summaryrefslogtreecommitdiff
path: root/mm/hugetlb_vmemmap.c
blob: b9a55322e52ce971fbcced7be83a5d7325fa7a3f (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
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
// SPDX-License-Identifier: GPL-2.0
/*
 * HugeTLB Vmemmap Optimization (HVO)
 *
 * Copyright (c) 2020, ByteDance. All rights reserved.
 *
 *     Author: Muchun Song <songmuchun@bytedance.com>
 *
 * See Documentation/mm/vmemmap_dedup.rst
 */
#define pr_fmt(fmt)	"HugeTLB: " fmt

#include <linux/pgtable.h>
#include <linux/moduleparam.h>
#include <linux/bootmem_info.h>
#include <linux/mmdebug.h>
#include <linux/pagewalk.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include "hugetlb_vmemmap.h"

/**
 * struct vmemmap_remap_walk - walk vmemmap page table
 *
 * @remap_pte:		called for each lowest-level entry (PTE).
 * @nr_walked:		the number of walked pte.
 * @reuse_page:		the page which is reused for the tail vmemmap pages.
 * @reuse_addr:		the virtual address of the @reuse_page page.
 * @vmemmap_pages:	the list head of the vmemmap pages that can be freed
 *			or is mapped from.
 * @flags:		used to modify behavior in vmemmap page table walking
 *			operations.
 */
struct vmemmap_remap_walk {
	void			(*remap_pte)(pte_t *pte, unsigned long addr,
					     struct vmemmap_remap_walk *walk);
	unsigned long		nr_walked;
	struct page		*reuse_page;
	unsigned long		reuse_addr;
	struct list_head	*vmemmap_pages;

/* Skip the TLB flush when we split the PMD */
#define VMEMMAP_SPLIT_NO_TLB_FLUSH	BIT(0)
/* Skip the TLB flush when we remap the PTE */
#define VMEMMAP_REMAP_NO_TLB_FLUSH	BIT(1)
	unsigned long		flags;
};

static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start,
			     struct vmemmap_remap_walk *walk)
{
	pmd_t __pmd;
	int i;
	unsigned long addr = start;
	pte_t *pgtable;

	pgtable = pte_alloc_one_kernel(&init_mm);
	if (!pgtable)
		return -ENOMEM;

	pmd_populate_kernel(&init_mm, &__pmd, pgtable);

	for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
		pte_t entry, *pte;
		pgprot_t pgprot = PAGE_KERNEL;

		entry = mk_pte(head + i, pgprot);
		pte = pte_offset_kernel(&__pmd, addr);
		set_pte_at(&init_mm, addr, pte, entry);
	}

	spin_lock(&init_mm.page_table_lock);
	if (likely(pmd_leaf(*pmd))) {
		/*
		 * Higher order allocations from buddy allocator must be able to
		 * be treated as indepdenent small pages (as they can be freed
		 * individually).
		 */
		if (!PageReserved(head))
			split_page(head, get_order(PMD_SIZE));

		/* Make pte visible before pmd. See comment in pmd_install(). */
		smp_wmb();
		pmd_populate_kernel(&init_mm, pmd, pgtable);
		if (!(walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH))
			flush_tlb_kernel_range(start, start + PMD_SIZE);
	} else {
		pte_free_kernel(&init_mm, pgtable);
	}
	spin_unlock(&init_mm.page_table_lock);

	return 0;
}

static int vmemmap_pmd_entry(pmd_t *pmd, unsigned long addr,
			     unsigned long next, struct mm_walk *walk)
{
	int ret = 0;
	struct page *head;
	struct vmemmap_remap_walk *vmemmap_walk = walk->private;

	/* Only splitting, not remapping the vmemmap pages. */
	if (!vmemmap_walk->remap_pte)
		walk->action = ACTION_CONTINUE;

	spin_lock(&init_mm.page_table_lock);
	head = pmd_leaf(*pmd) ? pmd_page(*pmd) : NULL;
	/*
	 * Due to HugeTLB alignment requirements and the vmemmap
	 * pages being at the start of the hotplugged memory
	 * region in memory_hotplug.memmap_on_memory case. Checking
	 * the vmemmap page associated with the first vmemmap page
	 * if it is self-hosted is sufficient.
	 *
	 * [                  hotplugged memory                  ]
	 * [        section        ][...][        section        ]
	 * [ vmemmap ][              usable memory               ]
	 *   ^  | ^                        |
	 *   +--+ |                        |
	 *        +------------------------+
	 */
	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG) && unlikely(!vmemmap_walk->nr_walked)) {
		struct page *page = head ? head + pte_index(addr) :
				    pte_page(ptep_get(pte_offset_kernel(pmd, addr)));

		if (PageVmemmapSelfHosted(page))
			ret = -ENOTSUPP;
	}
	spin_unlock(&init_mm.page_table_lock);
	if (!head || ret)
		return ret;

	return vmemmap_split_pmd(pmd, head, addr & PMD_MASK, vmemmap_walk);
}

static int vmemmap_pte_entry(pte_t *pte, unsigned long addr,
			     unsigned long next, struct mm_walk *walk)
{
	struct vmemmap_remap_walk *vmemmap_walk = walk->private;

