Linux preempt-rt

Check our new training course

Real-Time Linux with PREEMPT_RT

Check our new training course
with Creative Commons CC-BY-SA
lecture and lab materials

Bootlin logo

Elixir Cross Referencer

  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
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
/* SPDX-License-Identifier: GPL-2.0
 *
 * page_pool.c
 *	Author:	Jesper Dangaard Brouer <netoptimizer@brouer.com>
 *	Copyright (C) 2016 Red Hat, Inc.
 */

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/device.h>

#include <net/page_pool.h>
#include <net/xdp.h>

#include <linux/dma-direction.h>
#include <linux/dma-mapping.h>
#include <linux/page-flags.h>
#include <linux/mm.h> /* for __put_page() */
#include <linux/poison.h>

#include <trace/events/page_pool.h>

#define DEFER_TIME (msecs_to_jiffies(1000))
#define DEFER_WARN_INTERVAL (60 * HZ)

#define BIAS_MAX	LONG_MAX

static int page_pool_init(struct page_pool *pool,
			  const struct page_pool_params *params)
{
	unsigned int ring_qsize = 1024; /* Default */

	memcpy(&pool->p, params, sizeof(pool->p));

	/* Validate only known flags were used */
	if (pool->p.flags & ~(PP_FLAG_ALL))
		return -EINVAL;

	if (pool->p.pool_size)
		ring_qsize = pool->p.pool_size;

	/* Sanity limit mem that can be pinned down */
	if (ring_qsize > 32768)
		return -E2BIG;

	/* DMA direction is either DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
	 * DMA_BIDIRECTIONAL is for allowing page used for DMA sending,
	 * which is the XDP_TX use-case.
	 */
	if (pool->p.flags & PP_FLAG_DMA_MAP) {
		if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
		    (pool->p.dma_dir != DMA_BIDIRECTIONAL))
			return -EINVAL;
	}

	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) {
		/* In order to request DMA-sync-for-device the page
		 * needs to be mapped
		 */
		if (!(pool->p.flags & PP_FLAG_DMA_MAP))
			return -EINVAL;

		if (!pool->p.max_len)
			return -EINVAL;

		/* pool->p.offset has to be set according to the address
		 * offset used by the DMA engine to start copying rx data
		 */
	}

	if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
	    pool->p.flags & PP_FLAG_PAGE_FRAG)
		return -EINVAL;

	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
		return -ENOMEM;

	atomic_set(&pool->pages_state_release_cnt, 0);

	/* Driver calling page_pool_create() also call page_pool_destroy() */
	refcount_set(&pool->user_cnt, 1);

	if (pool->p.flags & PP_FLAG_DMA_MAP)
		get_device(pool->p.dev);

	return 0;
}

struct page_pool *page_pool_create(const struct page_pool_params *params)
{
	struct page_pool *pool;
	int err;

	pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, params->nid);
	if (!pool)
		return ERR_PTR(-ENOMEM);

	err = page_pool_init(pool, params);
	if (err < 0) {
		pr_warn("%s() gave up with errno %d\n", __func__, err);
		kfree(pool);
		return ERR_PTR(err);
	}

	return pool;
}
EXPORT_SYMBOL(page_pool_create);

static void page_pool_return_page(struct page_pool *pool, struct page *page);

noinline
static struct page *page_pool_refill_alloc_cache(struct page_pool *pool)
{
	struct ptr_ring *r = &pool->ring;
	struct page *page;
	int pref_nid; /* preferred NUMA node */

	/* Quicker fallback, avoid locks when ring is empty */
	if (__ptr_ring_empty(r))
		return NULL;

	/* Softirq guarantee CPU and thus NUMA node is stable. This,
	 * assumes CPU refilling driver RX-ring will also run RX-NAPI.
	 */
#ifdef CONFIG_NUMA
	pref_nid = (pool->p.nid == NUMA_NO_NODE) ? numa_mem_id() : pool->p.nid;
#else
	/* Ignore pool->p.nid setting if !CONFIG_NUMA, helps compiler */
	pref_nid = numa_mem_id(); /* will be zero like page_to_nid() */
#endif

