xref: /linux/mm/huge_memory.c (revision 04eeb606a8383b306f4bc6991da8231b5f3924b0)
1 /*
2  *  Copyright (C) 2009  Red Hat, Inc.
3  *
4  *  This work is licensed under the terms of the GNU GPL, version 2. See
5  *  the COPYING file in the top-level directory.
6  */
7 
8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9 
10 #include <linux/mm.h>
11 #include <linux/sched.h>
12 #include <linux/highmem.h>
13 #include <linux/hugetlb.h>
14 #include <linux/mmu_notifier.h>
15 #include <linux/rmap.h>
16 #include <linux/swap.h>
17 #include <linux/shrinker.h>
18 #include <linux/mm_inline.h>
19 #include <linux/kthread.h>
20 #include <linux/khugepaged.h>
21 #include <linux/freezer.h>
22 #include <linux/mman.h>
23 #include <linux/pagemap.h>
24 #include <linux/migrate.h>
25 #include <linux/hashtable.h>
26 
27 #include <asm/tlb.h>
28 #include <asm/pgalloc.h>
29 #include "internal.h"
30 
31 /*
32  * By default transparent hugepage support is disabled in order that avoid
33  * to risk increase the memory footprint of applications without a guaranteed
34  * benefit. When transparent hugepage support is enabled, is for all mappings,
35  * and khugepaged scans all mappings.
36  * Defrag is invoked by khugepaged hugepage allocations and by page faults
37  * for all hugepage allocations.
38  */
39 unsigned long transparent_hugepage_flags __read_mostly =
40 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
41 	(1<<TRANSPARENT_HUGEPAGE_FLAG)|
42 #endif
43 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
44 	(1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
45 #endif
46 	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
47 	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
48 	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
49 
50 /* default scan 8*512 pte (or vmas) every 30 second */
51 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
52 static unsigned int khugepaged_pages_collapsed;
53 static unsigned int khugepaged_full_scans;
54 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
55 /* during fragmentation poll the hugepage allocator once every minute */
56 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
57 static struct task_struct *khugepaged_thread __read_mostly;
58 static DEFINE_MUTEX(khugepaged_mutex);
59 static DEFINE_SPINLOCK(khugepaged_mm_lock);
60 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
61 /*
62  * default collapse hugepages if there is at least one pte mapped like
63  * it would have happened if the vma was large enough during page
64  * fault.
65  */
66 static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
67 
68 static int khugepaged(void *none);
69 static int khugepaged_slab_init(void);
70 
71 #define MM_SLOTS_HASH_BITS 10
72 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
73 
74 static struct kmem_cache *mm_slot_cache __read_mostly;
75 
76 /**
77  * struct mm_slot - hash lookup from mm to mm_slot
78  * @hash: hash collision list
79  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
80  * @mm: the mm that this information is valid for
81  */
82 struct mm_slot {
83 	struct hlist_node hash;
84 	struct list_head mm_node;
85 	struct mm_struct *mm;
86 };
87 
88 /**
89  * struct khugepaged_scan - cursor for scanning
90  * @mm_head: the head of the mm list to scan
91  * @mm_slot: the current mm_slot we are scanning
92  * @address: the next address inside that to be scanned
93  *
94  * There is only the one khugepaged_scan instance of this cursor structure.
95  */
96 struct khugepaged_scan {
97 	struct list_head mm_head;
98 	struct mm_slot *mm_slot;
99 	unsigned long address;
100 };
101 static struct khugepaged_scan khugepaged_scan = {
102 	.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
103 };
104 
105 
106 static int set_recommended_min_free_kbytes(void)
107 {
108 	struct zone *zone;
109 	int nr_zones = 0;
110 	unsigned long recommended_min;
111 
112 	if (!khugepaged_enabled())
113 		return 0;
114 
115 	for_each_populated_zone(zone)
116 		nr_zones++;
117 
118 	/* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
119 	recommended_min = pageblock_nr_pages * nr_zones * 2;
120 
121 	/*
122 	 * Make sure that on average at least two pageblocks are almost free
123 	 * of another type, one for a migratetype to fall back to and a
124 	 * second to avoid subsequent fallbacks of other types There are 3
125 	 * MIGRATE_TYPES we care about.
126 	 */
127 	recommended_min += pageblock_nr_pages * nr_zones *
128 			   MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
129 
130 	/* don't ever allow to reserve more than 5% of the lowmem */
131 	recommended_min = min(recommended_min,
132 			      (unsigned long) nr_free_buffer_pages() / 20);
133 	recommended_min <<= (PAGE_SHIFT-10);
134 
135 	if (recommended_min > min_free_kbytes) {
136 		if (user_min_free_kbytes >= 0)
137 			pr_info("raising min_free_kbytes from %d to %lu "
138 				"to help transparent hugepage allocations\n",
139 				min_free_kbytes, recommended_min);
140 
141 		min_free_kbytes = recommended_min;
142 	}
143 	setup_per_zone_wmarks();
144 	return 0;
145 }
146 late_initcall(set_recommended_min_free_kbytes);
147 
148 static int start_khugepaged(void)
149 {
150 	int err = 0;
151 	if (khugepaged_enabled()) {
152 		if (!khugepaged_thread)
153 			khugepaged_thread = kthread_run(khugepaged, NULL,
154 							"khugepaged");
155 		if (unlikely(IS_ERR(khugepaged_thread))) {
156 			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
157 			err = PTR_ERR(khugepaged_thread);
158 			khugepaged_thread = NULL;
159 		}
160 
161 		if (!list_empty(&khugepaged_scan.mm_head))
162 			wake_up_interruptible(&khugepaged_wait);
163 
164 		set_recommended_min_free_kbytes();
165 	} else if (khugepaged_thread) {
166 		kthread_stop(khugepaged_thread);
167 		khugepaged_thread = NULL;
168 	}
169 
170 	return err;
171 }
172 
173 static atomic_t huge_zero_refcount;
174 static struct page *huge_zero_page __read_mostly;
175 
176 static inline bool is_huge_zero_page(struct page *page)
177 {
178 	return ACCESS_ONCE(huge_zero_page) == page;
179 }
180 
181 static inline bool is_huge_zero_pmd(pmd_t pmd)
182 {
183 	return is_huge_zero_page(pmd_page(pmd));
184 }
185 
186 static struct page *get_huge_zero_page(void)
187 {
188 	struct page *zero_page;
189 retry:
190 	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
191 		return ACCESS_ONCE(huge_zero_page);
192 
193 	zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
194 			HPAGE_PMD_ORDER);
195 	if (!zero_page) {
196 		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
197 		return NULL;
198 	}
199 	count_vm_event(THP_ZERO_PAGE_ALLOC);
200 	preempt_disable();
201 	if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
202 		preempt_enable();
203 		__free_page(zero_page);
204 		goto retry;
205 	}
206 
207 	/* We take additional reference here. It will be put back by shrinker */
208 	atomic_set(&huge_zero_refcount, 2);
209 	preempt_enable();
210 	return ACCESS_ONCE(huge_zero_page);
211 }
212 
213 static void put_huge_zero_page(void)
214 {
215 	/*
216 	 * Counter should never go to zero here. Only shrinker can put
217 	 * last reference.
218 	 */
219 	BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
220 }
221 
222 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
223 					struct shrink_control *sc)
224 {
225 	/* we can free zero page only if last reference remains */
226 	return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
227 }
228 
229 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
230 				       struct shrink_control *sc)
231 {
232 	if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
233 		struct page *zero_page = xchg(&huge_zero_page, NULL);
234 		BUG_ON(zero_page == NULL);
235 		__free_page(zero_page);
236 		return HPAGE_PMD_NR;
237 	}
238 
239 	return 0;
240 }
241 
242 static struct shrinker huge_zero_page_shrinker = {
243 	.count_objects = shrink_huge_zero_page_count,
244 	.scan_objects = shrink_huge_zero_page_scan,
245 	.seeks = DEFAULT_SEEKS,
246 };
247 
248 #ifdef CONFIG_SYSFS
249 
250 static ssize_t double_flag_show(struct kobject *kobj,
251 				struct kobj_attribute *attr, char *buf,
252 				enum transparent_hugepage_flag enabled,
253 				enum transparent_hugepage_flag req_madv)
254 {
255 	if (test_bit(enabled, &transparent_hugepage_flags)) {
256 		VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
257 		return sprintf(buf, "[always] madvise never\n");
258 	} else if (test_bit(req_madv, &transparent_hugepage_flags))
259 		return sprintf(buf, "always [madvise] never\n");
260 	else
261 		return sprintf(buf, "always madvise [never]\n");
262 }
263 static ssize_t double_flag_store(struct kobject *kobj,
264 				 struct kobj_attribute *attr,
265 				 const char *buf, size_t count,
266 				 enum transparent_hugepage_flag enabled,
267 				 enum transparent_hugepage_flag req_madv)
268 {
269 	if (!memcmp("always", buf,
270 		    min(sizeof("always")-1, count))) {
271 		set_bit(enabled, &transparent_hugepage_flags);
272 		clear_bit(req_madv, &transparent_hugepage_flags);
273 	} else if (!memcmp("madvise", buf,
274 			   min(sizeof("madvise")-1, count))) {
275 		clear_bit(enabled, &transparent_hugepage_flags);
276 		set_bit(req_madv, &transparent_hugepage_flags);
277 	} else if (!memcmp("never", buf,
278 			   min(sizeof("never")-1, count))) {
279 		clear_bit(enabled, &transparent_hugepage_flags);
280 		clear_bit(req_madv, &transparent_hugepage_flags);
281 	} else
282 		return -EINVAL;
283 
284 	return count;
285 }
286 
287 static ssize_t enabled_show(struct kobject *kobj,
288 			    struct kobj_attribute *attr, char *buf)
289 {
290 	return double_flag_show(kobj, attr, buf,
291 				TRANSPARENT_HUGEPAGE_FLAG,
292 				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
293 }
294 static ssize_t enabled_store(struct kobject *kobj,
295 			     struct kobj_attribute *attr,
296 			     const char *buf, size_t count)
297 {
298 	ssize_t ret;
299 
300 	ret = double_flag_store(kobj, attr, buf, count,
301 				TRANSPARENT_HUGEPAGE_FLAG,
302 				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
303 
304 	if (ret > 0) {
305 		int err;
306 
307 		mutex_lock(&khugepaged_mutex);
308 		err = start_khugepaged();
309 		mutex_unlock(&khugepaged_mutex);
310 
311 		if (err)
312 			ret = err;
313 	}
314 
315 	return ret;
316 }
317 static struct kobj_attribute enabled_attr =
318 	__ATTR(enabled, 0644, enabled_show, enabled_store);
319 
320 static ssize_t single_flag_show(struct kobject *kobj,
321 				struct kobj_attribute *attr, char *buf,
322 				enum transparent_hugepage_flag flag)
323 {
324 	return sprintf(buf, "%d\n",
325 		       !!test_bit(flag, &transparent_hugepage_flags));
326 }
327 
328 static ssize_t single_flag_store(struct kobject *kobj,
329 				 struct kobj_attribute *attr,
330 				 const char *buf, size_t count,
331 				 enum transparent_hugepage_flag flag)
332 {
333 	unsigned long value;
334 	int ret;
335 
336 	ret = kstrtoul(buf, 10, &value);
337 	if (ret < 0)
338 		return ret;
339 	if (value > 1)
340 		return -EINVAL;
341 
342 	if (value)
343 		set_bit(flag, &transparent_hugepage_flags);
344 	else
345 		clear_bit(flag, &transparent_hugepage_flags);
346 
347 	return count;
348 }
349 
350 /*
351  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
352  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
353  * memory just to allocate one more hugepage.