	/*
	 * The reuse_page is found 'first' in page table walking before
	 * starting remapping.
	 */
	if (!vmemmap_walk->reuse_page)
		vmemmap_walk->reuse_page = pte_page(ptep_get(pte));
	else
		vmemmap_walk->remap_pte(pte, addr, vmemmap_walk);
	vmemmap_walk->nr_walked++;

	return 0;
}

static const struct mm_walk_ops vmemmap_remap_ops = {
	.pmd_entry	= vmemmap_pmd_entry,
	.pte_entry	= vmemmap_pte_entry,
};

static int vmemmap_remap_range(unsigned long start, unsigned long end,
			       struct vmemmap_remap_walk *walk)
{
	int ret;

	VM_BUG_ON(!PAGE_ALIGNED(start | end));

	mmap_read_lock(&init_mm);
	ret = walk_page_range_novma(&init_mm, start, end, &vmemmap_remap_ops,
				    NULL, walk);
	mmap_read_unlock(&init_mm);
	if (ret)
		return ret;

	if (walk->remap_pte && !(walk->flags & VMEMMAP_REMAP_NO_TLB_FLUSH))
		flush_tlb_kernel_range(start, end);

	return 0;
}

/*
 * Free a vmemmap page. A vmemmap page can be allocated from the memblock
 * allocator or buddy allocator. If the PG_reserved flag is set, it means
 * that it allocated from the memblock allocator, just free it via the
 * free_bootmem_page(). Otherwise, use __free_page().
 */
static inline void free_vmemmap_page(struct page *page)
{
	if (PageReserved(page))
		free_bootmem_page(page);
	else
		__free_page(page);
}

/* Free a list of the vmemmap pages */
static void free_vmemmap_page_list(struct list_head *list)
{
	struct page *page, *next;

	list_for_each_entry_safe(page, next, list, lru)
		free_vmemmap_page(page);
}

static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
			      struct vmemmap_remap_walk *walk)
{
	/*
	 * Remap the tail pages as read-only to catch illegal write operation
	 * to the tail pages.
	 */
	pgprot_t pgprot = PAGE_KERNEL_RO;
	struct page *page = pte_page(ptep_get(pte));
	pte_t entry;

	/* Remapping the head page requires r/w */
	if (unlikely(addr == walk->reuse_addr)) {
		pgprot = PAGE_KERNEL;
		list_del(&walk->reuse_page->lru);

		/*
		 * Makes sure that preceding stores to the page contents from
		 * vmemmap_remap_free() become visible before the set_pte_at()
		 * write.
		 */
		smp_wmb();
	}

	entry = mk_pte(walk->reuse_page, pgprot);
	list_add(&page->lru, walk->vmemmap_pages);
	set_pte_at(&init_mm, addr, pte, entry);
}

/*
 * How many struct page structs need to be reset. When we reuse the head
 * struct page, the special metadata (e.g. page->flags or page->mapping)
 * cannot copy to the tail struct page structs. The invalid value will be
 * checked in the free_tail_page_prepare(). In order to avoid the message
 * of "corrupted mapping in tail page". We need to reset at least 3 (one
 * head struct page struct and two tail struct page structs) struct page
 * structs.
 */
#define NR_RESET_STRUCT_PAGE		3

static inline void reset_struct_pages(struct page *start)
{
	struct page *from = start + NR_RESET_STRUCT_PAGE;

	BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
	memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
}

static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
				struct vmemmap_remap_walk *walk)
{
	pgprot_t pgprot = PAGE_KERNEL;
	struct page *page;
	void *to;

	BUG_ON(pte_page(ptep_get(pte)) != walk->reuse_page);

	page = list_first_entry(walk->vmemmap_pages, struct page, lru);
	list_del(&page->lru);
	to = page_to_virt(page);
	copy_page(to, (void *)walk->reuse_addr);
	reset_struct_pages(to);

	/*
	 * Makes sure that preceding stores to the page contents become visible
	 * before the set_pte_at() write.
	 */
	smp_wmb();
	set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
}

