xref: /openbmc/linux/mm/huge_memory.c (revision ee8a99bd)
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 #include <linux/mm.h>
9 #include <linux/sched.h>
10 #include <linux/highmem.h>
11 #include <linux/hugetlb.h>
12 #include <linux/mmu_notifier.h>
13 #include <linux/rmap.h>
14 #include <linux/swap.h>
15 #include <linux/shrinker.h>
16 #include <linux/mm_inline.h>
17 #include <linux/kthread.h>
18 #include <linux/khugepaged.h>
19 #include <linux/freezer.h>
20 #include <linux/mman.h>
21 #include <linux/pagemap.h>
22 #include <linux/migrate.h>
23 #include <linux/hashtable.h>
24 
25 #include <asm/tlb.h>
26 #include <asm/pgalloc.h>
27 #include "internal.h"
28 
29 /*
30  * By default transparent hugepage support is enabled for all mappings
31  * and khugepaged scans all mappings. Defrag is only invoked by
32  * khugepaged hugepage allocations and by page faults inside
33  * MADV_HUGEPAGE regions to avoid the risk of slowing down short lived
34  * allocations.
35  */
36 unsigned long transparent_hugepage_flags __read_mostly =
37 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
38 	(1<<TRANSPARENT_HUGEPAGE_FLAG)|
39 #endif
40 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
41 	(1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
42 #endif
43 	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
44 	(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
45 	(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
46 
47 /* default scan 8*512 pte (or vmas) every 30 second */
48 static unsigned int khugepaged_pages_to_scan __read_mostly = HPAGE_PMD_NR*8;
49 static unsigned int khugepaged_pages_collapsed;
50 static unsigned int khugepaged_full_scans;
51 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
52 /* during fragmentation poll the hugepage allocator once every minute */
53 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
54 static struct task_struct *khugepaged_thread __read_mostly;
55 static DEFINE_MUTEX(khugepaged_mutex);
56 static DEFINE_SPINLOCK(khugepaged_mm_lock);
57 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
58 /*
59  * default collapse hugepages if there is at least one pte mapped like
60  * it would have happened if the vma was large enough during page
61  * fault.
62  */
63 static unsigned int khugepaged_max_ptes_none __read_mostly = HPAGE_PMD_NR-1;
64 
65 static int khugepaged(void *none);
66 static int khugepaged_slab_init(void);
67 
68 #define MM_SLOTS_HASH_BITS 10
69 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
70 
71 static struct kmem_cache *mm_slot_cache __read_mostly;
72 
73 /**
74  * struct mm_slot - hash lookup from mm to mm_slot
75  * @hash: hash collision list
76  * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
77  * @mm: the mm that this information is valid for
78  */
79 struct mm_slot {
80 	struct hlist_node hash;
81 	struct list_head mm_node;
82 	struct mm_struct *mm;
83 };
84 
85 /**
86  * struct khugepaged_scan - cursor for scanning
87  * @mm_head: the head of the mm list to scan
88  * @mm_slot: the current mm_slot we are scanning
89  * @address: the next address inside that to be scanned
90  *
91  * There is only the one khugepaged_scan instance of this cursor structure.
92  */
93 struct khugepaged_scan {
94 	struct list_head mm_head;
95 	struct mm_slot *mm_slot;
96 	unsigned long address;
97 };
98 static struct khugepaged_scan khugepaged_scan = {
99 	.mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
100 };
101 
102 
103 static int set_recommended_min_free_kbytes(void)
104 {
105 	struct zone *zone;
106 	int nr_zones = 0;
107 	unsigned long recommended_min;
108 
109 	if (!khugepaged_enabled())
110 		return 0;
111 
112 	for_each_populated_zone(zone)
113 		nr_zones++;
114 
115 	/* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
116 	recommended_min = pageblock_nr_pages * nr_zones * 2;
117 
118 	/*
119 	 * Make sure that on average at least two pageblocks are almost free
120 	 * of another type, one for a migratetype to fall back to and a
121 	 * second to avoid subsequent fallbacks of other types There are 3
122 	 * MIGRATE_TYPES we care about.
123 	 */
124 	recommended_min += pageblock_nr_pages * nr_zones *
125 			   MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
126 
127 	/* don't ever allow to reserve more than 5% of the lowmem */
128 	recommended_min = min(recommended_min,
129 			      (unsigned long) nr_free_buffer_pages() / 20);
130 	recommended_min <<= (PAGE_SHIFT-10);
131 
132 	if (recommended_min > min_free_kbytes)
133 		min_free_kbytes = recommended_min;
134 	setup_per_zone_wmarks();
135 	return 0;
136 }
137 late_initcall(set_recommended_min_free_kbytes);
138 
139 static int start_khugepaged(void)
140 {
141 	int err = 0;
142 	if (khugepaged_enabled()) {
143 		if (!khugepaged_thread)
144 			khugepaged_thread = kthread_run(khugepaged, NULL,
145 							"khugepaged");
146 		if (unlikely(IS_ERR(khugepaged_thread))) {
147 			printk(KERN_ERR
148 			       "khugepaged: kthread_run(khugepaged) failed\n");
149 			err = PTR_ERR(khugepaged_thread);
150 			khugepaged_thread = NULL;
151 		}
152 
153 		if (!list_empty(&khugepaged_scan.mm_head))
154 			wake_up_interruptible(&khugepaged_wait);
155 
156 		set_recommended_min_free_kbytes();
157 	} else if (khugepaged_thread) {
158 		kthread_stop(khugepaged_thread);
159 		khugepaged_thread = NULL;
160 	}
161 
162 	return err;
163 }
164 
165 static atomic_t huge_zero_refcount;
166 static struct page *huge_zero_page __read_mostly;
167 
168 static inline bool is_huge_zero_page(struct page *page)
169 {
170 	return ACCESS_ONCE(huge_zero_page) == page;
171 }
172 
173 static inline bool is_huge_zero_pmd(pmd_t pmd)
174 {
175 	return is_huge_zero_page(pmd_page(pmd));
176 }
177 
178 static struct page *get_huge_zero_page(void)
179 {
180 	struct page *zero_page;
181 retry:
182 	if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
183 		return ACCESS_ONCE(huge_zero_page);
184 
185 	zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
186 			HPAGE_PMD_ORDER);
187 	if (!zero_page) {
188 		count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
189 		return NULL;
190 	}
191 	count_vm_event(THP_ZERO_PAGE_ALLOC);
192 	preempt_disable();
193 	if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
194 		preempt_enable();
195 		__free_page(zero_page);
196 		goto retry;
197 	}
198 
199 	/* We take additional reference here. It will be put back by shrinker */
200 	atomic_set(&huge_zero_refcount, 2);
201 	preempt_enable();
202 	return ACCESS_ONCE(huge_zero_page);
203 }
204 
205 static void put_huge_zero_page(void)
206 {
207 	/*
208 	 * Counter should never go to zero here. Only shrinker can put
209 	 * last reference.