354  */
355 static ssize_t defrag_show(struct kobject *kobj,
356 			   struct kobj_attribute *attr, char *buf)
357 {
358 	return double_flag_show(kobj, attr, buf,
359 				TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
360 				TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
361 }
362 static ssize_t defrag_store(struct kobject *kobj,
363 			    struct kobj_attribute *attr,
364 			    const char *buf, size_t count)
365 {
366 	return double_flag_store(kobj, attr, buf, count,
367 				 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
368 				 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
369 }
370 static struct kobj_attribute defrag_attr =
371 	__ATTR(defrag, 0644, defrag_show, defrag_store);
372 
373 static ssize_t use_zero_page_show(struct kobject *kobj,
374 		struct kobj_attribute *attr, char *buf)
375 {
376 	return single_flag_show(kobj, attr, buf,
377 				TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
378 }
379 static ssize_t use_zero_page_store(struct kobject *kobj,
380 		struct kobj_attribute *attr, const char *buf, size_t count)
381 {
382 	return single_flag_store(kobj, attr, buf, count,
383 				 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
384 }
385 static struct kobj_attribute use_zero_page_attr =
386 	__ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
387 #ifdef CONFIG_DEBUG_VM
388 static ssize_t debug_cow_show(struct kobject *kobj,
389 				struct kobj_attribute *attr, char *buf)
390 {
391 	return single_flag_show(kobj, attr, buf,
392 				TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
393 }
394 static ssize_t debug_cow_store(struct kobject *kobj,
395 			       struct kobj_attribute *attr,
396 			       const char *buf, size_t count)
397 {
398 	return single_flag_store(kobj, attr, buf, count,
399 				 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
400 }
401 static struct kobj_attribute debug_cow_attr =
402 	__ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
403 #endif /* CONFIG_DEBUG_VM */
404 
405 static struct attribute *hugepage_attr[] = {
406 	&enabled_attr.attr,
407 	&defrag_attr.attr,
408 	&use_zero_page_attr.attr,
409 #ifdef CONFIG_DEBUG_VM
410 	&debug_cow_attr.attr,
411 #endif
412 	NULL,
413 };
414 
415 static struct attribute_group hugepage_attr_group = {
416 	.attrs = hugepage_attr,
417 };
418 
419 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
420 					 struct kobj_attribute *attr,
421 					 char *buf)
422 {
423 	return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
424 }
425 
426 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
427 					  struct kobj_attribute *attr,
428 					  const char *buf, size_t count)
429 {
430 	unsigned long msecs;
431 	int err;
432 
433 	err = kstrtoul(buf, 10, &msecs);
434 	if (err || msecs > UINT_MAX)
435 		return -EINVAL;
436 
437 	khugepaged_scan_sleep_millisecs = msecs;
438 	wake_up_interruptible(&khugepaged_wait);
439 
440 	return count;
441 }
442 static struct kobj_attribute scan_sleep_millisecs_attr =
443 	__ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
444 	       scan_sleep_millisecs_store);
445 
446 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
447 					  struct kobj_attribute *attr,
448 					  char *buf)
449 {
450 	return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
451 }
452 
453 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
454 					   struct kobj_attribute *attr,
455 					   const char *buf, size_t count)
456 {
457 	unsigned long msecs;
458 	int err;
459 
460 	err = kstrtoul(buf, 10, &msecs);
461 	if (err || msecs > UINT_MAX)
462 		return -EINVAL;
463 
464 	khugepaged_alloc_sleep_millisecs = msecs;
465 	wake_up_interruptible(&khugepaged_wait);
466 
467 	return count;
468 }
469 static struct kobj_attribute alloc_sleep_millisecs_attr =
470 	__ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
471 	       alloc_sleep_millisecs_store);
472 
473 static ssize_t pages_to_scan_show(struct kobject *kobj,
474 				  struct kobj_attribute *attr,
475 				  char *buf)
476 {
477 	return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
478 }
479 static ssize_t pages_to_scan_store(struct kobject *kobj,
480 				   struct kobj_attribute *attr,
481 				   const char *buf, size_t count)
482 {
483 	int err;
484 	unsigned long pages;
485 
486 	err = kstrtoul(buf, 10, &pages);
487 	if (err || !pages || pages > UINT_MAX)
488 		return -EINVAL;
489 
490 	khugepaged_pages_to_scan = pages;
491 
492 	return count;
493 }
494 static struct kobj_attribute pages_to_scan_attr =
495 	__ATTR(pages_to_scan, 0644, pages_to_scan_show,
496 	       pages_to_scan_store);
497 
498 static ssize_t pages_collapsed_show(struct kobject *kobj,
499 				    struct kobj_attribute *attr,
500 				    char *buf)
501 {
502 	return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
503 }
504 static struct kobj_attribute pages_collapsed_attr =
505 	__ATTR_RO(pages_collapsed);
506 
507 static ssize_t full_scans_show(struct kobject *kobj,
508 			       struct kobj_attribute *attr,
509 			       char *buf)
510 {
511 	return sprintf(buf, "%u\n", khugepaged_full_scans);
512 }
513 static struct kobj_attribute full_scans_attr =
514 	__ATTR_RO(full_scans);
515 
516 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
517 				      struct kobj_attribute *attr, char *buf)
518 {
519 	return single_flag_show(kobj, attr, buf,
520 				TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
521 }
522 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
523 				       struct kobj_attribute *attr,
524 				       const char *buf, size_t count)
525 {
526 	return single_flag_store(kobj, attr, buf, count,
527 				 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
528 }
529 static struct kobj_attribute khugepaged_defrag_attr =
530 	__ATTR(defrag, 0644, khugepaged_defrag_show,
531 	       khugepaged_defrag_store);
532 
533 /*
534  * max_ptes_none controls if khugepaged should collapse hugepages over
535  * any unmapped ptes in turn potentially increasing the memory
536  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
537  * reduce the available free memory in the system as it
538  * runs. Increasing max_ptes_none will instead potentially reduce the
539  * free memory in the system during the khugepaged scan.
540  */
541 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
542 					     struct kobj_attribute *attr,
543 					     char *buf)
544 {
545 	return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
546 }
547 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
548 					      struct kobj_attribute *attr,
549 					      const char *buf, size_t count)
550 {
551 	int err;
552 	unsigned long max_ptes_none;
553 
554 	err = kstrtoul(buf, 10, &max_ptes_none);
555 	if (err || max_ptes_none > HPAGE_PMD_NR-1)
556 		return -EINVAL;
557 
558 	khugepaged_max_ptes_none = max_ptes_none;
559 
560 	return count;
561 }
562 static struct kobj_attribute khugepaged_max_ptes_none_attr =
563 	__ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
564 	       khugepaged_max_ptes_none_store);
565 
566 static struct attribute *khugepaged_attr[] = {
567 	&khugepaged_defrag_attr.attr,
568 	&khugepaged_max_ptes_none_attr.attr,
569 	&pages_to_scan_attr.attr,
570 	&pages_collapsed_attr.attr,
571 	&full_scans_attr.attr,
572 	&scan_sleep_millisecs_attr.attr,
573 	&alloc_sleep_millisecs_attr.attr,
574 	NULL,
575 };
576 
577 static struct attribute_group khugepaged_attr_group = {
578 	.attrs = khugepaged_attr,
579 	.name = "khugepaged",
580 };
581 
582 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
583 {
584 	int err;
585 
586 	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
587 	if (unlikely(!*hugepage_kobj)) {
588 		pr_err("failed to create transparent hugepage kobject\n");
589 		return -ENOMEM;
590 	}
591 
592 	err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
593 	if (err) {
594 		pr_err("failed to register transparent hugepage group\n");
595 		goto delete_obj;
596 	}
597 
598 	err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
599 	if (err) {
600 		pr_err("failed to register transparent hugepage group\n");
601 		goto remove_hp_group;
602 	}
603 
604 	return 0;
605 
606 remove_hp_group:
607 	sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
608 delete_obj:
609 	kobject_put(*hugepage_kobj);
610 	return err;
611 }
612 
613 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
614 {
615 	sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
616 	sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
617 	kobject_put(hugepage_kobj);
618 }
619 #else
620 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
621 {
622 	return 0;
623 }
624 
625 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
626 {
627 }
628 #endif /* CONFIG_SYSFS */
629 
630 static int __init hugepage_init(void)
631 {
632 	int err;
633 	struct kobject *hugepage_kobj;
634 
635 	if (!has_transparent_hugepage()) {
636 		transparent_hugepage_flags = 0;
637 		return -EINVAL;
638 	}
639 
640 	err = hugepage_init_sysfs(&hugepage_kobj);
641 	if (err)
642 		return err;
643 
644 	err = khugepaged_slab_init();
645 	if (err)
646 		goto out;
647 
648 	register_shrinker(&huge_zero_page_shrinker);
649 
650 	/*
651 	 * By default disable transparent hugepages on smaller systems,
652 	 * where the extra memory used could hurt more than TLB overhead
653 	 * is likely to save.  The admin can still enable it through /sys.
654 	 */
655 	if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
656 		transparent_hugepage_flags = 0;
657 
658 	start_khugepaged();
659 
660 	return 0;
661 out:
662 	hugepage_exit_sysfs(hugepage_kobj);
663 	return err;
664 }
665 subsys_initcall(hugepage_init);
666 
667 static int __init setup_transparent_hugepage(char *str)
668 {
669 	int ret = 0;
670 	if (!str)
671 		goto out;
672 	if (!strcmp(str, "always")) {
673 		set_bit(TRANSPARENT_HUGEPAGE_FLAG,
674 			&transparent_hugepage_flags);
675 		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
676 			  &transparent_hugepage_flags);
677 		ret = 1;
678 	} else if (!strcmp(str, "madvise")) {
679 		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
680 			  &transparent_hugepage_flags);
681 		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
682 			&transparent_hugepage_flags);
683 		ret = 1;
684 	} else if (!strcmp(str, "never")) {
685 		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
686 			  &transparent_hugepage_flags);
687 		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
688 			  &transparent_hugepage_flags);
689 		ret = 1;
690 	}
691 out:
692 	if (!ret)
693 		pr_warn("transparent_hugepage= cannot parse, ignored\n");
694 	return ret;
695 }
696 __setup("transparent_hugepage=", setup_transparent_hugepage);
697 
698 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
699 {
700 	if (likely(vma->vm_flags & VM_WRITE))
701 		pmd = pmd_mkwrite(pmd);
702 	return pmd;
703 }
704 
705 static inline pmd_t mk_huge_pmd(struct page *page, pgprot_t prot)
706 {
707 	pmd_t entry;
708 	entry = mk_pmd(page, prot);
709 	entry = pmd_mkhuge(entry);
710 	return entry;
711 }
712 
713 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
714 					struct vm_area_struct *vma,
715 					unsigned long haddr, pmd_t *pmd,
716 					struct page *page)
717 {
718 	struct mem_cgroup *memcg;
719 	pgtable_t pgtable;
720 	spinlock_t *ptl;
721 
722 	VM_BUG_ON_PAGE(!PageCompound(page), page);
723 
724 	if (mem_cgroup_try_charge(page, mm, GFP_TRANSHUGE, &memcg))
725 		return VM_FAULT_OOM;
726 
727 	pgtable = pte_alloc_one(mm, haddr);
728 	if (unlikely(!pgtable)) {
729 		mem_cgroup_cancel_charge(page, memcg);
730 		return VM_FAULT_OOM;
731 	}
732 
733 	clear_huge_page(page, haddr, HPAGE_PMD_NR);
734 	/*
735 	 * The memory barrier inside __SetPageUptodate makes sure that
736 	 * clear_huge_page writes become visible before the set_pmd_at()
737 	 * write.
