aboutsummaryrefslogtreecommitdiffstats
path: root/mm/hugetlb.c
blob: de4cf458d6e1979432aad46613d0816146347fc1 (plain) (blame)
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
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
/*
 * Generic hugetlb support.
 * (C) William Irwin, April 2004
 */
#include <linux/gfp.h>
#include <linux/list.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/sysctl.h>
#include <linux/highmem.h>
#include <linux/nodemask.h>
#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/cpuset.h>
#include <linux/mutex.h>

#include <asm/page.h>
#include <asm/pgtable.h>

#include <linux/hugetlb.h>
#include "internal.h"

const unsigned long hugetlb_zero = 0, hugetlb_infinity = ~0UL;
static unsigned long nr_huge_pages, free_huge_pages, resv_huge_pages;
unsigned long max_huge_pages;
static struct list_head hugepage_freelists[MAX_NUMNODES];
static unsigned int nr_huge_pages_node[MAX_NUMNODES];
static unsigned int free_huge_pages_node[MAX_NUMNODES];
static gfp_t htlb_alloc_mask = GFP_HIGHUSER;
unsigned long hugepages_treat_as_movable;

/*
 * Protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages
 */
static DEFINE_SPINLOCK(hugetlb_lock);

static void clear_huge_page(struct page *page, unsigned long addr)
{
	int i;

	might_sleep();
	for (i = 0; i < (HPAGE_SIZE/PAGE_SIZE); i++) {
		cond_resched();
		clear_user_highpage(page + i, addr);
	}
}

static void copy_huge_page(struct page *dst, struct page *src,
			   unsigned long addr, struct vm_area_struct *vma)
{
	int i;

	might_sleep();
	for (i = 0; i < HPAGE_SIZE/PAGE_SIZE; i++) {
		cond_resched();
		copy_user_highpage(dst + i, src + i, addr + i*PAGE_SIZE, vma);
	}
}

static void enqueue_huge_page(struct page *page)
{
	int nid = page_to_nid(page);
	list_add(&page->lru, &hugepage_freelists[nid]);
	free_huge_pages++;
	free_huge_pages_node[nid]++;
}

static struct page *dequeue_huge_page(struct vm_area_struct *vma,
				unsigned long address)
{
	int nid;
	struct page *page = NULL;
	struct zonelist *zonelist = huge_zonelist(vma, address,
						htlb_alloc_mask);
	struct zone **z;

	for (z = zonelist->zones; *z; z++) {
		nid = zone_to_nid(*z);
		if (cpuset_zone_allowed_softwall(*z, htlb_alloc_mask) &&
		    !list_empty(&hugepage_freelists[nid])) {
			page = list_entry(hugepage_freelists[nid].next,
					  struct page, lru);
			list_del(&page->lru);
			free_huge_pages--;
			free_huge_pages_node[nid]--;
			break;
		}
	}
	return page;
}

static void free_huge_page(struct page *page)
{
	BUG_ON(page_count(page));

	INIT_LIST_HEAD(&page->lru);

	spin_lock(&hugetlb_lock);
	enqueue_huge_page(page);
	spin_unlock(&hugetlb_lock);
}

static int alloc_fresh_huge_page(void)
{
	static int prev_nid;
	struct page *page;
	int nid;

	/*
	 * Copy static prev_nid to local nid, work on that, then copy it
	 * back to prev_nid afterwards: otherwise there's a window in which
	 * a racer might pass invalid nid MAX_NUMNODES to alloc_pages_node.
	 * But we don't need to use a spin_lock here: it really doesn't
	 * matter if occasionally a racer chooses the same nid as we do.
	 */
	nid = next_node(prev_nid, node_online_map);
	if (nid == MAX_NUMNODES)
		nid = first_node(node_online_map);
	prev_nid = nid;

	page = alloc_pages_node(nid, htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
					HUGETLB_PAGE_ORDER);
	if (page) {
		set_compound_page_dtor(page, free_huge_page);
		spin_lock(&hugetlb_lock);
		nr_huge_pages++;
		nr_huge_pages_node[page_to_nid(page)]++;
		spin_unlock(&hugetlb_lock);
		put_page(page); /* free it into the hugepage allocator */
		return 1;
	}
	return 0;
}

static struct page *alloc_huge_page(struct vm_area_struct *vma,
				    unsigned long addr)
{
	struct page *page;