	/* Refill alloc array, but only if NUMA match */
	do {
		page = __ptr_ring_consume(r);
		if (unlikely(!page))
			break;

		if (likely(page_to_nid(page) == pref_nid)) {
			pool->alloc.cache[pool->alloc.count++] = page;
		} else {
			/* NUMA mismatch;
			 * (1) release 1 page to page-allocator and
			 * (2) break out to fallthrough to alloc_pages_node.
			 * This limit stress on page buddy alloactor.
			 */
			page_pool_return_page(pool, page);
			page = NULL;
			break;
		}
	} while (pool->alloc.count < PP_ALLOC_CACHE_REFILL);

	/* Return last page */
	if (likely(pool->alloc.count > 0))
		page = pool->alloc.cache[--pool->alloc.count];

	return page;
}

/* fast path */
static struct page *__page_pool_get_cached(struct page_pool *pool)
{
	struct page *page;

	/* Caller MUST guarantee safe non-concurrent access, e.g. softirq */
	if (likely(pool->alloc.count)) {
		/* Fast-path */
		page = pool->alloc.cache[--pool->alloc.count];
	} else {
		page = page_pool_refill_alloc_cache(pool);
	}

	return page;
}

static void page_pool_dma_sync_for_device(struct page_pool *pool,
					  struct page *page,
					  unsigned int dma_sync_size)
{
	dma_addr_t dma_addr = page_pool_get_dma_addr(page);

	dma_sync_size = min(dma_sync_size, pool->p.max_len);
	dma_sync_single_range_for_device(pool->p.dev, dma_addr,
					 pool->p.offset, dma_sync_size,
					 pool->p.dma_dir);
}

static bool page_pool_dma_map(struct page_pool *pool, struct page *page)
{
	dma_addr_t dma;

	/* Setup DMA mapping: use 'struct page' area for storing DMA-addr
	 * since dma_addr_t can be either 32 or 64 bits and does not always fit
	 * into page private data (i.e 32bit cpu with 64bit DMA caps)
	 * This mapping is kept for lifetime of page, until leaving pool.
	 */
	dma = dma_map_page_attrs(pool->p.dev, page, 0,
				 (PAGE_SIZE << pool->p.order),
				 pool->p.dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
	if (dma_mapping_error(pool->p.dev, dma))
		return false;

	page_pool_set_dma_addr(page, dma);

	if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
		page_pool_dma_sync_for_device(pool, page, pool->p.max_len);

	return true;
}

static void page_pool_set_pp_info(struct page_pool *pool,
				  struct page *page)
{
	page->pp = pool;
	page->pp_magic |= PP_SIGNATURE;
	if (pool->p.init_callback)
		pool->p.init_callback(page, pool->p.init_arg);
}

static void page_pool_clear_pp_info(struct page *page)
{
	page->pp_magic = 0;
	page->pp = NULL;
}

static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
						 gfp_t gfp)
{
	struct page *page;

	gfp |= __GFP_COMP;
	page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
	if (unlikely(!page))
		return NULL;

	if ((pool->p.flags & PP_FLAG_DMA_MAP) &&
	    unlikely(!page_pool_dma_map(pool, page))) {
		put_page(page);
		return NULL;
	}

	page_pool_set_pp_info(pool, page);

	/* Track how many pages are held 'in-flight' */
	pool->pages_state_hold_cnt++;
	trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);
	return page;
}

/* slow path */
noinline
static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
						 gfp_t gfp)
{
	const int bulk = PP_ALLOC_CACHE_REFILL;
	unsigned int pp_flags = pool->p.flags;
	unsigned int pp_order = pool->p.order;
	struct page *page;
	int i, nr_pages;

