xref: /openbmc/linux/mm/huge_memory.c (revision d7a3d85e)
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 static void khugepaged_slab_exit(void);
71 
72 #define MM_SLOTS_HASH_BITS 10
73 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
74 
75 static struct kmem_cache *mm_slot_cache __read_mostly;
76 
77 /**
78  * struct mm_slot - hash lookup from mm to mm_slot
79  * @hash: hash collision list
80  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
81  * @mm: the mm that this information is valid for
82  */
83 struct mm_slot {
84 	struct hlist_node hash;
85 	struct list_head mm_node;
86 	struct mm_struct *mm;
87 };
88 
89 /**
90  * struct khugepaged_scan - cursor for scanning
91  * @mm_head: the head of the mm list to scan
92  * @mm_slot: the current mm_slot we are scanning
93  * @address: the next address inside that to be scanned
94  *
95  * There is only the one khugepaged_scan instance of this cursor structure.
96  */
97 struct khugepaged_scan {
98 	struct list_head mm_head;
99 	struct mm_slot *mm_slot;
100 	unsigned long address;
101 };
102 static struct khugepaged_scan khugepaged_scan = {
103 	.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
104 };
105 
106 
107 static int set_recommended_min_free_kbytes(void)
108 {
109 	struct zone *zone;
110 	int nr_zones = 0;
111 	unsigned long recommended_min;
112 
113 	for_each_populated_zone(zone)
114 		nr_zones++;
115 
116 	/* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
117 	recommended_min = pageblock_nr_pages * nr_zones * 2;
118 
119 	/*
120 	 * Make sure that on average at least two pageblocks are almost free
121 	 * of another type, one for a migratetype to fall back to and a
122 	 * second to avoid subsequent fallbacks of other types There are 3
123 	 * MIGRATE_TYPES we care about.
124 	 */
125 	recommended_min += pageblock_nr_pages * nr_zones *
126 			   MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
127 
128 	/* don't ever allow to reserve more than 5% of the lowmem */
129 	recommended_min = min(recommended_min,
130 			      (unsigned long) nr_free_buffer_pages() / 20);
131 	recommended_min <<= (PAGE_SHIFT-10);
132 
133 	if (recommended_min > min_free_kbytes) {
134 		if (user_min_free_kbytes >= 0)
135 			pr_info("raising min_free_kbytes from %d to %lu "
136 				"to help transparent hugepage allocations\n",
137 				min_free_kbytes, recommended_min);
138 
139 		min_free_kbytes = recommended_min;
140 	}
141 	setup_per_zone_wmarks();
142 	return 0;
143 }
144 
145 static int start_stop_khugepaged(void)
146 {
147 	int err = 0;
148 	if (khugepaged_enabled()) {
149 		if (!khugepaged_thread)
150 			khugepaged_thread = kthread_run(khugepaged, NULL,
151 							"khugepaged");
152 		if (unlikely(IS_ERR(khugepaged_thread))) {
153 			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
154 			err = PTR_ERR(khugepaged_thread);
155 			khugepaged_thread = NULL;
156 			goto fail;
157 		}
158 
159 		if (!list_empty(&khugepaged_scan.mm_head))
160 			wake_up_interruptible(&khugepaged_wait);
161 
162 		set_recommended_min_free_kbytes();
163 	} else if (khugepaged_thread) {
164 		kthread_stop(khugepaged_thread);
165 		khugepaged_thread = NULL;
166 	}
167 fail:
168 	return err;
169 }
170 
171 static atomic_t huge_zero_refcount;
172 struct page *huge_zero_page __read_mostly;
173 
174 static inline bool is_huge_zero_pmd(pmd_t pmd)
175 {
176 	return is_huge_zero_page(pmd_page(pmd));
177 }
178 
179 static struct page *get_huge_zero_page(void)
180 {
181 	struct page *zero_page;
182 retry:
183 	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
184 		return READ_ONCE(huge_zero_page);
185 
186 	zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
187 			HPAGE_PMD_ORDER);
188 	if (!zero_page) {
189 		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
190 		return NULL;
191 	}
192 	count_vm_event(THP_ZERO_PAGE_ALLOC);
193 	preempt_disable();
194 	if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
195 		preempt_enable();
196 		__free_pages(zero_page, compound_order(zero_page));
197 		goto retry;
198 	}
199 
200 	/* We take additional reference here. It will be put back by shrinker */
201 	atomic_set(&huge_zero_refcount, 2);
202 	preempt_enable();
203 	return READ_ONCE(huge_zero_page);
204 }
205 
206 static void put_huge_zero_page(void)
207 {
208 	/*
209 	 * Counter should never go to zero here. Only shrinker can put
210 	 * last reference.
211 	 */
212 	BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
213 }
214 
215 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
216 					struct shrink_control *sc)
217 {
218 	/* we can free zero page only if last reference remains */
219 	return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
220 }
221 
222 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
223 				       struct shrink_control *sc)
224 {
225 	if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
226 		struct page *zero_page = xchg(&huge_zero_page, NULL);
227 		BUG_ON(zero_page == NULL);
228 		__free_pages(zero_page, compound_order(zero_page));
229 		return HPAGE_PMD_NR;
230 	}
231 
232 	return 0;
233 }
234 
235 static struct shrinker huge_zero_page_shrinker = {
236 	.count_objects = shrink_huge_zero_page_count,
237 	.scan_objects = shrink_huge_zero_page_scan,
238 	.seeks = DEFAULT_SEEKS,
239 };
240 
241 #ifdef CONFIG_SYSFS
242 
243 static ssize_t double_flag_show(struct kobject *kobj,
244 				struct kobj_attribute *attr, char *buf,
245 				enum transparent_hugepage_flag enabled,
246 				enum transparent_hugepage_flag req_madv)
247 {
248 	if (test_bit(enabled, &transparent_hugepage_flags)) {
249 		VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
250 		return sprintf(buf, "[always] madvise never\n");
251 	} else if (test_bit(req_madv, &transparent_hugepage_flags))
252 		return sprintf(buf, "always [madvise] never\n");
253 	else
254 		return sprintf(buf, "always madvise [never]\n");
255 }
256 static ssize_t double_flag_store(struct kobject *kobj,
257 				 struct kobj_attribute *attr,
258 				 const char *buf, size_t count,
259 				 enum transparent_hugepage_flag enabled,
260 				 enum transparent_hugepage_flag req_madv)
261 {
262 	if (!memcmp("always", buf,
263 		    min(sizeof("always")-1, count))) {
264 		set_bit(enabled, &transparent_hugepage_flags);
265 		clear_bit(req_madv, &transparent_hugepage_flags);
266 	} else if (!memcmp("madvise", buf,
267 			   min(sizeof("madvise")-1, count))) {
268 		clear_bit(enabled, &transparent_hugepage_flags);
269 		set_bit(req_madv, &transparent_hugepage_flags);
270 	} else if (!memcmp("never", buf,
271 			   min(sizeof("never")-1, count))) {
272 		clear_bit(enabled, &transparent_hugepage_flags);
273 		clear_bit(req_madv, &transparent_hugepage_flags);
274 	} else
275 		return -EINVAL;
276 
277 	return count;
278 }
279 
280 static ssize_t enabled_show(struct kobject *kobj,
281 			    struct kobj_attribute *attr, char *buf)
282 {
283 	return double_flag_show(kobj, attr, buf,
284 				TRANSPARENT_HUGEPAGE_FLAG,
285 				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
286 }
287 static ssize_t enabled_store(struct kobject *kobj,
288 			     struct kobj_attribute *attr,
289 			     const char *buf, size_t count)
290 {
291 	ssize_t ret;
292 
293 	ret = double_flag_store(kobj, attr, buf, count,
294 				TRANSPARENT_HUGEPAGE_FLAG,
295 				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
296 
297 	if (ret > 0) {
298 		int err;
299 
300 		mutex_lock(&khugepaged_mutex);
301 		err = start_stop_khugepaged();
302 		mutex_unlock(&khugepaged_mutex);
303 
304 		if (err)
305 			ret = err;
306 	}
307 
308 	return ret;
309 }
310 static struct kobj_attribute enabled_attr =
311 	__ATTR(enabled, 0644, enabled_show, enabled_store);
312 
313 static ssize_t single_flag_show(struct kobject *kobj,
314 				struct kobj_attribute *attr, char *buf,
315 				enum transparent_hugepage_flag flag)
316 {
317 	return sprintf(buf, "%d\n",
318 		       !!test_bit(flag, &transparent_hugepage_flags));
319 }
320 
321 static ssize_t single_flag_store(struct kobject *kobj,
322 				 struct kobj_attribute *attr,
323 				 const char *buf, size_t count,
324 				 enum transparent_hugepage_flag flag)
325 {
326 	unsigned long value;
327 	int ret;
328 
329 	ret = kstrtoul(buf, 10, &value);
330 	if (ret < 0)
331 		return ret;
332 	if (value > 1)
333 		return -EINVAL;
334 
335 	if (value)
336 		set_bit(flag, &transparent_hugepage_flags);
337 	else
338 		clear_bit(flag, &transparent_hugepage_flags);
339 
340 	return count;
341 }
342 
343 /*
344  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
345  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
346  * memory just to allocate one more hugepage.
347  */
348 static ssize_t defrag_show(struct kobject *kobj,
349 			   struct kobj_attribute *attr, char *buf)
350 {
351 	return double_flag_show(kobj, attr, buf,
352 				TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
353 				TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
354 }
355 static ssize_t defrag_store(struct kobject *kobj,
356 			    struct kobj_attribute *attr,
357 			    const char *buf, size_t count)
358 {
359 	return double_flag_store(kobj, attr, buf, count,
360 				 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
361 				 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
362 }
363 static struct kobj_attribute defrag_attr =
364 	__ATTR(defrag, 0644, defrag_show, defrag_store);
365 
366 static ssize_t use_zero_page_show(struct kobject *kobj,
367 		struct kobj_attribute *attr, char *buf)
368 {
369 	return single_flag_show(kobj, attr, buf,
370 				TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
371 }
372 static ssize_t use_zero_page_store(struct kobject *kobj,
373 		struct kobj_attribute *attr, const char *buf, size_t count)
374 {
375 	return single_flag_store(kobj, attr, buf, count,
376 				 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
377 }
378 static struct kobj_attribute use_zero_page_attr =
379 	__ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
380 #ifdef CONFIG_DEBUG_VM
381 static ssize_t debug_cow_show(struct kobject *kobj,
382 				struct kobj_attribute *attr, char *buf)
383 {
384 	return single_flag_show(kobj, attr, buf,
385 				TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
386 }
387 static ssize_t debug_cow_store(struct kobject *kobj,
388 			       struct kobj_attribute *attr,
389 			       const char *buf, size_t count)
390 {
391 	return single_flag_store(kobj, attr, buf, count,
392 				 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
393 }
394 static struct kobj_attribute debug_cow_attr =
395 	__ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
396 #endif /* CONFIG_DEBUG_VM */
397 
398 static struct attribute *hugepage_attr[] = {
399 	&enabled_attr.attr,
400 	&defrag_attr.attr,
401 	&use_zero_page_attr.attr,
402 #ifdef CONFIG_DEBUG_VM
403 	&debug_cow_attr.attr,
404 #endif
405 	NULL,
406 };
407 
408 static struct attribute_group hugepage_attr_group = {
409 	.attrs = hugepage_attr,
410 };
411 
412 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
413 					 struct kobj_attribute *attr,
414 					 char *buf)
415 {
416 	return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
417 }
418 
419 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
420 					  struct kobj_attribute *attr,
421 					  const char *buf, size_t count)
422 {
423 	unsigned long msecs;
424 	int err;
425 
426 	err = kstrtoul(buf, 10, &msecs);
427 	if (err || msecs > UINT_MAX)
428 		return -EINVAL;
429 
430 	khugepaged_scan_sleep_millisecs = msecs;
431 	wake_up_interruptible(&khugepaged_wait);
432 
433 	return count;
434 }
435 static struct kobj_attribute scan_sleep_millisecs_attr =
436 	__ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
437 	       scan_sleep_millisecs_store);
438 
439 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
440 					  struct kobj_attribute *attr,
441 					  char *buf)
442 {
443 	return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
444 }
445 
446 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
447 					   struct kobj_attribute *attr,
448 					   const char *buf, size_t count)
449 {
450 	unsigned long msecs;
451 	int err;
452 
453 	err = kstrtoul(buf, 10, &msecs);
454 	if (err || msecs > UINT_MAX)
455 		return -EINVAL;
456 
457 	khugepaged_alloc_sleep_millisecs = msecs;
458 	wake_up_interruptible(&khugepaged_wait);
459 
460 	return count;
461 }
462 static struct kobj_attribute alloc_sleep_millisecs_attr =
463 	__ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
464 	       alloc_sleep_millisecs_store);
465 
466 static ssize_t pages_to_scan_show(struct kobject *kobj,
467 				  struct kobj_attribute *attr,
468 				  char *buf)
469 {
470 	return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
471 }
472 static ssize_t pages_to_scan_store(struct kobject *kobj,
473 				   struct kobj_attribute *attr,
474 				   const char *buf, size_t count)
475 {
476 	int err;
477 	unsigned long pages;
478 
479 	err = kstrtoul(buf, 10, &pages);
480 	if (err || !pages || pages > UINT_MAX)
481 		return -EINVAL;
482 
483 	khugepaged_pages_to_scan = pages;
484 
485 	return count;
486 }
487 static struct kobj_attribute pages_to_scan_attr =
488 	__ATTR(pages_to_scan, 0644, pages_to_scan_show,
489 	       pages_to_scan_store);
490 
491 static ssize_t pages_collapsed_show(struct kobject *kobj,
492 				    struct kobj_attribute *attr,
493 				    char *buf)
494 {
495 	return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
496 }
497 static struct kobj_attribute pages_collapsed_attr =
498 	__ATTR_RO(pages_collapsed);
499 
500 static ssize_t full_scans_show(struct kobject *kobj,
501 			       struct kobj_attribute *attr,
502 			       char *buf)
503 {
504 	return sprintf(buf, "%u\n", khugepaged_full_scans);
505 }
506 static struct kobj_attribute full_scans_attr =
507 	__ATTR_RO(full_scans);
508 
509 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
510 				      struct kobj_attribute *attr, char *buf)
511 {
512 	return single_flag_show(kobj, attr, buf,
513 				TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
514 }
515 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
516 				       struct kobj_attribute *attr,
517 				       const char *buf, size_t count)
518 {
519 	return single_flag_store(kobj, attr, buf, count,
520 				 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
521 }
522 static struct kobj_attribute khugepaged_defrag_attr =
523 	__ATTR(defrag, 0644, khugepaged_defrag_show,
524 	       khugepaged_defrag_store);
525 
526 /*
527  * max_ptes_none controls if khugepaged should collapse hugepages over
528  * any unmapped ptes in turn potentially increasing the memory
529  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
530  * reduce the available free memory in the system as it
531  * runs. Increasing max_ptes_none will instead potentially reduce the
532  * free memory in the system during the khugepaged scan.