738 	 */
739 	__SetPageUptodate(page);
740 
741 	ptl = pmd_lock(mm, pmd);
742 	if (unlikely(!pmd_none(*pmd))) {
743 		spin_unlock(ptl);
744 		mem_cgroup_cancel_charge(page, memcg);
745 		put_page(page);
746 		pte_free(mm, pgtable);
747 	} else {
748 		pmd_t entry;
749 		entry = mk_huge_pmd(page, vma->vm_page_prot);
750 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
751 		page_add_new_anon_rmap(page, vma, haddr);
752 		mem_cgroup_commit_charge(page, memcg, false);
753 		lru_cache_add_active_or_unevictable(page, vma);
754 		pgtable_trans_huge_deposit(mm, pmd, pgtable);
755 		set_pmd_at(mm, haddr, pmd, entry);
756 		add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
757 		atomic_long_inc(&mm->nr_ptes);
758 		spin_unlock(ptl);
759 	}
760 
761 	return 0;
762 }
763 
764 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
765 {
766 	return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
767 }
768 
769 static inline struct page *alloc_hugepage_vma(int defrag,
770 					      struct vm_area_struct *vma,
771 					      unsigned long haddr, int nd,
772 					      gfp_t extra_gfp)
773 {
774 	return alloc_pages_vma(alloc_hugepage_gfpmask(defrag, extra_gfp),
775 			       HPAGE_PMD_ORDER, vma, haddr, nd);
776 }
777 
778 /* Caller must hold page table lock. */
779 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
780 		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
781 		struct page *zero_page)
782 {
783 	pmd_t entry;
784 	if (!pmd_none(*pmd))
785 		return false;
786 	entry = mk_pmd(zero_page, vma->vm_page_prot);
787 	entry = pmd_wrprotect(entry);
788 	entry = pmd_mkhuge(entry);
789 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
790 	set_pmd_at(mm, haddr, pmd, entry);
791 	atomic_long_inc(&mm->nr_ptes);
792 	return true;
793 }
794 
795 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
796 			       unsigned long address, pmd_t *pmd,
797 			       unsigned int flags)
798 {
799 	struct page *page;
800 	unsigned long haddr = address & HPAGE_PMD_MASK;
801 
802 	if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
803 		return VM_FAULT_FALLBACK;
804 	if (unlikely(anon_vma_prepare(vma)))
805 		return VM_FAULT_OOM;
806 	if (unlikely(khugepaged_enter(vma)))
807 		return VM_FAULT_OOM;
808 	if (!(flags & FAULT_FLAG_WRITE) &&
809 			transparent_hugepage_use_zero_page()) {
810 		spinlock_t *ptl;
811 		pgtable_t pgtable;
812 		struct page *zero_page;
813 		bool set;
814 		pgtable = pte_alloc_one(mm, haddr);
815 		if (unlikely(!pgtable))
816 			return VM_FAULT_OOM;
817 		zero_page = get_huge_zero_page();
818 		if (unlikely(!zero_page)) {
819 			pte_free(mm, pgtable);
820 			count_vm_event(THP_FAULT_FALLBACK);
821 			return VM_FAULT_FALLBACK;
822 		}
823 		ptl = pmd_lock(mm, pmd);
824 		set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
825 				zero_page);
826 		spin_unlock(ptl);
827 		if (!set) {
828 			pte_free(mm, pgtable);
829 			put_huge_zero_page();
830 		}
831 		return 0;
832 	}
833 	page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
834 			vma, haddr, numa_node_id(), 0);
835 	if (unlikely(!page)) {
836 		count_vm_event(THP_FAULT_FALLBACK);
837 		return VM_FAULT_FALLBACK;
838 	}
839 	if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page))) {
840 		put_page(page);
841 		count_vm_event(THP_FAULT_FALLBACK);
842 		return VM_FAULT_FALLBACK;
843 	}
844 
845 	count_vm_event(THP_FAULT_ALLOC);
846 	return 0;
847 }
848 
849 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
850 		  pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
851 		  struct vm_area_struct *vma)
852 {
853 	spinlock_t *dst_ptl, *src_ptl;
854 	struct page *src_page;
855 	pmd_t pmd;
856 	pgtable_t pgtable;
857 	int ret;
858 
859 	ret = -ENOMEM;
860 	pgtable = pte_alloc_one(dst_mm, addr);
861 	if (unlikely(!pgtable))
862 		goto out;
863 
864 	dst_ptl = pmd_lock(dst_mm, dst_pmd);
865 	src_ptl = pmd_lockptr(src_mm, src_pmd);
866 	spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
867 
868 	ret = -EAGAIN;
869 	pmd = *src_pmd;
870 	if (unlikely(!pmd_trans_huge(pmd))) {
871 		pte_free(dst_mm, pgtable);
872 		goto out_unlock;
873 	}
874 	/*
875 	 * When page table lock is held, the huge zero pmd should not be
876 	 * under splitting since we don't split the page itself, only pmd to
877 	 * a page table.
878 	 */
879 	if (is_huge_zero_pmd(pmd)) {
880 		struct page *zero_page;
881 		bool set;
882 		/*
883 		 * get_huge_zero_page() will never allocate a new page here,
884 		 * since we already have a zero page to copy. It just takes a
885 		 * reference.
886 		 */
887 		zero_page = get_huge_zero_page();
888 		set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
889 				zero_page);
890 		BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
891 		ret = 0;
892 		goto out_unlock;
893 	}
894 
895 	if (unlikely(pmd_trans_splitting(pmd))) {
896 		/* split huge page running from under us */
897 		spin_unlock(src_ptl);
898 		spin_unlock(dst_ptl);
899 		pte_free(dst_mm, pgtable);
900 
901 		wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
902 		goto out;
903 	}
904 	src_page = pmd_page(pmd);
905 	VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
906 	get_page(src_page);
907 	page_dup_rmap(src_page);
908 	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
909 
910 	pmdp_set_wrprotect(src_mm, addr, src_pmd);
911 	pmd = pmd_mkold(pmd_wrprotect(pmd));
912 	pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
913 	set_pmd_at(dst_mm, addr, dst_pmd, pmd);
914 	atomic_long_inc(&dst_mm->nr_ptes);
915 
916 	ret = 0;
917 out_unlock:
918 	spin_unlock(src_ptl);
919 	spin_unlock(dst_ptl);
920 out:
921 	return ret;
922 }
923 
924 void huge_pmd_set_accessed(struct mm_struct *mm,
925 			   struct vm_area_struct *vma,
926 			   unsigned long address,
927 			   pmd_t *pmd, pmd_t orig_pmd,
928 			   int dirty)
929 {
930 	spinlock_t *ptl;
931 	pmd_t entry;
932 	unsigned long haddr;
933 
934 	ptl = pmd_lock(mm, pmd);
935 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
936 		goto unlock;
937 
938 	entry = pmd_mkyoung(orig_pmd);
939 	haddr = address & HPAGE_PMD_MASK;
940 	if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
941 		update_mmu_cache_pmd(vma, address, pmd);
942 
943 unlock:
944 	spin_unlock(ptl);
945 }
946 
947 /*
948  * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
949  * during copy_user_huge_page()'s copy_page_rep(): in the case when
950  * the source page gets split and a tail freed before copy completes.
951  * Called under pmd_lock of checked pmd, so safe from splitting itself.
952  */
953 static void get_user_huge_page(struct page *page)
954 {
955 	if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
956 		struct page *endpage = page + HPAGE_PMD_NR;
957 
958 		atomic_add(HPAGE_PMD_NR, &page->_count);
959 		while (++page < endpage)
960 			get_huge_page_tail(page);
961 	} else {
962 		get_page(page);
963 	}
964 }
965 
966 static void put_user_huge_page(struct page *page)
967 {
968 	if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
969 		struct page *endpage = page + HPAGE_PMD_NR;
970 
971 		while (page < endpage)
972 			put_page(page++);
973 	} else {
974 		put_page(page);
975 	}
976 }
977 
978 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
979 					struct vm_area_struct *vma,
980 					unsigned long address,
981 					pmd_t *pmd, pmd_t orig_pmd,
982 					struct page *page,
983 					unsigned long haddr)
984 {
985 	struct mem_cgroup *memcg;
986 	spinlock_t *ptl;
987 	pgtable_t pgtable;
988 	pmd_t _pmd;
989 	int ret = 0, i;
990 	struct page **pages;
991 	unsigned long mmun_start;	/* For mmu_notifiers */
992 	unsigned long mmun_end;		/* For mmu_notifiers */
993 
994 	pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
995 			GFP_KERNEL);
996 	if (unlikely(!pages)) {
997 		ret |= VM_FAULT_OOM;
998 		goto out;
999 	}
1000 
1001 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1002 		pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
1003 					       __GFP_OTHER_NODE,
1004 					       vma, address, page_to_nid(page));
1005 		if (unlikely(!pages[i] ||
1006 			     mem_cgroup_try_charge(pages[i], mm, GFP_KERNEL,
1007 						   &memcg))) {
1008 			if (pages[i])
1009 				put_page(pages[i]);
1010 			while (--i >= 0) {
1011 				memcg = (void *)page_private(pages[i]);
1012 				set_page_private(pages[i], 0);
1013 				mem_cgroup_cancel_charge(pages[i], memcg);
1014 				put_page(pages[i]);
1015 			}
1016 			kfree(pages);
1017 			ret |= VM_FAULT_OOM;
1018 			goto out;
1019 		}
1020 		set_page_private(pages[i], (unsigned long)memcg);
1021 	}
1022 
1023 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1024 		copy_user_highpage(pages[i], page + i,
1025 				   haddr + PAGE_SIZE * i, vma);
1026 		__SetPageUptodate(pages[i]);
1027 		cond_resched();
1028 	}
1029 
1030 	mmun_start = haddr;
1031 	mmun_end   = haddr + HPAGE_PMD_SIZE;
1032 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1033 
1034 	ptl = pmd_lock(mm, pmd);
1035 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
1036 		goto out_free_pages;
1037 	VM_BUG_ON_PAGE(!PageHead(page), page);
1038 
1039 	pmdp_clear_flush(vma, haddr, pmd);
1040 	/* leave pmd empty until pte is filled */
1041 
1042 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1043 	pmd_populate(mm, &_pmd, pgtable);
1044 
1045 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1046 		pte_t *pte, entry;
1047 		entry = mk_pte(pages[i], vma->vm_page_prot);
1048 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1049 		memcg = (void *)page_private(pages[i]);
1050 		set_page_private(pages[i], 0);
1051 		page_add_new_anon_rmap(pages[i], vma, haddr);
1052 		mem_cgroup_commit_charge(pages[i], memcg, false);
1053 		lru_cache_add_active_or_unevictable(pages[i], vma);
1054 		pte = pte_offset_map(&_pmd, haddr);
1055 		VM_BUG_ON(!pte_none(*pte));
1056 		set_pte_at(mm, haddr, pte, entry);
1057 		pte_unmap(pte);
1058 	}
1059 	kfree(pages);
1060 
1061 	smp_wmb(); /* make pte visible before pmd */
1062 	pmd_populate(mm, pmd, pgtable);
1063 	page_remove_rmap(page);
1064 	spin_unlock(ptl);
1065 
1066 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1067 
1068 	ret |= VM_FAULT_WRITE;
1069 	put_page(page);
1070 
1071 out:
1072 	return ret;
1073 
1074 out_free_pages:
1075 	spin_unlock(ptl);
1076 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1077 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1078 		memcg = (void *)page_private(pages[i]);
1079 		set_page_private(pages[i], 0);
1080 		mem_cgroup_cancel_charge(pages[i], memcg);
1081 		put_page(pages[i]);
1082 	}
1083 	kfree(pages);
1084 	goto out;
1085 }
1086 
1087 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1088 			unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1089 {
1090 	spinlock_t *ptl;
1091 	int ret = 0;
1092 	struct page *page = NULL, *new_page;
1093 	struct mem_cgroup *memcg;
1094 	unsigned long haddr;
1095 	unsigned long mmun_start;	/* For mmu_notifiers */
1096 	unsigned long mmun_end;		/* For mmu_notifiers */
1097 
1098 	ptl = pmd_lockptr(mm, pmd);
1099 	VM_BUG_ON_VMA(!vma->anon_vma, vma);
1100 	haddr = address & HPAGE_PMD_MASK;
1101 	if (is_huge_zero_pmd(orig_pmd))
1102 		goto alloc;
1103 	spin_lock(ptl);
1104 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
1105 		goto out_unlock;
1106 
1107 	page = pmd_page(orig_pmd);
1108 	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1109 	if (page_mapcount(page) == 1) {
1110 		pmd_t entry;
1111 		entry = pmd_mkyoung(orig_pmd);
1112 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1113 		if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1114 			update_mmu_cache_pmd(vma, address, pmd);
1115 		ret |= VM_FAULT_WRITE;
1116 		goto out_unlock;
1117 	}
1118 	get_user_huge_page(page);
1119 	spin_unlock(ptl);
1120 alloc:
1121 	if (transparent_hugepage_enabled(vma) &&
1122 	    !transparent_hugepage_debug_cow())
1123 		new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
1124 					      vma, haddr, numa_node_id(), 0);
1125 	else
1126 		new_page = NULL;
1127 
1128 	if (unlikely(!new_page)) {
1129 		if (!page) {
1130 			split_huge_page_pmd(vma, address, pmd);
1131 			ret |= VM_FAULT_FALLBACK;
1132 		} else {
1133 			ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1134 					pmd, orig_pmd, page, haddr);
1135 			if (ret & VM_FAULT_OOM) {
1136 				split_huge_page(page);
1137 				ret |= VM_FAULT_FALLBACK;
1138 			}
1139 			put_user_huge_page(page);
1140 		}
1141 		count_vm_event(THP_FAULT_FALLBACK);
1142 		goto out;
1143 	}
1144 
1145 	if (unlikely(mem_cgroup_try_charge(new_page, mm,
1146 					   GFP_TRANSHUGE, &memcg))) {
1147 		put_page(new_page);
1148 		if (page) {
1149 			split_huge_page(page);
1150 			put_user_huge_page(page);
1151 		} else
1152 			split_huge_page_pmd(vma, address, pmd);
1153 		ret |= VM_FAULT_FALLBACK;
1154 		count_vm_event(THP_FAULT_FALLBACK);
1155 		goto out;
1156 	}
1157 
1158 	count_vm_event(THP_FAULT_ALLOC);
1159 
1160 	if (!page)
1161 		clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1162 	else
1163 		copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1164 	__SetPageUptodate(new_page);
1165 
1166 	mmun_start = haddr;
1167 	mmun_end   = haddr + HPAGE_PMD_SIZE;
1168 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1169 
1170 	spin_lock(ptl);
1171 	if (page)
1172 		put_user_huge_page(page);
1173 	if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1174 		spin_unlock(ptl);
1175 		mem_cgroup_cancel_charge(new_page, memcg);
1176 		put_page(new_page);
1177 		goto out_mn;
1178 	} else {
1179 		pmd_t entry;
1180 		entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1181 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1182 		pmdp_clear_flush(vma, haddr, pmd);
1183 		page_add_new_anon_rmap(new_page, vma, haddr);
1184 		mem_cgroup_commit_charge(new_page, memcg, false);
1185 		lru_cache_add_active_or_unevictable(new_page, vma);
1186 		set_pmd_at(mm, haddr, pmd, entry);
1187 		update_mmu_cache_pmd(vma, address, pmd);
1188 		if (!page) {
1189 			add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1190 			put_huge_zero_page();
1191 		} else {
1192 			VM_BUG_ON_PAGE(!PageHead(page), page);
1193 			page_remove_rmap(page);
1194 			put_page(page);
1195 		}
1196 		ret |= VM_FAULT_WRITE;
1197 	}
1198 	spin_unlock(ptl);
1199 out_mn:
1200 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1201 out:
1202 	return ret;
1203 out_unlock:
1204 	spin_unlock(ptl);
1205 	return ret;
1206 }
1207 
1208 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1209 				   unsigned long addr,
1210 				   pmd_t *pmd,
1211 				   unsigned int flags)
1212 {
1213 	struct mm_struct *mm = vma->vm_mm;
1214 	struct page *page = NULL;
1215 
1216 	assert_spin_locked(pmd_lockptr(mm, pmd));
1217 
1218 	if (flags & FOLL_WRITE && !pmd_write(*pmd))
1219 		goto out;
1220 
1221 	/* Avoid dumping huge zero page */
1222 	if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1223 		return ERR_PTR(-EFAULT);
1224 
1225 	/* Full NUMA hinting faults to serialise migration in fault paths */
1226 	if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
1227 		goto out;
1228 
1229 	page = pmd_page(*pmd);
1230 	VM_BUG_ON_PAGE(!PageHead(page), page);
1231 	if (flags & FOLL_TOUCH) {
1232 		pmd_t _pmd;
1233 		/*
1234 		 * We should set the dirty bit only for FOLL_WRITE but
1235 		 * for now the dirty bit in the pmd is meaningless.