210 	 */
211 	BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
212 }
213 
214 static int shrink_huge_zero_page(struct shrinker *shrink,
215 		struct shrink_control *sc)
216 {
217 	if (!sc->nr_to_scan)
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 	if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
222 		struct page *zero_page = xchg(&huge_zero_page, NULL);
223 		BUG_ON(zero_page == NULL);
224 		__free_page(zero_page);
225 	}
226 
227 	return 0;
228 }
229 
230 static struct shrinker huge_zero_page_shrinker = {
231 	.shrink = shrink_huge_zero_page,
232 	.seeks = DEFAULT_SEEKS,
233 };
234 
235 #ifdef CONFIG_SYSFS
236 
237 static ssize_t double_flag_show(struct kobject *kobj,
238 				struct kobj_attribute *attr, char *buf,
239 				enum transparent_hugepage_flag enabled,
240 				enum transparent_hugepage_flag req_madv)
241 {
242 	if (test_bit(enabled, &transparent_hugepage_flags)) {
243 		VM_BUG_ON(test_bit(req_madv, &transparent_hugepage_flags));
244 		return sprintf(buf, "[always] madvise never\n");
245 	} else if (test_bit(req_madv, &transparent_hugepage_flags))
246 		return sprintf(buf, "always [madvise] never\n");
247 	else
248 		return sprintf(buf, "always madvise [never]\n");
249 }
250 static ssize_t double_flag_store(struct kobject *kobj,
251 				 struct kobj_attribute *attr,
252 				 const char *buf, size_t count,
253 				 enum transparent_hugepage_flag enabled,
254 				 enum transparent_hugepage_flag req_madv)
255 {
256 	if (!memcmp("always", buf,
257 		    min(sizeof("always")-1, count))) {
258 		set_bit(enabled, &transparent_hugepage_flags);
259 		clear_bit(req_madv, &transparent_hugepage_flags);
260 	} else if (!memcmp("madvise", buf,
261 			   min(sizeof("madvise")-1, count))) {
262 		clear_bit(enabled, &transparent_hugepage_flags);
263 		set_bit(req_madv, &transparent_hugepage_flags);
264 	} else if (!memcmp("never", buf,
265 			   min(sizeof("never")-1, count))) {
266 		clear_bit(enabled, &transparent_hugepage_flags);
267 		clear_bit(req_madv, &transparent_hugepage_flags);
268 	} else
269 		return -EINVAL;
270 
271 	return count;
272 }
273 
274 static ssize_t enabled_show(struct kobject *kobj,
275 			    struct kobj_attribute *attr, char *buf)
276 {
277 	return double_flag_show(kobj, attr, buf,
278 				TRANSPARENT_HUGEPAGE_FLAG,
279 				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
280 }
281 static ssize_t enabled_store(struct kobject *kobj,
282 			     struct kobj_attribute *attr,
283 			     const char *buf, size_t count)
284 {
285 	ssize_t ret;
286 
287 	ret = double_flag_store(kobj, attr, buf, count,
288 				TRANSPARENT_HUGEPAGE_FLAG,
289 				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
290 
291 	if (ret > 0) {
292 		int err;
293 
294 		mutex_lock(&khugepaged_mutex);
295 		err = start_khugepaged();
296 		mutex_unlock(&khugepaged_mutex);
297 
298 		if (err)
299 			ret = err;
300 	}
301 
302 	return ret;
303 }
304 static struct kobj_attribute enabled_attr =
305 	__ATTR(enabled, 0644, enabled_show, enabled_store);
306 
307 static ssize_t single_flag_show(struct kobject *kobj,
308 				struct kobj_attribute *attr, char *buf,
309 				enum transparent_hugepage_flag flag)
310 {
311 	return sprintf(buf, "%d\n",
312 		       !!test_bit(flag, &transparent_hugepage_flags));
313 }
314 
315 static ssize_t single_flag_store(struct kobject *kobj,
316 				 struct kobj_attribute *attr,
317 				 const char *buf, size_t count,
318 				 enum transparent_hugepage_flag flag)
319 {
320 	unsigned long value;
321 	int ret;
322 
323 	ret = kstrtoul(buf, 10, &value);
324 	if (ret < 0)
325 		return ret;
326 	if (value > 1)
327 		return -EINVAL;
328 
329 	if (value)
330 		set_bit(flag, &transparent_hugepage_flags);
331 	else
332 		clear_bit(flag, &transparent_hugepage_flags);
333 
334 	return count;
335 }
336 
337 /*
338  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
339  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
340  * memory just to allocate one more hugepage.
341  */
342 static ssize_t defrag_show(struct kobject *kobj,
343 			   struct kobj_attribute *attr, char *buf)
344 {
345 	return double_flag_show(kobj, attr, buf,
346 				TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
347 				TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
348 }
349 static ssize_t defrag_store(struct kobject *kobj,
350 			    struct kobj_attribute *attr,
351 			    const char *buf, size_t count)
352 {
353 	return double_flag_store(kobj, attr, buf, count,
354 				 TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
355 				 TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
356 }
357 static struct kobj_attribute defrag_attr =
358 	__ATTR(defrag, 0644, defrag_show, defrag_store);
359 
360 static ssize_t use_zero_page_show(struct kobject *kobj,
361 		struct kobj_attribute *attr, char *buf)
362 {
363 	return single_flag_show(kobj, attr, buf,
364 				TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
365 }
366 static ssize_t use_zero_page_store(struct kobject *kobj,
367 		struct kobj_attribute *attr, const char *buf, size_t count)
368 {
369 	return single_flag_store(kobj, attr, buf, count,
370 				 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
371 }
372 static struct kobj_attribute use_zero_page_attr =
373 	__ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
374 #ifdef CONFIG_DEBUG_VM
375 static ssize_t debug_cow_show(struct kobject *kobj,
376 				struct kobj_attribute *attr, char *buf)
377 {
378 	return single_flag_show(kobj, attr, buf,
379 				TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
380 }
381 static ssize_t debug_cow_store(struct kobject *kobj,
382 			       struct kobj_attribute *attr,
383 			       const char *buf, size_t count)
384 {
385 	return single_flag_store(kobj, attr, buf, count,
386 				 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
387 }
388 static struct kobj_attribute debug_cow_attr =
389 	__ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
390 #endif /* CONFIG_DEBUG_VM */
391 
392 static struct attribute *hugepage_attr[] = {
393 	&enabled_attr.attr,
394 	&defrag_attr.attr,
395 	&use_zero_page_attr.attr,
396 #ifdef CONFIG_DEBUG_VM
397 	&debug_cow_attr.attr,
398 #endif
399 	NULL,
400 };
401 
402 static struct attribute_group hugepage_attr_group = {
403 	.attrs = hugepage_attr,
404 };
405 
406 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
407 					 struct kobj_attribute *attr,
408 					 char *buf)
409 {
410 	return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
411 }
412 
413 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
414 					  struct kobj_attribute *attr,
415 					  const char *buf, size_t count)
416 {
417 	unsigned long msecs;
418 	int err;
419 
420 	err = strict_strtoul(buf, 10, &msecs);