533  */
534 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
535 					     struct kobj_attribute *attr,
536 					     char *buf)
537 {
538 	return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
539 }
540 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
541 					      struct kobj_attribute *attr,
542 					      const char *buf, size_t count)
543 {
544 	int err;
545 	unsigned long max_ptes_none;
546 
547 	err = kstrtoul(buf, 10, &max_ptes_none);
548 	if (err || max_ptes_none > HPAGE_PMD_NR-1)
549 		return -EINVAL;
550 
551 	khugepaged_max_ptes_none = max_ptes_none;
552 
553 	return count;
554 }
555 static struct kobj_attribute khugepaged_max_ptes_none_attr =
556 	__ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
557 	       khugepaged_max_ptes_none_store);
558 
559 static struct attribute *khugepaged_attr[] = {
560 	&khugepaged_defrag_attr.attr,
561 	&khugepaged_max_ptes_none_attr.attr,
562 	&pages_to_scan_attr.attr,
563 	&pages_collapsed_attr.attr,
564 	&full_scans_attr.attr,
565 	&scan_sleep_millisecs_attr.attr,
566 	&alloc_sleep_millisecs_attr.attr,
567 	NULL,
568 };
569 
570 static struct attribute_group khugepaged_attr_group = {
571 	.attrs = khugepaged_attr,
572 	.name = "khugepaged",
573 };
574 
575 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
576 {
577 	int err;
578 
579 	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
580 	if (unlikely(!*hugepage_kobj)) {
581 		pr_err("failed to create transparent hugepage kobject\n");
582 		return -ENOMEM;
583 	}
584 
585 	err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
586 	if (err) {
587 		pr_err("failed to register transparent hugepage group\n");
588 		goto delete_obj;
589 	}
590 
591 	err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
592 	if (err) {
593 		pr_err("failed to register transparent hugepage group\n");
594 		goto remove_hp_group;
595 	}
596 
597 	return 0;
598 
599 remove_hp_group:
600 	sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
601 delete_obj:
602 	kobject_put(*hugepage_kobj);
603 	return err;
604 }
605 
606 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
607 {
608 	sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
609 	sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
610 	kobject_put(hugepage_kobj);
611 }
612 #else
613 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
614 {
615 	return 0;
616 }
617 
618 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
619 {
620 }
621 #endif /* CONFIG_SYSFS */
622 
623 static int __init hugepage_init(void)
624 {
625 	int err;
626 	struct kobject *hugepage_kobj;
627 
628 	if (!has_transparent_hugepage()) {
629 		transparent_hugepage_flags = 0;
630 		return -EINVAL;
631 	}
632 
633 	err = hugepage_init_sysfs(&hugepage_kobj);
634 	if (err)
635 		goto err_sysfs;
636 
637 	err = khugepaged_slab_init();
638 	if (err)
639 		goto err_slab;
640 
641 	err = register_shrinker(&huge_zero_page_shrinker);
642 	if (err)
643 		goto err_hzp_shrinker;
644 
645 	/*
646 	 * By default disable transparent hugepages on smaller systems,
647 	 * where the extra memory used could hurt more than TLB overhead
648 	 * is likely to save.  The admin can still enable it through /sys.
649 	 */
650 	if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
651 		transparent_hugepage_flags = 0;
652 		return 0;
653 	}
654 
655 	err = start_stop_khugepaged();
656 	if (err)
657 		goto err_khugepaged;
658 
659 	return 0;
660 err_khugepaged:
661 	unregister_shrinker(&huge_zero_page_shrinker);
662 err_hzp_shrinker:
663 	khugepaged_slab_exit();
664 err_slab:
665 	hugepage_exit_sysfs(hugepage_kobj);
666 err_sysfs:
667 	return err;
668 }
669 subsys_initcall(hugepage_init);
670 
671 static int __init setup_transparent_hugepage(char *str)
672 {
673 	int ret = 0;
674 	if (!str)
675 		goto out;
676 	if (!strcmp(str, "always")) {
677 		set_bit(TRANSPARENT_HUGEPAGE_FLAG,
678 			&transparent_hugepage_flags);
679 		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
680 			  &transparent_hugepage_flags);
681 		ret = 1;
682 	} else if (!strcmp(str, "madvise")) {
683 		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
684 			  &transparent_hugepage_flags);
685 		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
686 			&transparent_hugepage_flags);
687 		ret = 1;
688 	} else if (!strcmp(str, "never")) {
689 		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
690 			  &transparent_hugepage_flags);
691 		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
692 			  &transparent_hugepage_flags);
693 		ret = 1;
694 	}
695 out:
696 	if (!ret)
697 		pr_warn("transparent_hugepage= cannot parse, ignored\n");
698 	return ret;
699 }
700 __setup("transparent_hugepage=", setup_transparent_hugepage);
701 
702 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
703 {
704 	if (likely(vma->vm_flags & VM_WRITE))
705 		pmd = pmd_mkwrite(pmd);
706 	return pmd;
707 }
708 
709 static inline pmd_t mk_huge_pmd(struct page *page, pgprot_t prot)
710 {
711 	pmd_t entry;
712 	entry = mk_pmd(page, prot);
713 	entry = pmd_mkhuge(entry);
714 	return entry;
715 }
716 
717 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
718 					struct vm_area_struct *vma,
719 					unsigned long haddr, pmd_t *pmd,
720 					struct page *page, gfp_t gfp)
721 {
722 	struct mem_cgroup *memcg;
723 	pgtable_t pgtable;
724 	spinlock_t *ptl;
725 
726 	VM_BUG_ON_PAGE(!PageCompound(page), page);
727 
728 	if (mem_cgroup_try_charge(page, mm, gfp, &memcg))
729 		return VM_FAULT_OOM;
730 
731 	pgtable = pte_alloc_one(mm, haddr);
732 	if (unlikely(!pgtable)) {
733 		mem_cgroup_cancel_charge(page, memcg);
734 		return VM_FAULT_OOM;
735 	}
736 
737 	clear_huge_page(page, haddr, HPAGE_PMD_NR);
738 	/*
739 	 * The memory barrier inside __SetPageUptodate makes sure that
740 	 * clear_huge_page writes become visible before the set_pmd_at()
741 	 * write.
742 	 */
743 	__SetPageUptodate(page);
744 
745 	ptl = pmd_lock(mm, pmd);
746 	if (unlikely(!pmd_none(*pmd))) {
747 		spin_unlock(ptl);
748 		mem_cgroup_cancel_charge(page, memcg);
749 		put_page(page);
750 		pte_free(mm, pgtable);
751 	} else {
752 		pmd_t entry;
753 		entry = mk_huge_pmd(page, vma->vm_page_prot);
754 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
755 		page_add_new_anon_rmap(page, vma, haddr);
756 		mem_cgroup_commit_charge(page, memcg, false);
757 		lru_cache_add_active_or_unevictable(page, vma);
758 		pgtable_trans_huge_deposit(mm, pmd, pgtable);
759 		set_pmd_at(mm, haddr, pmd, entry);
760 		add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
761 		atomic_long_inc(&mm->nr_ptes);
762 		spin_unlock(ptl);
763 	}
764 
765 	return 0;
766 }
767 
768 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
769 {
770 	return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
771 }
772 
773 /* Caller must hold page table lock. */
774 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
775 		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
776 		struct page *zero_page)
777 {
778 	pmd_t entry;
779 	if (!pmd_none(*pmd))
780 		return false;
781 	entry = mk_pmd(zero_page, vma->vm_page_prot);
782 	entry = pmd_mkhuge(entry);
783 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
784 	set_pmd_at(mm, haddr, pmd, entry);
785 	atomic_long_inc(&mm->nr_ptes);
786 	return true;
787 }
788 
789 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
790 			       unsigned long address, pmd_t *pmd,
791 			       unsigned int flags)
792 {
793 	gfp_t gfp;
794 	struct page *page;
795 	unsigned long haddr = address & HPAGE_PMD_MASK;
796 
797 	if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
798 		return VM_FAULT_FALLBACK;
799 	if (unlikely(anon_vma_prepare(vma)))
800 		return VM_FAULT_OOM;
801 	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
802 		return VM_FAULT_OOM;
803 	if (!(flags & FAULT_FLAG_WRITE) && !mm_forbids_zeropage(mm) &&
804 			transparent_hugepage_use_zero_page()) {
805 		spinlock_t *ptl;
806 		pgtable_t pgtable;
807 		struct page *zero_page;
808 		bool set;
809 		pgtable = pte_alloc_one(mm, haddr);
810 		if (unlikely(!pgtable))
811 			return VM_FAULT_OOM;
812 		zero_page = get_huge_zero_page();
813 		if (unlikely(!zero_page)) {
814 			pte_free(mm, pgtable);
815 			count_vm_event(THP_FAULT_FALLBACK);
816 			return VM_FAULT_FALLBACK;
817 		}
818 		ptl = pmd_lock(mm, pmd);
819 		set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
820 				zero_page);
821 		spin_unlock(ptl);
822 		if (!set) {
823 			pte_free(mm, pgtable);
824 			put_huge_zero_page();
825 		}
826 		return 0;
827 	}
828 	gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
829 	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
830 	if (unlikely(!page)) {
831 		count_vm_event(THP_FAULT_FALLBACK);
832 		return VM_FAULT_FALLBACK;
833 	}
834 	if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd, page, gfp))) {
835 		put_page(page);
836 		count_vm_event(THP_FAULT_FALLBACK);
837 		return VM_FAULT_FALLBACK;
838 	}
839 
840 	count_vm_event(THP_FAULT_ALLOC);
841 	return 0;
842 }
843 
844 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
845 		  pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
846 		  struct vm_area_struct *vma)
847 {
848 	spinlock_t *dst_ptl, *src_ptl;
849 	struct page *src_page;
850 	pmd_t pmd;
851 	pgtable_t pgtable;
852 	int ret;
853 
854 	ret = -ENOMEM;
855 	pgtable = pte_alloc_one(dst_mm, addr);
856 	if (unlikely(!pgtable))
857 		goto out;
858 
859 	dst_ptl = pmd_lock(dst_mm, dst_pmd);
860 	src_ptl = pmd_lockptr(src_mm, src_pmd);
861 	spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
862 
863 	ret = -EAGAIN;
864 	pmd = *src_pmd;
865 	if (unlikely(!pmd_trans_huge(pmd))) {
866 		pte_free(dst_mm, pgtable);
867 		goto out_unlock;
868 	}
869 	/*
870 	 * When page table lock is held, the huge zero pmd should not be
871 	 * under splitting since we don't split the page itself, only pmd to
872 	 * a page table.