/**
 * vmemmap_remap_split - split the vmemmap virtual address range [@start, @end)
 *                      backing PMDs of the directmap into PTEs
 * @start:     start address of the vmemmap virtual address range that we want
 *             to remap.
 * @end:       end address of the vmemmap virtual address range that we want to
 *             remap.
 * @reuse:     reuse address.
 *
 * Return: %0 on success, negative error code otherwise.
 */
static int vmemmap_remap_split(unsigned long start, unsigned long end,
			       unsigned long reuse)
{
	struct vmemmap_remap_walk walk = {
		.remap_pte	= NULL,
		.flags		= VMEMMAP_SPLIT_NO_TLB_FLUSH,
	};

	/* See the comment in the vmemmap_remap_free(). */
	BUG_ON(start - reuse != PAGE_SIZE);

	return vmemmap_remap_range(reuse, end, &walk);
}

/**
 * vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
 *			to the page which @reuse is mapped to, then free vmemmap
 *			which the range are mapped to.
 * @start:	start address of the vmemmap virtual address range that we want
 *		to remap.
 * @end:	end address of the vmemmap virtual address range that we want to
 *		remap.
 * @reuse:	reuse address.
 * @vmemmap_pages: list to deposit vmemmap pages to be freed.  It is callers
 *		responsibility to free pages.
 * @flags:	modifications to vmemmap_remap_walk flags
 *
 * Return: %0 on success, negative error code otherwise.
 */
static int vmemmap_remap_free(unsigned long start, unsigned long end,
			      unsigned long reuse,
			      struct list_head *vmemmap_pages,
			      unsigned long flags)
{
	int ret;
	struct vmemmap_remap_walk walk = {
		.remap_pte	= vmemmap_remap_pte,
		.reuse_addr	= reuse,
		.vmemmap_pages	= vmemmap_pages,
		.flags		= flags,
	};
	int nid = page_to_nid((struct page *)reuse);
	gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;

	/*
	 * Allocate a new head vmemmap page to avoid breaking a contiguous
	 * block of struct page memory when freeing it back to page allocator
	 * in free_vmemmap_page_list(). This will allow the likely contiguous
	 * struct page backing memory to be kept contiguous and allowing for
	 * more allocations of hugepages. Fallback to the currently
	 * mapped head page in case should it fail to allocate.
	 */
	walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0);
	if (walk.reuse_page) {
		copy_page(page_to_virt(walk.reuse_page),
			  (void *)walk.reuse_addr);
		list_add(&walk.reuse_page->lru, vmemmap_pages);
	}

	/*
	 * In order to make remapping routine most efficient for the huge pages,
	 * the routine of vmemmap page table walking has the following rules
	 * (see more details from the vmemmap_pte_range()):
	 *
	 * - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
	 *   should be continuous.
	 * - The @reuse address is part of the range [@reuse, @end) that we are
	 *   walking which is passed to vmemmap_remap_range().
	 * - The @reuse address is the first in the complete range.
	 *
	 * So we need to make sure that @start and @reuse meet the above rules.
	 */
	BUG_ON(start - reuse != PAGE_SIZE);

	ret = vmemmap_remap_range(reuse, end, &walk);
	if (ret && walk.nr_walked) {
		end = reuse + walk.nr_walked * PAGE_SIZE;
		/*
		 * vmemmap_pages contains pages from the previous
		 * vmemmap_remap_range call which failed.  These
		 * are pages which were removed from the vmemmap.
		 * They will be restored in the following call.
		 */
		walk = (struct vmemmap_remap_walk) {
			.remap_pte	= vmemmap_restore_pte,
			.reuse_addr	= reuse,
			.vmemmap_pages	= vmemmap_pages,
			.flags		= 0,
		};

		vmemmap_remap_range(reuse, end, &walk);
	}

	return ret;
}

static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
				   struct list_head *list)
{
	gfp_t gfp_mask = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
	int nid = page_to_nid((struct page *)start);
	struct page *page, *next;

	while (nr_pages--) {
		page = alloc_pages_node(nid, gfp_mask, 0);
		if (!page)
			goto out;
		list_add(&page->lru, list);
	}

	return 0;
out:
	list_for_each_entry_safe(page, next, list, lru)
		__free_page(page);
	return -ENOMEM;
}

