summaryrefslogtreecommitdiffstats
path: root/mm/page_reporting.c
blob: 3bbd471cfc81438a5f2935378be35c5860574bfe (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
// 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/delay.h>
#include <linux/scatterlist.h>

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

#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) && page_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 (&page->lru != list && !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 (&next->lru != list && !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_MIN_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_MIN_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;
	}

	/* 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);