873 	 */
874 	if (is_huge_zero_pmd(pmd)) {
875 		struct page *zero_page;
876 		bool set;
877 		/*
878 		 * get_huge_zero_page() will never allocate a new page here,
879 		 * since we already have a zero page to copy. It just takes a
880 		 * reference.
881 		 */
882 		zero_page = get_huge_zero_page();
883 		set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
884 				zero_page);
885 		BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
886 		ret = 0;
887 		goto out_unlock;
888 	}
889 
890 	if (unlikely(pmd_trans_splitting(pmd))) {
891 		/* split huge page running from under us */
892 		spin_unlock(src_ptl);
893 		spin_unlock(dst_ptl);
894 		pte_free(dst_mm, pgtable);
895 
896 		wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
897 		goto out;
898 	}
899 	src_page = pmd_page(pmd);
900 	VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
901 	get_page(src_page);
902 	page_dup_rmap(src_page);
903 	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
904 
905 	pmdp_set_wrprotect(src_mm, addr, src_pmd);
906 	pmd = pmd_mkold(pmd_wrprotect(pmd));
907 	pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
908 	set_pmd_at(dst_mm, addr, dst_pmd, pmd);
909 	atomic_long_inc(&dst_mm->nr_ptes);
910 
911 	ret = 0;
912 out_unlock:
913 	spin_unlock(src_ptl);
914 	spin_unlock(dst_ptl);
915 out:
916 	return ret;
917 }
918 
919 void huge_pmd_set_accessed(struct mm_struct *mm,
920 			   struct vm_area_struct *vma,
921 			   unsigned long address,
922 			   pmd_t *pmd, pmd_t orig_pmd,
923 			   int dirty)
924 {
925 	spinlock_t *ptl;
926 	pmd_t entry;
927 	unsigned long haddr;
928 
929 	ptl = pmd_lock(mm, pmd);
930 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
931 		goto unlock;
932 
933 	entry = pmd_mkyoung(orig_pmd);
934 	haddr = address & HPAGE_PMD_MASK;
935 	if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
936 		update_mmu_cache_pmd(vma, address, pmd);
937 
938 unlock:
939 	spin_unlock(ptl);
940 }
941 
942 /*
943  * Save CONFIG_DEBUG_PAGEALLOC from faulting falsely on tail pages
944  * during copy_user_huge_page()'s copy_page_rep(): in the case when
945  * the source page gets split and a tail freed before copy completes.
946  * Called under pmd_lock of checked pmd, so safe from splitting itself.
947  */
948 static void get_user_huge_page(struct page *page)
949 {
950 	if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
951 		struct page *endpage = page + HPAGE_PMD_NR;
952 
953 		atomic_add(HPAGE_PMD_NR, &page->_count);
954 		while (++page < endpage)
955 			get_huge_page_tail(page);
956 	} else {
957 		get_page(page);
958 	}
959 }
960 
961 static void put_user_huge_page(struct page *page)
962 {
963 	if (IS_ENABLED(CONFIG_DEBUG_PAGEALLOC)) {
964 		struct page *endpage = page + HPAGE_PMD_NR;
965 
966 		while (page < endpage)
967 			put_page(page++);
968 	} else {
969 		put_page(page);
970 	}
971 }
972 
973 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
974 					struct vm_area_struct *vma,
975 					unsigned long address,
976 					pmd_t *pmd, pmd_t orig_pmd,
977 					struct page *page,
978 					unsigned long haddr)
979 {
980 	struct mem_cgroup *memcg;
981 	spinlock_t *ptl;
982 	pgtable_t pgtable;
983 	pmd_t _pmd;
984 	int ret = 0, i;
985 	struct page **pages;
986 	unsigned long mmun_start;	/* For mmu_notifiers */
987 	unsigned long mmun_end;		/* For mmu_notifiers */
988 
989 	pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
990 			GFP_KERNEL);
991 	if (unlikely(!pages)) {
992 		ret |= VM_FAULT_OOM;
993 		goto out;
994 	}
995 
996 	for (i = 0; i < HPAGE_PMD_NR; i++) {
997 		pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
998 					       __GFP_OTHER_NODE,
999 					       vma, address, page_to_nid(page));
1000 		if (unlikely(!pages[i] ||
1001 			     mem_cgroup_try_charge(pages[i], mm, GFP_KERNEL,
1002 						   &memcg))) {
1003 			if (pages[i])
1004 				put_page(pages[i]);
1005 			while (--i >= 0) {
1006 				memcg = (void *)page_private(pages[i]);
1007 				set_page_private(pages[i], 0);
1008 				mem_cgroup_cancel_charge(pages[i], memcg);
1009 				put_page(pages[i]);
1010 			}
1011 			kfree(pages);
1012 			ret |= VM_FAULT_OOM;
1013 			goto out;
1014 		}
1015 		set_page_private(pages[i], (unsigned long)memcg);
1016 	}
1017 
1018 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1019 		copy_user_highpage(pages[i], page + i,
1020 				   haddr + PAGE_SIZE * i, vma);
1021 		__SetPageUptodate(pages[i]);
1022 		cond_resched();
1023 	}
1024 
1025 	mmun_start = haddr;
1026 	mmun_end   = haddr + HPAGE_PMD_SIZE;
1027 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1028 
1029 	ptl = pmd_lock(mm, pmd);
1030 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
1031 		goto out_free_pages;
1032 	VM_BUG_ON_PAGE(!PageHead(page), page);
1033 
1034 	pmdp_clear_flush_notify(vma, haddr, pmd);
1035 	/* leave pmd empty until pte is filled */
1036 
1037 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1038 	pmd_populate(mm, &_pmd, pgtable);
1039 
1040 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1041 		pte_t *pte, entry;
1042 		entry = mk_pte(pages[i], vma->vm_page_prot);
1043 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1044 		memcg = (void *)page_private(pages[i]);
1045 		set_page_private(pages[i], 0);
1046 		page_add_new_anon_rmap(pages[i], vma, haddr);
1047 		mem_cgroup_commit_charge(pages[i], memcg, false);
1048 		lru_cache_add_active_or_unevictable(pages[i], vma);
1049 		pte = pte_offset_map(&_pmd, haddr);
1050 		VM_BUG_ON(!pte_none(*pte));
1051 		set_pte_at(mm, haddr, pte, entry);
1052 		pte_unmap(pte);
1053 	}
1054 	kfree(pages);
1055 
1056 	smp_wmb(); /* make pte visible before pmd */
1057 	pmd_populate(mm, pmd, pgtable);
1058 	page_remove_rmap(page);
1059 	spin_unlock(ptl);
1060 
1061 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1062 
1063 	ret |= VM_FAULT_WRITE;
1064 	put_page(page);
1065 
1066 out:
1067 	return ret;
1068 
1069 out_free_pages:
1070 	spin_unlock(ptl);
1071 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1072 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1073 		memcg = (void *)page_private(pages[i]);
1074 		set_page_private(pages[i], 0);
1075 		mem_cgroup_cancel_charge(pages[i], memcg);
1076 		put_page(pages[i]);
1077 	}
1078 	kfree(pages);
1079 	goto out;
1080 }
1081 
1082 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1083 			unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1084 {
1085 	spinlock_t *ptl;
1086 	int ret = 0;
1087 	struct page *page = NULL, *new_page;
1088 	struct mem_cgroup *memcg;
1089 	unsigned long haddr;
1090 	unsigned long mmun_start;	/* For mmu_notifiers */
1091 	unsigned long mmun_end;		/* For mmu_notifiers */
1092 	gfp_t huge_gfp;			/* for allocation and charge */
1093 
1094 	ptl = pmd_lockptr(mm, pmd);
1095 	VM_BUG_ON_VMA(!vma->anon_vma, vma);
1096 	haddr = address & HPAGE_PMD_MASK;
1097 	if (is_huge_zero_pmd(orig_pmd))
1098 		goto alloc;
1099 	spin_lock(ptl);
1100 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
1101 		goto out_unlock;
1102 
1103 	page = pmd_page(orig_pmd);
1104 	VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1105 	if (page_mapcount(page) == 1) {
1106 		pmd_t entry;
1107 		entry = pmd_mkyoung(orig_pmd);
1108 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1109 		if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1110 			update_mmu_cache_pmd(vma, address, pmd);
1111 		ret |= VM_FAULT_WRITE;
1112 		goto out_unlock;
1113 	}
1114 	get_user_huge_page(page);
1115 	spin_unlock(ptl);
1116 alloc:
1117 	if (transparent_hugepage_enabled(vma) &&
1118 	    !transparent_hugepage_debug_cow()) {
1119 		huge_gfp = alloc_hugepage_gfpmask(transparent_hugepage_defrag(vma), 0);
1120 		new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1121 	} else
1122 		new_page = NULL;
1123 
1124 	if (unlikely(!new_page)) {
1125 		if (!page) {
1126 			split_huge_page_pmd(vma, address, pmd);
1127 			ret |= VM_FAULT_FALLBACK;
1128 		} else {
1129 			ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1130 					pmd, orig_pmd, page, haddr);
1131 			if (ret & VM_FAULT_OOM) {
1132 				split_huge_page(page);
1133 				ret |= VM_FAULT_FALLBACK;
1134 			}
1135 			put_user_huge_page(page);
1136 		}
1137 		count_vm_event(THP_FAULT_FALLBACK);
1138 		goto out;
1139 	}
1140 
1141 	if (unlikely(mem_cgroup_try_charge(new_page, mm, huge_gfp, &memcg))) {
1142 		put_page(new_page);
1143 		if (page) {
1144 			split_huge_page(page);
1145 			put_user_huge_page(page);
1146 		} else
1147 			split_huge_page_pmd(vma, address, pmd);
1148 		ret |= VM_FAULT_FALLBACK;
1149 		count_vm_event(THP_FAULT_FALLBACK);
1150 		goto out;
1151 	}
1152 
1153 	count_vm_event(THP_FAULT_ALLOC);
1154 
1155 	if (!page)
1156 		clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1157 	else
1158 		copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1159 	__SetPageUptodate(new_page);
1160 
1161 	mmun_start = haddr;
1162 	mmun_end   = haddr + HPAGE_PMD_SIZE;
1163 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1164 
1165 	spin_lock(ptl);
1166 	if (page)
1167 		put_user_huge_page(page);
1168 	if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1169 		spin_unlock(ptl);
1170 		mem_cgroup_cancel_charge(new_page, memcg);
1171 		put_page(new_page);
1172 		goto out_mn;
1173 	} else {
1174 		pmd_t entry;
1175 		entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1176 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1177 		pmdp_clear_flush_notify(vma, haddr, pmd);
1178 		page_add_new_anon_rmap(new_page, vma, haddr);
1179 		mem_cgroup_commit_charge(new_page, memcg, false);
1180 		lru_cache_add_active_or_unevictable(new_page, vma);
1181 		set_pmd_at(mm, haddr, pmd, entry);
1182 		update_mmu_cache_pmd(vma, address, pmd);
1183 		if (!page) {
1184 			add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1185 			put_huge_zero_page();
1186 		} else {
1187 			VM_BUG_ON_PAGE(!PageHead(page), page);
1188 			page_remove_rmap(page);
1189 			put_page(page);
1190 		}
1191 		ret |= VM_FAULT_WRITE;
1192 	}
1193 	spin_unlock(ptl);
1194 out_mn:
1195 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1196 out:
1197 	return ret;
1198 out_unlock:
1199 	spin_unlock(ptl);
1200 	return ret;
1201 }
1202 
1203 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1204 				   unsigned long addr,
1205 				   pmd_t *pmd,
1206 				   unsigned int flags)
1207 {
1208 	struct mm_struct *mm = vma->vm_mm;
1209 	struct page *page = NULL;
1210 
1211 	assert_spin_locked(pmd_lockptr(mm, pmd));
1212 
1213 	if (flags & FOLL_WRITE && !pmd_write(*pmd))
1214 		goto out;
1215 
1216 	/* Avoid dumping huge zero page */
1217 	if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1218 		return ERR_PTR(-EFAULT);
1219 
1220 	/* Full NUMA hinting faults to serialise migration in fault paths */
1221 	if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1222 		goto out;
1223 
1224 	page = pmd_page(*pmd);
1225 	VM_BUG_ON_PAGE(!PageHead(page), page);
1226 	if (flags & FOLL_TOUCH) {
1227 		pmd_t _pmd;
1228 		/*
1229 		 * We should set the dirty bit only for FOLL_WRITE but
1230 		 * for now the dirty bit in the pmd is meaningless.