421 	if (err || msecs > UINT_MAX)
422 		return -EINVAL;
423 
424 	khugepaged_scan_sleep_millisecs = msecs;
425 	wake_up_interruptible(&khugepaged_wait);
426 
427 	return count;
428 }
429 static struct kobj_attribute scan_sleep_millisecs_attr =
430 	__ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
431 	       scan_sleep_millisecs_store);
432 
433 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
434 					  struct kobj_attribute *attr,
435 					  char *buf)
436 {
437 	return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
438 }
439 
440 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
441 					   struct kobj_attribute *attr,
442 					   const char *buf, size_t count)
443 {
444 	unsigned long msecs;
445 	int err;
446 
447 	err = strict_strtoul(buf, 10, &msecs);
448 	if (err || msecs > UINT_MAX)
449 		return -EINVAL;
450 
451 	khugepaged_alloc_sleep_millisecs = msecs;
452 	wake_up_interruptible(&khugepaged_wait);
453 
454 	return count;
455 }
456 static struct kobj_attribute alloc_sleep_millisecs_attr =
457 	__ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
458 	       alloc_sleep_millisecs_store);
459 
460 static ssize_t pages_to_scan_show(struct kobject *kobj,
461 				  struct kobj_attribute *attr,
462 				  char *buf)
463 {
464 	return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
465 }
466 static ssize_t pages_to_scan_store(struct kobject *kobj,
467 				   struct kobj_attribute *attr,
468 				   const char *buf, size_t count)
469 {
470 	int err;
471 	unsigned long pages;
472 
473 	err = strict_strtoul(buf, 10, &pages);
474 	if (err || !pages || pages > UINT_MAX)
475 		return -EINVAL;
476 
477 	khugepaged_pages_to_scan = pages;
478 
479 	return count;
480 }
481 static struct kobj_attribute pages_to_scan_attr =
482 	__ATTR(pages_to_scan, 0644, pages_to_scan_show,
483 	       pages_to_scan_store);
484 
485 static ssize_t pages_collapsed_show(struct kobject *kobj,
486 				    struct kobj_attribute *attr,
487 				    char *buf)
488 {
489 	return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
490 }
491 static struct kobj_attribute pages_collapsed_attr =
492 	__ATTR_RO(pages_collapsed);
493 
494 static ssize_t full_scans_show(struct kobject *kobj,
495 			       struct kobj_attribute *attr,
496 			       char *buf)
497 {
498 	return sprintf(buf, "%u\n", khugepaged_full_scans);
499 }
500 static struct kobj_attribute full_scans_attr =
501 	__ATTR_RO(full_scans);
502 
503 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
504 				      struct kobj_attribute *attr, char *buf)
505 {
506 	return single_flag_show(kobj, attr, buf,
507 				TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
508 }
509 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
510 				       struct kobj_attribute *attr,
511 				       const char *buf, size_t count)
512 {
513 	return single_flag_store(kobj, attr, buf, count,
514 				 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
515 }
516 static struct kobj_attribute khugepaged_defrag_attr =
517 	__ATTR(defrag, 0644, khugepaged_defrag_show,
518 	       khugepaged_defrag_store);
519 
520 /*
521  * max_ptes_none controls if khugepaged should collapse hugepages over
522  * any unmapped ptes in turn potentially increasing the memory
523  * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
524  * reduce the available free memory in the system as it
525  * runs. Increasing max_ptes_none will instead potentially reduce the
526  * free memory in the system during the khugepaged scan.
527  */
528 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
529 					     struct kobj_attribute *attr,
530 					     char *buf)
531 {
532 	return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
533 }
534 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
535 					      struct kobj_attribute *attr,
536 					      const char *buf, size_t count)
537 {
538 	int err;
539 	unsigned long max_ptes_none;
540 
541 	err = strict_strtoul(buf, 10, &max_ptes_none);
542 	if (err || max_ptes_none > HPAGE_PMD_NR-1)
543 		return -EINVAL;
544 
545 	khugepaged_max_ptes_none = max_ptes_none;
546 
547 	return count;
548 }
549 static struct kobj_attribute khugepaged_max_ptes_none_attr =
550 	__ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
551 	       khugepaged_max_ptes_none_store);
552 
553 static struct attribute *khugepaged_attr[] = {
554 	&khugepaged_defrag_attr.attr,
555 	&khugepaged_max_ptes_none_attr.attr,
556 	&pages_to_scan_attr.attr,
557 	&pages_collapsed_attr.attr,
558 	&full_scans_attr.attr,
559 	&scan_sleep_millisecs_attr.attr,
560 	&alloc_sleep_millisecs_attr.attr,
561 	NULL,
562 };
563 
564 static struct attribute_group khugepaged_attr_group = {
565 	.attrs = khugepaged_attr,
566 	.name = "khugepaged",
567 };
568 
569 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
570 {
571 	int err;
572 
573 	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
574 	if (unlikely(!*hugepage_kobj)) {
575 		printk(KERN_ERR "hugepage: failed to create transparent hugepage kobject\n");
576 		return -ENOMEM;
577 	}
578 
579 	err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
580 	if (err) {
581 		printk(KERN_ERR "hugepage: failed to register transparent hugepage group\n");
582 		goto delete_obj;
583 	}
584 
585 	err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
586 	if (err) {
587 		printk(KERN_ERR "hugepage: failed to register transparent hugepage group\n");
588 		goto remove_hp_group;
589 	}
590 
591 	return 0;
592 
593 remove_hp_group:
594 	sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
595 delete_obj:
596 	kobject_put(*hugepage_kobj);
597 	return err;
598 }
599 
600 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
601 {
602 	sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
603 	sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
604 	kobject_put(hugepage_kobj);
605 }
606 #else
607 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
608 {
609 	return 0;
610 }
611 
612 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
613 {
614 }
615 #endif /* CONFIG_SYSFS */
616 
617 static int __init hugepage_init(void)
618 {
619 	int err;
620 	struct kobject *hugepage_kobj;
621 
622 	if (!has_transparent_hugepage()) {
623 		transparent_hugepage_flags = 0;
624 		return -EINVAL;
625 	}
626 
627 	err = hugepage_init_sysfs(&hugepage_kobj);
628 	if (err)
629 		return err;
630 
631 	err = khugepaged_slab_init();
632 	if (err)
633 		goto out;
634 
635 	register_shrinker(&huge_zero_page_shrinker);
636 
637 	/*
638 	 * By default disable transparent hugepages on smaller systems,
639 	 * where the extra memory used could hurt more than TLB overhead
640 	 * is likely to save.  The admin can still enable it through /sys.