	spin_lock(&hugetlb_lock);
	if (vma->vm_flags & VM_MAYSHARE)
		resv_huge_pages--;
	else if (free_huge_pages <= resv_huge_pages)
		goto fail;

	page = dequeue_huge_page(vma, addr);
	if (!page)
		goto fail;

	spin_unlock(&hugetlb_lock);
	set_page_refcounted(page);
	return page;

fail:
	if (vma->vm_flags & VM_MAYSHARE)
		resv_huge_pages++;
	spin_unlock(&hugetlb_lock);
	return NULL;
}

static int __init hugetlb_init(void)
{
	unsigned long i;

	if (HPAGE_SHIFT == 0)
		return 0;

	for (i = 0; i < MAX_NUMNODES; ++i)
		INIT_LIST_HEAD(&hugepage_freelists[i]);

	for (i = 0; i < max_huge_pages; ++i) {
		if (!alloc_fresh_huge_page())
			break;
	}
	max_huge_pages = free_huge_pages = nr_huge_pages = i;
	printk("Total HugeTLB memory allocated, %ld\n", free_huge_pages);
	return 0;
}
module_init(hugetlb_init);

static int __init hugetlb_setup(char *s)
{
	if (sscanf(s, "%lu", &max_huge_pages) <= 0)
		max_huge_pages = 0;
	return 1;
}
__setup("hugepages=", hugetlb_setup);

static unsigned int cpuset_mems_nr(unsigned int *array)
{
	int node;
	unsigned int nr = 0;

	for_each_node_mask(node, cpuset_current_mems_allowed)
		nr += array[node];

	return nr;
}

#ifdef CONFIG_SYSCTL
static void update_and_free_page(struct page *page)
{
	int i;
	nr_huge_pages--;
	nr_huge_pages_node[page_to_nid(page)]--;
	for (i = 0; i < (HPAGE_SIZE / PAGE_SIZE); i++) {
		page[i].flags &= ~(1 << PG_locked | 1 << PG_error | 1 << PG_referenced |
				1 << PG_dirty | 1 << PG_active | 1 << PG_reserved |
				1 << PG_private | 1<< PG_writeback);
	}
	set_compound_page_dtor(page, NULL);
	set_page_refcounted(page);
	__free_pages(page, HUGETLB_PAGE_ORDER);
}

#ifdef CONFIG_HIGHMEM
static void try_to_free_low(unsigned long count)
{
	int i;

	for (i = 0; i < MAX_NUMNODES; ++i) {
		struct page *page, *next;
		list_for_each_entry_safe(page, next, &hugepage_freelists[i], lru) {
			if (PageHighMem(page))
				continue;
			list_del(&page->lru);
			update_and_free_page(page);
			free_huge_pages--;
			free_huge_pages_node[page_to_nid(page)]--;
			if (count >= nr_huge_pages)
				return;
		}
	}
}
#else
static inline void try_to_free_low(unsigned long count)
{
}
#endif

static unsigned long set_max_huge_pages(unsigned long count)
{
	while (count > nr_huge_pages) {
		if (!alloc_fresh_huge_page())
			return nr_huge_pages;
	}
	if (count >= nr_huge_pages)
		return nr_huge_pages;

	spin_lock(&hugetlb_lock);
	count = max(count, resv_huge_pages);
	try_to_free_low(count);
	while (count < nr_huge_pages) {
		struct page *page = dequeue_huge_page(NULL, 0);
		if (!page)
			break;
		update_and_free_page(page);
	}
	spin_unlock(&hugetlb_lock);
	return nr_huge_pages;
}

int hugetlb_sysctl_handler(struct ctl_table *table, int write,
			   struct file *file, void __user *buffer,
			   size_t *length, loff_t *ppos)
{
	proc_doulongvec_minmax(table, write, file, buffer, length, ppos);
	max_huge_pages = set_max_huge_pages(max_huge_pages);
	return 0;
}

int hugetlb_treat_movable_handler(struct ctl_table *table, int write,
			struct file *file, void __user *buffer,
			size_t *length, loff_t *ppos)
{
	proc_dointvec(table, write, file, buffer, length, ppos);
	if (hugepages_treat_as_movable)
		htlb_alloc_mask = GFP_HIGHUSER_MOVABLE;
	else
		htlb_alloc_mask = GFP_HIGHUSER;
	return 0;
}

