[mirror_ubuntu-jammy-kernel.git] / mm / page_reporting.c

// 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"

unsigned int page_reporting_order = MAX_ORDER;
module_param(page_reporting_order, uint, 0644);
MODULE_PARM_DESC(page_reporting_order, "Set 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 < MAX_ORDER; 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_access_pointer(pr_dev_info)) {
		err = -EBUSY;
		goto err_out;
	}

	/*
	 * Update the page reporting order if it's specified by driver.
	 * Otherwise, it falls back to @pageblock_order.
	 */
	page_reporting_order = prdev->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 (rcu_access_pointer(pr_dev_info) == prdev) {
		/* 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);
Commit	Line	Data
36e66c55 AD	1	// SPDX-License-Identifier: GPL-2.0
	2	#include <linux/mm.h>
	3	#include <linux/mmzone.h>
	4	#include <linux/page_reporting.h>
	5	#include <linux/gfp.h>
	6	#include <linux/export.h>
f58780a8	7	#include <linux/module.h>
36e66c55 AD	8	#include <linux/delay.h>
	9	#include <linux/scatterlist.h>
	10
	11	#include "page_reporting.h"
	12	#include "internal.h"
	13
f58780a8 GS	14	unsigned int page_reporting_order = MAX_ORDER;
	15	module_param(page_reporting_order, uint, 0644);
	16	MODULE_PARM_DESC(page_reporting_order, "Set page reporting order");
	17
36e66c55 AD	18	#define PAGE_REPORTING_DELAY (2 * HZ)
	19	static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
	20
	21	enum {
	22	PAGE_REPORTING_IDLE = 0,
	23	PAGE_REPORTING_REQUESTED,
	24	PAGE_REPORTING_ACTIVE
	25	};
	26
	27	/* request page reporting */
	28	static void
	29	__page_reporting_request(struct page_reporting_dev_info *prdev)
	30	{
	31	unsigned int state;
	32
	33	/* Check to see if we are in desired state */
	34	state = atomic_read(&prdev->state);
	35	if (state == PAGE_REPORTING_REQUESTED)
	36	return;
	37
	38	/*
5631de54 GS	39	* If reporting is already active there is nothing we need to do.
5631de54 GS	40	* Test against 0 as that represents PAGE_REPORTING_IDLE.
36e66c55 AD	41	*/
	42	state = atomic_xchg(&prdev->state, PAGE_REPORTING_REQUESTED);
	43	if (state != PAGE_REPORTING_IDLE)
	44	return;
	45
	46	/*
	47	* Delay the start of work to allow a sizable queue to build. For
	48	* now we are limiting this to running no more than once every
	49	* couple of seconds.
	50	*/
	51	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
	52	}
	53
	54	/* notify prdev of free page reporting request */
	55	void __page_reporting_notify(void)
	56	{
	57	struct page_reporting_dev_info *prdev;
	58
	59	/*
	60	* We use RCU to protect the pr_dev_info pointer. In almost all
	61	* cases this should be present, however in the unlikely case of
	62	* a shutdown this will be NULL and we should exit.
	63	*/
	64	rcu_read_lock();
	65	prdev = rcu_dereference(pr_dev_info);
	66	if (likely(prdev))
	67	__page_reporting_request(prdev);
	68
	69	rcu_read_unlock();
	70	}
	71
	72	static void
	73	page_reporting_drain(struct page_reporting_dev_info *prdev,
	74	struct scatterlist *sgl, unsigned int nents, bool reported)
	75	{
	76	struct scatterlist *sg = sgl;
	77
	78	/*
	79	* Drain the now reported pages back into their respective
	80	* free lists/areas. We assume at least one page is populated.
	81	*/
	82	do {
	83	struct page *page = sg_page(sg);
	84	int mt = get_pageblock_migratetype(page);
	85	unsigned int order = get_order(sg->length);
	86
	87	__putback_isolated_page(page, order, mt);
	88
	89	/* If the pages were not reported due to error skip flagging */
	90	if (!reported)
	91	continue;
	92
	93	/*
	94	* If page was not comingled with another page we can
	95	* consider the result to be "reported" since the page
	96	* hasn't been modified, otherwise we will need to
	97	* report on the new larger page when we make our way
	98	* up to that higher order.
	99	*/
ab130f91	100	if (PageBuddy(page) && buddy_order(page) == order)
36e66c55 AD	101	__SetPageReported(page);
	102	} while ((sg = sg_next(sg)));
	103
	104	/* reinitialize scatterlist now that it is empty */
	105	sg_init_table(sgl, nents);
	106	}
	107
	108	/*
	109	* The page reporting cycle consists of 4 stages, fill, report, drain, and
	110	* idle. We will cycle through the first 3 stages until we cannot obtain a
	111	* full scatterlist of pages, in that case we will switch to idle.