1231 		 * And if the dirty bit will become meaningful and
1232 		 * we'll only set it with FOLL_WRITE, an atomic
1233 		 * set_bit will be required on the pmd to set the
1234 		 * young bit, instead of the current set_pmd_at.
1235 		 */
1236 		_pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1237 		if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
1238 					  pmd, _pmd,  1))
1239 			update_mmu_cache_pmd(vma, addr, pmd);
1240 	}
1241 	if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) {
1242 		if (page->mapping && trylock_page(page)) {
1243 			lru_add_drain();
1244 			if (page->mapping)
1245 				mlock_vma_page(page);
1246 			unlock_page(page);
1247 		}
1248 	}
1249 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1250 	VM_BUG_ON_PAGE(!PageCompound(page), page);
1251 	if (flags & FOLL_GET)
1252 		get_page_foll(page);
1253 
1254 out:
1255 	return page;
1256 }
1257 
1258 /* NUMA hinting page fault entry point for trans huge pmds */
1259 int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
1260 				unsigned long addr, pmd_t pmd, pmd_t *pmdp)
1261 {
1262 	spinlock_t *ptl;
1263 	struct anon_vma *anon_vma = NULL;
1264 	struct page *page;
1265 	unsigned long haddr = addr & HPAGE_PMD_MASK;
1266 	int page_nid = -1, this_nid = numa_node_id();
1267 	int target_nid, last_cpupid = -1;
1268 	bool page_locked;
1269 	bool migrated = false;
1270 	bool was_writable;
1271 	int flags = 0;
1272 
1273 	/* A PROT_NONE fault should not end up here */
1274 	BUG_ON(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)));
1275 
1276 	ptl = pmd_lock(mm, pmdp);
1277 	if (unlikely(!pmd_same(pmd, *pmdp)))
1278 		goto out_unlock;
1279 
1280 	/*
1281 	 * If there are potential migrations, wait for completion and retry
1282 	 * without disrupting NUMA hinting information. Do not relock and
1283 	 * check_same as the page may no longer be mapped.
1284 	 */
1285 	if (unlikely(pmd_trans_migrating(*pmdp))) {
1286 		page = pmd_page(*pmdp);
1287 		spin_unlock(ptl);
1288 		wait_on_page_locked(page);
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 	/* See similar comment in do_numa_page for explanation */
1303 	if (!(vma->vm_flags & VM_WRITE))
1304 		flags |= TNF_NO_GROUP;
1305 
1306 	/*
1307 	 * Acquire the page lock to serialise THP migrations but avoid dropping
1308 	 * page_table_lock if at all possible
1309 	 */
1310 	page_locked = trylock_page(page);
1311 	target_nid = mpol_misplaced(page, vma, haddr);
1312 	if (target_nid == -1) {
1313 		/* If the page was locked, there are no parallel migrations */
1314 		if (page_locked)
1315 			goto clear_pmdnuma;
1316 	}
1317 
1318 	/* Migration could have started since the pmd_trans_migrating check */
1319 	if (!page_locked) {
1320 		spin_unlock(ptl);
1321 		wait_on_page_locked(page);
1322 		page_nid = -1;
1323 		goto out;
1324 	}
1325 
1326 	/*
1327 	 * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1328 	 * to serialises splits
1329 	 */
1330 	get_page(page);
1331 	spin_unlock(ptl);
1332 	anon_vma = page_lock_anon_vma_read(page);
1333 
1334 	/* Confirm the PMD did not change while page_table_lock was released */
1335 	spin_lock(ptl);
1336 	if (unlikely(!pmd_same(pmd, *pmdp))) {
1337 		unlock_page(page);
1338 		put_page(page);
1339 		page_nid = -1;
1340 		goto out_unlock;
1341 	}
1342 
1343 	/* Bail if we fail to protect against THP splits for any reason */
1344 	if (unlikely(!anon_vma)) {
1345 		put_page(page);
1346 		page_nid = -1;
1347 		goto clear_pmdnuma;
1348 	}
1349 
1350 	/*
1351 	 * Migrate the THP to the requested node, returns with page unlocked
1352 	 * and access rights restored.
1353 	 */
1354 	spin_unlock(ptl);
1355 	migrated = migrate_misplaced_transhuge_page(mm, vma,
1356 				pmdp, pmd, addr, page, target_nid);
1357 	if (migrated) {
1358 		flags |= TNF_MIGRATED;
1359 		page_nid = target_nid;
1360 	} else
1361 		flags |= TNF_MIGRATE_FAIL;
1362 
1363 	goto out;
1364 clear_pmdnuma:
1365 	BUG_ON(!PageLocked(page));
1366 	was_writable = pmd_write(pmd);
1367 	pmd = pmd_modify(pmd, vma->vm_page_prot);
1368 	pmd = pmd_mkyoung(pmd);
1369 	if (was_writable)
1370 		pmd = pmd_mkwrite(pmd);
1371 	set_pmd_at(mm, haddr, pmdp, pmd);
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_full(tlb->mm, addr, pmd,
1404 						   tlb->fullmm);
1405 		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1406 		pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1407 		if (is_huge_zero_pmd(orig_pmd)) {
1408 			atomic_long_dec(&tlb->mm->nr_ptes);
1409 			spin_unlock(ptl);
1410 			put_huge_zero_page();
1411 		} else {
1412 			page = pmd_page(orig_pmd);
1413 			page_remove_rmap(page);
1414 			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1415 			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1416 			VM_BUG_ON_PAGE(!PageHead(page), page);
1417 			atomic_long_dec(&tlb->mm->nr_ptes);
1418 			spin_unlock(ptl);
1419 			tlb_remove_page(tlb, page);
1420 		}
1421 		pte_free(tlb->mm, pgtable);
1422 		ret = 1;
1423 	}
1424 	return ret;
1425 }
1426 
1427 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1428 		  unsigned long old_addr,
1429 		  unsigned long new_addr, unsigned long old_end,
1430 		  pmd_t *old_pmd, pmd_t *new_pmd)
1431 {
1432 	spinlock_t *old_ptl, *new_ptl;
1433 	int ret = 0;
1434 	pmd_t pmd;
1435 
1436 	struct mm_struct *mm = vma->vm_mm;
1437 
1438 	if ((old_addr & ~HPAGE_PMD_MASK) ||
1439 	    (new_addr & ~HPAGE_PMD_MASK) ||
1440 	    old_end - old_addr < HPAGE_PMD_SIZE ||
1441 	    (new_vma->vm_flags & VM_NOHUGEPAGE))
1442 		goto out;
1443 
1444 	/*
1445 	 * The destination pmd shouldn't be established, free_pgtables()
1446 	 * should have release it.
1447 	 */
1448 	if (WARN_ON(!pmd_none(*new_pmd))) {
1449 		VM_BUG_ON(pmd_trans_huge(*new_pmd));
1450 		goto out;
1451 	}
1452 
1453 	/*
1454 	 * We don't have to worry about the ordering of src and dst
1455 	 * ptlocks because exclusive mmap_sem prevents deadlock.
1456 	 */
1457 	ret = __pmd_trans_huge_lock(old_pmd, vma, &old_ptl);
1458 	if (ret == 1) {
1459 		new_ptl = pmd_lockptr(mm, new_pmd);
1460 		if (new_ptl != old_ptl)
1461 			spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1462 		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
1463 		VM_BUG_ON(!pmd_none(*new_pmd));
1464 
1465 		if (pmd_move_must_withdraw(new_ptl, old_ptl)) {
1466 			pgtable_t pgtable;
1467 			pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1468 			pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1469 		}
1470 		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1471 		if (new_ptl != old_ptl)
1472 			spin_unlock(new_ptl);
1473 		spin_unlock(old_ptl);
1474 	}
1475 out:
1476 	return ret;
1477 }
1478 
1479 /*
1480  * Returns
1481  *  - 0 if PMD could not be locked
1482  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1483  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1484  */
1485 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1486 		unsigned long addr, pgprot_t newprot, int prot_numa)
1487 {
1488 	struct mm_struct *mm = vma->vm_mm;
1489 	spinlock_t *ptl;
1490 	int ret = 0;
1491 
1492 	if (__pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
1493 		pmd_t entry;
1494 		bool preserve_write = prot_numa && pmd_write(*pmd);
1495 		ret = 1;
1496 
1497 		/*
1498 		 * Avoid trapping faults against the zero page. The read-only
1499 		 * data is likely to be read-cached on the local CPU and
1500 		 * local/remote hits to the zero page are not interesting.
1501 		 */
1502 		if (prot_numa && is_huge_zero_pmd(*pmd)) {
1503 			spin_unlock(ptl);
1504 			return ret;
1505 		}
1506 
1507 		if (!prot_numa || !pmd_protnone(*pmd)) {
1508 			entry = pmdp_get_and_clear_notify(mm, addr, pmd);
1509 			entry = pmd_modify(entry, newprot);
1510 			if (preserve_write)
1511 				entry = pmd_mkwrite(entry);
1512 			ret = HPAGE_PMD_NR;
1513 			set_pmd_at(mm, addr, pmd, entry);
1514 			BUG_ON(!preserve_write && pmd_write(entry));
1515 		}
1516 		spin_unlock(ptl);
1517 	}
1518 
1519 	return ret;
1520 }
1521 
1522 /*
1523  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1524  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1525  *
1526  * Note that if it returns 1, this routine returns without unlocking page
1527  * table locks. So callers must unlock them.
1528  */
1529 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma,
1530 		spinlock_t **ptl)
1531 {
1532 	*ptl = pmd_lock(vma->vm_mm, pmd);
1533 	if (likely(pmd_trans_huge(*pmd))) {
1534 		if (unlikely(pmd_trans_splitting(*pmd))) {
1535 			spin_unlock(*ptl);
1536 			wait_split_huge_page(vma->anon_vma, pmd);
1537 			return -1;
1538 		} else {
1539 			/* Thp mapped by 'pmd' is stable, so we can
1540 			 * handle it as it is. */
1541 			return 1;
1542 		}
1543 	}
1544 	spin_unlock(*ptl);
1545 	return 0;
1546 }
1547 
1548 /*
1549  * This function returns whether a given @page is mapped onto the @address
1550  * in the virtual space of @mm.
1551  *
1552  * When it's true, this function returns *pmd with holding the page table lock
1553  * and passing it back to the caller via @ptl.
1554  * If it's false, returns NULL without holding the page table lock.
1555  */
1556 pmd_t *page_check_address_pmd(struct page *page,
1557 			      struct mm_struct *mm,
1558 			      unsigned long address,
1559 			      enum page_check_address_pmd_flag flag,
1560 			      spinlock_t **ptl)
1561 {
1562 	pgd_t *pgd;
1563 	pud_t *pud;
1564 	pmd_t *pmd;
1565 
1566 	if (address & ~HPAGE_PMD_MASK)
1567 		return NULL;
1568 
1569 	pgd = pgd_offset(mm, address);
1570 	if (!pgd_present(*pgd))
1571 		return NULL;
1572 	pud = pud_offset(pgd, address);
1573 	if (!pud_present(*pud))
1574 		return NULL;
1575 	pmd = pmd_offset(pud, address);
1576 
1577 	*ptl = pmd_lock(mm, pmd);
1578 	if (!pmd_present(*pmd))
1579 		goto unlock;
1580 	if (pmd_page(*pmd) != page)
1581 		goto unlock;
1582 	/*
1583 	 * split_vma() may create temporary aliased mappings. There is
1584 	 * no risk as long as all huge pmd are found and have their
1585 	 * splitting bit set before __split_huge_page_refcount
1586 	 * runs. Finding the same huge pmd more than once during the
1587 	 * same rmap walk is not a problem.
