	/* request page reporting */
	static void
	__page_reporting_request(struct page_reporting_dev_info *prdev)
	{
	unsigned int state;

	/* Check to see if we are in desired state */
	state = atomic_read(&prdev->state);
	if (state == PAGE_REPORTING_REQUESTED)
	return;

	/*
	* If reporting is already active there is nothing we need to do.
	* Test against 0 as that represents PAGE_REPORTING_IDLE.
	*/
	state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
	if (state != PAGE_REPORTING_IDLE)
	return;

	/*
	* Delay the start of work to allow a sizable queue to build. For
	* now we are limiting this to running no more than once every
	* couple of seconds.
	*/
	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
	}

	/* notify prdev of free page reporting request */
	void __page_reporting_notify(void)
	{
	struct page_reporting_dev_info *prdev;

	/*
	* We use RCU to protect the pr_dev_info pointer. In almost all
	* cases this should be present, however in the unlikely case of
	* a shutdown this will be NULL and we should exit.
	*/
	rcu_read_lock();
	prdev = rcu_dereference(pr_dev_info);
	if (likely(prdev))
	__page_reporting_request(prdev);

	rcu_read_unlock();
	}

	static void
	page_reporting_drain(struct page_reporting_dev_info *prdev,
	struct scatterlist *sgl, unsigned int nents, bool reported)
	{
	struct scatterlist *sg = sgl;

	/*
	* Drain the now reported pages back into their respective
	* free lists/areas. We assume at least one page is populated.
	*/
	do {
	struct page *page = sg_page(sg);
	int mt = get_pageblock_migratetype(page);
	unsigned int order = get_order(sg->length);

	__putback_isolated_page(page, order, mt);

	/* If the pages were not reported due to error skip flagging */
	if (!reported)
	continue;

	/*
	* If page was not comingled with another page we can
	* consider the result to be "reported" since the page
	* hasn't been modified, otherwise we will need to
	* report on the new larger page when we make our way
	* up to that higher order.
	*/
	if (PageBuddy(page) && buddy_order(page) == order)
	__SetPageReported(page);
	} while ((sg = sg_next(sg)));

	/* reinitialize scatterlist now that it is empty */
	sg_init_table(sgl, nents);
	}

	/*
	* The page reporting cycle consists of 4 stages, fill, report, drain, and
	* idle. We will cycle through the first 3 stages until we cannot obtain a
	* full scatterlist of pages, in that case we will switch to idle.
	*/
	static int
	page_reporting_cycle(struct page_reporting_dev_info prdev, struct zone zone,
	unsigned int order, unsigned int mt,
	struct scatterlist sgl, unsigned int offset)
	{
	struct free_area *area = &zone->free_area[order];
	struct list_head *list = &area->free_list[mt];
	unsigned int page_len = PAGE_SIZE << order;
	struct page page, next;
	long budget;
	int err = 0;

	/*
	* Perform early check, if free area is empty there is
	* nothing to process so we can skip this free_list.
	*/
	if (list_empty(list))
	return err;

	spin_lock_irq(&zone->lock);

	/*
	* Limit how many calls we will be making to the page reporting
	* device for this list. By doing this we avoid processing any
	* given list for too long.
	*
	* The current value used allows us enough calls to process over a
	* sixteenth of the current list plus one additional call to handle
	* any pages that may have already been present from the previous
	* list processed. This should result in us reporting all pages on
	* an idle system in about 30 seconds.
	*
	* The division here should be cheap since PAGE_REPORTING_CAPACITY
	* should always be a power of 2.
	*/
	budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16);

	/* loop through free list adding unreported pages to sg list */
	list_for_each_entry_safe(page, next, list, lru) {
	/* We are going to skip over the reported pages. */
	if (PageReported(page))
	continue;

	/*
	* If we fully consumed our budget then update our
	* state to indicate that we are requesting additional
	* processing and exit this list.
	*/
	if (budget < 0) {
	atomic_set(&prdev->state, PAGE_REPORTING_REQUESTED);
	next = page;
	break;
	}

	/* Attempt to pull page from list and place in scatterlist */
	if (*offset) {
	if (!__isolate_free_page(page, order)) {
	next = page;
	break;
	}

	/* Add page to scatter list */
	--(*offset);
	sg_set_page(&sgl[*offset], page, page_len, 0);

	continue;
	}

	/*
	* Make the first non-reported page in the free list
	* the new head of the free list before we release the
	* zone lock.
	*/
	if (!list_is_first(&page->lru, list))
	list_rotate_to_front(&page->lru, list);

	/* release lock before waiting on report processing */
	spin_unlock_irq(&zone->lock);

	/* begin processing pages in local list */
	err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);

	/* reset offset since the full list was reported */
	*offset = PAGE_REPORTING_CAPACITY;

	/* update budget to reflect call to report function */
	budget--;

	/* reacquire zone lock and resume processing */
	spin_lock_irq(&zone->lock);

	/* flush reported pages from the sg list */
	page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);

	/*
	* Reset next to first entry, the old next isn't valid
	* since we dropped the lock to report the pages
	*/
	next = list_first_entry(list, struct page, lru);