#endif /* CONFIG_SYSCTL */

int hugetlb_report_meminfo(char *buf)
{
	return sprintf(buf,
			"HugePages_Total: %5lu\n"
			"HugePages_Free:  %5lu\n"
			"HugePages_Rsvd:  %5lu\n"
			"Hugepagesize:    %5lu kB\n",
			nr_huge_pages,
			free_huge_pages,
			resv_huge_pages,
			HPAGE_SIZE/1024);
}

int hugetlb_report_node_meminfo(int nid, char *buf)
{
	return sprintf(buf,
		"Node %d HugePages_Total: %5u\n"
		"Node %d HugePages_Free:  %5u\n",
		nid, nr_huge_pages_node[nid],
		nid, free_huge_pages_node[nid]);
}

/* Return the number pages of memory we physically have, in PAGE_SIZE units. */
unsigned long hugetlb_total_pages(void)
{
	return nr_huge_pages * (HPAGE_SIZE / PAGE_SIZE);
}

/*
 * We cannot handle pagefaults against hugetlb pages at all.  They cause
 * handle_mm_fault() to try to instantiate regular-sized pages in the
 * hugegpage VMA.  do_page_fault() is supposed to trap this, so BUG is we get
 * this far.
 */
static int hugetlb_vm_op_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
	BUG();
	return 0;
}

struct vm_operations_struct hugetlb_vm_ops = {
	.fault = hugetlb_vm_op_fault,
};

static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
				int writable)
{
	pte_t entry;

	if (writable) {
		entry =
		    pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
	} else {
		entry = pte_wrprotect(mk_pte(page, vma->vm_page_prot));
	}
	entry = pte_mkyoung(entry);
	entry = pte_mkhuge(entry);

	return entry;
}

static void set_huge_ptep_writable(struct vm_area_struct *vma,
				   unsigned long address, pte_t *ptep)
{
	pte_t entry;

	entry = pte_mkwrite(pte_mkdirty(*ptep));
	if (ptep_set_access_flags(vma, address, ptep, entry, 1)) {
		update_mmu_cache(vma, address, entry);
		lazy_mmu_prot_update(entry);
	}
}


int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
			    struct vm_area_struct *vma)
{
	pte_t *src_pte, *dst_pte, entry;
	struct page *ptepage;
	unsigned long addr;
	int cow;

	cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;

	for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
		src_pte = huge_pte_offset(src, addr);
		if (!src_pte)
			continue;
		dst_pte = huge_pte_alloc(dst, addr);
		if (!dst_pte)
			goto nomem;
		spin_lock(&dst->page_table_lock);
		spin_lock(&src->page_table_lock);
		if (!pte_none(*src_pte)) {
			if (cow)
				ptep_set_wrprotect(src, addr, src_pte);
			entry = *src_pte;
			ptepage = pte_page(entry);
			get_page(ptepage);
			set_huge_pte_at(dst, addr, dst_pte, entry);
		}
		spin_unlock(&src->page_table_lock);
		spin_unlock(&dst->page_table_lock);
	}
	return 0;

nomem:
	return -ENOMEM;
}

void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
			    unsigned long end)
{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long address;
	pte_t *ptep;
	pte_t pte;
	struct page *page;
	struct page *tmp;
	/*
	 * A page gathering list, protected by per file i_mmap_lock. The
	 * lock is used to avoid list corruption from multiple unmapping
	 * of the same page since we are using page->lru.
	 */
	LIST_HEAD(page_list);

	WARN_ON(!is_vm_hugetlb_page(vma));
	BUG_ON(start & ~HPAGE_MASK);
	BUG_ON(end & ~HPAGE_MASK);

	spin_lock(&mm->page_table_lock);
	for (address = start; address < end; address += HPAGE_SIZE) {
		ptep = huge_pte_offset(mm, address);
		if (!ptep)
			continue;

		if (huge_pmd_unshare(mm, &address, ptep))
			continue;

		pte = huge_ptep_get_and_clear(mm, address, ptep);
		if (pte_none(pte))
			continue;

		page = pte_page(pte);
		if (pte_dirty(pte))
			set_page_dirty(page);
		list_add(&page->lru, &page_list);
	}
	spin_unlock(&mm->page_table_lock);
	flush_tlb_range(vma, start, end);
	list_for_each_entry_safe(page, tmp, &page_list, lru) {
		list_del(&page->lru);
		put_page(page);
	}
}