1588 	 */
1589 	if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1590 	    pmd_trans_splitting(*pmd))
1591 		goto unlock;
1592 	if (pmd_trans_huge(*pmd)) {
1593 		VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1594 			  !pmd_trans_splitting(*pmd));
1595 		return pmd;
1596 	}
1597 unlock:
1598 	spin_unlock(*ptl);
1599 	return NULL;
1600 }
1601 
1602 static int __split_huge_page_splitting(struct page *page,
1603 				       struct vm_area_struct *vma,
1604 				       unsigned long address)
1605 {
1606 	struct mm_struct *mm = vma->vm_mm;
1607 	spinlock_t *ptl;
1608 	pmd_t *pmd;
1609 	int ret = 0;
1610 	/* For mmu_notifiers */
1611 	const unsigned long mmun_start = address;
1612 	const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1613 
1614 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1615 	pmd = page_check_address_pmd(page, mm, address,
1616 			PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG, &ptl);
1617 	if (pmd) {
1618 		/*
1619 		 * We can't temporarily set the pmd to null in order
1620 		 * to split it, the pmd must remain marked huge at all
1621 		 * times or the VM won't take the pmd_trans_huge paths
1622 		 * and it won't wait on the anon_vma->root->rwsem to
1623 		 * serialize against split_huge_page*.
1624 		 */
1625 		pmdp_splitting_flush(vma, address, pmd);
1626 
1627 		ret = 1;
1628 		spin_unlock(ptl);
1629 	}
1630 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1631 
1632 	return ret;
1633 }
1634 
1635 static void __split_huge_page_refcount(struct page *page,
1636 				       struct list_head *list)
1637 {
1638 	int i;
1639 	struct zone *zone = page_zone(page);
1640 	struct lruvec *lruvec;
1641 	int tail_count = 0;
1642 
1643 	/* prevent PageLRU to go away from under us, and freeze lru stats */
1644 	spin_lock_irq(&zone->lru_lock);
1645 	lruvec = mem_cgroup_page_lruvec(page, zone);
1646 
1647 	compound_lock(page);
1648 	/* complete memcg works before add pages to LRU */
1649 	mem_cgroup_split_huge_fixup(page);
1650 
1651 	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1652 		struct page *page_tail = page + i;
1653 
1654 		/* tail_page->_mapcount cannot change */
1655 		BUG_ON(page_mapcount(page_tail) < 0);
1656 		tail_count += page_mapcount(page_tail);
1657 		/* check for overflow */
1658 		BUG_ON(tail_count < 0);
1659 		BUG_ON(atomic_read(&page_tail->_count) != 0);
1660 		/*
1661 		 * tail_page->_count is zero and not changing from
1662 		 * under us. But get_page_unless_zero() may be running
1663 		 * from under us on the tail_page. If we used
1664 		 * atomic_set() below instead of atomic_add(), we
1665 		 * would then run atomic_set() concurrently with
1666 		 * get_page_unless_zero(), and atomic_set() is
1667 		 * implemented in C not using locked ops. spin_unlock
1668 		 * on x86 sometime uses locked ops because of PPro
1669 		 * errata 66, 92, so unless somebody can guarantee
1670 		 * atomic_set() here would be safe on all archs (and
1671 		 * not only on x86), it's safer to use atomic_add().
1672 		 */
1673 		atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1674 			   &page_tail->_count);
1675 
1676 		/* after clearing PageTail the gup refcount can be released */
1677 		smp_mb__after_atomic();
1678 
1679 		/*
1680 		 * retain hwpoison flag of the poisoned tail page:
1681 		 *   fix for the unsuitable process killed on Guest Machine(KVM)
1682 		 *   by the memory-failure.
1683 		 */
1684 		page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
1685 		page_tail->flags |= (page->flags &
1686 				     ((1L << PG_referenced) |
1687 				      (1L << PG_swapbacked) |
1688 				      (1L << PG_mlocked) |
1689 				      (1L << PG_uptodate) |
1690 				      (1L << PG_active) |
1691 				      (1L << PG_unevictable)));
1692 		page_tail->flags |= (1L << PG_dirty);
1693 
1694 		/* clear PageTail before overwriting first_page */
1695 		smp_wmb();
1696 
1697 		/*
1698 		 * __split_huge_page_splitting() already set the
1699 		 * splitting bit in all pmd that could map this
1700 		 * hugepage, that will ensure no CPU can alter the
1701 		 * mapcount on the head page. The mapcount is only
1702 		 * accounted in the head page and it has to be
1703 		 * transferred to all tail pages in the below code. So
1704 		 * for this code to be safe, the split the mapcount
1705 		 * can't change. But that doesn't mean userland can't
1706 		 * keep changing and reading the page contents while
1707 		 * we transfer the mapcount, so the pmd splitting
1708 		 * status is achieved setting a reserved bit in the
1709 		 * pmd, not by clearing the present bit.
1710 		*/
1711 		page_tail->_mapcount = page->_mapcount;
1712 
1713 		BUG_ON(page_tail->mapping);
1714 		page_tail->mapping = page->mapping;
1715 
1716 		page_tail->index = page->index + i;
1717 		page_cpupid_xchg_last(page_tail, page_cpupid_last(page));
1718 
1719 		BUG_ON(!PageAnon(page_tail));
1720 		BUG_ON(!PageUptodate(page_tail));
1721 		BUG_ON(!PageDirty(page_tail));
1722 		BUG_ON(!PageSwapBacked(page_tail));
1723 
1724 		lru_add_page_tail(page, page_tail, lruvec, list);
1725 	}
1726 	atomic_sub(tail_count, &page->_count);
1727 	BUG_ON(atomic_read(&page->_count) <= 0);
1728 
1729 	__mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1730 
1731 	ClearPageCompound(page);
1732 	compound_unlock(page);
1733 	spin_unlock_irq(&zone->lru_lock);
1734 
1735 	for (i = 1; i < HPAGE_PMD_NR; i++) {
1736 		struct page *page_tail = page + i;
1737 		BUG_ON(page_count(page_tail) <= 0);
1738 		/*
1739 		 * Tail pages may be freed if there wasn't any mapping
1740 		 * like if add_to_swap() is running on a lru page that
1741 		 * had its mapping zapped. And freeing these pages
1742 		 * requires taking the lru_lock so we do the put_page
1743 		 * of the tail pages after the split is complete.
1744 		 */
1745 		put_page(page_tail);
1746 	}
1747 
1748 	/*
1749 	 * Only the head page (now become a regular page) is required
1750 	 * to be pinned by the caller.
1751 	 */
1752 	BUG_ON(page_count(page) <= 0);
1753 }
1754 
1755 static int __split_huge_page_map(struct page *page,
1756 				 struct vm_area_struct *vma,
1757 				 unsigned long address)
1758 {
1759 	struct mm_struct *mm = vma->vm_mm;
1760 	spinlock_t *ptl;
1761 	pmd_t *pmd, _pmd;
1762 	int ret = 0, i;
1763 	pgtable_t pgtable;
1764 	unsigned long haddr;
1765 
1766 	pmd = page_check_address_pmd(page, mm, address,
1767 			PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG, &ptl);
1768 	if (pmd) {
1769 		pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1770 		pmd_populate(mm, &_pmd, pgtable);
1771 		if (pmd_write(*pmd))
1772 			BUG_ON(page_mapcount(page) != 1);
1773 
1774 		haddr = address;
1775 		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1776 			pte_t *pte, entry;
1777 			BUG_ON(PageCompound(page+i));
1778 			/*
1779 			 * Note that NUMA hinting access restrictions are not
1780 			 * transferred to avoid any possibility of altering
1781 			 * permissions across VMAs.
1782 			 */
1783 			entry = mk_pte(page + i, vma->vm_page_prot);
1784 			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1785 			if (!pmd_write(*pmd))
1786 				entry = pte_wrprotect(entry);
1787 			if (!pmd_young(*pmd))
1788 				entry = pte_mkold(entry);
1789 			pte = pte_offset_map(&_pmd, haddr);
1790 			BUG_ON(!pte_none(*pte));
1791 			set_pte_at(mm, haddr, pte, entry);
1792 			pte_unmap(pte);
1793 		}
1794 
1795 		smp_wmb(); /* make pte visible before pmd */
1796 		/*
1797 		 * Up to this point the pmd is present and huge and
1798 		 * userland has the whole access to the hugepage
1799 		 * during the split (which happens in place). If we
1800 		 * overwrite the pmd with the not-huge version
1801 		 * pointing to the pte here (which of course we could
1802 		 * if all CPUs were bug free), userland could trigger
1803 		 * a small page size TLB miss on the small sized TLB
1804 		 * while the hugepage TLB entry is still established
1805 		 * in the huge TLB. Some CPU doesn't like that. See
1806 		 * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1807 		 * Erratum 383 on page 93. Intel should be safe but is
1808 		 * also warns that it's only safe if the permission
1809 		 * and cache attributes of the two entries loaded in
1810 		 * the two TLB is identical (which should be the case
1811 		 * here). But it is generally safer to never allow
1812 		 * small and huge TLB entries for the same virtual
1813 		 * address to be loaded simultaneously. So instead of
1814 		 * doing "pmd_populate(); flush_tlb_range();" we first
1815 		 * mark the current pmd notpresent (atomically because
1816 		 * here the pmd_trans_huge and pmd_trans_splitting
1817 		 * must remain set at all times on the pmd until the
1818 		 * split is complete for this pmd), then we flush the
1819 		 * SMP TLB and finally we write the non-huge version
1820 		 * of the pmd entry with pmd_populate.
1821 		 */
1822 		pmdp_invalidate(vma, address, pmd);
1823 		pmd_populate(mm, pmd, pgtable);
1824 		ret = 1;
1825 		spin_unlock(ptl);
1826 	}
1827 
1828 	return ret;
1829 }
1830 
1831 /* must be called with anon_vma->root->rwsem held */
1832 static void __split_huge_page(struct page *page,
1833 			      struct anon_vma *anon_vma,
1834 			      struct list_head *list)
1835 {
1836 	int mapcount, mapcount2;
1837 	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1838 	struct anon_vma_chain *avc;
1839 
1840 	BUG_ON(!PageHead(page));
1841 	BUG_ON(PageTail(page));
1842 
1843 	mapcount = 0;
1844 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1845 		struct vm_area_struct *vma = avc->vma;
1846 		unsigned long addr = vma_address(page, vma);
1847 		BUG_ON(is_vma_temporary_stack(vma));
1848 		mapcount += __split_huge_page_splitting(page, vma, addr);
1849 	}
1850 	/*
1851 	 * It is critical that new vmas are added to the tail of the
1852 	 * anon_vma list. This guarantes that if copy_huge_pmd() runs
1853 	 * and establishes a child pmd before
1854 	 * __split_huge_page_splitting() freezes the parent pmd (so if
1855 	 * we fail to prevent copy_huge_pmd() from running until the
1856 	 * whole __split_huge_page() is complete), we will still see
1857 	 * the newly established pmd of the child later during the
1858 	 * walk, to be able to set it as pmd_trans_splitting too.
1859 	 */
1860 	if (mapcount != page_mapcount(page)) {
1861 		pr_err("mapcount %d page_mapcount %d\n",
1862 			mapcount, page_mapcount(page));
1863 		BUG();
1864 	}
1865 
1866 	__split_huge_page_refcount(page, list);
1867 
1868 	mapcount2 = 0;
1869 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1870 		struct vm_area_struct *vma = avc->vma;
1871 		unsigned long addr = vma_address(page, vma);
1872 		BUG_ON(is_vma_temporary_stack(vma));
1873 		mapcount2 += __split_huge_page_map(page, vma, addr);
1874 	}
1875 	if (mapcount != mapcount2) {
1876 		pr_err("mapcount %d mapcount2 %d page_mapcount %d\n",
1877 			mapcount, mapcount2, page_mapcount(page));
1878 		BUG();
1879 	}
1880 }
1881 
1882 /*
1883  * Split a hugepage into normal pages. This doesn't change the position of head
1884  * page. If @list is null, tail pages will be added to LRU list, otherwise, to
1885  * @list. Both head page and tail pages will inherit mapping, flags, and so on
1886  * from the hugepage.
1887  * Return 0 if the hugepage is split successfully otherwise return 1.
1888  */
1889 int split_huge_page_to_list(struct page *page, struct list_head *list)
1890 {
1891 	struct anon_vma *anon_vma;
1892 	int ret = 1;
1893 
1894 	BUG_ON(is_huge_zero_page(page));
1895 	BUG_ON(!PageAnon(page));
1896 
1897 	/*
1898 	 * The caller does not necessarily hold an mmap_sem that would prevent
1899 	 * the anon_vma disappearing so we first we take a reference to it
1900 	 * and then lock the anon_vma for write. This is similar to
1901 	 * page_lock_anon_vma_read except the write lock is taken to serialise
1902 	 * against parallel split or collapse operations.