	112	*/
	113	static int
	114	page_reporting_cycle(struct page_reporting_dev_info prdev, struct zone zone,
	115	unsigned int order, unsigned int mt,
	116	struct scatterlist sgl, unsigned int offset)
	117	{
	118	struct free_area *area = &zone->free_area[order];
	119	struct list_head *list = &area->free_list[mt];
	120	unsigned int page_len = PAGE_SIZE << order;
	121	struct page page, next;
43b76f29	122	long budget;
36e66c55 AD	123	int err = 0;
	124
	125	/*
	126	* Perform early check, if free area is empty there is
	127	* nothing to process so we can skip this free_list.
	128	*/
	129	if (list_empty(list))
	130	return err;
	131
	132	spin_lock_irq(&zone->lock);
	133
43b76f29 AD	134	/*
	135	* Limit how many calls we will be making to the page reporting
	136	* device for this list. By doing this we avoid processing any
	137	* given list for too long.
	138	*
	139	* The current value used allows us enough calls to process over a
	140	* sixteenth of the current list plus one additional call to handle
	141	* any pages that may have already been present from the previous
	142	* list processed. This should result in us reporting all pages on
	143	* an idle system in about 30 seconds.
	144	*
	145	* The division here should be cheap since PAGE_REPORTING_CAPACITY
	146	* should always be a power of 2.
	147	*/
	148	budget = DIV_ROUND_UP(area->nr_free, PAGE_REPORTING_CAPACITY * 16);
	149
36e66c55 AD	150	/* loop through free list adding unreported pages to sg list */
	151	list_for_each_entry_safe(page, next, list, lru) {
	152	/* We are going to skip over the reported pages. */
	153	if (PageReported(page))
	154	continue;
	155
43b76f29 AD	156	/*
	157	* If we fully consumed our budget then update our
	158	* state to indicate that we are requesting additional
	159	* processing and exit this list.
	160	*/
	161	if (budget < 0) {
	162	atomic_set(&prdev->state, PAGE_REPORTING_REQUESTED);
	163	next = page;
	164	break;
	165	}
	166
02cf8719 AD	167	/* Attempt to pull page from list and place in scatterlist */
	168	if (*offset) {
	169	if (!__isolate_free_page(page, order)) {
	170	next = page;
	171	break;
	172	}
36e66c55	173
02cf8719 AD	174	/* Add page to scatter list */
	175	--(*offset);
	176	sg_set_page(&sgl[*offset], page, page_len, 0);
36e66c55	177
36e66c55	178	continue;
02cf8719 AD	179	}
	180
	181	/*
43b76f29	182	* Make the first non-reported page in the free list
02cf8719 AD	183	* the new head of the free list before we release the
	184	* zone lock.
	185	*/
58f6f034	186	if (!list_is_first(&page->lru, list))
02cf8719	187	list_rotate_to_front(&page->lru, list);
36e66c55 AD	188
	189	/* release lock before waiting on report processing */
	190	spin_unlock_irq(&zone->lock);
	191
	192	/* begin processing pages in local list */
	193	err = prdev->report(prdev, sgl, PAGE_REPORTING_CAPACITY);
	194
	195	/* reset offset since the full list was reported */
	196	*offset = PAGE_REPORTING_CAPACITY;
	197
43b76f29 AD	198	/* update budget to reflect call to report function */
	199	budget--;
	200
36e66c55 AD	201	/* reacquire zone lock and resume processing */
	202	spin_lock_irq(&zone->lock);
	203
	204	/* flush reported pages from the sg list */
	205	page_reporting_drain(prdev, sgl, PAGE_REPORTING_CAPACITY, !err);
	206
	207	/*
	208	* Reset next to first entry, the old next isn't valid
	209	* since we dropped the lock to report the pages
	210	*/
	211	next = list_first_entry(list, struct page, lru);
	212
	213	/* exit on error */
	214	if (err)
	215	break;
	216	}
	217
02cf8719	218	/* Rotate any leftover pages to the head of the freelist */
5df6d792	219	if (!list_entry_is_head(next, list, lru) && !list_is_first(&next->lru, list))
02cf8719 AD	220	list_rotate_to_front(&next->lru, list);
02cf8719 AD	221
36e66c55 AD	222	spin_unlock_irq(&zone->lock);
	223
	224	return err;
	225	}
	226
	227	static int
	228	page_reporting_process_zone(struct page_reporting_dev_info *prdev,
	229	struct scatterlist sgl, struct zone zone)
	230	{
	231	unsigned int order, mt, leftover, offset = PAGE_REPORTING_CAPACITY;
	232	unsigned long watermark;
	233	int err = 0;
	234
	235	/* Generate minimum watermark to be able to guarantee progress */
	236	watermark = low_wmark_pages(zone) +
f58780a8	237	(PAGE_REPORTING_CAPACITY << page_reporting_order);
36e66c55 AD	238
	239	/*
	240	* Cancel request if insufficient free memory or if we failed
	241	* to allocate page reporting statistics for the zone.