void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
			  unsigned long end)
{
	/*
	 * It is undesirable to test vma->vm_file as it should be non-null
	 * for valid hugetlb area. However, vm_file will be NULL in the error
	 * cleanup path of do_mmap_pgoff. When hugetlbfs ->mmap method fails,
	 * do_mmap_pgoff() nullifies vma->vm_file before calling this function
	 * to clean up. Since no pte has actually been setup, it is safe to
	 * do nothing in this case.
	 */
	if (vma->vm_file) {
		spin_lock(&vma->vm_file->f_mapping->i_mmap_lock);
		__unmap_hugepage_range(vma, start, end);
		spin_unlock(&vma->vm_file->f_mapping->i_mmap_lock);
	}
}

static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
			unsigned long address, pte_t *ptep, pte_t pte)
{
	struct page *old_page, *new_page;
	int avoidcopy;

	old_page = pte_page(pte);

	/* If no-one else is actually using this page, avoid the copy
	 * and just make the page writable */
	avoidcopy = (page_count(old_page) == 1);
	if (avoidcopy) {
		set_huge_ptep_writable(vma, address, ptep);
		return 0;
	}

	page_cache_get(old_page);
	new_page = alloc_huge_page(vma, address);

	if (!new_page) {
		page_cache_release(old_page);
		return VM_FAULT_OOM;
	}

	spin_unlock(&mm->page_table_lock);
	copy_huge_page(new_page, old_page, address, vma);
	spin_lock(&mm->page_table_lock);

	ptep = huge_pte_offset(mm, address & HPAGE_MASK);
	if (likely(pte_same(*ptep, pte))) {
		/* Break COW */
		set_huge_pte_at(mm, address, ptep,
				make_huge_pte(vma, new_page, 1));
		/* Make the old page be freed below */
		new_page = old_page;
	}
	page_cache_release(new_page);
	page_cache_release(old_page);
	return 0;
}

static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
			unsigned long address, pte_t *ptep, int write_access)
{
	int ret = VM_FAULT_SIGBUS;
	unsigned long idx;
	unsigned long size;
	struct page *page;
	struct address_space *mapping;
	pte_t new_pte;

	mapping = vma->vm_file->f_mapping;
	idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
		+ (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));

	/*
	 * Use page lock to guard against racing truncation
	 * before we get page_table_lock.
	 */
retry:
	page = find_lock_page(mapping, idx);
	if (!page) {
		size = i_size_read(mapping->host) >> HPAGE_SHIFT;
		if (idx >= size)
			goto out;
		if (hugetlb_get_quota(mapping))
			goto out;
		page = alloc_huge_page(vma, address);
		if (!page) {
			hugetlb_put_quota(mapping);
			ret = VM_FAULT_OOM;
			goto out;
		}
		clear_huge_page(page, address);

		if (vma->vm_flags & VM_SHARED) {
			int err;

			err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
			if (err) {
				put_page(page);
				hugetlb_put_quota(mapping);
				if (err == -EEXIST)
					goto retry;
				goto out;
			}
		} else
			lock_page(page);
	}

	spin_lock(&mm->page_table_lock);
	size = i_size_read(mapping->host) >> HPAGE_SHIFT;
	if (idx >= size)
		goto backout;

	ret = 0;
	if (!pte_none(*ptep))
		goto backout;

	new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
				&& (vma->vm_flags & VM_SHARED)));
	set_huge_pte_at(mm, address, ptep, new_pte);

	if (write_access && !(vma->vm_flags & VM_SHARED)) {
		/* Optimization, do the COW without a second fault */
		ret = hugetlb_cow(mm, vma, address, ptep, new_pte);
	}

	spin_unlock(&mm->page_table_lock);
	unlock_page(page);
out:
	return ret;

backout:
	spin_unlock(&mm->page_table_lock);
	hugetlb_put_quota(mapping);
	unlock_page(page);
	put_page(page);
	goto out;
}

int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
			unsigned long address, int write_access)
{
	pte_t *ptep;
	pte_t entry;
	int ret;
	static DEFINE_MUTEX(hugetlb_instantiation_mutex);

	ptep = huge_pte_alloc(mm, address);
	if (!ptep)
		return VM_FAULT_OOM;