641 	 */
642 	if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
643 		transparent_hugepage_flags = 0;
644 
645 	start_khugepaged();
646 
647 	return 0;
648 out:
649 	hugepage_exit_sysfs(hugepage_kobj);
650 	return err;
651 }
652 module_init(hugepage_init)
653 
654 static int __init setup_transparent_hugepage(char *str)
655 {
656 	int ret = 0;
657 	if (!str)
658 		goto out;
659 	if (!strcmp(str, "always")) {
660 		set_bit(TRANSPARENT_HUGEPAGE_FLAG,
661 			&transparent_hugepage_flags);
662 		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
663 			  &transparent_hugepage_flags);
664 		ret = 1;
665 	} else if (!strcmp(str, "madvise")) {
666 		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
667 			  &transparent_hugepage_flags);
668 		set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
669 			&transparent_hugepage_flags);
670 		ret = 1;
671 	} else if (!strcmp(str, "never")) {
672 		clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
673 			  &transparent_hugepage_flags);
674 		clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
675 			  &transparent_hugepage_flags);
676 		ret = 1;
677 	}
678 out:
679 	if (!ret)
680 		printk(KERN_WARNING
681 		       "transparent_hugepage= cannot parse, ignored\n");
682 	return ret;
683 }
684 __setup("transparent_hugepage=", setup_transparent_hugepage);
685 
686 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
687 {
688 	if (likely(vma->vm_flags & VM_WRITE))
689 		pmd = pmd_mkwrite(pmd);
690 	return pmd;
691 }
692 
693 static inline pmd_t mk_huge_pmd(struct page *page, struct vm_area_struct *vma)
694 {
695 	pmd_t entry;
696 	entry = mk_pmd(page, vma->vm_page_prot);
697 	entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
698 	entry = pmd_mkhuge(entry);
699 	return entry;
700 }
701 
702 static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
703 					struct vm_area_struct *vma,
704 					unsigned long haddr, pmd_t *pmd,
705 					struct page *page)
706 {
707 	pgtable_t pgtable;
708 
709 	VM_BUG_ON(!PageCompound(page));
710 	pgtable = pte_alloc_one(mm, haddr);
711 	if (unlikely(!pgtable))
712 		return VM_FAULT_OOM;
713 
714 	clear_huge_page(page, haddr, HPAGE_PMD_NR);
715 	/*
716 	 * The memory barrier inside __SetPageUptodate makes sure that
717 	 * clear_huge_page writes become visible before the set_pmd_at()
718 	 * write.
719 	 */
720 	__SetPageUptodate(page);
721 
722 	spin_lock(&mm->page_table_lock);
723 	if (unlikely(!pmd_none(*pmd))) {
724 		spin_unlock(&mm->page_table_lock);
725 		mem_cgroup_uncharge_page(page);
726 		put_page(page);
727 		pte_free(mm, pgtable);
728 	} else {
729 		pmd_t entry;
730 		entry = mk_huge_pmd(page, vma);
731 		page_add_new_anon_rmap(page, vma, haddr);
732 		pgtable_trans_huge_deposit(mm, pmd, pgtable);
733 		set_pmd_at(mm, haddr, pmd, entry);
734 		add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
735 		mm->nr_ptes++;
736 		spin_unlock(&mm->page_table_lock);
737 	}
738 
739 	return 0;
740 }
741 
742 static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
743 {
744 	return (GFP_TRANSHUGE & ~(defrag ? 0 : __GFP_WAIT)) | extra_gfp;
745 }
746 
747 static inline struct page *alloc_hugepage_vma(int defrag,
748 					      struct vm_area_struct *vma,
749 					      unsigned long haddr, int nd,
750 					      gfp_t extra_gfp)
751 {
752 	return alloc_pages_vma(alloc_hugepage_gfpmask(defrag, extra_gfp),
753 			       HPAGE_PMD_ORDER, vma, haddr, nd);
754 }
755 
756 #ifndef CONFIG_NUMA
757 static inline struct page *alloc_hugepage(int defrag)
758 {
759 	return alloc_pages(alloc_hugepage_gfpmask(defrag, 0),
760 			   HPAGE_PMD_ORDER);
761 }
762 #endif
763 
764 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
765 		struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
766 		struct page *zero_page)
767 {
768 	pmd_t entry;
769 	if (!pmd_none(*pmd))
770 		return false;
771 	entry = mk_pmd(zero_page, vma->vm_page_prot);
772 	entry = pmd_wrprotect(entry);
773 	entry = pmd_mkhuge(entry);
774 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
775 	set_pmd_at(mm, haddr, pmd, entry);
776 	mm->nr_ptes++;
777 	return true;
778 }
779 
780 int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
781 			       unsigned long address, pmd_t *pmd,
782 			       unsigned int flags)
783 {
784 	struct page *page;
785 	unsigned long haddr = address & HPAGE_PMD_MASK;
786 	pte_t *pte;
787 
788 	if (haddr >= vma->vm_start && haddr + HPAGE_PMD_SIZE <= vma->vm_end) {
789 		if (unlikely(anon_vma_prepare(vma)))
790 			return VM_FAULT_OOM;
791 		if (unlikely(khugepaged_enter(vma)))
792 			return VM_FAULT_OOM;
793 		if (!(flags & FAULT_FLAG_WRITE) &&
794 				transparent_hugepage_use_zero_page()) {
795 			pgtable_t pgtable;
796 			struct page *zero_page;
797 			bool set;
798 			pgtable = pte_alloc_one(mm, haddr);
799 			if (unlikely(!pgtable))
800 				return VM_FAULT_OOM;
801 			zero_page = get_huge_zero_page();
802 			if (unlikely(!zero_page)) {
803 				pte_free(mm, pgtable);
804 				count_vm_event(THP_FAULT_FALLBACK);
805 				goto out;
806 			}
807 			spin_lock(&mm->page_table_lock);
808 			set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
809 					zero_page);
810 			spin_unlock(&mm->page_table_lock);
811 			if (!set) {
812 				pte_free(mm, pgtable);
813 				put_huge_zero_page();
814 			}
815 			return 0;
816 		}
817 		page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
818 					  vma, haddr, numa_node_id(), 0);
819 		if (unlikely(!page)) {
820 			count_vm_event(THP_FAULT_FALLBACK);
821 			goto out;
822 		}
823 		count_vm_event(THP_FAULT_ALLOC);
824 		if (unlikely(mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))) {
825 			put_page(page);
826 			goto out;
827 		}
828 		if (unlikely(__do_huge_pmd_anonymous_page(mm, vma, haddr, pmd,
829 							  page))) {
830 			mem_cgroup_uncharge_page(page);
831 			put_page(page);
832 			goto out;
833 		}
834 
835 		return 0;
836 	}
837 out:
838 	/*
839 	 * Use __pte_alloc instead of pte_alloc_map, because we can't
840 	 * run pte_offset_map on the pmd, if an huge pmd could
841 	 * materialize from under us from a different thread.