	/* Don't support bulk alloc for high-order pages */
	if (unlikely(pp_order))
		return __page_pool_alloc_page_order(pool, gfp);

	/* Unnecessary as alloc cache is empty, but guarantees zero count */
	if (unlikely(pool->alloc.count > 0))
		return pool->alloc.cache[--pool->alloc.count];

	/* Mark empty alloc.cache slots "empty" for alloc_pages_bulk_array */
	memset(&pool->alloc.cache, 0, sizeof(void *) * bulk);

	nr_pages = alloc_pages_bulk_array(gfp, bulk, pool->alloc.cache);
	if (unlikely(!nr_pages))
		return NULL;

	/* Pages have been filled into alloc.cache array, but count is zero and
	 * page element have not been (possibly) DMA mapped.
	 */
	for (i = 0; i < nr_pages; i++) {
		page = pool->alloc.cache[i];
		if ((pp_flags & PP_FLAG_DMA_MAP) &&
		    unlikely(!page_pool_dma_map(pool, page))) {
			put_page(page);
			continue;
		}

		page_pool_set_pp_info(pool, page);
		pool->alloc.cache[pool->alloc.count++] = page;
		/* Track how many pages are held 'in-flight' */
		pool->pages_state_hold_cnt++;
		trace_page_pool_state_hold(pool, page,
					   pool->pages_state_hold_cnt);
	}

	/* Return last page */
	if (likely(pool->alloc.count > 0))
		page = pool->alloc.cache[--pool->alloc.count];
	else
		page = NULL;

	/* When page just alloc'ed is should/must have refcnt 1. */
	return page;
}

/* For using page_pool replace: alloc_pages() API calls, but provide
 * synchronization guarantee for allocation side.
 */
struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
{
	struct page *page;

	/* Fast-path: Get a page from cache */
	page = __page_pool_get_cached(pool);
	if (page)
		return page;

	/* Slow-path: cache empty, do real allocation */
	page = __page_pool_alloc_pages_slow(pool, gfp);
	return page;
}
EXPORT_SYMBOL(page_pool_alloc_pages);

/* Calculate distance between two u32 values, valid if distance is below 2^(31)
 *  https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
 */
#define _distance(a, b)	(s32)((a) - (b))

static s32 page_pool_inflight(struct page_pool *pool)
{
	u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
	u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
	s32 inflight;

	inflight = _distance(hold_cnt, release_cnt);

	trace_page_pool_release(pool, inflight, hold_cnt, release_cnt);
	WARN(inflight < 0, "Negative(%d) inflight packet-pages", inflight);

	return inflight;
}

/* Disconnects a page (from a page_pool).  API users can have a need
 * to disconnect a page (from a page_pool), to allow it to be used as
 * a regular page (that will eventually be returned to the normal
 * page-allocator via put_page).
 */
void page_pool_release_page(struct page_pool *pool, struct page *page)
{
	dma_addr_t dma;
	int count;

	if (!(pool->p.flags & PP_FLAG_DMA_MAP))
		/* Always account for inflight pages, even if we didn't
		 * map them
		 */
		goto skip_dma_unmap;

	dma = page_pool_get_dma_addr(page);

	/* When page is unmapped, it cannot be returned to our pool */
	dma_unmap_page_attrs(pool->p.dev, dma,
			     PAGE_SIZE << pool->p.order, pool->p.dma_dir,
			     DMA_ATTR_SKIP_CPU_SYNC);
	page_pool_set_dma_addr(page, 0);
skip_dma_unmap:
	page_pool_clear_pp_info(page);

	/* This may be the last page returned, releasing the pool, so
	 * it is not safe to reference pool afterwards.
	 */
	count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt);
	trace_page_pool_state_release(pool, page, count);
}
EXPORT_SYMBOL(page_pool_release_page);