	/*
	 * Serialize hugepage allocation and instantiation, so that we don't
	 * get spurious allocation failures if two CPUs race to instantiate
	 * the same page in the page cache.
	 */
	mutex_lock(&hugetlb_instantiation_mutex);
	entry = *ptep;
	if (pte_none(entry)) {
		ret = hugetlb_no_page(mm, vma, address, ptep, write_access);
		mutex_unlock(&hugetlb_instantiation_mutex);
		return ret;
	}

	ret = 0;

	spin_lock(&mm->page_table_lock);
	/* Check for a racing update before calling hugetlb_cow */
	if (likely(pte_same(entry, *ptep)))
		if (write_access && !pte_write(entry))
			ret = hugetlb_cow(mm, vma, address, ptep, entry);
	spin_unlock(&mm->page_table_lock);
	mutex_unlock(&hugetlb_instantiation_mutex);

	return ret;
}

int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
			struct page **pages, struct vm_area_struct **vmas,
			unsigned long *position, int *length, int i)
{
	unsigned long pfn_offset;
	unsigned long vaddr = *position;
	int remainder = *length;

	spin_lock(&mm->page_table_lock);
	while (vaddr < vma->vm_end && remainder) {
		pte_t *pte;
		struct page *page;

		/*
		 * Some archs (sparc64, sh*) have multiple pte_ts to
		 * each hugepage.  We have to make * sure we get the
		 * first, for the page indexing below to work.
		 */
		pte = huge_pte_offset(mm, vaddr & HPAGE_MASK);

		if (!pte || pte_none(*pte)) {
			int ret;

			spin_unlock(&mm->page_table_lock);
			ret = hugetlb_fault(mm, vma, vaddr, 0);
			spin_lock(&mm->page_table_lock);
			if (!(ret & VM_FAULT_ERROR))
				continue;

			remainder = 0;
			if (!i)
				i = -EFAULT;
			break;
		}

		pfn_offset = (vaddr & ~HPAGE_MASK) >> PAGE_SHIFT;
		page = pte_page(*pte);
same_page:
		if (pages) {
			get_page(page);
			pages[i] = page + pfn_offset;
		}

		if (vmas)
			vmas[i] = vma;

		vaddr += PAGE_SIZE;
		++pfn_offset;
		--remainder;
		++i;
		if (vaddr < vma->vm_end && remainder &&
				pfn_offset < HPAGE_SIZE/PAGE_SIZE) {
			/*
			 * We use pfn_offset to avoid touching the pageframes
			 * of this compound page.
			 */
			goto same_page;
		}
	}
	spin_unlock(&mm->page_table_lock);
	*length = remainder;
	*position = vaddr;

	return i;
}

void hugetlb_change_protection(struct vm_area_struct *vma,
		unsigned long address, unsigned long end, pgprot_t newprot)
{
	struct mm_struct *mm = vma->vm_mm;
	unsigned long start = address;
	pte_t *ptep;
	pte_t pte;

	BUG_ON(address >= end);
	flush_cache_range(vma, address, end);

	spin_lock(&vma->vm_file->f_mapping->i_mmap_lock);
	spin_lock(&mm->page_table_lock);
	for (; address < end; address += HPAGE_SIZE) {
		ptep = huge_pte_offset(mm, address);
		if (!ptep)
			continue;
		if (huge_pmd_unshare(mm, &address, ptep))
			continue;
		if (!pte_none(*ptep)) {
			pte = huge_ptep_get_and_clear(mm, address, ptep);
			pte = pte_mkhuge(pte_modify(pte, newprot));
			set_huge_pte_at(mm, address, ptep, pte);
			lazy_mmu_prot_update(pte);
		}
	}
	spin_unlock(&mm->page_table_lock);
	spin_unlock(&vma->vm_file->f_mapping->i_mmap_lock);

	flush_tlb_range(vma, start, end);
}

struct file_region {
	struct list_head link;
	long from;
	long to;
};

static long region_add(struct list_head *head, long f, long t)
{
	struct file_region *rg, *nrg, *trg;

	/* Locate the region we are either in or before. */
	list_for_each_entry(rg, head, link)
		if (f <= rg->to)
			break;

	/* Round our left edge to the current segment if it encloses us. */
	if (f > rg->from)
		f = rg->from;