/**
 * vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
 *			 to the page which is from the @vmemmap_pages
 *			 respectively.
 * @start:	start address of the vmemmap virtual address range that we want
 *		to remap.
 * @end:	end address of the vmemmap virtual address range that we want to
 *		remap.
 * @reuse:	reuse address.
 * @flags:	modifications to vmemmap_remap_walk flags
 *
 * Return: %0 on success, negative error code otherwise.
 */
static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
			       unsigned long reuse, unsigned long flags)
{
	LIST_HEAD(vmemmap_pages);
	struct vmemmap_remap_walk walk = {
		.remap_pte	= vmemmap_restore_pte,
		.reuse_addr	= reuse,
		.vmemmap_pages	= &vmemmap_pages,
		.flags		= flags,
	};

	/* See the comment in the vmemmap_remap_free(). */
	BUG_ON(start - reuse != PAGE_SIZE);

	if (alloc_vmemmap_page_list(start, end, &vmemmap_pages))
		return -ENOMEM;

	return vmemmap_remap_range(reuse, end, &walk);
}

DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);

static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);

static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
					   struct folio *folio, unsigned long flags)
{
	int ret;
	unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
	unsigned long vmemmap_reuse;

	VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
	if (!folio_test_hugetlb_vmemmap_optimized(folio))
		return 0;

	vmemmap_end	= vmemmap_start + hugetlb_vmemmap_size(h);
	vmemmap_reuse	= vmemmap_start;
	vmemmap_start	+= HUGETLB_VMEMMAP_RESERVE_SIZE;

	/*
	 * The pages which the vmemmap virtual address range [@vmemmap_start,
	 * @vmemmap_end) are mapped to are freed to the buddy allocator, and
	 * the range is mapped to the page which @vmemmap_reuse is mapped to.
	 * When a HugeTLB page is freed to the buddy allocator, previously
	 * discarded vmemmap pages must be allocated and remapping.
	 */
	ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse, flags);
	if (!ret) {
		folio_clear_hugetlb_vmemmap_optimized(folio);
		static_branch_dec(&hugetlb_optimize_vmemmap_key);
	}

	return ret;
}

/**
 * hugetlb_vmemmap_restore_folio - restore previously optimized (by
 *				hugetlb_vmemmap_optimize_folio()) vmemmap pages which
 *				will be reallocated and remapped.
 * @h:		struct hstate.
 * @folio:     the folio whose vmemmap pages will be restored.
 *
 * Return: %0 if @folio's vmemmap pages have been reallocated and remapped,
 * negative error code otherwise.
 */
int hugetlb_vmemmap_restore_folio(const struct hstate *h, struct folio *folio)
{
	return __hugetlb_vmemmap_restore_folio(h, folio, 0);
}

/**
 * hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list.
 * @h:			hstate.
 * @folio_list:		list of folios.
 * @non_hvo_folios:	Output list of folios for which vmemmap exists.
 *
 * Return: number of folios for which vmemmap was restored, or an error code
 *		if an error was encountered restoring vmemmap for a folio.
 *		Folios that have vmemmap are moved to the non_hvo_folios
 *		list.  Processing of entries stops when the first error is
 *		encountered. The folio that experienced the error and all
 *		non-processed folios will remain on folio_list.
 */
long hugetlb_vmemmap_restore_folios(const struct hstate *h,
					struct list_head *folio_list,
					struct list_head *non_hvo_folios)
{
	struct folio *folio, *t_folio;
	long restored = 0;
	long ret = 0;

	list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
		if (folio_test_hugetlb_vmemmap_optimized(folio)) {
			ret = __hugetlb_vmemmap_restore_folio(h, folio,
							      VMEMMAP_REMAP_NO_TLB_FLUSH);
			if (ret)
				break;
			restored++;
		}

		/* Add non-optimized folios to output list */
		list_move(&folio->lru, non_hvo_folios);
	}

	if (restored)
		flush_tlb_all();
	if (!ret)
		ret = restored;
	return ret;
}

/* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
static bool vmemmap_should_optimize_folio(const struct hstate *h, struct folio *folio)
{
	if (folio_test_hugetlb_vmemmap_optimized(folio))
		return false;

	if (!READ_ONCE(vmemmap_optimize_enabled))
		return false;

	if (!hugetlb_vmemmap_optimizable(h))
		return false;

	return true;
}

static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h,
					    struct folio *folio,
					    struct list_head *vmemmap_pages,
					    unsigned long flags)
{
	int ret = 0;
	unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
	unsigned long vmemmap_reuse;

	VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
	if (!vmemmap_should_optimize_folio(h, folio))
		return ret;

	static_branch_inc(&hugetlb_optimize_vmemmap_key);
	/*
	 * Very Subtle
	 * If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed
	 * immediately after remapping.  As a result, subsequent accesses
	 * and modifications to struct pages associated with the hugetlb
	 * page could be to the OLD struct pages.  Set the vmemmap optimized
	 * flag here so that it is copied to the new head page.  This keeps
	 * the old and new struct pages in sync.
	 * If there is an error during optimization, we will immediately FLUSH
	 * the TLB and clear the flag below.
	 */
	folio_set_hugetlb_vmemmap_optimized(folio);

	vmemmap_end	= vmemmap_start + hugetlb_vmemmap_size(h);
	vmemmap_reuse	= vmemmap_start;
	vmemmap_start	+= HUGETLB_VMEMMAP_RESERVE_SIZE;

	/*
	 * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
	 * to the page which @vmemmap_reuse is mapped to.  Add pages previously
	 * mapping the range to vmemmap_pages list so that they can be freed by
	 * the caller.
	 */
	ret = vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse,
				 vmemmap_pages, flags);
	if (ret) {
		static_branch_dec(&hugetlb_optimize_vmemmap_key);
		folio_clear_hugetlb_vmemmap_optimized(folio);
	}

	return ret;
}

/**
 * hugetlb_vmemmap_optimize_folio - optimize @folio's vmemmap pages.
 * @h:		struct hstate.
 * @folio:     the folio whose vmemmap pages will be optimized.
 *
 * This function only tries to optimize @folio's vmemmap pages and does not
 * guarantee that the optimization will succeed after it returns. The caller
 * can use folio_test_hugetlb_vmemmap_optimized(@folio) to detect if @folio's
 * vmemmap pages have been optimized.
 */
void hugetlb_vmemmap_optimize_folio(const struct hstate *h, struct folio *folio)
{
	LIST_HEAD(vmemmap_pages);

	__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, 0);
	free_vmemmap_page_list(&vmemmap_pages);
}

static int hugetlb_vmemmap_split_folio(const struct hstate *h, struct folio *folio)
{
	unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
	unsigned long vmemmap_reuse;

	if (!vmemmap_should_optimize_folio(h, folio))
		return 0;

	vmemmap_end	= vmemmap_start + hugetlb_vmemmap_size(h);
	vmemmap_reuse	= vmemmap_start;
	vmemmap_start	+= HUGETLB_VMEMMAP_RESERVE_SIZE;

	/*
	 * Split PMDs on the vmemmap virtual address range [@vmemmap_start,
	 * @vmemmap_end]
	 */
	return vmemmap_remap_split(vmemmap_start, vmemmap_end, vmemmap_reuse);
}

void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
{
	struct folio *folio;
	LIST_HEAD(vmemmap_pages);

	list_for_each_entry(folio, folio_list, lru) {
		int ret = hugetlb_vmemmap_split_folio(h, folio);

		/*
		 * Spliting the PMD requires allocating a page, thus lets fail
		 * early once we encounter the first OOM. No point in retrying
		 * as it can be dynamically done on remap with the memory
		 * we get back from the vmemmap deduplication.
		 */
		if (ret == -ENOMEM)
			break;
	}

	flush_tlb_all();

	list_for_each_entry(folio, folio_list, lru) {
		int ret;

		ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages,
						       VMEMMAP_REMAP_NO_TLB_FLUSH);

		/*
		 * Pages to be freed may have been accumulated.  If we
		 * encounter an ENOMEM,  free what we have and try again.
		 * This can occur in the case that both spliting fails
		 * halfway and head page allocation also failed. In this
		 * case __hugetlb_vmemmap_optimize_folio() would free memory
		 * allowing more vmemmap remaps to occur.
		 */
		if (ret == -ENOMEM && !list_empty(&vmemmap_pages)) {
			flush_tlb_all();
			free_vmemmap_page_list(&vmemmap_pages);
			INIT_LIST_HEAD(&vmemmap_pages);
			__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages,
							 VMEMMAP_REMAP_NO_TLB_FLUSH);
		}
	}

	flush_tlb_all();
	free_vmemmap_page_list(&vmemmap_pages);
}

static struct ctl_table hugetlb_vmemmap_sysctls[] = {
	{
		.procname	= "hugetlb_optimize_vmemmap",
		.data		= &vmemmap_optimize_enabled,
		.maxlen		= sizeof(vmemmap_optimize_enabled),
		.mode		= 0644,
		.proc_handler	= proc_dobool,
	},
};

static int __init hugetlb_vmemmap_init(void)
{
	const struct hstate *h;

	/* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
	BUILD_BUG_ON(__NR_USED_SUBPAGE > HUGETLB_VMEMMAP_RESERVE_PAGES);

	for_each_hstate(h) {
		if (hugetlb_vmemmap_optimizable(h)) {
			register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
			break;
		}
	}
	return 0;
}
late_initcall(hugetlb_vmemmap_init);