842 	 */
843 	if (unlikely(pmd_none(*pmd)) &&
844 	    unlikely(__pte_alloc(mm, vma, pmd, address)))
845 		return VM_FAULT_OOM;
846 	/* if an huge pmd materialized from under us just retry later */
847 	if (unlikely(pmd_trans_huge(*pmd)))
848 		return 0;
849 	/*
850 	 * A regular pmd is established and it can't morph into a huge pmd
851 	 * from under us anymore at this point because we hold the mmap_sem
852 	 * read mode and khugepaged takes it in write mode. So now it's
853 	 * safe to run pte_offset_map().
854 	 */
855 	pte = pte_offset_map(pmd, address);
856 	return handle_pte_fault(mm, vma, address, pte, pmd, flags);
857 }
858 
859 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
860 		  pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
861 		  struct vm_area_struct *vma)
862 {
863 	struct page *src_page;
864 	pmd_t pmd;
865 	pgtable_t pgtable;
866 	int ret;
867 
868 	ret = -ENOMEM;
869 	pgtable = pte_alloc_one(dst_mm, addr);
870 	if (unlikely(!pgtable))
871 		goto out;
872 
873 	spin_lock(&dst_mm->page_table_lock);
874 	spin_lock_nested(&src_mm->page_table_lock, SINGLE_DEPTH_NESTING);
875 
876 	ret = -EAGAIN;
877 	pmd = *src_pmd;
878 	if (unlikely(!pmd_trans_huge(pmd))) {
879 		pte_free(dst_mm, pgtable);
880 		goto out_unlock;
881 	}
882 	/*
883 	 * mm->page_table_lock is enough to be sure that huge zero pmd is not
884 	 * under splitting since we don't split the page itself, only pmd to
885 	 * a page table.
886 	 */
887 	if (is_huge_zero_pmd(pmd)) {
888 		struct page *zero_page;
889 		bool set;
890 		/*
891 		 * get_huge_zero_page() will never allocate a new page here,
892 		 * since we already have a zero page to copy. It just takes a
893 		 * reference.
894 		 */
895 		zero_page = get_huge_zero_page();
896 		set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
897 				zero_page);
898 		BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
899 		ret = 0;
900 		goto out_unlock;
901 	}
902 	if (unlikely(pmd_trans_splitting(pmd))) {
903 		/* split huge page running from under us */
904 		spin_unlock(&src_mm->page_table_lock);
905 		spin_unlock(&dst_mm->page_table_lock);
906 		pte_free(dst_mm, pgtable);
907 
908 		wait_split_huge_page(vma->anon_vma, src_pmd); /* src_vma */
909 		goto out;
910 	}
911 	src_page = pmd_page(pmd);
912 	VM_BUG_ON(!PageHead(src_page));
913 	get_page(src_page);
914 	page_dup_rmap(src_page);
915 	add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
916 
917 	pmdp_set_wrprotect(src_mm, addr, src_pmd);
918 	pmd = pmd_mkold(pmd_wrprotect(pmd));
919 	pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
920 	set_pmd_at(dst_mm, addr, dst_pmd, pmd);
921 	dst_mm->nr_ptes++;
922 
923 	ret = 0;
924 out_unlock:
925 	spin_unlock(&src_mm->page_table_lock);
926 	spin_unlock(&dst_mm->page_table_lock);
927 out:
928 	return ret;
929 }
930 
931 void huge_pmd_set_accessed(struct mm_struct *mm,
932 			   struct vm_area_struct *vma,
933 			   unsigned long address,
934 			   pmd_t *pmd, pmd_t orig_pmd,
935 			   int dirty)
936 {
937 	pmd_t entry;
938 	unsigned long haddr;
939 
940 	spin_lock(&mm->page_table_lock);
941 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
942 		goto unlock;
943 
944 	entry = pmd_mkyoung(orig_pmd);
945 	haddr = address & HPAGE_PMD_MASK;
946 	if (pmdp_set_access_flags(vma, haddr, pmd, entry, dirty))
947 		update_mmu_cache_pmd(vma, address, pmd);
948 
949 unlock:
950 	spin_unlock(&mm->page_table_lock);
951 }
952 
953 static int do_huge_pmd_wp_zero_page_fallback(struct mm_struct *mm,
954 		struct vm_area_struct *vma, unsigned long address,
955 		pmd_t *pmd, pmd_t orig_pmd, unsigned long haddr)
956 {
957 	pgtable_t pgtable;
958 	pmd_t _pmd;
959 	struct page *page;
960 	int i, ret = 0;
961 	unsigned long mmun_start;	/* For mmu_notifiers */
962 	unsigned long mmun_end;		/* For mmu_notifiers */
963 
964 	page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
965 	if (!page) {
966 		ret |= VM_FAULT_OOM;
967 		goto out;
968 	}
969 
970 	if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL)) {
971 		put_page(page);
972 		ret |= VM_FAULT_OOM;
973 		goto out;
974 	}
975 
976 	clear_user_highpage(page, address);
977 	__SetPageUptodate(page);
978 
979 	mmun_start = haddr;
980 	mmun_end   = haddr + HPAGE_PMD_SIZE;
981 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
982 
983 	spin_lock(&mm->page_table_lock);
984 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
985 		goto out_free_page;
986 
987 	pmdp_clear_flush(vma, haddr, pmd);
988 	/* leave pmd empty until pte is filled */
989 
990 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
991 	pmd_populate(mm, &_pmd, pgtable);
992 
993 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
994 		pte_t *pte, entry;
995 		if (haddr == (address & PAGE_MASK)) {
996 			entry = mk_pte(page, vma->vm_page_prot);
997 			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
998 			page_add_new_anon_rmap(page, vma, haddr);
999 		} else {
1000 			entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1001 			entry = pte_mkspecial(entry);
1002 		}
1003 		pte = pte_offset_map(&_pmd, haddr);
1004 		VM_BUG_ON(!pte_none(*pte));
1005 		set_pte_at(mm, haddr, pte, entry);
1006 		pte_unmap(pte);
1007 	}
1008 	smp_wmb(); /* make pte visible before pmd */
1009 	pmd_populate(mm, pmd, pgtable);
1010 	spin_unlock(&mm->page_table_lock);
1011 	put_huge_zero_page();
1012 	inc_mm_counter(mm, MM_ANONPAGES);
1013 
1014 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1015 