1903 	 */
1904 	anon_vma = page_get_anon_vma(page);
1905 	if (!anon_vma)
1906 		goto out;
1907 	anon_vma_lock_write(anon_vma);
1908 
1909 	ret = 0;
1910 	if (!PageCompound(page))
1911 		goto out_unlock;
1912 
1913 	BUG_ON(!PageSwapBacked(page));
1914 	__split_huge_page(page, anon_vma, list);
1915 	count_vm_event(THP_SPLIT);
1916 
1917 	BUG_ON(PageCompound(page));
1918 out_unlock:
1919 	anon_vma_unlock_write(anon_vma);
1920 	put_anon_vma(anon_vma);
1921 out:
1922 	return ret;
1923 }
1924 
1925 #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE)
1926 
1927 int hugepage_madvise(struct vm_area_struct *vma,
1928 		     unsigned long *vm_flags, int advice)
1929 {
1930 	switch (advice) {
1931 	case MADV_HUGEPAGE:
1932 #ifdef CONFIG_S390
1933 		/*
1934 		 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
1935 		 * can't handle this properly after s390_enable_sie, so we simply
1936 		 * ignore the madvise to prevent qemu from causing a SIGSEGV.
1937 		 */
1938 		if (mm_has_pgste(vma->vm_mm))
1939 			return 0;
1940 #endif
1941 		/*
1942 		 * Be somewhat over-protective like KSM for now!
1943 		 */
1944 		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
1945 			return -EINVAL;
1946 		*vm_flags &= ~VM_NOHUGEPAGE;
1947 		*vm_flags |= VM_HUGEPAGE;
1948 		/*
1949 		 * If the vma become good for khugepaged to scan,
1950 		 * register it here without waiting a page fault that
1951 		 * may not happen any time soon.
1952 		 */
1953 		if (unlikely(khugepaged_enter_vma_merge(vma, *vm_flags)))
1954 			return -ENOMEM;
1955 		break;
1956 	case MADV_NOHUGEPAGE:
1957 		/*
1958 		 * Be somewhat over-protective like KSM for now!
1959 		 */
1960 		if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
1961 			return -EINVAL;
1962 		*vm_flags &= ~VM_HUGEPAGE;
1963 		*vm_flags |= VM_NOHUGEPAGE;
1964 		/*
1965 		 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
1966 		 * this vma even if we leave the mm registered in khugepaged if
1967 		 * it got registered before VM_NOHUGEPAGE was set.
1968 		 */
1969 		break;
1970 	}
1971 
1972 	return 0;
1973 }
1974 
1975 static int __init khugepaged_slab_init(void)
1976 {
1977 	mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
1978 					  sizeof(struct mm_slot),
1979 					  __alignof__(struct mm_slot), 0, NULL);
1980 	if (!mm_slot_cache)
1981 		return -ENOMEM;
1982 
1983 	return 0;
1984 }
1985 
1986 static void __init khugepaged_slab_exit(void)
1987 {
1988 	kmem_cache_destroy(mm_slot_cache);
1989 }
1990 
1991 static inline struct mm_slot *alloc_mm_slot(void)
1992 {
1993 	if (!mm_slot_cache)	/* initialization failed */
1994 		return NULL;
1995 	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
1996 }
1997 
1998 static inline void free_mm_slot(struct mm_slot *mm_slot)
1999 {
2000 	kmem_cache_free(mm_slot_cache, mm_slot);
2001 }
2002 
2003 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
2004 {
2005 	struct mm_slot *mm_slot;
2006 
2007 	hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
2008 		if (mm == mm_slot->mm)
2009 			return mm_slot;
2010 
2011 	return NULL;
2012 }
2013 
2014 static void insert_to_mm_slots_hash(struct mm_struct *mm,
2015 				    struct mm_slot *mm_slot)
2016 {
2017 	mm_slot->mm = mm;
2018 	hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
2019 }
2020 
2021 static inline int khugepaged_test_exit(struct mm_struct *mm)
2022 {
2023 	return atomic_read(&mm->mm_users) == 0;
2024 }
2025 
2026 int __khugepaged_enter(struct mm_struct *mm)
2027 {
2028 	struct mm_slot *mm_slot;
2029 	int wakeup;
2030 
2031 	mm_slot = alloc_mm_slot();
2032 	if (!mm_slot)
2033 		return -ENOMEM;
2034 
2035 	/* __khugepaged_exit() must not run from under us */
2036 	VM_BUG_ON_MM(khugepaged_test_exit(mm), mm);
2037 	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
2038 		free_mm_slot(mm_slot);
2039 		return 0;
2040 	}
2041 
2042 	spin_lock(&khugepaged_mm_lock);
2043 	insert_to_mm_slots_hash(mm, mm_slot);
2044 	/*
2045 	 * Insert just behind the scanning cursor, to let the area settle
2046 	 * down a little.
2047 	 */
2048 	wakeup = list_empty(&khugepaged_scan.mm_head);
2049 	list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
2050 	spin_unlock(&khugepaged_mm_lock);
2051 
2052 	atomic_inc(&mm->mm_count);
2053 	if (wakeup)
2054 		wake_up_interruptible(&khugepaged_wait);
2055 
2056 	return 0;
2057 }
2058 
2059 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
2060 			       unsigned long vm_flags)
2061 {
2062 	unsigned long hstart, hend;
2063 	if (!vma->anon_vma)
2064 		/*
2065 		 * Not yet faulted in so we will register later in the
2066 		 * page fault if needed.
2067 		 */
2068 		return 0;
2069 	if (vma->vm_ops)
2070 		/* khugepaged not yet working on file or special mappings */
2071 		return 0;
2072 	VM_BUG_ON_VMA(vm_flags & VM_NO_THP, vma);
2073 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2074 	hend = vma->vm_end & HPAGE_PMD_MASK;
2075 	if (hstart < hend)
2076 		return khugepaged_enter(vma, vm_flags);
2077 	return 0;
2078 }
2079 
2080 void __khugepaged_exit(struct mm_struct *mm)
2081 {
2082 	struct mm_slot *mm_slot;
2083 	int free = 0;
2084 
2085 	spin_lock(&khugepaged_mm_lock);
2086 	mm_slot = get_mm_slot(mm);
2087 	if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
2088 		hash_del(&mm_slot->hash);
2089 		list_del(&mm_slot->mm_node);
2090 		free = 1;
2091 	}
2092 	spin_unlock(&khugepaged_mm_lock);
2093 
2094 	if (free) {
2095 		clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2096 		free_mm_slot(mm_slot);
2097 		mmdrop(mm);
2098 	} else if (mm_slot) {
2099 		/*
2100 		 * This is required to serialize against
2101 		 * khugepaged_test_exit() (which is guaranteed to run
2102 		 * under mmap sem read mode). Stop here (after we
2103 		 * return all pagetables will be destroyed) until
2104 		 * khugepaged has finished working on the pagetables
2105 		 * under the mmap_sem.
2106 		 */
2107 		down_write(&mm->mmap_sem);
2108 		up_write(&mm->mmap_sem);
2109 	}
2110 }
2111 
2112 static void release_pte_page(struct page *page)
2113 {
2114 	/* 0 stands for page_is_file_cache(page) == false */
2115 	dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
2116 	unlock_page(page);
2117 	putback_lru_page(page);
2118 }
2119 
2120 static void release_pte_pages(pte_t *pte, pte_t *_pte)
2121 {
2122 	while (--_pte >= pte) {
2123 		pte_t pteval = *_pte;
2124 		if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
2125 			release_pte_page(pte_page(pteval));
2126 	}
2127 }
2128 
2129 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
2130 					unsigned long address,
2131 					pte_t *pte)
2132 {
2133 	struct page *page;
2134 	pte_t *_pte;
2135 	int none_or_zero = 0;
2136 	bool referenced = false, writable = false;
2137 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
2138 	     _pte++, address += PAGE_SIZE) {
2139 		pte_t pteval = *_pte;
2140 		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2141 			if (++none_or_zero <= khugepaged_max_ptes_none)
2142 				continue;
2143 			else
2144 				goto out;
2145 		}
2146 		if (!pte_present(pteval))
2147 			goto out;
2148 		page = vm_normal_page(vma, address, pteval);
2149 		if (unlikely(!page))
2150 			goto out;
2151 
2152 		VM_BUG_ON_PAGE(PageCompound(page), page);
2153 		VM_BUG_ON_PAGE(!PageAnon(page), page);
2154 		VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2155 
2156 		/*
2157 		 * We can do it before isolate_lru_page because the
2158 		 * page can't be freed from under us. NOTE: PG_lock
2159 		 * is needed to serialize against split_huge_page
2160 		 * when invoked from the VM.
2161 		 */
2162 		if (!trylock_page(page))
2163 			goto out;
2164 
2165 		/*
2166 		 * cannot use mapcount: can't collapse if there's a gup pin.
2167 		 * The page must only be referenced by the scanned process
2168 		 * and page swap cache.
2169 		 */
2170 		if (page_count(page) != 1 + !!PageSwapCache(page)) {
2171 			unlock_page(page);
2172 			goto out;
2173 		}
2174 		if (pte_write(pteval)) {
2175 			writable = true;
2176 		} else {
2177 			if (PageSwapCache(page) && !reuse_swap_page(page)) {
2178 				unlock_page(page);
2179 				goto out;
2180 			}
2181 			/*
2182 			 * Page is not in the swap cache. It can be collapsed
2183 			 * into a THP.
2184 			 */
2185 		}
2186 
2187 		/*
2188 		 * Isolate the page to avoid collapsing an hugepage
2189 		 * currently in use by the VM.
2190 		 */
2191 		if (isolate_lru_page(page)) {
2192 			unlock_page(page);
2193 			goto out;
2194 		}
2195 		/* 0 stands for page_is_file_cache(page) == false */
2196 		inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
2197 		VM_BUG_ON_PAGE(!PageLocked(page), page);
2198 		VM_BUG_ON_PAGE(PageLRU(page), page);
2199 
2200 		/* If there is no mapped pte young don't collapse the page */
2201 		if (pte_young(pteval) || PageReferenced(page) ||
2202 		    mmu_notifier_test_young(vma->vm_mm, address))
2203 			referenced = true;
2204 	}
2205 	if (likely(referenced && writable))
2206 		return 1;
2207 out:
2208 	release_pte_pages(pte, _pte);
2209 	return 0;
2210 }
2211 
2212 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
2213 				      struct vm_area_struct *vma,
2214 				      unsigned long address,
2215 				      spinlock_t *ptl)
2216 {
2217 	pte_t *_pte;
2218 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2219 		pte_t pteval = *_pte;
2220 		struct page *src_page;
2221 
2222 		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2223 			clear_user_highpage(page, address);
2224 			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2225 			if (is_zero_pfn(pte_pfn(pteval))) {
2226 				/*
2227 				 * ptl mostly unnecessary.
2228 				 */
2229 				spin_lock(ptl);
2230 				/*
2231 				 * paravirt calls inside pte_clear here are
2232 				 * superfluous.
2233 				 */
2234 				pte_clear(vma->vm_mm, address, _pte);
2235 				spin_unlock(ptl);
2236 			}
2237 		} else {
2238 			src_page = pte_page(pteval);
2239 			copy_user_highpage(page, src_page, address, vma);
2240 			VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page);
2241 			release_pte_page(src_page);
2242 			/*
2243 			 * ptl mostly unnecessary, but preempt has to
2244 			 * be disabled to update the per-cpu stats
2245 			 * inside page_remove_rmap().
2246 			 */
2247 			spin_lock(ptl);
2248 			/*
2249 			 * paravirt calls inside pte_clear here are
2250 			 * superfluous.
2251 			 */
2252 			pte_clear(vma->vm_mm, address, _pte);
2253 			page_remove_rmap(src_page);
2254 			spin_unlock(ptl);
2255 			free_page_and_swap_cache(src_page);
2256 		}
2257 
2258 		address += PAGE_SIZE;
2259 		page++;
2260 	}
2261 }
2262 
2263 static void khugepaged_alloc_sleep(void)
2264 {
2265 	wait_event_freezable_timeout(khugepaged_wait, false,
2266 			msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2267 }
2268 
2269 static int khugepaged_node_load[MAX_NUMNODES];
2270 
2271 static bool khugepaged_scan_abort(int nid)
2272 {
2273 	int i;
2274 
2275 	/*
2276 	 * If zone_reclaim_mode is disabled, then no extra effort is made to
2277 	 * allocate memory locally.