	242	*/
	243	if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA))
	244	return err;
	245
	246	/* Process each free list starting from lowest order/mt */
f58780a8	247	for (order = page_reporting_order; order < MAX_ORDER; order++) {
36e66c55 AD	248	for (mt = 0; mt < MIGRATE_TYPES; mt++) {
	249	/* We do not pull pages from the isolate free list */
	250	if (is_migrate_isolate(mt))
	251	continue;
	252
	253	err = page_reporting_cycle(prdev, zone, order, mt,
	254	sgl, &offset);
	255	if (err)
	256	return err;
	257	}
	258	}
	259
	260	/* report the leftover pages before going idle */
	261	leftover = PAGE_REPORTING_CAPACITY - offset;
	262	if (leftover) {
	263	sgl = &sgl[offset];
	264	err = prdev->report(prdev, sgl, leftover);
	265
	266	/* flush any remaining pages out from the last report */
	267	spin_lock_irq(&zone->lock);
	268	page_reporting_drain(prdev, sgl, leftover, !err);
	269	spin_unlock_irq(&zone->lock);
	270	}
	271
	272	return err;
	273	}
	274
	275	static void page_reporting_process(struct work_struct *work)
	276	{
	277	struct delayed_work *d_work = to_delayed_work(work);
	278	struct page_reporting_dev_info *prdev =
	279	container_of(d_work, struct page_reporting_dev_info, work);
	280	int err = 0, state = PAGE_REPORTING_ACTIVE;
	281	struct scatterlist *sgl;
	282	struct zone *zone;
	283
	284	/*
	285	* Change the state to "Active" so that we can track if there is
	286	* anyone requests page reporting after we complete our pass. If
	287	* the state is not altered by the end of the pass we will switch
	288	* to idle and quit scheduling reporting runs.
	289	*/
	290	atomic_set(&prdev->state, state);
	291
	292	/* allocate scatterlist to store pages being reported on */
	293	sgl = kmalloc_array(PAGE_REPORTING_CAPACITY, sizeof(*sgl), GFP_KERNEL);
	294	if (!sgl)
	295	goto err_out;
	296
	297	sg_init_table(sgl, PAGE_REPORTING_CAPACITY);
	298
	299	for_each_zone(zone) {
	300	err = page_reporting_process_zone(prdev, sgl, zone);
	301	if (err)
	302	break;
	303	}
	304
	305	kfree(sgl);
	306	err_out:
	307	/*
	308	* If the state has reverted back to requested then there may be
	309	* additional pages to be processed. We will defer for 2s to allow
	310	* more pages to accumulate.
	311	*/
312	state = atomic_cmpxchg(&prdev->state, state, PAGE_REPORTING_IDLE);
313	if (state == PAGE_REPORTING_REQUESTED)
314	schedule_delayed_work(&prdev->work, PAGE_REPORTING_DELAY);
315	}
316
317	static DEFINE_MUTEX(page_reporting_mutex);
318	DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);
319
320	int page_reporting_register(struct page_reporting_dev_info *prdev)
321	{
322	int err = 0;
323
324	mutex_lock(&page_reporting_mutex);
325
326	/* nothing to do if already in use */
327	if (rcu_access_pointer(pr_dev_info)) {
328	err = -EBUSY;
329	goto err_out;
330	}
331
9f849c6f GS	332	/*
	333	* Update the page reporting order if it's specified by driver.
	334	* Otherwise, it falls back to @pageblock_order.
	335	*/
	336	page_reporting_order = prdev->order ? : pageblock_order;
	337
36e66c55 AD	338	/* initialize state and work structures */
	339	atomic_set(&prdev->state, PAGE_REPORTING_IDLE);
	340	INIT_DELAYED_WORK(&prdev->work, &page_reporting_process);
	341
	342	/* Begin initial flush of zones */
	343	__page_reporting_request(prdev);
	344
	345	/* Assign device to allow notifications */
	346	rcu_assign_pointer(pr_dev_info, prdev);
	347
	348	/* enable page reporting notification */
	349	if (!static_key_enabled(&page_reporting_enabled)) {
	350	static_branch_enable(&page_reporting_enabled);
	351	pr_info("Free page reporting enabled\n");
	352	}
	353	err_out:
	354	mutex_unlock(&page_reporting_mutex);
	355
	356	return err;
	357	}
	358	EXPORT_SYMBOL_GPL(page_reporting_register);
	359
	360	void page_reporting_unregister(struct page_reporting_dev_info *prdev)
	361	{
	362	mutex_lock(&page_reporting_mutex);
	363
	364	if (rcu_access_pointer(pr_dev_info) == prdev) {
	365	/* Disable page reporting notification */
	366	RCU_INIT_POINTER(pr_dev_info, NULL);
	367	synchronize_rcu();
	368
	369	/* Flush any existing work, and lock it out */
	370	cancel_delayed_work_sync(&prdev->work);
	371	}
	372
	373	mutex_unlock(&page_reporting_mutex);
	374	}
	375	EXPORT_SYMBOL_GPL(page_reporting_unregister);