/* Return a page to the page allocator, cleaning up our state */
static void page_pool_return_page(struct page_pool *pool, struct page *page)
{
	page_pool_release_page(pool, page);

	put_page(page);
	/* An optimization would be to call __free_pages(page, pool->p.order)
	 * knowing page is not part of page-cache (thus avoiding a
	 * __page_cache_release() call).
	 */
}

static bool page_pool_recycle_in_ring(struct page_pool *pool, struct page *page)
{
	int ret;
	/* BH protection not needed if current is serving softirq */
	if (in_serving_softirq())
		ret = ptr_ring_produce(&pool->ring, page);
	else
		ret = ptr_ring_produce_bh(&pool->ring, page);

	return (ret == 0) ? true : false;
}

/* Only allow direct recycling in special circumstances, into the
 * alloc side cache.  E.g. during RX-NAPI processing for XDP_DROP use-case.
 *
 * Caller must provide appropriate safe context.
 */
static bool page_pool_recycle_in_cache(struct page *page,
				       struct page_pool *pool)
{
	if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
		return false;

	/* Caller MUST have verified/know (page_ref_count(page) == 1) */
	pool->alloc.cache[pool->alloc.count++] = page;
	return true;
}

/* If the page refcnt == 1, this will try to recycle the page.
 * if PP_FLAG_DMA_SYNC_DEV is set, we'll try to sync the DMA area for
 * the configured size min(dma_sync_size, pool->max_len).
 * If the page refcnt != 1, then the page will be returned to memory
 * subsystem.
 */
static __always_inline struct page *
__page_pool_put_page(struct page_pool *pool, struct page *page,
		     unsigned int dma_sync_size, bool allow_direct)
{
	/* It is not the last user for the page frag case */
	if (pool->p.flags & PP_FLAG_PAGE_FRAG &&
	    page_pool_atomic_sub_frag_count_return(page, 1))
		return NULL;

	/* This allocator is optimized for the XDP mode that uses
	 * one-frame-per-page, but have fallbacks that act like the
	 * regular page allocator APIs.
	 *
	 * refcnt == 1 means page_pool owns page, and can recycle it.
	 *
	 * page is NOT reusable when allocated when system is under
	 * some pressure. (page_is_pfmemalloc)
	 */
	if (likely(page_ref_count(page) == 1 && !page_is_pfmemalloc(page))) {
		/* Read barrier done in page_ref_count / READ_ONCE */

		if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
			page_pool_dma_sync_for_device(pool, page,
						      dma_sync_size);

		if (allow_direct && in_serving_softirq() &&
		    page_pool_recycle_in_cache(page, pool))
			return NULL;

		/* Page found as candidate for recycling */
		return page;
	}
	/* Fallback/non-XDP mode: API user have elevated refcnt.
	 *
	 * Many drivers split up the page into fragments, and some
	 * want to keep doing this to save memory and do refcnt based
	 * recycling. Support this use case too, to ease drivers
	 * switching between XDP/non-XDP.
	 *
	 * In-case page_pool maintains the DMA mapping, API user must
	 * call page_pool_put_page once.  In this elevated refcnt
	 * case, the DMA is unmapped/released, as driver is likely
	 * doing refcnt based recycle tricks, meaning another process
	 * will be invoking put_page.
	 */
	/* Do not replace this with page_pool_return_page() */
	page_pool_release_page(pool, page);
	put_page(page);

	return NULL;
}

void page_pool_put_page(struct page_pool *pool, struct page *page,
			unsigned int dma_sync_size, bool allow_direct)
{
	page = __page_pool_put_page(pool, page, dma_sync_size, allow_direct);
	if (page && !page_pool_recycle_in_ring(pool, page)) {
		/* Cache full, fallback to free pages */
		page_pool_return_page(pool, page);
	}
}
EXPORT_SYMBOL(page_pool_put_page);

/* Caller must not use data area after call, as this function overwrites it */
void page_pool_put_page_bulk(struct page_pool *pool, void **data,
			     int count)
{
	int i, bulk_len = 0;

	for (i = 0; i < count; i++) {
		struct page *page = virt_to_head_page(data[i]);

		page = __page_pool_put_page(pool, page, -1, false);
		/* Approved for bulk recycling in ptr_ring cache */
		if (page)
			data[bulk_len++] = page;
	}

	if (unlikely(!bulk_len))
		return;

