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)
14 static struct page_reporting_dev_info __rcu *pr_dev_info __read_mostly;
15
16 enum {
17 PAGE_REPORTING_IDLE = 0,
18 PAGE_REPORTING_REQUESTED,
19 PAGE_REPORTING_ACTIVE
20 };
21
22 /* request page reporting */
23 static void
__page_reporting_request(struct page_reporting_dev_info * prdev)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 */
__page_reporting_notify(void)50 void __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
67 static void
page_reporting_drain(struct page_reporting_dev_info * prdev,struct scatterlist * sgl,unsigned int nents,bool reported)68 page_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) && buddy_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 */
108 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)109 page_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 (!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
222 static int
page_reporting_process_zone(struct page_reporting_dev_info * prdev,struct scatterlist * sgl,struct zone * zone)223 page_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
page_reporting_process(struct work_struct * work)270 static 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);
301 err_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
312 static DEFINE_MUTEX(page_reporting_mutex);
313 DEFINE_STATIC_KEY_FALSE(page_reporting_enabled);
314
page_reporting_register(struct page_reporting_dev_info * prdev)315 int 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 }
342 err_out:
343 mutex_unlock(&page_reporting_mutex);
344
345 return err;
346 }
347 EXPORT_SYMBOL_GPL(page_reporting_register);
348
page_reporting_unregister(struct page_reporting_dev_info * prdev)349 void 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 }
364 EXPORT_SYMBOL_GPL(page_reporting_unregister);
365