1016 	ret |= VM_FAULT_WRITE;
1017 out:
1018 	return ret;
1019 out_free_page:
1020 	spin_unlock(&mm->page_table_lock);
1021 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1022 	mem_cgroup_uncharge_page(page);
1023 	put_page(page);
1024 	goto out;
1025 }
1026 
1027 static int do_huge_pmd_wp_page_fallback(struct mm_struct *mm,
1028 					struct vm_area_struct *vma,
1029 					unsigned long address,
1030 					pmd_t *pmd, pmd_t orig_pmd,
1031 					struct page *page,
1032 					unsigned long haddr)
1033 {
1034 	pgtable_t pgtable;
1035 	pmd_t _pmd;
1036 	int ret = 0, i;
1037 	struct page **pages;
1038 	unsigned long mmun_start;	/* For mmu_notifiers */
1039 	unsigned long mmun_end;		/* For mmu_notifiers */
1040 
1041 	pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
1042 			GFP_KERNEL);
1043 	if (unlikely(!pages)) {
1044 		ret |= VM_FAULT_OOM;
1045 		goto out;
1046 	}
1047 
1048 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1049 		pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE |
1050 					       __GFP_OTHER_NODE,
1051 					       vma, address, page_to_nid(page));
1052 		if (unlikely(!pages[i] ||
1053 			     mem_cgroup_newpage_charge(pages[i], mm,
1054 						       GFP_KERNEL))) {
1055 			if (pages[i])
1056 				put_page(pages[i]);
1057 			mem_cgroup_uncharge_start();
1058 			while (--i >= 0) {
1059 				mem_cgroup_uncharge_page(pages[i]);
1060 				put_page(pages[i]);
1061 			}
1062 			mem_cgroup_uncharge_end();
1063 			kfree(pages);
1064 			ret |= VM_FAULT_OOM;
1065 			goto out;
1066 		}
1067 	}
1068 
1069 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1070 		copy_user_highpage(pages[i], page + i,
1071 				   haddr + PAGE_SIZE * i, vma);
1072 		__SetPageUptodate(pages[i]);
1073 		cond_resched();
1074 	}
1075 
1076 	mmun_start = haddr;
1077 	mmun_end   = haddr + HPAGE_PMD_SIZE;
1078 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1079 
1080 	spin_lock(&mm->page_table_lock);
1081 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
1082 		goto out_free_pages;
1083 	VM_BUG_ON(!PageHead(page));
1084 
1085 	pmdp_clear_flush(vma, haddr, pmd);
1086 	/* leave pmd empty until pte is filled */
1087 
1088 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1089 	pmd_populate(mm, &_pmd, pgtable);
1090 
1091 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1092 		pte_t *pte, entry;
1093 		entry = mk_pte(pages[i], vma->vm_page_prot);
1094 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1095 		page_add_new_anon_rmap(pages[i], vma, haddr);
1096 		pte = pte_offset_map(&_pmd, haddr);
1097 		VM_BUG_ON(!pte_none(*pte));
1098 		set_pte_at(mm, haddr, pte, entry);
1099 		pte_unmap(pte);
1100 	}
1101 	kfree(pages);
1102 
1103 	smp_wmb(); /* make pte visible before pmd */
1104 	pmd_populate(mm, pmd, pgtable);
1105 	page_remove_rmap(page);
1106 	spin_unlock(&mm->page_table_lock);
1107 
1108 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1109 
1110 	ret |= VM_FAULT_WRITE;
1111 	put_page(page);
1112 
1113 out:
1114 	return ret;
1115 
1116 out_free_pages:
1117 	spin_unlock(&mm->page_table_lock);
1118 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1119 	mem_cgroup_uncharge_start();
1120 	for (i = 0; i < HPAGE_PMD_NR; i++) {
1121 		mem_cgroup_uncharge_page(pages[i]);
1122 		put_page(pages[i]);
1123 	}
1124 	mem_cgroup_uncharge_end();
1125 	kfree(pages);
1126 	goto out;
1127 }
1128 
1129 int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
1130 			unsigned long address, pmd_t *pmd, pmd_t orig_pmd)
1131 {
1132 	int ret = 0;
1133 	struct page *page = NULL, *new_page;
1134 	unsigned long haddr;
1135 	unsigned long mmun_start;	/* For mmu_notifiers */
1136 	unsigned long mmun_end;		/* For mmu_notifiers */
1137 
1138 	VM_BUG_ON(!vma->anon_vma);
1139 	haddr = address & HPAGE_PMD_MASK;
1140 	if (is_huge_zero_pmd(orig_pmd))
1141 		goto alloc;
1142 	spin_lock(&mm->page_table_lock);
1143 	if (unlikely(!pmd_same(*pmd, orig_pmd)))
1144 		goto out_unlock;
1145 
1146 	page = pmd_page(orig_pmd);
1147 	VM_BUG_ON(!PageCompound(page) || !PageHead(page));
1148 	if (page_mapcount(page) == 1) {
1149 		pmd_t entry;
1150 		entry = pmd_mkyoung(orig_pmd);
1151 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1152 		if (pmdp_set_access_flags(vma, haddr, pmd, entry,  1))
1153 			update_mmu_cache_pmd(vma, address, pmd);
1154 		ret |= VM_FAULT_WRITE;
1155 		goto out_unlock;
1156 	}
1157 	get_page(page);
1158 	spin_unlock(&mm->page_table_lock);
1159 alloc:
1160 	if (transparent_hugepage_enabled(vma) &&
1161 	    !transparent_hugepage_debug_cow())
1162 		new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
1163 					      vma, haddr, numa_node_id(), 0);
1164 	else
1165 		new_page = NULL;
1166 
1167 	if (unlikely(!new_page)) {
1168 		count_vm_event(THP_FAULT_FALLBACK);
1169 		if (is_huge_zero_pmd(orig_pmd)) {
1170 			ret = do_huge_pmd_wp_zero_page_fallback(mm, vma,
1171 					address, pmd, orig_pmd, haddr);
1172 		} else {
1173 			ret = do_huge_pmd_wp_page_fallback(mm, vma, address,
1174 					pmd, orig_pmd, page, haddr);
1175 			if (ret & VM_FAULT_OOM)
1176 				split_huge_page(page);
1177 			put_page(page);
1178 		}
1179 		goto out;
1180 	}
1181 	count_vm_event(THP_FAULT_ALLOC);
1182 
1183 	if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))) {
1184 		put_page(new_page);
1185 		if (page) {
1186 			split_huge_page(page);
1187 			put_page(page);
1188 		}
1189 		ret |= VM_FAULT_OOM;
1190 		goto out;
1191 	}
1192 
1193 	if (is_huge_zero_pmd(orig_pmd))