	/* Bulk producer into ptr_ring page_pool cache */
	page_pool_ring_lock(pool);
	for (i = 0; i < bulk_len; i++) {
		if (__ptr_ring_produce(&pool->ring, data[i]))
			break; /* ring full */
	}
	page_pool_ring_unlock(pool);

	/* Hopefully all pages was return into ptr_ring */
	if (likely(i == bulk_len))
		return;

	/* ptr_ring cache full, free remaining pages outside producer lock
	 * since put_page() with refcnt == 1 can be an expensive operation
	 */
	for (; i < bulk_len; i++)
		page_pool_return_page(pool, data[i]);
}
EXPORT_SYMBOL(page_pool_put_page_bulk);

static struct page *page_pool_drain_frag(struct page_pool *pool,
					 struct page *page)
{
	long drain_count = BIAS_MAX - pool->frag_users;

	/* Some user is still using the page frag */
	if (likely(page_pool_atomic_sub_frag_count_return(page,
							  drain_count)))
		return NULL;

	if (page_ref_count(page) == 1 && !page_is_pfmemalloc(page)) {
		if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
			page_pool_dma_sync_for_device(pool, page, -1);

		return page;
	}

	page_pool_return_page(pool, page);
	return NULL;
}

static void page_pool_free_frag(struct page_pool *pool)
{
	long drain_count = BIAS_MAX - pool->frag_users;
	struct page *page = pool->frag_page;

	pool->frag_page = NULL;

	if (!page ||
	    page_pool_atomic_sub_frag_count_return(page, drain_count))
		return;

	page_pool_return_page(pool, page);
}

struct page *page_pool_alloc_frag(struct page_pool *pool,
				  unsigned int *offset,
				  unsigned int size, gfp_t gfp)
{
	unsigned int max_size = PAGE_SIZE << pool->p.order;
	struct page *page = pool->frag_page;

	if (WARN_ON(!(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
		    size > max_size))
		return NULL;

	size = ALIGN(size, dma_get_cache_alignment());
	*offset = pool->frag_offset;

	if (page && *offset + size > max_size) {
		page = page_pool_drain_frag(pool, page);
		if (page)
			goto frag_reset;
	}

	if (!page) {
		page = page_pool_alloc_pages(pool, gfp);
		if (unlikely(!page)) {
			pool->frag_page = NULL;
			return NULL;
		}

		pool->frag_page = page;

frag_reset:
		pool->frag_users = 1;
		*offset = 0;
		pool->frag_offset = size;
		page_pool_set_frag_count(page, BIAS_MAX);
		return page;
	}

	pool->frag_users++;
	pool->frag_offset = *offset + size;
	return page;
}
EXPORT_SYMBOL(page_pool_alloc_frag);

static void page_pool_empty_ring(struct page_pool *pool)
{
	struct page *page;

	/* Empty recycle ring */
	while ((page = ptr_ring_consume_bh(&pool->ring))) {
		/* Verify the refcnt invariant of cached pages */
		if (!(page_ref_count(page) == 1))
			pr_crit("%s() page_pool refcnt %d violation\n",
				__func__, page_ref_count(page));

		page_pool_return_page(pool, page);
	}
}

static void page_pool_free(struct page_pool *pool)
{
	if (pool->disconnect)
		pool->disconnect(pool);

	ptr_ring_cleanup(&pool->ring, NULL);

	if (pool->p.flags & PP_FLAG_DMA_MAP)
		put_device(pool->p.dev);

	kfree(pool);
}

static void page_pool_empty_alloc_cache_once(struct page_pool *pool)
{
	struct page *page;

	if (pool->destroy_cnt)
		return;