1236 		 * And if the dirty bit will become meaningful and
1237 		 * we'll only set it with FOLL_WRITE, an atomic
1238 		 * set_bit will be required on the pmd to set the
1239 		 * young bit, instead of the current set_pmd_at.
1240 		 */
1241 		_pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1242 		if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
1243 					  pmd, _pmd,  1))
1244 			update_mmu_cache_pmd(vma, addr, pmd);
1245 	}
1246 	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1247 		if (page->mapping && trylock_page(page)) {
1248 			lru_add_drain();
1249 			if (page->mapping)
1250 				mlock_vma_page(page);
1251 			unlock_page(page);
1252 		}
1253 	}
1254 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1255 	VM_BUG_ON_PAGE(!PageCompound(page), page);
1256 	if (flags & FOLL_GET)
1257 		get_page_foll(page);
1258 
1259 out:
1260 	return page;
1261 }
1262 
1263 /* NUMA hinting page fault entry point for trans huge pmds */
1264 int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
1265 				unsigned long addr, pmd_t pmd, pmd_t *pmdp)
1266 {
1267 	spinlock_t *ptl;
1268 	struct anon_vma *anon_vma = NULL;
1269 	struct page *page;
1270 	unsigned long haddr = addr & HPAGE_PMD_MASK;
1271 	int page_nid = -1, this_nid = numa_node_id();
1272 	int target_nid, last_cpupid = -1;
1273 	bool page_locked;
1274 	bool migrated = false;
1275 	int flags = 0;
1276 
1277 	ptl = pmd_lock(mm, pmdp);
1278 	if (unlikely(!pmd_same(pmd, *pmdp)))
1279 		goto out_unlock;
1280 
1281 	/*
1282 	 * If there are potential migrations, wait for completion and retry
1283 	 * without disrupting NUMA hinting information. Do not relock and
1284 	 * check_same as the page may no longer be mapped.
1285 	 */
1286 	if (unlikely(pmd_trans_migrating(*pmdp))) {
1287 		spin_unlock(ptl);
1288 		wait_migrate_huge_page(vma->anon_vma, pmdp);
1289 		goto out;
1290 	}
1291 
1292 	page = pmd_page(pmd);
1293 	BUG_ON(is_huge_zero_page(page));
1294 	page_nid = page_to_nid(page);
1295 	last_cpupid = page_cpupid_last(page);
1296 	count_vm_numa_event(NUMA_HINT_FAULTS);
1297 	if (page_nid == this_nid) {
1298 		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1299 		flags |= TNF_FAULT_LOCAL;
1300 	}
1301 
1302 	/*
1303 	 * Avoid grouping on DSO/COW pages in specific and RO pages
1304 	 * in general, RO pages shouldn't hurt as much anyway since
1305 	 * they can be in shared cache state.
1306 	 */
1307 	if (!pmd_write(pmd))
1308 		flags |= TNF_NO_GROUP;
1309 
1310 	/*
1311 	 * Acquire the page lock to serialise THP migrations but avoid dropping
1312 	 * page_table_lock if at all possible
1313 	 */
1314 	page_locked = trylock_page(page);
1315 	target_nid = mpol_misplaced(page, vma, haddr);
1316 	if (target_nid == -1) {
1317 		/* If the page was locked, there are no parallel migrations */
1318 		if (page_locked)
1319 			goto clear_pmdnuma;
1320 	}
1321 
1322 	/* Migration could have started since the pmd_trans_migrating check */
1323 	if (!page_locked) {
1324 		spin_unlock(ptl);
1325 		wait_on_page_locked(page);
1326 		page_nid = -1;
1327 		goto out;
1328 	}
1329 
1330 	/*
1331 	 * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1332 	 * to serialises splits
1333 	 */
1334 	get_page(page);
1335 	spin_unlock(ptl);
1336 	anon_vma = page_lock_anon_vma_read(page);
1337 
1338 	/* Confirm the PMD did not change while page_table_lock was released */
1339 	spin_lock(ptl);
1340 	if (unlikely(!pmd_same(pmd, *pmdp))) {
1341 		unlock_page(page);
1342 		put_page(page);
1343 		page_nid = -1;
1344 		goto out_unlock;
1345 	}
1346 
1347 	/* Bail if we fail to protect against THP splits for any reason */
1348 	if (unlikely(!anon_vma)) {
1349 		put_page(page);
1350 		page_nid = -1;
1351 		goto clear_pmdnuma;
1352 	}
1353 
1354 	/*
1355 	 * Migrate the THP to the requested node, returns with page unlocked
1356 	 * and pmd_numa cleared.
1357 	 */
1358 	spin_unlock(ptl);
1359 	migrated = migrate_misplaced_transhuge_page(mm, vma,
1360 				pmdp, pmd, addr, page, target_nid);
1361 	if (migrated) {
1362 		flags |= TNF_MIGRATED;
1363 		page_nid = target_nid;
1364 	}
1365 
1366 	goto out;
1367 clear_pmdnuma:
1368 	BUG_ON(!PageLocked(page));
1369 	pmd = pmd_mknonnuma(pmd);
1370 	set_pmd_at(mm, haddr, pmdp, pmd);
1371 	VM_BUG_ON(pmd_numa(*pmdp));
1372 	update_mmu_cache_pmd(vma, addr, pmdp);
1373 	unlock_page(page);
1374 out_unlock:
1375 	spin_unlock(ptl);
1376 
1377 out:
1378 	if (anon_vma)
1379 		page_unlock_anon_vma_read(anon_vma);
1380 
1381 	if (page_nid != -1)
1382 		task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR, flags);
1383 
1384 	return 0;
1385 }
1386 
1387 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1388 		 pmd_t *pmd, unsigned long addr)
1389 {
1390 	spinlock_t *ptl;
1391 	int ret = 0;
1392 
1393 	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1394 		struct page *page;
1395 		pgtable_t pgtable;
1396 		pmd_t orig_pmd;
1397 		/*
1398 		 * For architectures like ppc64 we look at deposited pgtable
1399 		 * when calling pmdp_get_and_clear. So do the
1400 		 * pgtable_trans_huge_withdraw after finishing pmdp related
1401 		 * operations.
1402 		 */
1403 		orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
1404 		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1405 		pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1406 		if (is_huge_zero_pmd(orig_pmd)) {
1407 			atomic_long_dec(&tlb->mm->nr_ptes);
1408 			spin_unlock(ptl);
1409 			put_huge_zero_page();
1410 		} else {
1411 			page = pmd_page(orig_pmd);
1412 			page_remove_rmap(page);
1413 			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1414 			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1415 			VM_BUG_ON_PAGE(!PageHead(page), page);
1416 			atomic_long_dec(&tlb->mm->nr_ptes);
1417 			spin_unlock(ptl);
1418 			tlb_remove_page(tlb, page);
1419 		}
1420 		pte_free(tlb->mm, pgtable);
1421 		ret = 1;
1422 	}
1423 	return ret;
1424 }
1425 
1426 int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1427 		unsigned long addr, unsigned long end,
1428 		unsigned char *vec)
1429 {
1430 	spinlock_t *ptl;
1431 	int ret = 0;
1432 
1433 	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1434 		/*
1435 		 * All logical pages in the range are present
1436 		 * if backed by a huge page.
1437 		 */
1438 		spin_unlock(ptl);
1439 		memset(vec, 1, (end - addr) >> PAGE_SHIFT);
1440 		ret = 1;
1441 	}
1442 
1443 	return ret;
1444 }
1445 
1446 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1447 		  unsigned long old_addr,
1448 		  unsigned long new_addr, unsigned long old_end,
1449 		  pmd_t *old_pmd, pmd_t *new_pmd)
1450 {
1451 	spinlock_t *old_ptl, *new_ptl;
1452 	int ret = 0;
1453 	pmd_t pmd;
1454 
1455 	struct mm_struct *mm = vma->vm_mm;
1456 
1457 	if ((old_addr & ~HPAGE_PMD_MASK) ||
1458 	    (new_addr & ~HPAGE_PMD_MASK) ||
1459 	    old_end - old_addr < HPAGE_PMD_SIZE ||
1460 	    (new_vma->vm_flags & VM_NOHUGEPAGE))
1461 		goto out;
1462 
1463 	/*
1464 	 * The destination pmd shouldn't be established, free_pgtables()
1465 	 * should have release it.
1466 	 */
1467 	if (WARN_ON(!pmd_none(*new_pmd))) {
1468 		VM_BUG_ON(pmd_trans_huge(*new_pmd));
1469 		goto out;
1470 	}
1471 
1472 	/*
1473 	 * We don't have to worry about the ordering of src and dst
1474 	 * ptlocks because exclusive mmap_sem prevents deadlock.
1475 	 */
1476 	ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
1477 	if (ret == 1) {
1478 		new_ptl = pmd_lockptr(mm, new_pmd);
1479 		if (new_ptl != old_ptl)
1480 			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1481 		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
1482 		VM_BUG_ON(!pmd_none(*new_pmd));
1483 
1484 		if (pmd_move_must_withdraw(new_ptl, old_ptl)) {
1485 			pgtable_t pgtable;
1486 			pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1487 			pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1488 		}
1489 		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1490 		if (new_ptl != old_ptl)
1491 			spin_unlock(new_ptl);
1492 		spin_unlock(old_ptl);
1493 	}
1494 out:
1495 	return ret;
1496 }
1497 
1498 /*
1499  * Returns
1500  *  - 0 if PMD could not be locked
1501  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1502  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1503  */
1504 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1505 		unsigned long addr, pgprot_t newprot, int prot_numa)
1506 {
1507 	struct mm_struct *mm = vma->vm_mm;
1508 	spinlock_t *ptl;
1509 	int ret = 0;
1510 
1511 	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1512 		pmd_t entry;
1513 		ret = 1;
1514 		if (!prot_numa) {
1515 			entry = pmdp_get_and_clear(mm, addr, pmd);
1516 			if (pmd_numa(entry))
1517 				entry = pmd_mknonnuma(entry);
1518 			entry = pmd_modify(entry, newprot);
1519 			ret = HPAGE_PMD_NR;
1520 			set_pmd_at(mm, addr, pmd, entry);
1521 			BUG_ON(pmd_write(entry));
1522 		} else {
1523 			struct page *page = pmd_page(*pmd);
1524 
1525 			/*
1526 			 * Do not trap faults against the zero page. The
1527 			 * read-only data is likely to be read-cached on the
1528 			 * local CPU cache and it is less useful to know about
1529 			 * local vs remote hits on the zero page.
1530 			 */
1531 			if (!is_huge_zero_page(page) &&
1532 			    !pmd_numa(*pmd)) {
1533 				pmdp_set_numa(mm, addr, pmd);
1534 				ret = HPAGE_PMD_NR;
1535 			}
1536 		}
1537 		spin_unlock(ptl);
1538 	}
1539 
1540 	return ret;
1541 }
1542 
1543 /*
1544  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1545  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1546  *
1547  * Note that if it returns 1, this routine returns without unlocking page
1548  * table locks. So callers must unlock them.
