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