2278 	 */
2279 	if (!zone_reclaim_mode)
2280 		return false;
2281 
2282 	/* If there is a count for this node already, it must be acceptable */
2283 	if (khugepaged_node_load[nid])
2284 		return false;
2285 
2286 	for (i = 0; i < MAX_NUMNODES; i++) {
2287 		if (!khugepaged_node_load[i])
2288 			continue;
2289 		if (node_distance(nid, i) > RECLAIM_DISTANCE)
2290 			return true;
2291 	}
2292 	return false;
2293 }
2294 
2295 #ifdef CONFIG_NUMA
2296 static int khugepaged_find_target_node(void)
2297 {
2298 	static int last_khugepaged_target_node = NUMA_NO_NODE;
2299 	int nid, target_node = 0, max_value = 0;
2300 
2301 	/* find first node with max normal pages hit */
2302 	for (nid = 0; nid < MAX_NUMNODES; nid++)
2303 		if (khugepaged_node_load[nid] > max_value) {
2304 			max_value = khugepaged_node_load[nid];
2305 			target_node = nid;
2306 		}
2307 
2308 	/* do some balance if several nodes have the same hit record */
2309 	if (target_node <= last_khugepaged_target_node)
2310 		for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
2311 				nid++)
2312 			if (max_value == khugepaged_node_load[nid]) {
2313 				target_node = nid;
2314 				break;
2315 			}
2316 
2317 	last_khugepaged_target_node = target_node;
2318 	return target_node;
2319 }
2320 
2321 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2322 {
2323 	if (IS_ERR(*hpage)) {
2324 		if (!*wait)
2325 			return false;
2326 
2327 		*wait = false;
2328 		*hpage = NULL;
2329 		khugepaged_alloc_sleep();
2330 	} else if (*hpage) {
2331 		put_page(*hpage);
2332 		*hpage = NULL;
2333 	}
2334 
2335 	return true;
2336 }
2337 
2338 static struct page *
2339 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
2340 		       struct vm_area_struct *vma, unsigned long address,
2341 		       int node)
2342 {
2343 	VM_BUG_ON_PAGE(*hpage, *hpage);
2344 
2345 	/*
2346 	 * Before allocating the hugepage, release the mmap_sem read lock.
2347 	 * The allocation can take potentially a long time if it involves
2348 	 * sync compaction, and we do not need to hold the mmap_sem during
2349 	 * that. We will recheck the vma after taking it again in write mode.
2350 	 */
2351 	up_read(&mm->mmap_sem);
2352 
2353 	*hpage = alloc_pages_exact_node(node, gfp, HPAGE_PMD_ORDER);
2354 	if (unlikely(!*hpage)) {
2355 		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2356 		*hpage = ERR_PTR(-ENOMEM);
2357 		return NULL;
2358 	}
2359 
2360 	count_vm_event(THP_COLLAPSE_ALLOC);
2361 	return *hpage;
2362 }
2363 #else
2364 static int khugepaged_find_target_node(void)
2365 {
2366 	return 0;
2367 }
2368 
2369 static inline struct page *alloc_hugepage(int defrag)
2370 {
2371 	return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
2372 			   HPAGE_PMD_ORDER);
2373 }
2374 
2375 static struct page *khugepaged_alloc_hugepage(bool *wait)
2376 {
2377 	struct page *hpage;
2378 
2379 	do {
2380 		hpage = alloc_hugepage(khugepaged_defrag());
2381 		if (!hpage) {
2382 			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2383 			if (!*wait)
2384 				return NULL;
2385 
2386 			*wait = false;
2387 			khugepaged_alloc_sleep();
2388 		} else
2389 			count_vm_event(THP_COLLAPSE_ALLOC);
2390 	} while (unlikely(!hpage) && likely(khugepaged_enabled()));
2391 
2392 	return hpage;
2393 }
2394 
2395 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2396 {
2397 	if (!*hpage)
2398 		*hpage = khugepaged_alloc_hugepage(wait);
2399 
2400 	if (unlikely(!*hpage))
2401 		return false;
2402 
2403 	return true;
2404 }
2405 
2406 static struct page *
2407 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, struct mm_struct *mm,
2408 		       struct vm_area_struct *vma, unsigned long address,
2409 		       int node)
2410 {
2411 	up_read(&mm->mmap_sem);
2412 	VM_BUG_ON(!*hpage);
2413 
2414 	return  *hpage;
2415 }
2416 #endif
2417 
2418 static bool hugepage_vma_check(struct vm_area_struct *vma)
2419 {
2420 	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2421 	    (vma->vm_flags & VM_NOHUGEPAGE))
2422 		return false;
2423 
2424 	if (!vma->anon_vma || vma->vm_ops)
2425 		return false;
2426 	if (is_vma_temporary_stack(vma))
2427 		return false;
2428 	VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma);
2429 	return true;
2430 }
2431 
2432 static void collapse_huge_page(struct mm_struct *mm,
2433 				   unsigned long address,
2434 				   struct page **hpage,
2435 				   struct vm_area_struct *vma,
2436 				   int node)
2437 {
2438 	pmd_t *pmd, _pmd;
2439 	pte_t *pte;
2440 	pgtable_t pgtable;
2441 	struct page *new_page;
2442 	spinlock_t *pmd_ptl, *pte_ptl;
2443 	int isolated;
2444 	unsigned long hstart, hend;
2445 	struct mem_cgroup *memcg;
2446 	unsigned long mmun_start;	/* For mmu_notifiers */
2447 	unsigned long mmun_end;		/* For mmu_notifiers */
2448 	gfp_t gfp;
2449 
2450 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2451 
2452 	/* Only allocate from the target node */
2453 	gfp = alloc_hugepage_gfpmask(khugepaged_defrag(), __GFP_OTHER_NODE) |
2454 		__GFP_THISNODE;
2455 
2456 	/* release the mmap_sem read lock. */
2457 	new_page = khugepaged_alloc_page(hpage, gfp, mm, vma, address, node);
2458 	if (!new_page)
2459 		return;
2460 
2461 	if (unlikely(mem_cgroup_try_charge(new_page, mm,
2462 					   gfp, &memcg)))
2463 		return;
2464 
2465 	/*
2466 	 * Prevent all access to pagetables with the exception of
2467 	 * gup_fast later hanlded by the ptep_clear_flush and the VM
2468 	 * handled by the anon_vma lock + PG_lock.
2469 	 */
2470 	down_write(&mm->mmap_sem);
2471 	if (unlikely(khugepaged_test_exit(mm)))
2472 		goto out;
2473 
2474 	vma = find_vma(mm, address);
2475 	if (!vma)
2476 		goto out;
2477 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2478 	hend = vma->vm_end & HPAGE_PMD_MASK;
2479 	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2480 		goto out;
2481 	if (!hugepage_vma_check(vma))
2482 		goto out;
2483 	pmd = mm_find_pmd(mm, address);
2484 	if (!pmd)
2485 		goto out;
2486 
2487 	anon_vma_lock_write(vma->anon_vma);
2488 
2489 	pte = pte_offset_map(pmd, address);
2490 	pte_ptl = pte_lockptr(mm, pmd);
2491 
2492 	mmun_start = address;
2493 	mmun_end   = address + HPAGE_PMD_SIZE;
2494 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2495 	pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
2496 	/*
2497 	 * After this gup_fast can't run anymore. This also removes
2498 	 * any huge TLB entry from the CPU so we won't allow
2499 	 * huge and small TLB entries for the same virtual address
2500 	 * to avoid the risk of CPU bugs in that area.
2501 	 */
2502 	_pmd = pmdp_clear_flush(vma, address, pmd);
2503 	spin_unlock(pmd_ptl);
2504 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2505 
2506 	spin_lock(pte_ptl);
2507 	isolated = __collapse_huge_page_isolate(vma, address, pte);
2508 	spin_unlock(pte_ptl);
2509 
2510 	if (unlikely(!isolated)) {
2511 		pte_unmap(pte);
2512 		spin_lock(pmd_ptl);
2513 		BUG_ON(!pmd_none(*pmd));
2514 		/*
2515 		 * We can only use set_pmd_at when establishing
2516 		 * hugepmds and never for establishing regular pmds that
2517 		 * points to regular pagetables. Use pmd_populate for that
2518 		 */
2519 		pmd_populate(mm, pmd, pmd_pgtable(_pmd));
2520 		spin_unlock(pmd_ptl);
2521 		anon_vma_unlock_write(vma->anon_vma);
2522 		goto out;
2523 	}
2524 
2525 	/*
2526 	 * All pages are isolated and locked so anon_vma rmap
2527 	 * can't run anymore.
2528 	 */
2529 	anon_vma_unlock_write(vma->anon_vma);
2530 
2531 	__collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
2532 	pte_unmap(pte);
2533 	__SetPageUptodate(new_page);
2534 	pgtable = pmd_pgtable(_pmd);
2535 
2536 	_pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
2537 	_pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
2538 
2539 	/*
2540 	 * spin_lock() below is not the equivalent of smp_wmb(), so
2541 	 * this is needed to avoid the copy_huge_page writes to become
2542 	 * visible after the set_pmd_at() write.
2543 	 */
2544 	smp_wmb();
2545 
2546 	spin_lock(pmd_ptl);
2547 	BUG_ON(!pmd_none(*pmd));
2548 	page_add_new_anon_rmap(new_page, vma, address);
2549 	mem_cgroup_commit_charge(new_page, memcg, false);
2550 	lru_cache_add_active_or_unevictable(new_page, vma);
2551 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
2552 	set_pmd_at(mm, address, pmd, _pmd);
2553 	update_mmu_cache_pmd(vma, address, pmd);
2554 	spin_unlock(pmd_ptl);
2555 
2556 	*hpage = NULL;
2557 
2558 	khugepaged_pages_collapsed++;
2559 out_up_write:
2560 	up_write(&mm->mmap_sem);
2561 	return;
2562 
2563 out:
2564 	mem_cgroup_cancel_charge(new_page, memcg);
2565 	goto out_up_write;
2566 }
2567 
2568 static int khugepaged_scan_pmd(struct mm_struct *mm,
2569 			       struct vm_area_struct *vma,
2570 			       unsigned long address,
2571 			       struct page **hpage)
2572 {
2573 	pmd_t *pmd;
2574 	pte_t *pte, *_pte;
2575 	int ret = 0, none_or_zero = 0;
2576 	struct page *page;
2577 	unsigned long _address;
2578 	spinlock_t *ptl;
2579 	int node = NUMA_NO_NODE;
2580 	bool writable = false, referenced = false;
2581 
2582 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2583 
2584 	pmd = mm_find_pmd(mm, address);
2585 	if (!pmd)
2586 		goto out;
2587 
2588 	memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
2589 	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2590 	for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2591 	     _pte++, _address += PAGE_SIZE) {
2592 		pte_t pteval = *_pte;
2593 		if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
2594 			if (++none_or_zero <= khugepaged_max_ptes_none)
2595 				continue;
2596 			else
2597 				goto out_unmap;
2598 		}
2599 		if (!pte_present(pteval))
2600 			goto out_unmap;
2601 		if (pte_write(pteval))
2602 			writable = true;
2603 
2604 		page = vm_normal_page(vma, _address, pteval);
2605 		if (unlikely(!page))
2606 			goto out_unmap;
2607 		/*
2608 		 * Record which node the original page is from and save this
2609 		 * information to khugepaged_node_load[].
2610 		 * Khupaged will allocate hugepage from the node has the max
2611 		 * hit record.
2612 		 */
2613 		node = page_to_nid(page);
2614 		if (khugepaged_scan_abort(node))
2615 			goto out_unmap;
2616 		khugepaged_node_load[node]++;
2617 		VM_BUG_ON_PAGE(PageCompound(page), page);
2618 		if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2619 			goto out_unmap;
2620 		/*
2621 		 * cannot use mapcount: can't collapse if there's a gup pin.
2622 		 * The page must only be referenced by the scanned process
2623 		 * and page swap cache.
2624 		 */
2625 		if (page_count(page) != 1 + !!PageSwapCache(page))
2626 			goto out_unmap;
2627 		if (pte_young(pteval) || PageReferenced(page) ||
2628 		    mmu_notifier_test_young(vma->vm_mm, address))
2629 			referenced = true;
2630 	}
2631 	if (referenced && writable)
2632 		ret = 1;
2633 out_unmap:
2634 	pte_unmap_unlock(pte, ptl);
2635 	if (ret) {
2636 		node = khugepaged_find_target_node();
2637 		/* collapse_huge_page will return with the mmap_sem released */
2638 		collapse_huge_page(mm, address, hpage, vma, node);
2639 	}
2640 out:
2641 	return ret;
2642 }
2643 
2644 static void collect_mm_slot(struct mm_slot *mm_slot)
2645 {
2646 	struct mm_struct *mm = mm_slot->mm;
2647 
2648 	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2649 
2650 	if (khugepaged_test_exit(mm)) {
2651 		/* free mm_slot */
2652 		hash_del(&mm_slot->hash);
2653 		list_del(&mm_slot->mm_node);
2654 
2655 		/*
2656 		 * Not strictly needed because the mm exited already.