1549  */
1550 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
1551 		spinlock_t **ptl)
1552 {
1553 	*ptl = pmd_lock(vma->vm_mm, pmd);
1554 	if (likely(pmd_trans_huge(*pmd))) {
1555 		if (unlikely(pmd_trans_splitting(*pmd))) {
1556 			spin_unlock(*ptl);
1557 			wait_split_huge_page(vma->anon_vma, pmd);
1558 			return -1;
1559 		} else {
1560 			/* Thp mapped by 'pmd' is stable, so we can
1561 			 * handle it as it is. */
1562 			return 1;
1563 		}
1564 	}
1565 	spin_unlock(*ptl);
1566 	return 0;
1567 }
1568 
1569 /*
1570  * This function returns whether a given @page is mapped onto the @address
1571  * in the virtual space of @mm.
1572  *
1573  * When it's true, this function returns *pmd with holding the page table lock
1574  * and passing it back to the caller via @ptl.
1575  * If it's false, returns NULL without holding the page table lock.
1576  */
1577 pmd_t *page_check_address_pmd(struct page *page,
1578 			      struct mm_struct *mm,
1579 			      unsigned long address,
1580 			      enum page_check_address_pmd_flag flag,
1581 			      spinlock_t **ptl)
1582 {
1583 	pgd_t *pgd;
1584 	pud_t *pud;
1585 	pmd_t *pmd;
1586 
1587 	if (address & ~HPAGE_PMD_MASK)
1588 		return NULL;
1589 
1590 	pgd = pgd_offset(mm, address);
1591 	if (!pgd_present(*pgd))
1592 		return NULL;
1593 	pud = pud_offset(pgd, address);
1594 	if (!pud_present(*pud))
1595 		return NULL;
1596 	pmd = pmd_offset(pud, address);
1597 
1598 	*ptl = pmd_lock(mm, pmd);
1599 	if (!pmd_present(*pmd))
1600 		goto unlock;
1601 	if (pmd_page(*pmd) != page)
1602 		goto unlock;
1603 	/*
1604 	 * split_vma() may create temporary aliased mappings. There is
1605 	 * no risk as long as all huge pmd are found and have their
1606 	 * splitting bit set before __split_huge_page_refcount
1607 	 * runs. Finding the same huge pmd more than once during the
1608 	 * same rmap walk is not a problem.
1609 	 */
1610 	if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1611 	    pmd_trans_splitting(*pmd))
1612 		goto unlock;
1613 	if (pmd_trans_huge(*pmd)) {
1614 		VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1615 			  !pmd_trans_splitting(*pmd));
1616 		return pmd;
1617 	}
1618 unlock:
1619 	spin_unlock(*ptl);
1620 	return NULL;
1621 }
1622 
1623 static int __split_huge_page_splitting(struct page *page,
1624 				       struct vm_area_struct *vma,
1625 				       unsigned long address)
1626 {
1627 	struct mm_struct *mm = vma->vm_mm;
1628 	spinlock_t *ptl;
1629 	pmd_t *pmd;
1630 	int ret = 0;
1631 	/* For mmu_notifiers */
1632 	const unsigned long mmun_start = address;
1633 	const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1634 
1635 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1636 	pmd = page_check_address_pmd(page, mm, address,
1637 			PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG, &ptl);
1638 	if (pmd) {
1639 		/*
1640 		 * We can't temporarily set the pmd to null in order
1641 		 * to split it, the pmd must remain marked huge at all
1642 		 * times or the VM won't take the pmd_trans_huge paths
1643 		 * and it won't wait on the anon_vma->root->rwsem to
1644 		 * serialize against split_huge_page*.
1645 		 */
1646 		pmdp_splitting_flush(vma, address, pmd);
1647 		ret = 1;
1648 		spin_unlock(ptl);
1649 	}
1650 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1651 
1652 	return ret;
1653 }
1654 
1655 static void __split_huge_page_refcount(struct page *page,
1656 				       struct list_head *list)
1657 {
1658 	int i;
1659 	struct zone *zone = page_zone(page);
1660 	struct lruvec *lruvec;
1661 	int tail_count = 0;
1662 
1663 	/* prevent PageLRU to go away from under us, and freeze lru stats */
1664 	spin_lock_irq(&zone->lru_lock);
1665 	lruvec = mem_cgroup_page_lruvec(page, zone);
1666 
1667 	compound_lock(page);
1668 	/* complete memcg works before add pages to LRU */
1669 	mem_cgroup_split_huge_fixup(page);
1670 
1671 	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1672 		struct page *page_tail = page + i;
1673 
1674 		/* tail_page->_mapcount cannot change */
1675 		BUG_ON(page_mapcount(page_tail) < 0);
1676 		tail_count += page_mapcount(page_tail);
1677 		/* check for overflow */
1678 		BUG_ON(tail_count < 0);
1679 		BUG_ON(atomic_read(&page_tail->_count) != 0);
1680 		/*
1681 		 * tail_page->_count is zero and not changing from
1682 		 * under us. But get_page_unless_zero() may be running
1683 		 * from under us on the tail_page. If we used
1684 		 * atomic_set() below instead of atomic_add(), we
1685 		 * would then run atomic_set() concurrently with
1686 		 * get_page_unless_zero(), and atomic_set() is
1687 		 * implemented in C not using locked ops. spin_unlock
1688 		 * on x86 sometime uses locked ops because of PPro
1689 		 * errata 66, 92, so unless somebody can guarantee
1690 		 * atomic_set() here would be safe on all archs (and
1691 		 * not only on x86), it's safer to use atomic_add().
1692 		 */
1693 		atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1694 			   &page_tail->_count);
1695 
1696 		/* after clearing PageTail the gup refcount can be released */
1697 		smp_mb__after_atomic();
1698 
1699 		/*
1700 		 * retain hwpoison flag of the poisoned tail page:
1701 		 *   fix for the unsuitable process killed on Guest Machine(KVM)
1702 		 *   by the memory-failure.
1703 		 */
1704 		page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
1705 		page_tail->flags |= (page->flags &
1706 				     ((1L << PG_referenced) |
1707 				      (1L << PG_swapbacked) |
1708 				      (1L << PG_mlocked) |
1709 				      (1L << PG_uptodate) |
1710 				      (1L << PG_active) |
1711 				      (1L << PG_unevictable)));
1712 		page_tail->flags |= (1L << PG_dirty);
1713 
1714 		/* clear PageTail before overwriting first_page */
1715 		smp_wmb();
1716 
1717 		/*
1718 		 * __split_huge_page_splitting() already set the
1719 		 * splitting bit in all pmd that could map this
1720 		 * hugepage, that will ensure no CPU can alter the
1721 		 * mapcount on the head page. The mapcount is only
1722 		 * accounted in the head page and it has to be
1723 		 * transferred to all tail pages in the below code. So
1724 		 * for this code to be safe, the split the mapcount
1725 		 * can't change. But that doesn't mean userland can't
1726 		 * keep changing and reading the page contents while
1727 		 * we transfer the mapcount, so the pmd splitting
1728 		 * status is achieved setting a reserved bit in the
1729 		 * pmd, not by clearing the present bit.
1730 		*/
1731 		page_tail->_mapcount = page->_mapcount;
1732 
1733 		BUG_ON(page_tail->mapping);
1734 		page_tail->mapping = page->mapping;
1735 
1736 		page_tail->index = page->index + i;
1737 		page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
1738 
1739 		BUG_ON(!PageAnon(page_tail));
1740 		BUG_ON(!PageUptodate(page_tail));
1741 		BUG_ON(!PageDirty(page_tail));
1742 		BUG_ON(!PageSwapBacked(page_tail));
1743 
1744 		lru_add_page_tail(page, page_tail, lruvec, list);
1745 	}
1746 	atomic_sub(tail_count, &page->_count);
1747 	BUG_ON(atomic_read(&page->_count) <= 0);
1748 
1749 	__mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1750 
1751 	ClearPageCompound(page);
1752 	compound_unlock(page);
1753 	spin_unlock_irq(&zone->lru_lock);
1754 
1755 	for (i = 1; i < HPAGE_PMD_NR; i++) {
1756 		struct page *page_tail = page + i;
1757 		BUG_ON(page_count(page_tail) <= 0);
1758 		/*
1759 		 * Tail pages may be freed if there wasn't any mapping
1760 		 * like if add_to_swap() is running on a lru page that
1761 		 * had its mapping zapped. And freeing these pages
1762 		 * requires taking the lru_lock so we do the put_page
1763 		 * of the tail pages after the split is complete.
1764 		 */
1765 		put_page(page_tail);
1766 	}
1767 
1768 	/*
1769 	 * Only the head page (now become a regular page) is required
1770 	 * to be pinned by the caller.
1771 	 */
1772 	BUG_ON(page_count(page) <= 0);
1773 }
1774 
1775 static int __split_huge_page_map(struct page *page,
1776 				 struct vm_area_struct *vma,
1777 				 unsigned long address)
1778 {
1779 	struct mm_struct *mm = vma->vm_mm;
1780 	spinlock_t *ptl;
1781 	pmd_t *pmd, _pmd;
1782 	int ret = 0, i;
1783 	pgtable_t pgtable;
1784 	unsigned long haddr;
1785 
1786 	pmd = page_check_address_pmd(page, mm, address,
1787 			PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG, &ptl);
1788 	if (pmd) {
1789 		pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1790 		pmd_populate(mm, &_pmd, pgtable);
1791 		if (pmd_write(*pmd))
1792 			BUG_ON(page_mapcount(page) != 1);
1793 
1794 		haddr = address;
1795 		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1796 			pte_t *pte, entry;
1797 			BUG_ON(PageCompound(page+i));
1798 			/*
1799 			 * Note that pmd_numa is not transferred deliberately
1800 			 * to avoid any possibility that pte_numa leaks to
1801 			 * a PROT_NONE VMA by accident.
1802 			 */
1803 			entry = mk_pte(page + i, vma->vm_page_prot);
1804 			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1805 			if (!pmd_write(*pmd))
1806 				entry = pte_wrprotect(entry);
1807 			if (!pmd_young(*pmd))
1808 				entry = pte_mkold(entry);
1809 			pte = pte_offset_map(&_pmd, haddr);
1810 			BUG_ON(!pte_none(*pte));
1811 			set_pte_at(mm, haddr, pte, entry);
1812 			pte_unmap(pte);
1813 		}
1814 
1815 		smp_wmb(); /* make pte visible before pmd */
1816 		/*
1817 		 * Up to this point the pmd is present and huge and
1818 		 * userland has the whole access to the hugepage
1819 		 * during the split (which happens in place). If we
1820 		 * overwrite the pmd with the not-huge version
1821 		 * pointing to the pte here (which of course we could
1822 		 * if all CPUs were bug free), userland could trigger
1823 		 * a small page size TLB miss on the small sized TLB
1824 		 * while the hugepage TLB entry is still established
1825 		 * in the huge TLB. Some CPU doesn't like that. See
1826 		 * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1827 		 * Erratum 383 on page 93. Intel should be safe but is
1828 		 * also warns that it's only safe if the permission
1829 		 * and cache attributes of the two entries loaded in
1830 		 * the two TLB is identical (which should be the case
1831 		 * here). But it is generally safer to never allow
1832 		 * small and huge TLB entries for the same virtual
1833 		 * address to be loaded simultaneously. So instead of
1834 		 * doing "pmd_populate(); flush_tlb_range();" we first
1835 		 * mark the current pmd notpresent (atomically because
1836 		 * here the pmd_trans_huge and pmd_trans_splitting
1837 		 * must remain set at all times on the pmd until the
1838 		 * split is complete for this pmd), then we flush the
1839 		 * SMP TLB and finally we write the non-huge version
1840 		 * of the pmd entry with pmd_populate.
1841 		 */
1842 		pmdp_invalidate(vma, address, pmd);
1843 		pmd_populate(mm, pmd, pgtable);
1844 		ret = 1;
1845 		spin_unlock(ptl);
1846 	}
1847 
1848 	return ret;
1849 }
1850 
1851 /* must be called with anon_vma->root->rwsem held */
1852 static void __split_huge_page(struct page *page,
1853 			      struct anon_vma *anon_vma,
1854 			      struct list_head *list)
1855 {
1856 	int mapcount, mapcount2;
1857 	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1858 	struct anon_vma_chain *avc;
1859 
1860 	BUG_ON(!PageHead(page));
1861 	BUG_ON(PageTail(page));
1862 
1863 	mapcount = 0;
1864 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1865 		struct vm_area_struct *vma = avc->vma;
1866 		unsigned long addr = vma_address(page, vma);
1867 		BUG_ON(is_vma_temporary_stack(vma));
1868 		mapcount += __split_huge_page_splitting(page, vma, addr);
1869 	}
1870 	/*
1871 	 * It is critical that new vmas are added to the tail of the
1872 	 * anon_vma list. This guarantes that if copy_huge_pmd() runs
1873 	 * and establishes a child pmd before
1874 	 * __split_huge_page_splitting() freezes the parent pmd (so if
1875 	 * we fail to prevent copy_huge_pmd() from running until the
1876 	 * whole __split_huge_page() is complete), we will still see
1877 	 * the newly established pmd of the child later during the
1878 	 * walk, to be able to set it as pmd_trans_splitting too.