1194 		clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1195 	else
1196 		copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1197 	__SetPageUptodate(new_page);
1198 
1199 	mmun_start = haddr;
1200 	mmun_end   = haddr + HPAGE_PMD_SIZE;
1201 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1202 
1203 	spin_lock(&mm->page_table_lock);
1204 	if (page)
1205 		put_page(page);
1206 	if (unlikely(!pmd_same(*pmd, orig_pmd))) {
1207 		spin_unlock(&mm->page_table_lock);
1208 		mem_cgroup_uncharge_page(new_page);
1209 		put_page(new_page);
1210 		goto out_mn;
1211 	} else {
1212 		pmd_t entry;
1213 		entry = mk_huge_pmd(new_page, vma);
1214 		pmdp_clear_flush(vma, haddr, pmd);
1215 		page_add_new_anon_rmap(new_page, vma, haddr);
1216 		set_pmd_at(mm, haddr, pmd, entry);
1217 		update_mmu_cache_pmd(vma, address, pmd);
1218 		if (is_huge_zero_pmd(orig_pmd)) {
1219 			add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
1220 			put_huge_zero_page();
1221 		} else {
1222 			VM_BUG_ON(!PageHead(page));
1223 			page_remove_rmap(page);
1224 			put_page(page);
1225 		}
1226 		ret |= VM_FAULT_WRITE;
1227 	}
1228 	spin_unlock(&mm->page_table_lock);
1229 out_mn:
1230 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1231 out:
1232 	return ret;
1233 out_unlock:
1234 	spin_unlock(&mm->page_table_lock);
1235 	return ret;
1236 }
1237 
1238 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1239 				   unsigned long addr,
1240 				   pmd_t *pmd,
1241 				   unsigned int flags)
1242 {
1243 	struct mm_struct *mm = vma->vm_mm;
1244 	struct page *page = NULL;
1245 
1246 	assert_spin_locked(&mm->page_table_lock);
1247 
1248 	if (flags & FOLL_WRITE && !pmd_write(*pmd))
1249 		goto out;
1250 
1251 	/* Avoid dumping huge zero page */
1252 	if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1253 		return ERR_PTR(-EFAULT);
1254 
1255 	page = pmd_page(*pmd);
1256 	VM_BUG_ON(!PageHead(page));
1257 	if (flags & FOLL_TOUCH) {
1258 		pmd_t _pmd;
1259 		/*
1260 		 * We should set the dirty bit only for FOLL_WRITE but
1261 		 * for now the dirty bit in the pmd is meaningless.
1262 		 * And if the dirty bit will become meaningful and
1263 		 * we'll only set it with FOLL_WRITE, an atomic
1264 		 * set_bit will be required on the pmd to set the
1265 		 * young bit, instead of the current set_pmd_at.
1266 		 */
1267 		_pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
1268 		if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
1269 					  pmd, _pmd,  1))
1270 			update_mmu_cache_pmd(vma, addr, pmd);
1271 	}
1272 	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1273 		if (page->mapping && trylock_page(page)) {
1274 			lru_add_drain();
1275 			if (page->mapping)
1276 				mlock_vma_page(page);
1277 			unlock_page(page);
1278 		}
1279 	}
1280 	page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1281 	VM_BUG_ON(!PageCompound(page));
1282 	if (flags & FOLL_GET)
1283 		get_page_foll(page);
1284 
1285 out:
1286 	return page;
1287 }
1288 
1289 /* NUMA hinting page fault entry point for trans huge pmds */
1290 int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
1291 				unsigned long addr, pmd_t pmd, pmd_t *pmdp)
1292 {
1293 	struct page *page;
1294 	unsigned long haddr = addr & HPAGE_PMD_MASK;
1295 	int target_nid;
1296 	int current_nid = -1;
1297 	bool migrated;
1298 
1299 	spin_lock(&mm->page_table_lock);
1300 	if (unlikely(!pmd_same(pmd, *pmdp)))
1301 		goto out_unlock;
1302 
1303 	page = pmd_page(pmd);
1304 	get_page(page);
1305 	current_nid = page_to_nid(page);
1306 	count_vm_numa_event(NUMA_HINT_FAULTS);
1307 	if (current_nid == numa_node_id())
1308 		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1309 
1310 	target_nid = mpol_misplaced(page, vma, haddr);
1311 	if (target_nid == -1) {
1312 		put_page(page);
1313 		goto clear_pmdnuma;
1314 	}
1315 
1316 	/* Acquire the page lock to serialise THP migrations */
1317 	spin_unlock(&mm->page_table_lock);
1318 	lock_page(page);
1319 
1320 	/* Confirm the PTE did not while locked */
1321 	spin_lock(&mm->page_table_lock);
1322 	if (unlikely(!pmd_same(pmd, *pmdp))) {
1323 		unlock_page(page);
1324 		put_page(page);
1325 		goto out_unlock;
1326 	}
1327 	spin_unlock(&mm->page_table_lock);
1328 
1329 	/* Migrate the THP to the requested node */
1330 	migrated = migrate_misplaced_transhuge_page(mm, vma,
1331 				pmdp, pmd, addr, page, target_nid);
1332 	if (!migrated)
1333 		goto check_same;
1334 
1335 	task_numa_fault(target_nid, HPAGE_PMD_NR, true);
1336 	return 0;
1337 
1338 check_same:
1339 	spin_lock(&mm->page_table_lock);
1340 	if (unlikely(!pmd_same(pmd, *pmdp)))
1341 		goto out_unlock;
1342 clear_pmdnuma:
1343 	pmd = pmd_mknonnuma(pmd);
1344 	set_pmd_at(mm, haddr, pmdp, pmd);
1345 	VM_BUG_ON(pmd_numa(*pmdp));
1346 	update_mmu_cache_pmd(vma, addr, pmdp);
1347 out_unlock:
1348 	spin_unlock(&mm->page_table_lock);
1349 	if (current_nid != -1)
1350 		task_numa_fault(current_nid, HPAGE_PMD_NR, false);
1351 	return 0;
1352 }
1353 
1354 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1355 		 pmd_t *pmd, unsigned long addr)
1356 {
1357 	int ret = 0;
1358 
1359 	if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1360 		struct page *page;
1361 		pgtable_t pgtable;
1362 		pmd_t orig_pmd;
1363 		/*
1364 		 * For architectures like ppc64 we look at deposited pgtable
1365 		 * when calling pmdp_get_and_clear. So do the
1366 		 * pgtable_trans_huge_withdraw after finishing pmdp related
1367 		 * operations.