2657 		 *
2658 		 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2659 		 */
2660 
2661 		/* khugepaged_mm_lock actually not necessary for the below */
2662 		free_mm_slot(mm_slot);
2663 		mmdrop(mm);
2664 	}
2665 }
2666 
2667 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2668 					    struct page **hpage)
2669 	__releases(&khugepaged_mm_lock)
2670 	__acquires(&khugepaged_mm_lock)
2671 {
2672 	struct mm_slot *mm_slot;
2673 	struct mm_struct *mm;
2674 	struct vm_area_struct *vma;
2675 	int progress = 0;
2676 
2677 	VM_BUG_ON(!pages);
2678 	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2679 
2680 	if (khugepaged_scan.mm_slot)
2681 		mm_slot = khugepaged_scan.mm_slot;
2682 	else {
2683 		mm_slot = list_entry(khugepaged_scan.mm_head.next,
2684 				     struct mm_slot, mm_node);
2685 		khugepaged_scan.address = 0;
2686 		khugepaged_scan.mm_slot = mm_slot;
2687 	}
2688 	spin_unlock(&khugepaged_mm_lock);
2689 
2690 	mm = mm_slot->mm;
2691 	down_read(&mm->mmap_sem);
2692 	if (unlikely(khugepaged_test_exit(mm)))
2693 		vma = NULL;
2694 	else
2695 		vma = find_vma(mm, khugepaged_scan.address);
2696 
2697 	progress++;
2698 	for (; vma; vma = vma->vm_next) {
2699 		unsigned long hstart, hend;
2700 
2701 		cond_resched();
2702 		if (unlikely(khugepaged_test_exit(mm))) {
2703 			progress++;
2704 			break;
2705 		}
2706 		if (!hugepage_vma_check(vma)) {
2707 skip:
2708 			progress++;
2709 			continue;
2710 		}
2711 		hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2712 		hend = vma->vm_end & HPAGE_PMD_MASK;
2713 		if (hstart >= hend)
2714 			goto skip;
2715 		if (khugepaged_scan.address > hend)
2716 			goto skip;
2717 		if (khugepaged_scan.address < hstart)
2718 			khugepaged_scan.address = hstart;
2719 		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2720 
2721 		while (khugepaged_scan.address < hend) {
2722 			int ret;
2723 			cond_resched();
2724 			if (unlikely(khugepaged_test_exit(mm)))
2725 				goto breakouterloop;
2726 
2727 			VM_BUG_ON(khugepaged_scan.address < hstart ||
2728 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
2729 				  hend);
2730 			ret = khugepaged_scan_pmd(mm, vma,
2731 						  khugepaged_scan.address,
2732 						  hpage);
2733 			/* move to next address */
2734 			khugepaged_scan.address += HPAGE_PMD_SIZE;
2735 			progress += HPAGE_PMD_NR;
2736 			if (ret)
2737 				/* we released mmap_sem so break loop */
2738 				goto breakouterloop_mmap_sem;
2739 			if (progress >= pages)
2740 				goto breakouterloop;
2741 		}
2742 	}
2743 breakouterloop:
2744 	up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2745 breakouterloop_mmap_sem:
2746 
2747 	spin_lock(&khugepaged_mm_lock);
2748 	VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2749 	/*
2750 	 * Release the current mm_slot if this mm is about to die, or
2751 	 * if we scanned all vmas of this mm.
2752 	 */
2753 	if (khugepaged_test_exit(mm) || !vma) {
2754 		/*
2755 		 * Make sure that if mm_users is reaching zero while
2756 		 * khugepaged runs here, khugepaged_exit will find
2757 		 * mm_slot not pointing to the exiting mm.
2758 		 */
2759 		if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2760 			khugepaged_scan.mm_slot = list_entry(
2761 				mm_slot->mm_node.next,
2762 				struct mm_slot, mm_node);
2763 			khugepaged_scan.address = 0;
2764 		} else {
2765 			khugepaged_scan.mm_slot = NULL;
2766 			khugepaged_full_scans++;
2767 		}
2768 
2769 		collect_mm_slot(mm_slot);
2770 	}
2771 
2772 	return progress;
2773 }
2774 
2775 static int khugepaged_has_work(void)
2776 {
2777 	return !list_empty(&khugepaged_scan.mm_head) &&
2778 		khugepaged_enabled();
2779 }
2780 
2781 static int khugepaged_wait_event(void)
2782 {
2783 	return !list_empty(&khugepaged_scan.mm_head) ||
2784 		kthread_should_stop();
2785 }
2786 
2787 static void khugepaged_do_scan(void)
2788 {
2789 	struct page *hpage = NULL;
2790 	unsigned int progress = 0, pass_through_head = 0;
2791 	unsigned int pages = khugepaged_pages_to_scan;
2792 	bool wait = true;
2793 
2794 	barrier(); /* write khugepaged_pages_to_scan to local stack */
2795 
2796 	while (progress < pages) {
2797 		if (!khugepaged_prealloc_page(&hpage, &wait))
2798 			break;
2799 
2800 		cond_resched();
2801 
2802 		if (unlikely(kthread_should_stop() || freezing(current)))
2803 			break;
2804 
2805 		spin_lock(&khugepaged_mm_lock);
2806 		if (!khugepaged_scan.mm_slot)
2807 			pass_through_head++;
2808 		if (khugepaged_has_work() &&
2809 		    pass_through_head < 2)
2810 			progress += khugepaged_scan_mm_slot(pages - progress,
2811 							    &hpage);
2812 		else
2813 			progress = pages;
2814 		spin_unlock(&khugepaged_mm_lock);
2815 	}
2816 
2817 	if (!IS_ERR_OR_NULL(hpage))
2818 		put_page(hpage);
2819 }
2820 
2821 static void khugepaged_wait_work(void)
2822 {
2823 	try_to_freeze();
2824 
2825 	if (khugepaged_has_work()) {
2826 		if (!khugepaged_scan_sleep_millisecs)
2827 			return;
2828 
2829 		wait_event_freezable_timeout(khugepaged_wait,
2830 					     kthread_should_stop(),
2831 			msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2832 		return;
2833 	}
2834 
2835 	if (khugepaged_enabled())
2836 		wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2837 }
2838 
2839 static int khugepaged(void *none)
2840 {
2841 	struct mm_slot *mm_slot;
2842 
2843 	set_freezable();
2844 	set_user_nice(current, MAX_NICE);
2845 
2846 	while (!kthread_should_stop()) {
2847 		khugepaged_do_scan();
2848 		khugepaged_wait_work();
2849 	}
2850 
2851 	spin_lock(&khugepaged_mm_lock);
2852 	mm_slot = khugepaged_scan.mm_slot;
2853 	khugepaged_scan.mm_slot = NULL;
2854 	if (mm_slot)
2855 		collect_mm_slot(mm_slot);
2856 	spin_unlock(&khugepaged_mm_lock);
2857 	return 0;
2858 }
2859 
2860 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2861 		unsigned long haddr, pmd_t *pmd)
2862 {
2863 	struct mm_struct *mm = vma->vm_mm;
2864 	pgtable_t pgtable;
2865 	pmd_t _pmd;
2866 	int i;
2867 
2868 	pmdp_clear_flush_notify(vma, haddr, pmd);
2869 	/* leave pmd empty until pte is filled */
2870 
2871 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2872 	pmd_populate(mm, &_pmd, pgtable);
2873 
2874 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2875 		pte_t *pte, entry;
2876 		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2877 		entry = pte_mkspecial(entry);
2878 		pte = pte_offset_map(&_pmd, haddr);
2879 		VM_BUG_ON(!pte_none(*pte));
2880 		set_pte_at(mm, haddr, pte, entry);
2881 		pte_unmap(pte);
2882 	}
2883 	smp_wmb(); /* make pte visible before pmd */
2884 	pmd_populate(mm, pmd, pgtable);
2885 	put_huge_zero_page();
2886 }
2887 
2888 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2889 		pmd_t *pmd)
2890 {
2891 	spinlock_t *ptl;
2892 	struct page *page;
2893 	struct mm_struct *mm = vma->vm_mm;
2894 	unsigned long haddr = address & HPAGE_PMD_MASK;
2895 	unsigned long mmun_start;	/* For mmu_notifiers */
2896 	unsigned long mmun_end;		/* For mmu_notifiers */
2897 
2898 	BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2899 
2900 	mmun_start = haddr;
2901 	mmun_end   = haddr + HPAGE_PMD_SIZE;
2902 again:
2903 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2904 	ptl = pmd_lock(mm, pmd);
2905 	if (unlikely(!pmd_trans_huge(*pmd))) {
2906 		spin_unlock(ptl);
2907 		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2908 		return;
2909 	}
2910 	if (is_huge_zero_pmd(*pmd)) {
2911 		__split_huge_zero_page_pmd(vma, haddr, pmd);
2912 		spin_unlock(ptl);
2913 		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2914 		return;
2915 	}
2916 	page = pmd_page(*pmd);
2917 	VM_BUG_ON_PAGE(!page_count(page), page);
2918 	get_page(page);
2919 	spin_unlock(ptl);
2920 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2921 
2922 	split_huge_page(page);
2923 
2924 	put_page(page);
2925 
2926 	/*
2927 	 * We don't always have down_write of mmap_sem here: a racing
2928 	 * do_huge_pmd_wp_page() might have copied-on-write to another
2929 	 * huge page before our split_huge_page() got the anon_vma lock.
2930 	 */
2931 	if (unlikely(pmd_trans_huge(*pmd)))
2932 		goto again;
2933 }
2934 
2935 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
2936 		pmd_t *pmd)
2937 {
2938 	struct vm_area_struct *vma;
2939 
2940 	vma = find_vma(mm, address);
2941 	BUG_ON(vma == NULL);
2942 	split_huge_page_pmd(vma, address, pmd);
2943 }
2944 
2945 static void split_huge_page_address(struct mm_struct *mm,
2946 				    unsigned long address)
2947 {
2948 	pgd_t *pgd;
2949 	pud_t *pud;
2950 	pmd_t *pmd;
2951 
2952 	VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
2953 
2954 	pgd = pgd_offset(mm, address);
2955 	if (!pgd_present(*pgd))
2956 		return;
2957 
2958 	pud = pud_offset(pgd, address);
2959 	if (!pud_present(*pud))
2960 		return;
2961 
2962 	pmd = pmd_offset(pud, address);
2963 	if (!pmd_present(*pmd))
2964 		return;
2965 	/*
2966 	 * Caller holds the mmap_sem write mode, so a huge pmd cannot
2967 	 * materialize from under us.
2968 	 */
2969 	split_huge_page_pmd_mm(mm, address, pmd);
2970 }
2971 
2972 void __vma_adjust_trans_huge(struct vm_area_struct *vma,
2973 			     unsigned long start,
2974 			     unsigned long end,
2975 			     long adjust_next)
2976 {
2977 	/*
2978 	 * If the new start address isn't hpage aligned and it could
2979 	 * previously contain an hugepage: check if we need to split
2980 	 * an huge pmd.
2981 	 */
2982 	if (start & ~HPAGE_PMD_MASK &&
2983 	    (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2984 	    (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2985 		split_huge_page_address(vma->vm_mm, start);
2986 
2987 	/*
2988 	 * If the new end address isn't hpage aligned and it could
2989 	 * previously contain an hugepage: check if we need to split
2990 	 * an huge pmd.
2991 	 */
2992 	if (end & ~HPAGE_PMD_MASK &&
2993 	    (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2994 	    (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2995 		split_huge_page_address(vma->vm_mm, end);
2996 
2997 	/*
2998 	 * If we're also updating the vma->vm_next->vm_start, if the new
2999 	 * vm_next->vm_start isn't page aligned and it could previously
3000 	 * contain an hugepage: check if we need to split an huge pmd.
3001 	 */
3002 	if (adjust_next > 0) {
3003 		struct vm_area_struct *next = vma->vm_next;
3004 		unsigned long nstart = next->vm_start;
3005 		nstart += adjust_next << PAGE_SHIFT;
3006 		if (nstart & ~HPAGE_PMD_MASK &&
3007 		    (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
3008 		    (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
3009 			split_huge_page_address(next->vm_mm, nstart);
3010 	}
3011 }
3012