1879 	 */
1880 	if (mapcount != page_mapcount(page)) {
1881 		pr_err("mapcount %d page_mapcount %d\n",
1882 			mapcount, page_mapcount(page));
1883 		BUG();
1884 	}
1885 
1886 	__split_huge_page_refcount(page, list);
1887 
1888 	mapcount2 = 0;
1889 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1890 		struct vm_area_struct *vma = avc->vma;
1891 		unsigned long addr = vma_address(page, vma);
1892 		BUG_ON(is_vma_temporary_stack(vma));
1893 		mapcount2 += __split_huge_page_map(page, vma, addr);
1894 	}
1895 	if (mapcount != mapcount2) {
1896 		pr_err("mapcount %d mapcount2 %d page_mapcount %d\n",
1897 			mapcount, mapcount2, page_mapcount(page));
1898 		BUG();
1899 	}
1900 }
1901 
1902 /*
1903  * Split a hugepage into normal pages. This doesn't change the position of head
1904  * page. If @list is null, tail pages will be added to LRU list, otherwise, to
1905  * @list. Both head page and tail pages will inherit mapping, flags, and so on
1906  * from the hugepage.
1907  * Return 0 if the hugepage is split successfully otherwise return 1.
1908  */
1909 int split_huge_page_to_list(struct page *page, struct list_head *list)
1910 {
1911 	struct anon_vma *anon_vma;
1912 	int ret = 1;
1913 
1914 	BUG_ON(is_huge_zero_page(page));
1915 	BUG_ON(!PageAnon(page));
1916 
1917 	/*
1918 	 * The caller does not necessarily hold an mmap_sem that would prevent
1919 	 * the anon_vma disappearing so we first we take a reference to it
1920 	 * and then lock the anon_vma for write. This is similar to
1921 	 * page_lock_anon_vma_read except the write lock is taken to serialise
1922 	 * against parallel split or collapse operations.
1923 	 */
1924 	anon_vma = page_get_anon_vma(page);
1925 	if (!anon_vma)
1926 		goto out;
1927 	anon_vma_lock_write(anon_vma);
1928 
1929 	ret = 0;
1930 	if (!PageCompound(page))
1931 		goto out_unlock;
1932 
1933 	BUG_ON(!PageSwapBacked(page));
1934 	__split_huge_page(page, anon_vma, list);
1935 	count_vm_event(THP_SPLIT);
1936 
1937 	BUG_ON(PageCompound(page));
1938 out_unlock:
1939 	anon_vma_unlock_write(anon_vma);
1940 	put_anon_vma(anon_vma);
1941 out:
1942 	return ret;
1943 }
1944 
1945 #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
1946 
1947 int hugepage_madvise(struct vm_area_struct *vma,
1948 		     unsigned long *vm_flags, int advice)
1949 {
1950 	switch (advice) {
1951 	case MADV_HUGEPAGE:
1952 #ifdef CONFIG_S390
1953 		/*
1954 		 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
1955 		 * can't handle this properly after s390_enable_sie, so we simply
1956 		 * ignore the madvise to prevent qemu from causing a SIGSEGV.
1957 		 */
1958 		if (mm_has_pgste(vma->vm_mm))
1959 			return 0;
1960 #endif
1961 		/*
1962 		 * Be somewhat over-protective like KSM for now!
1963 		 */
1964 		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
1965 			return -EINVAL;
1966 		*vm_flags &= ~VM_NOHUGEPAGE;
1967 		*vm_flags |= VM_HUGEPAGE;
1968 		/*
1969 		 * If the vma become good for khugepaged to scan,
1970 		 * register it here without waiting a page fault that
1971 		 * may not happen any time soon.
1972 		 */
1973 		if (unlikely(khugepaged_enter_vma_merge(vma)))
1974 			return -ENOMEM;
1975 		break;
1976 	case MADV_NOHUGEPAGE:
1977 		/*
1978 		 * Be somewhat over-protective like KSM for now!
1979 		 */
1980 		if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
1981 			return -EINVAL;
1982 		*vm_flags &= ~VM_HUGEPAGE;
1983 		*vm_flags |= VM_NOHUGEPAGE;
1984 		/*
1985 		 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
1986 		 * this vma even if we leave the mm registered in khugepaged if
1987 		 * it got registered before VM_NOHUGEPAGE was set.
1988 		 */
1989 		break;
1990 	}
1991 
1992 	return 0;
1993 }
1994 
1995 static int __init khugepaged_slab_init(void)
1996 {
1997 	mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
1998 					  sizeof(struct mm_slot),
1999 					  __alignof__(struct mm_slot), 0, NULL);
2000 	if (!mm_slot_cache)
2001 		return -ENOMEM;
2002 
2003 	return 0;
2004 }
2005 
2006 static inline struct mm_slot *alloc_mm_slot(void)
2007 {
2008 	if (!mm_slot_cache)	/* initialization failed */
2009 		return NULL;
2010 	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
2011 }
2012 
2013 static inline void free_mm_slot(struct mm_slot *mm_slot)
2014 {
2015 	kmem_cache_free(mm_slot_cache, mm_slot);
2016 }
2017 
2018 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
2019 {
2020 	struct mm_slot *mm_slot;
2021 
2022 	hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
2023 		if (mm == mm_slot->mm)
2024 			return mm_slot;
2025 
2026 	return NULL;
2027 }
2028 
2029 static void insert_to_mm_slots_hash(struct mm_struct *mm,
2030 				    struct mm_slot *mm_slot)
2031 {
2032 	mm_slot->mm = mm;
2033 	hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
2034 }
2035 
2036 static inline int khugepaged_test_exit(struct mm_struct *mm)
2037 {
2038 	return atomic_read(&mm->mm_users) == 0;
2039 }
2040 
2041 int __khugepaged_enter(struct mm_struct *mm)
2042 {
2043 	struct mm_slot *mm_slot;
2044 	int wakeup;
2045 
2046 	mm_slot = alloc_mm_slot();
2047 	if (!mm_slot)
2048 		return -ENOMEM;
2049 
2050 	/* __khugepaged_exit() must not run from under us */
2051 	VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
2052 	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
2053 		free_mm_slot(mm_slot);
2054 		return 0;
2055 	}
2056 
2057 	spin_lock(&khugepaged_mm_lock);
2058 	insert_to_mm_slots_hash(mm, mm_slot);
2059 	/*
2060 	 * Insert just behind the scanning cursor, to let the area settle
2061 	 * down a little.
2062 	 */
2063 	wakeup = list_empty(&khugepaged_scan.mm_head);
2064 	list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
2065 	spin_unlock(&khugepaged_mm_lock);
2066 
2067 	atomic_inc(&mm->mm_count);
2068 	if (wakeup)
2069 		wake_up_interruptible(&khugepaged_wait);
2070 
2071 	return 0;
2072 }
2073 
2074 int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
2075 {
2076 	unsigned long hstart, hend;
2077 	if (!vma->anon_vma)
2078 		/*
2079 		 * Not yet faulted in so we will register later in the
2080 		 * page fault if needed.
2081 		 */
2082 		return 0;
2083 	if (vma->vm_ops)
2084 		/* khugepaged not yet working on file or special mappings */
2085 		return 0;
2086 	VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
2087 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2088 	hend = vma->vm_end & HPAGE_PMD_MASK;
2089 	if (hstart < hend)
2090 		return khugepaged_enter(vma);
2091 	return 0;
2092 }
2093 
2094 void __khugepaged_exit(struct mm_struct *mm)
2095 {
2096 	struct mm_slot *mm_slot;
2097 	int free = 0;
2098 
2099 	spin_lock(&khugepaged_mm_lock);
2100 	mm_slot = get_mm_slot(mm);
2101 	if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
2102 		hash_del(&mm_slot->hash);
2103 		list_del(&mm_slot->mm_node);
2104 		free = 1;
2105 	}
2106 	spin_unlock(&khugepaged_mm_lock);
2107 
2108 	if (free) {
2109 		clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2110 		free_mm_slot(mm_slot);
2111 		mmdrop(mm);
2112 	} else if (mm_slot) {
2113 		/*
2114 		 * This is required to serialize against
2115 		 * khugepaged_test_exit() (which is guaranteed to run
2116 		 * under mmap sem read mode). Stop here (after we
2117 		 * return all pagetables will be destroyed) until
2118 		 * khugepaged has finished working on the pagetables
2119 		 * under the mmap_sem.
2120 		 */
2121 		down_write(&mm->mmap_sem);
2122 		up_write(&mm->mmap_sem);
2123 	}
2124 }
2125 
2126 static void release_pte_page(struct page *page)
2127 {
2128 	/* 0 stands for page_is_file_cache(page) == false */
2129 	dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
2130 	unlock_page(page);
2131 	putback_lru_page(page);
2132 }
2133 
2134 static void release_pte_pages(pte_t *pte, pte_t *_pte)
2135 {
2136 	while (--_pte >= pte) {
2137 		pte_t pteval = *_pte;
2138 		if (!pte_none(pteval))
2139 			release_pte_page(pte_page(pteval));
2140 	}
2141 }
2142 
2143 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
2144 					unsigned long address,
2145 					pte_t *pte)
2146 {
2147 	struct page *page;
2148 	pte_t *_pte;
2149 	int referenced = 0, none = 0;
2150 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
2151 	     _pte++, address += PAGE_SIZE) {
2152 		pte_t pteval = *_pte;
2153 		if (pte_none(pteval)) {
2154 			if (++none <= khugepaged_max_ptes_none)
2155 				continue;
2156 			else
2157 				goto out;
2158 		}
2159 		if (!pte_present(pteval) || !pte_write(pteval))
2160 			goto out;
2161 		page = vm_normal_page(vma, address, pteval);
2162 		if (unlikely(!page))
2163 			goto out;
2164 
2165 		VM_BUG_ON_PAGE(PageCompound(page), page);
2166 		VM_BUG_ON_PAGE(!PageAnon(page), page);
2167 		VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2168 
2169 		/* cannot use mapcount: can't collapse if there's a gup pin */
2170 		if (page_count(page) != 1)
2171 			goto out;
2172 		/*
2173 		 * We can do it before isolate_lru_page because the
2174 		 * page can't be freed from under us. NOTE: PG_lock
2175 		 * is needed to serialize against split_huge_page
2176 		 * when invoked from the VM.
2177 		 */
2178 		if (!trylock_page(page))
2179 			goto out;
2180 		/*
2181 		 * Isolate the page to avoid collapsing an hugepage
2182 		 * currently in use by the VM.
2183 		 */
2184 		if (isolate_lru_page(page)) {
2185 			unlock_page(page);
2186 			goto out;
2187 		}
2188 		/* 0 stands for page_is_file_cache(page) == false */
2189 		inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
2190 		VM_BUG_ON_PAGE(!PageLocked(page), page);
2191 		VM_BUG_ON_PAGE(PageLRU(page), page);
2192 
2193 		/* If there is no mapped pte young don't collapse the page */
2194 		if (pte_young(pteval) || PageReferenced(page) ||
2195 		    mmu_notifier_test_young(vma->vm_mm, address))
2196 			referenced = 1;
2197 	}
2198 	if (likely(referenced))
2199 		return 1;
2200 out:
2201 	release_pte_pages(pte, _pte);
2202 	return 0;
2203 }
2204 
2205 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
2206 				      struct vm_area_struct *vma,
2207 				      unsigned long address,
2208 				      spinlock_t *ptl)
2209 {
2210 	pte_t *_pte;
2211 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2212 		pte_t pteval = *_pte;
2213 		struct page *src_page;
2214 
2215 		if (pte_none(pteval)) {
2216 			clear_user_highpage(page, address);
2217 			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2218 		} else {
2219 			src_page = pte_page(pteval);
2220 			copy_user_highpage(page, src_page, address, vma);
2221 			VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
2222 			release_pte_page(src_page);
2223 			/*
2224 			 * ptl mostly unnecessary, but preempt has to
2225 			 * be disabled to update the per-cpu stats
2226 			 * inside page_remove_rmap().
2227 			 */
2228 			spin_lock(ptl);
2229 			/*
2230 			 * paravirt calls inside pte_clear here are
2231 			 * superfluous.