	/* Check for and consume any regions we now overlap with. */
	nrg = rg;
	list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
		if (&rg->link == head)
			break;
		if (rg->from > t)
			break;

		/* If this area reaches higher then extend our area to
		 * include it completely.  If this is not the first area
		 * which we intend to reuse, free it. */
		if (rg->to > t)
			t = rg->to;
		if (rg != nrg) {
			list_del(&rg->link);
			kfree(rg);
		}
	}
	nrg->from = f;
	nrg->to = t;
	return 0;
}

static long region_chg(struct list_head *head, long f, long t)
{
	struct file_region *rg, *nrg;
	long chg = 0;

	/* Locate the region we are before or in. */
	list_for_each_entry(rg, head, link)
		if (f <= rg->to)
			break;

	/* If we are below the current region then a new region is required.
	 * Subtle, allocate a new region at the position but make it zero
	 * size such that we can guarentee to record the reservation. */
	if (&rg->link == head || t < rg->from) {
		nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
		if (nrg == 0)
			return -ENOMEM;
		nrg->from = f;
		nrg->to   = f;
		INIT_LIST_HEAD(&nrg->link);
		list_add(&nrg->link, rg->link.prev);

		return t - f;
	}

	/* Round our left edge to the current segment if it encloses us. */
	if (f > rg->from)
		f = rg->from;
	chg = t - f;

	/* Check for and consume any regions we now overlap with. */
	list_for_each_entry(rg, rg->link.prev, link) {
		if (&rg->link == head)
			break;
		if (rg->from > t)
			return chg;

		/* We overlap with this area, if it extends futher than
		 * us then we must extend ourselves.  Account for its
		 * existing reservation. */
		if (rg->to > t) {
			chg += rg->to - t;
			t = rg->to;
		}
		chg -= rg->to - rg->from;
	}
	return chg;
}

static long region_truncate(struct list_head *head, long end)
{
	struct file_region *rg, *trg;
	long chg = 0;

	/* Locate the region we are either in or before. */
	list_for_each_entry(rg, head, link)
		if (end <= rg->to)
			break;
	if (&rg->link == head)
		return 0;

	/* If we are in the middle of a region then adjust it. */
	if (end > rg->from) {
		chg = rg->to - end;
		rg->to = end;
		rg = list_entry(rg->link.next, typeof(*rg), link);
	}

	/* Drop any remaining regions. */
	list_for_each_entry_safe(rg, trg, rg->link.prev, link) {
		if (&rg->link == head)
			break;
		chg += rg->to - rg->from;
		list_del(&rg->link);
		kfree(rg);
	}
	return chg;
}

static int hugetlb_acct_memory(long delta)
{
	int ret = -ENOMEM;

	spin_lock(&hugetlb_lock);
	if ((delta + resv_huge_pages) <= free_huge_pages) {
		resv_huge_pages += delta;
		ret = 0;
	}
	spin_unlock(&hugetlb_lock);
	return ret;
}

int hugetlb_reserve_pages(struct inode *inode, long from, long to)
{
	long ret, chg;

	chg = region_chg(&inode->i_mapping->private_list, from, to);
	if (chg < 0)
		return chg;
	/*
	 * When cpuset is configured, it breaks the strict hugetlb page
	 * reservation as the accounting is done on a global variable. Such
	 * reservation is completely rubbish in the presence of cpuset because
	 * the reservation is not checked against page availability for the
	 * current cpuset. Application can still potentially OOM'ed by kernel
	 * with lack of free htlb page in cpuset that the task is in.
	 * Attempt to enforce strict accounting with cpuset is almost
	 * impossible (or too ugly) because cpuset is too fluid that
	 * task or memory node can be dynamically moved between cpusets.
	 *
	 * The change of semantics for shared hugetlb mapping with cpuset is
	 * undesirable. However, in order to preserve some of the semantics,
	 * we fall back to check against current free page availability as
	 * a best attempt and hopefully to minimize the impact of changing
	 * semantics that cpuset has.
	 */
	if (chg > cpuset_mems_nr(free_huge_pages_node))
		return -ENOMEM;

	ret = hugetlb_acct_memory(chg);
	if (ret < 0)
		return ret;
	region_add(&inode->i_mapping->private_list, from, to);
	return 0;
}

void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed)
{
	long chg = region_truncate(&inode->i_mapping->private_list, offset);
	hugetlb_acct_memory(freed - chg);
}