	/* Empty alloc cache, assume caller made sure this is
	 * no-longer in use, and page_pool_alloc_pages() cannot be
	 * call concurrently.
	 */
	while (pool->alloc.count) {
		page = pool->alloc.cache[--pool->alloc.count];
		page_pool_return_page(pool, page);
	}
}

static void page_pool_scrub(struct page_pool *pool)
{
	page_pool_empty_alloc_cache_once(pool);
	pool->destroy_cnt++;

	/* No more consumers should exist, but producers could still
	 * be in-flight.
	 */
	page_pool_empty_ring(pool);
}

static int page_pool_release(struct page_pool *pool)
{
	int inflight;

	page_pool_scrub(pool);
	inflight = page_pool_inflight(pool);
	if (!inflight)
		page_pool_free(pool);

	return inflight;
}

static void page_pool_release_retry(struct work_struct *wq)
{
	struct delayed_work *dwq = to_delayed_work(wq);
	struct page_pool *pool = container_of(dwq, typeof(*pool), release_dw);
	int inflight;

	inflight = page_pool_release(pool);
	if (!inflight)
		return;

	/* Periodic warning */
	if (time_after_eq(jiffies, pool->defer_warn)) {
		int sec = (s32)((u32)jiffies - (u32)pool->defer_start) / HZ;

		pr_warn("%s() stalled pool shutdown %d inflight %d sec\n",
			__func__, inflight, sec);
		pool->defer_warn = jiffies + DEFER_WARN_INTERVAL;
	}

	/* Still not ready to be disconnected, retry later */
	schedule_delayed_work(&pool->release_dw, DEFER_TIME);
}

void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
			   struct xdp_mem_info *mem)
{
	refcount_inc(&pool->user_cnt);
	pool->disconnect = disconnect;
	pool->xdp_mem_id = mem->id;
}

void page_pool_destroy(struct page_pool *pool)
{
	if (!pool)
		return;

	if (!page_pool_put(pool))
		return;

	page_pool_free_frag(pool);

	if (!page_pool_release(pool))
		return;

	pool->defer_start = jiffies;
	pool->defer_warn  = jiffies + DEFER_WARN_INTERVAL;

	INIT_DELAYED_WORK(&pool->release_dw, page_pool_release_retry);
	schedule_delayed_work(&pool->release_dw, DEFER_TIME);
}
EXPORT_SYMBOL(page_pool_destroy);

/* Caller must provide appropriate safe context, e.g. NAPI. */
void page_pool_update_nid(struct page_pool *pool, int new_nid)
{
	struct page *page;

	trace_page_pool_update_nid(pool, new_nid);
	pool->p.nid = new_nid;

	/* Flush pool alloc cache, as refill will check NUMA node */
	while (pool->alloc.count) {
		page = pool->alloc.cache[--pool->alloc.count];
		page_pool_return_page(pool, page);
	}
}
EXPORT_SYMBOL(page_pool_update_nid);

bool page_pool_return_skb_page(struct page *page)
{
	struct page_pool *pp;

	page = compound_head(page);

	/* page->pp_magic is OR'ed with PP_SIGNATURE after the allocation
	 * in order to preserve any existing bits, such as bit 0 for the
	 * head page of compound page and bit 1 for pfmemalloc page, so
	 * mask those bits for freeing side when doing below checking,
	 * and page_is_pfmemalloc() is checked in __page_pool_put_page()
	 * to avoid recycling the pfmemalloc page.
	 */
	if (unlikely((page->pp_magic & ~0x3UL) != PP_SIGNATURE))
		return false;

	pp = page->pp;

	/* Driver set this to memory recycling info. Reset it on recycle.
	 * This will *not* work for NIC using a split-page memory model.
	 * The page will be returned to the pool here regardless of the
	 * 'flipped' fragment being in use or not.
	 */
	page_pool_put_full_page(pp, page, false);

	return true;
}
EXPORT_SYMBOL(page_pool_return_skb_page);