2232 			 */
2233 			pte_clear(vma->vm_mm, address, _pte);
2234 			page_remove_rmap(src_page);
2235 			spin_unlock(ptl);
2236 			free_page_and_swap_cache(src_page);
2237 		}
2238 
2239 		address += PAGE_SIZE;
2240 		page++;
2241 	}
2242 }
2243 
2244 static void khugepaged_alloc_sleep(void)
2245 {
2246 	wait_event_freezable_timeout(khugepaged_wait, false,
2247 			msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2248 }
2249 
2250 static int khugepaged_node_load[MAX_NUMNODES];
2251 
2252 static bool khugepaged_scan_abort(int nid)
2253 {
2254 	int i;
2255 
2256 	/*
2257 	 * If zone_reclaim_mode is disabled, then no extra effort is made to
2258 	 * allocate memory locally.
2259 	 */
2260 	if (!zone_reclaim_mode)
2261 		return false;
2262 
2263 	/* If there is a count for this node already, it must be acceptable */
2264 	if (khugepaged_node_load[nid])
2265 		return false;
2266 
2267 	for (i = 0; i < MAX_NUMNODES; i++) {
2268 		if (!khugepaged_node_load[i])
2269 			continue;
2270 		if (node_distance(nid, i) > RECLAIM_DISTANCE)
2271 			return true;
2272 	}
2273 	return false;
2274 }
2275 
2276 #ifdef CONFIG_NUMA
2277 static int khugepaged_find_target_node(void)
2278 {
2279 	static int last_khugepaged_target_node = NUMA_NO_NODE;
2280 	int nid, target_node = 0, max_value = 0;
2281 
2282 	/* find first node with max normal pages hit */
2283 	for (nid = 0; nid < MAX_NUMNODES; nid++)
2284 		if (khugepaged_node_load[nid] > max_value) {
2285 			max_value = khugepaged_node_load[nid];
2286 			target_node = nid;
2287 		}
2288 
2289 	/* do some balance if several nodes have the same hit record */
2290 	if (target_node <= last_khugepaged_target_node)
2291 		for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
2292 				nid++)
2293 			if (max_value == khugepaged_node_load[nid]) {
2294 				target_node = nid;
2295 				break;
2296 			}
2297 
2298 	last_khugepaged_target_node = target_node;
2299 	return target_node;
2300 }
2301 
2302 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2303 {
2304 	if (IS_ERR(*hpage)) {
2305 		if (!*wait)
2306 			return false;
2307 
2308 		*wait = false;
2309 		*hpage = NULL;
2310 		khugepaged_alloc_sleep();
2311 	} else if (*hpage) {
2312 		put_page(*hpage);
2313 		*hpage = NULL;
2314 	}
2315 
2316 	return true;
2317 }
2318 
2319 static struct page
2320 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2321 		       struct vm_area_struct *vma, unsigned long address,
2322 		       int node)
2323 {
2324 	VM_BUG_ON_PAGE(*hpage, *hpage);
2325 
2326 	/*
2327 	 * Before allocating the hugepage, release the mmap_sem read lock.
2328 	 * The allocation can take potentially a long time if it involves
2329 	 * sync compaction, and we do not need to hold the mmap_sem during
2330 	 * that. We will recheck the vma after taking it again in write mode.
2331 	 */
2332 	up_read(&mm->mmap_sem);
2333 
2334 	*hpage = alloc_pages_exact_node(node, alloc_hugepage_gfpmask(
2335 		khugepaged_defrag(), __GFP_OTHER_NODE), HPAGE_PMD_ORDER);
2336 	if (unlikely(!*hpage)) {
2337 		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2338 		*hpage = ERR_PTR(-ENOMEM);
2339 		return NULL;
2340 	}
2341 
2342 	count_vm_event(THP_COLLAPSE_ALLOC);
2343 	return *hpage;
2344 }
2345 #else
2346 static int khugepaged_find_target_node(void)
2347 {
2348 	return 0;
2349 }
2350 
2351 static inline struct page *alloc_hugepage(int defrag)
2352 {
2353 	return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
2354 			   HPAGE_PMD_ORDER);
2355 }
2356 
2357 static struct page *khugepaged_alloc_hugepage(bool *wait)
2358 {
2359 	struct page *hpage;
2360 
2361 	do {
2362 		hpage = alloc_hugepage(khugepaged_defrag());
2363 		if (!hpage) {
2364 			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2365 			if (!*wait)
2366 				return NULL;
2367 
2368 			*wait = false;
2369 			khugepaged_alloc_sleep();
2370 		} else
2371 			count_vm_event(THP_COLLAPSE_ALLOC);
2372 	} while (unlikely(!hpage) && likely(khugepaged_enabled()));
2373 
2374 	return hpage;
2375 }
2376 
2377 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2378 {
2379 	if (!*hpage)
2380 		*hpage = khugepaged_alloc_hugepage(wait);
2381 
2382 	if (unlikely(!*hpage))
2383 		return false;
2384 
2385 	return true;
2386 }
2387 
2388 static struct page
2389 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2390 		       struct vm_area_struct *vma, unsigned long address,
2391 		       int node)
2392 {
2393 	up_read(&mm->mmap_sem);
2394 	VM_BUG_ON(!*hpage);
2395 	return  *hpage;
2396 }
2397 #endif
2398 
2399 static bool hugepage_vma_check(struct vm_area_struct *vma)
2400 {
2401 	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2402 	    (vma->vm_flags & VM_NOHUGEPAGE))
2403 		return false;
2404 
2405 	if (!vma->anon_vma || vma->vm_ops)
2406 		return false;
2407 	if (is_vma_temporary_stack(vma))
2408 		return false;
2409 	VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
2410 	return true;
2411 }
2412 
2413 static void collapse_huge_page(struct mm_struct *mm,
2414 				   unsigned long address,
2415 				   struct page **hpage,
2416 				   struct vm_area_struct *vma,
2417 				   int node)
2418 {
2419 	pmd_t *pmd, _pmd;
2420 	pte_t *pte;
2421 	pgtable_t pgtable;
2422 	struct page *new_page;
2423 	spinlock_t *pmd_ptl, *pte_ptl;
2424 	int isolated;
2425 	unsigned long hstart, hend;
2426 	struct mem_cgroup *memcg;
2427 	unsigned long mmun_start;	/* For mmu_notifiers */
2428 	unsigned long mmun_end;		/* For mmu_notifiers */
2429 
2430 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2431 
2432 	/* release the mmap_sem read lock. */
2433 	new_page = khugepaged_alloc_page(hpage, mm, vma, address, node);
2434 	if (!new_page)
2435 		return;
2436 
2437 	if (unlikely(mem_cgroup_try_charge(new_page, mm,
2438 					   GFP_TRANSHUGE, &memcg)))
2439 		return;
2440 
2441 	/*
2442 	 * Prevent all access to pagetables with the exception of
2443 	 * gup_fast later hanlded by the ptep_clear_flush and the VM
2444 	 * handled by the anon_vma lock + PG_lock.
2445 	 */
2446 	down_write(&mm->mmap_sem);
2447 	if (unlikely(khugepaged_test_exit(mm)))
2448 		goto out;
2449 
2450 	vma = find_vma(mm, address);
2451 	if (!vma)
2452 		goto out;
2453 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2454 	hend = vma->vm_end & HPAGE_PMD_MASK;
2455 	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2456 		goto out;
2457 	if (!hugepage_vma_check(vma))
2458 		goto out;
2459 	pmd = mm_find_pmd(mm, address);
2460 	if (!pmd)
2461 		goto out;
2462 
2463 	anon_vma_lock_write(vma->anon_vma);
2464 
2465 	pte = pte_offset_map(pmd, address);
2466 	pte_ptl = pte_lockptr(mm, pmd);
2467 
2468 	mmun_start = address;
2469 	mmun_end   = address + HPAGE_PMD_SIZE;
2470 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2471 	pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
2472 	/*
2473 	 * After this gup_fast can't run anymore. This also removes
2474 	 * any huge TLB entry from the CPU so we won't allow
2475 	 * huge and small TLB entries for the same virtual address
2476 	 * to avoid the risk of CPU bugs in that area.
2477 	 */
2478 	_pmd = pmdp_clear_flush(vma, address, pmd);
2479 	spin_unlock(pmd_ptl);
2480 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2481 
2482 	spin_lock(pte_ptl);
2483 	isolated = __collapse_huge_page_isolate(vma, address, pte);
2484 	spin_unlock(pte_ptl);
2485 
2486 	if (unlikely(!isolated)) {
2487 		pte_unmap(pte);
2488 		spin_lock(pmd_ptl);
2489 		BUG_ON(!pmd_none(*pmd));
2490 		/*
2491 		 * We can only use set_pmd_at when establishing
2492 		 * hugepmds and never for establishing regular pmds that
2493 		 * points to regular pagetables. Use pmd_populate for that
2494 		 */
2495 		pmd_populate(mm, pmd, pmd_pgtable(_pmd));
2496 		spin_unlock(pmd_ptl);
2497 		anon_vma_unlock_write(vma->anon_vma);
2498 		goto out;
2499 	}
2500 
2501 	/*
2502 	 * All pages are isolated and locked so anon_vma rmap
2503 	 * can't run anymore.
2504 	 */
2505 	anon_vma_unlock_write(vma->anon_vma);
2506 
2507 	__collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
2508 	pte_unmap(pte);
2509 	__SetPageUptodate(new_page);
2510 	pgtable = pmd_pgtable(_pmd);
2511 
2512 	_pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
2513 	_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
2514 
2515 	/*
2516 	 * spin_lock() below is not the equivalent of smp_wmb(), so
2517 	 * this is needed to avoid the copy_huge_page writes to become
2518 	 * visible after the set_pmd_at() write.
2519 	 */
2520 	smp_wmb();
2521 
2522 	spin_lock(pmd_ptl);
2523 	BUG_ON(!pmd_none(*pmd));
2524 	page_add_new_anon_rmap(new_page, vma, address);
2525 	mem_cgroup_commit_charge(new_page, memcg, false);
2526 	lru_cache_add_active_or_unevictable(new_page, vma);
2527 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
2528 	set_pmd_at(mm, address, pmd, _pmd);
2529 	update_mmu_cache_pmd(vma, address, pmd);
2530 	spin_unlock(pmd_ptl);
2531 
2532 	*hpage = NULL;
2533 
2534 	khugepaged_pages_collapsed++;
2535 out_up_write:
2536 	up_write(&mm->mmap_sem);
2537 	return;
2538 
2539 out:
2540 	mem_cgroup_cancel_charge(new_page, memcg);
2541 	goto out_up_write;
2542 }
2543 
2544 static int khugepaged_scan_pmd(struct mm_struct *mm,
2545 			       struct vm_area_struct *vma,
2546 			       unsigned long address,
2547 			       struct page **hpage)
2548 {
2549 	pmd_t *pmd;
2550 	pte_t *pte, *_pte;
2551 	int ret = 0, referenced = 0, none = 0;
2552 	struct page *page;
2553 	unsigned long _address;
2554 	spinlock_t *ptl;
2555 	int node = NUMA_NO_NODE;
2556 
2557 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2558 
2559 	pmd = mm_find_pmd(mm, address);
2560 	if (!pmd)
2561 		goto out;
2562 
2563 	memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
2564 	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2565 	for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2566 	     _pte++, _address += PAGE_SIZE) {
2567 		pte_t pteval = *_pte;
2568 		if (pte_none(pteval)) {
2569 			if (++none <= khugepaged_max_ptes_none)
2570 				continue;
2571 			else
2572 				goto out_unmap;
2573 		}
2574 		if (!pte_present(pteval) || !pte_write(pteval))
2575 			goto out_unmap;
2576 		page = vm_normal_page(vma, _address, pteval);
2577 		if (unlikely(!page))
2578 			goto out_unmap;
2579 		/*
2580 		 * Record which node the original page is from and save this
2581 		 * information to khugepaged_node_load[].
2582 		 * Khupaged will allocate hugepage from the node has the max
2583 		 * hit record.
2584 		 */
2585 		node = page_to_nid(page);
2586 		if (khugepaged_scan_abort(node))
2587 			goto out_unmap;
2588 		khugepaged_node_load[node]++;
2589 		VM_BUG_ON_PAGE(PageCompound(page), page);
2590 		if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2591 			goto out_unmap;
2592 		/* cannot use mapcount: can't collapse if there's a gup pin */
2593 		if (page_count(page) != 1)
2594 			goto out_unmap;
2595 		if (pte_young(pteval) || PageReferenced(page) ||
2596 		    mmu_notifier_test_young(vma->vm_mm, address))
2597 			referenced = 1;
2598 	}
2599 	if (referenced)
2600 		ret = 1;
2601 out_unmap:
2602 	pte_unmap_unlock(pte, ptl);
2603 	if (ret) {
2604 		node = khugepaged_find_target_node();
2605 		/* collapse_huge_page will return with the mmap_sem released */
2606 		collapse_huge_page(mm, address, hpage, vma, node);
2607 	}
2608 out:
2609 	return ret;
2610 }
2611 
2612 static void collect_mm_slot(struct mm_slot *mm_slot)
2613 {
2614 	struct mm_struct *mm = mm_slot->mm;
2615 
2616 	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2617 
2618 	if (khugepaged_test_exit(mm)) {
2619 		/* free mm_slot */
2620 		hash_del(&mm_slot->hash);
2621 		list_del(&mm_slot->mm_node);
2622 
2623 		/*
2624 		 * Not strictly needed because the mm exited already.