	/* exit on error */
	if (err)
	break;
	}

	/* Rotate any leftover pages to the head of the freelist */
	if (!list_entry_is_head(next, list, lru) && !list_is_first(&next->lru, list))
	list_rotate_to_front(&next->lru, list);

	spin_unlock_irq(&zone->lock);

	return err;
	}

	static int
	page_reporting_process_zone(struct page_reporting_dev_info *prdev,
	struct scatterlist sgl, struct zone zone)
	{
	unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY;
	unsigned long watermark;
	int err = 0;

	/* Generate minimum watermark to be able to guarantee progress */
	watermark = low_wmark_pages(zone) +
	(PAGE_REPORTING_CAPACITY << page_reporting_order);

	/*
	* Cancel request if insufficient free memory or if we failed
	* to allocate page reporting statistics for the zone.
	*/
	if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
	return err;

	/* Process each free list starting from lowest order/mt */
	for (order = page_reporting_order; order < NR_PAGE_ORDERS; order++) {
	for (mt = 0; mt < MIGRATE_TYPES; mt++) {
	/* We do not pull pages from the isolate free list */
	if (is_migrate_isolate(mt))
	continue;

	err = page_reporting_cycle(prdev, zone, order, mt,
	sgl, &offset);
	if (err)
	return err;
	}
	}

	/* report the leftover pages before going idle */
	leftover = PAGE_REPORTING_CAPACITY - offset;
	if (leftover) {
	sgl = &sgl[offset];
	err = prdev->report(prdev, sgl, leftover);

	/* flush any remaining pages out from the last report */
	spin_lock_irq(&zone->lock);
	page_reporting_drain(prdev, sgl, leftover, !err);
	spin_unlock_irq(&zone->lock);
	}

	return err;
	}

	static void page_reporting_process(struct work_struct *work)
	{
	struct delayed_work *d_work = to_delayed_work(work);
	struct page_reporting_dev_info *prdev =
	container_of(d_work, struct page_reporting_dev_info, work);
	int err = 0, state = PAGE_REPORTING_ACTIVE;
	struct scatterlist *sgl;
	struct zone *zone;

	/*
	* Change the state to "Active" so that we can track if there is
	* anyone requests page reporting after we complete our pass. If
	* the state is not altered by the end of the pass we will switch
	* to idle and quit scheduling reporting runs.
	*/
	atomic_set(&prdev->state, state);

	/* allocate scatterlist to store pages being reported on */
	sgl = kmalloc_array(PAGE_REPORTING_CAPACITY, sizeof(*sgl), GFP_KERNEL);
	if (!sgl)
	goto err_out;

	sg_init_table(sgl, PAGE_REPORTING_CAPACITY);

	for_each_zone(zone) {
	err = page_reporting_process_zone(prdev, sgl, zone);
	if (err)
	break;
	}

	kfree(sgl);
	err_out:
	/*
	* If the state has reverted back to requested then there may be
	* additional pages to be processed. We will defer for 2s to allow
	* more pages to accumulate.
	*/
	state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE);
	if (state == PAGE_REPORTING_REQUESTED)
	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
	}

	static DEFINE_MUTEX(page_reporting_mutex);
	DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);

	int page_reporting_register(struct page_reporting_dev_info *prdev)
	{
	int err = 0;

	mutex_lock(&page_reporting_mutex);

	/* nothing to do if already in use */
	if (rcu_dereference_protected(pr_dev_info,
	lockdep_is_held(&page_reporting_mutex))) {
	err = -EBUSY;
	goto err_out;
	}

	/*
	* If the page_reporting_order value is not set, we check if
	* an order is provided from the driver that is performing the
	* registration. If that is not provided either, we default to
	* pageblock_order.
	*/

	if (page_reporting_order == -1) {
	if (prdev->order > 0 && prdev->order <= MAX_ORDER)
	page_reporting_order = prdev->order;
	else
	page_reporting_order = pageblock_order;
	}

	/* initialize state and work structures */
	atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
	INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);

	/* Begin initial flush of zones */
	__page_reporting_request(prdev);

	/* Assign device to allow notifications */
	rcu_assign_pointer(pr_dev_info, prdev);

	/* enable page reporting notification */
	if (!static_key_enabled(&page_reporting_enabled)) {
	static_branch_enable(&page_reporting_enabled);
	pr_info("Free page reporting enabled\n");
	}
	err_out:
	mutex_unlock(&page_reporting_mutex);

	return err;
	}
	EXPORT_SYMBOL_GPL(page_reporting_register);

	void page_reporting_unregister(struct page_reporting_dev_info *prdev)
	{
	mutex_lock(&page_reporting_mutex);

	if (prdev == rcu_dereference_protected(pr_dev_info,
	lockdep_is_held(&page_reporting_mutex))) {
	/* Disable page reporting notification */
	RCU_INIT_POINTER(pr_dev_info, NULL);
	synchronize_rcu();

	/* Flush any existing work, and lock it out */
	cancel_delayed_work_sync(&prdev->work);
	}

	mutex_unlock(&page_reporting_mutex);
	}
	EXPORT_SYMBOL_GPL(page_reporting_unregister);