2625 		 *
2626 		 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2627 		 */
2628 
2629 		/* khugepaged_mm_lock actually not necessary for the below */
2630 		free_mm_slot(mm_slot);
2631 		mmdrop(mm);
2632 	}
2633 }
2634 
2635 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2636 					    struct page **hpage)
2637 	__releases(&khugepaged_mm_lock)
2638 	__acquires(&khugepaged_mm_lock)
2639 {
2640 	struct mm_slot *mm_slot;
2641 	struct mm_struct *mm;
2642 	struct vm_area_struct *vma;
2643 	int progress = 0;
2644 
2645 	VM_BUG_ON(!pages);
2646 	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2647 
2648 	if (khugepaged_scan.mm_slot)
2649 		mm_slot = khugepaged_scan.mm_slot;
2650 	else {
2651 		mm_slot = list_entry(khugepaged_scan.mm_head.next,
2652 				     struct mm_slot, mm_node);
2653 		khugepaged_scan.address = 0;
2654 		khugepaged_scan.mm_slot = mm_slot;
2655 	}
2656 	spin_unlock(&khugepaged_mm_lock);
2657 
2658 	mm = mm_slot->mm;
2659 	down_read(&mm->mmap_sem);
2660 	if (unlikely(khugepaged_test_exit(mm)))
2661 		vma = NULL;
2662 	else
2663 		vma = find_vma(mm, khugepaged_scan.address);
2664 
2665 	progress++;
2666 	for (; vma; vma = vma->vm_next) {
2667 		unsigned long hstart, hend;
2668 
2669 		cond_resched();
2670 		if (unlikely(khugepaged_test_exit(mm))) {
2671 			progress++;
2672 			break;
2673 		}
2674 		if (!hugepage_vma_check(vma)) {
2675 skip:
2676 			progress++;
2677 			continue;
2678 		}
2679 		hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2680 		hend = vma->vm_end & HPAGE_PMD_MASK;
2681 		if (hstart >= hend)
2682 			goto skip;
2683 		if (khugepaged_scan.address > hend)
2684 			goto skip;
2685 		if (khugepaged_scan.address < hstart)
2686 			khugepaged_scan.address = hstart;
2687 		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2688 
2689 		while (khugepaged_scan.address < hend) {
2690 			int ret;
2691 			cond_resched();
2692 			if (unlikely(khugepaged_test_exit(mm)))
2693 				goto breakouterloop;
2694 
2695 			VM_BUG_ON(khugepaged_scan.address < hstart ||
2696 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
2697 				  hend);
2698 			ret = khugepaged_scan_pmd(mm, vma,
2699 						  khugepaged_scan.address,
2700 						  hpage);
2701 			/* move to next address */
2702 			khugepaged_scan.address += HPAGE_PMD_SIZE;
2703 			progress += HPAGE_PMD_NR;
2704 			if (ret)
2705 				/* we released mmap_sem so break loop */
2706 				goto breakouterloop_mmap_sem;
2707 			if (progress >= pages)
2708 				goto breakouterloop;
2709 		}
2710 	}
2711 breakouterloop:
2712 	up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2713 breakouterloop_mmap_sem:
2714 
2715 	spin_lock(&khugepaged_mm_lock);
2716 	VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2717 	/*
2718 	 * Release the current mm_slot if this mm is about to die, or
2719 	 * if we scanned all vmas of this mm.
2720 	 */
2721 	if (khugepaged_test_exit(mm) || !vma) {
2722 		/*
2723 		 * Make sure that if mm_users is reaching zero while
2724 		 * khugepaged runs here, khugepaged_exit will find
2725 		 * mm_slot not pointing to the exiting mm.
2726 		 */
2727 		if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2728 			khugepaged_scan.mm_slot = list_entry(
2729 				mm_slot->mm_node.next,
2730 				struct mm_slot, mm_node);
2731 			khugepaged_scan.address = 0;
2732 		} else {
2733 			khugepaged_scan.mm_slot = NULL;
2734 			khugepaged_full_scans++;
2735 		}
2736 
2737 		collect_mm_slot(mm_slot);
2738 	}
2739 
2740 	return progress;
2741 }
2742 
2743 static int khugepaged_has_work(void)
2744 {
2745 	return !list_empty(&khugepaged_scan.mm_head) &&
2746 		khugepaged_enabled();
2747 }
2748 
2749 static int khugepaged_wait_event(void)
2750 {
2751 	return !list_empty(&khugepaged_scan.mm_head) ||
2752 		kthread_should_stop();
2753 }
2754 
2755 static void khugepaged_do_scan(void)
2756 {
2757 	struct page *hpage = NULL;
2758 	unsigned int progress = 0, pass_through_head = 0;
2759 	unsigned int pages = khugepaged_pages_to_scan;
2760 	bool wait = true;
2761 
2762 	barrier(); /* write khugepaged_pages_to_scan to local stack */
2763 
2764 	while (progress < pages) {
2765 		if (!khugepaged_prealloc_page(&hpage, &wait))
2766 			break;
2767 
2768 		cond_resched();
2769 
2770 		if (unlikely(kthread_should_stop() || freezing(current)))
2771 			break;
2772 
2773 		spin_lock(&khugepaged_mm_lock);
2774 		if (!khugepaged_scan.mm_slot)
2775 			pass_through_head++;
2776 		if (khugepaged_has_work() &&
2777 		    pass_through_head < 2)
2778 			progress += khugepaged_scan_mm_slot(pages - progress,
2779 							    &hpage);
2780 		else
2781 			progress = pages;
2782 		spin_unlock(&khugepaged_mm_lock);
2783 	}
2784 
2785 	if (!IS_ERR_OR_NULL(hpage))
2786 		put_page(hpage);
2787 }
2788 
2789 static void khugepaged_wait_work(void)
2790 {
2791 	try_to_freeze();
2792 
2793 	if (khugepaged_has_work()) {
2794 		if (!khugepaged_scan_sleep_millisecs)
2795 			return;
2796 
2797 		wait_event_freezable_timeout(khugepaged_wait,
2798 					     kthread_should_stop(),
2799 			msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2800 		return;
2801 	}
2802 
2803 	if (khugepaged_enabled())
2804 		wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2805 }
2806 
2807 static int khugepaged(void *none)
2808 {
2809 	struct mm_slot *mm_slot;
2810 
2811 	set_freezable();
2812 	set_user_nice(current, MAX_NICE);
2813 
2814 	while (!kthread_should_stop()) {
2815 		khugepaged_do_scan();
2816 		khugepaged_wait_work();
2817 	}
2818 
2819 	spin_lock(&khugepaged_mm_lock);
2820 	mm_slot = khugepaged_scan.mm_slot;
2821 	khugepaged_scan.mm_slot = NULL;
2822 	if (mm_slot)
2823 		collect_mm_slot(mm_slot);
2824 	spin_unlock(&khugepaged_mm_lock);
2825 	return 0;
2826 }
2827 
2828 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2829 		unsigned long haddr, pmd_t *pmd)
2830 {
2831 	struct mm_struct *mm = vma->vm_mm;
2832 	pgtable_t pgtable;
2833 	pmd_t _pmd;
2834 	int i;
2835 
2836 	pmdp_clear_flush(vma, haddr, pmd);
2837 	/* leave pmd empty until pte is filled */
2838 
2839 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2840 	pmd_populate(mm, &_pmd, pgtable);
2841 
2842 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2843 		pte_t *pte, entry;
2844 		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2845 		entry = pte_mkspecial(entry);
2846 		pte = pte_offset_map(&_pmd, haddr);
2847 		VM_BUG_ON(!pte_none(*pte));
2848 		set_pte_at(mm, haddr, pte, entry);
2849 		pte_unmap(pte);
2850 	}
2851 	smp_wmb(); /* make pte visible before pmd */
2852 	pmd_populate(mm, pmd, pgtable);
2853 	put_huge_zero_page();
2854 }
2855 
2856 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2857 		pmd_t *pmd)
2858 {
2859 	spinlock_t *ptl;
2860 	struct page *page;
2861 	struct mm_struct *mm = vma->vm_mm;
2862 	unsigned long haddr = address & HPAGE_PMD_MASK;
2863 	unsigned long mmun_start;	/* For mmu_notifiers */
2864 	unsigned long mmun_end;		/* For mmu_notifiers */
2865 
2866 	BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2867 
2868 	mmun_start = haddr;
2869 	mmun_end   = haddr + HPAGE_PMD_SIZE;
2870 again:
2871 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2872 	ptl = pmd_lock(mm, pmd);
2873 	if (unlikely(!pmd_trans_huge(*pmd))) {
2874 		spin_unlock(ptl);
2875 		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2876 		return;
2877 	}
2878 	if (is_huge_zero_pmd(*pmd)) {
2879 		__split_huge_zero_page_pmd(vma, haddr, pmd);
2880 		spin_unlock(ptl);
2881 		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2882 		return;
2883 	}
2884 	page = pmd_page(*pmd);
2885 	VM_BUG_ON_PAGE(!page_count(page), page);
2886 	get_page(page);
2887 	spin_unlock(ptl);
2888 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2889 
2890 	split_huge_page(page);
2891 
2892 	put_page(page);
2893 
2894 	/*
2895 	 * We don't always have down_write of mmap_sem here: a racing
2896 	 * do_huge_pmd_wp_page() might have copied-on-write to another
2897 	 * huge page before our split_huge_page() got the anon_vma lock.
2898 	 */
2899 	if (unlikely(pmd_trans_huge(*pmd)))
2900 		goto again;
2901 }
2902 
2903 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
2904 		pmd_t *pmd)
2905 {
2906 	struct vm_area_struct *vma;
2907 
2908 	vma = find_vma(mm, address);
2909 	BUG_ON(vma == NULL);
2910 	split_huge_page_pmd(vma, address, pmd);
2911 }
2912 
2913 static void split_huge_page_address(struct mm_struct *mm,
2914 				    unsigned long address)
2915 {
2916 	pgd_t *pgd;
2917 	pud_t *pud;
2918 	pmd_t *pmd;
2919 
2920 	VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
2921 
2922 	pgd = pgd_offset(mm, address);
2923 	if (!pgd_present(*pgd))
2924 		return;
2925 
2926 	pud = pud_offset(pgd, address);
2927 	if (!pud_present(*pud))
2928 		return;
2929 
2930 	pmd = pmd_offset(pud, address);
2931 	if (!pmd_present(*pmd))
2932 		return;
2933 	/*
2934 	 * Caller holds the mmap_sem write mode, so a huge pmd cannot
2935 	 * materialize from under us.
2936 	 */
2937 	split_huge_page_pmd_mm(mm, address, pmd);
2938 }
2939 
2940 void __vma_adjust_trans_huge(struct vm_area_struct *vma,
2941 			     unsigned long start,
2942 			     unsigned long end,
2943 			     long adjust_next)
2944 {
2945 	/*
2946 	 * If the new start address isn't hpage aligned and it could
2947 	 * previously contain an hugepage: check if we need to split
2948 	 * an huge pmd.
2949 	 */
2950 	if (start & ~HPAGE_PMD_MASK &&
2951 	    (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2952 	    (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2953 		split_huge_page_address(vma->vm_mm, start);
2954 
2955 	/*
2956 	 * If the new end address isn't hpage aligned and it could
2957 	 * previously contain an hugepage: check if we need to split
2958 	 * an huge pmd.
2959 	 */
2960 	if (end & ~HPAGE_PMD_MASK &&
2961 	    (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2962 	    (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2963 		split_huge_page_address(vma->vm_mm, end);
2964 
2965 	/*
2966 	 * If we're also updating the vma->vm_next->vm_start, if the new
2967 	 * vm_next->vm_start isn't page aligned and it could previously
2968 	 * contain an hugepage: check if we need to split an huge pmd.
2969 	 */
2970 	if (adjust_next > 0) {
2971 		struct vm_area_struct *next = vma->vm_next;
2972 		unsigned long nstart = next->vm_start;
2973 		nstart += adjust_next << PAGE_SHIFT;
2974 		if (nstart & ~HPAGE_PMD_MASK &&
2975 		    (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
2976 		    (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
2977 			split_huge_page_address(next->vm_mm, nstart);
2978 	}
2979 }
2980