1368 		 */
1369 		orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
1370 		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1371 		pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1372 		if (is_huge_zero_pmd(orig_pmd)) {
1373 			tlb->mm->nr_ptes--;
1374 			spin_unlock(&tlb->mm->page_table_lock);
1375 			put_huge_zero_page();
1376 		} else {
1377 			page = pmd_page(orig_pmd);
1378 			page_remove_rmap(page);
1379 			VM_BUG_ON(page_mapcount(page) < 0);
1380 			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1381 			VM_BUG_ON(!PageHead(page));
1382 			tlb->mm->nr_ptes--;
1383 			spin_unlock(&tlb->mm->page_table_lock);
1384 			tlb_remove_page(tlb, page);
1385 		}
1386 		pte_free(tlb->mm, pgtable);
1387 		ret = 1;
1388 	}
1389 	return ret;
1390 }
1391 
1392 int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1393 		unsigned long addr, unsigned long end,
1394 		unsigned char *vec)
1395 {
1396 	int ret = 0;
1397 
1398 	if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1399 		/*
1400 		 * All logical pages in the range are present
1401 		 * if backed by a huge page.
1402 		 */
1403 		spin_unlock(&vma->vm_mm->page_table_lock);
1404 		memset(vec, 1, (end - addr) >> PAGE_SHIFT);
1405 		ret = 1;
1406 	}
1407 
1408 	return ret;
1409 }
1410 
1411 int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
1412 		  unsigned long old_addr,
1413 		  unsigned long new_addr, unsigned long old_end,
1414 		  pmd_t *old_pmd, pmd_t *new_pmd)
1415 {
1416 	int ret = 0;
1417 	pmd_t pmd;
1418 
1419 	struct mm_struct *mm = vma->vm_mm;
1420 
1421 	if ((old_addr & ~HPAGE_PMD_MASK) ||
1422 	    (new_addr & ~HPAGE_PMD_MASK) ||
1423 	    old_end - old_addr < HPAGE_PMD_SIZE ||
1424 	    (new_vma->vm_flags & VM_NOHUGEPAGE))
1425 		goto out;
1426 
1427 	/*
1428 	 * The destination pmd shouldn't be established, free_pgtables()
1429 	 * should have release it.
1430 	 */
1431 	if (WARN_ON(!pmd_none(*new_pmd))) {
1432 		VM_BUG_ON(pmd_trans_huge(*new_pmd));
1433 		goto out;
1434 	}
1435 
1436 	ret = __pmd_trans_huge_lock(old_pmd, vma);
1437 	if (ret == 1) {
1438 		pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
1439 		VM_BUG_ON(!pmd_none(*new_pmd));
1440 		set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1441 		spin_unlock(&mm->page_table_lock);
1442 	}
1443 out:
1444 	return ret;
1445 }
1446 
1447 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1448 		unsigned long addr, pgprot_t newprot, int prot_numa)
1449 {
1450 	struct mm_struct *mm = vma->vm_mm;
1451 	int ret = 0;
1452 
1453 	if (__pmd_trans_huge_lock(pmd, vma) == 1) {
1454 		pmd_t entry;
1455 		entry = pmdp_get_and_clear(mm, addr, pmd);
1456 		if (!prot_numa) {
1457 			entry = pmd_modify(entry, newprot);
1458 			BUG_ON(pmd_write(entry));
1459 		} else {
1460 			struct page *page = pmd_page(*pmd);
1461 
1462 			/* only check non-shared pages */
1463 			if (page_mapcount(page) == 1 &&
1464 			    !pmd_numa(*pmd)) {
1465 				entry = pmd_mknuma(entry);
1466 			}
1467 		}
1468 		set_pmd_at(mm, addr, pmd, entry);
1469 		spin_unlock(&vma->vm_mm->page_table_lock);
1470 		ret = 1;
1471 	}
1472 
1473 	return ret;
1474 }
1475 
1476 /*
1477  * Returns 1 if a given pmd maps a stable (not under splitting) thp.
1478  * Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
1479  *
1480  * Note that if it returns 1, this routine returns without unlocking page
1481  * table locks. So callers must unlock them.
1482  */
1483 int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1484 {
1485 	spin_lock(&vma->vm_mm->page_table_lock);
1486 	if (likely(pmd_trans_huge(*pmd))) {
1487 		if (unlikely(pmd_trans_splitting(*pmd))) {
1488 			spin_unlock(&vma->vm_mm->page_table_lock);
1489 			wait_split_huge_page(vma->anon_vma, pmd);
1490 			return -1;
1491 		} else {
1492 			/* Thp mapped by 'pmd' is stable, so we can
1493 			 * handle it as it is. */
1494 			return 1;
1495 		}
1496 	}
1497 	spin_unlock(&vma->vm_mm->page_table_lock);
1498 	return 0;
1499 }
1500 
1501 pmd_t *page_check_address_pmd(struct page *page,
1502 			      struct mm_struct *mm,
1503 			      unsigned long address,
1504 			      enum page_check_address_pmd_flag flag)
1505 {
1506 	pmd_t *pmd, *ret = NULL;
1507 
1508 	if (address & ~HPAGE_PMD_MASK)
1509 		goto out;
1510 
1511 	pmd = mm_find_pmd(mm, address);
1512 	if (!pmd)
1513 		goto out;
1514 	if (pmd_none(*pmd))
1515 		goto out;
1516 	if (pmd_page(*pmd) != page)
1517 		goto out;
1518 	/*
1519 	 * split_vma() may create temporary aliased mappings. There is
1520 	 * no risk as long as all huge pmd are found and have their
1521 	 * splitting bit set before __split_huge_page_refcount
1522 	 * runs. Finding the same huge pmd more than once during the
1523 	 * same rmap walk is not a problem.
1524 	 */
1525 	if (flag == PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG &&
1526 	    pmd_trans_splitting(*pmd))
1527 		goto out;
1528 	if (pmd_trans_huge(*pmd)) {
1529 		VM_BUG_ON(flag == PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG &&
1530 			  !pmd_trans_splitting(*pmd));
1531 		ret = pmd;
1532 	}
1533 out:
1534 	return ret;
1535 }
1536 
1537 static int __split_huge_page_splitting(struct page *page,
1538 				       struct vm_area_struct *vma,
1539 				       unsigned long address)
1540 {
1541 	struct mm_struct *mm = vma->vm_mm;
1542 	pmd_t *pmd;
1543 	int ret = 0;
1544 	/* For mmu_notifiers */
1545 	const unsigned long mmun_start = address;
1546 	const unsigned long mmun_end   = address + HPAGE_PMD_SIZE;
1547 
1548 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1549 	spin_lock(&mm->page_table_lock);
1550 	pmd = page_check_address_pmd(page, mm, address,
1551 				     PAGE_CHECK_ADDRESS_PMD_NOTSPLITTING_FLAG);
1552 	if (pmd) {
1553 		/*
1554 		 * We can't temporarily set the pmd to null in order
1555 		 * to split it, the pmd must remain marked huge at all
1556 		 * times or the VM won't take the pmd_trans_huge paths
1557 		 * and it won't wait on the anon_vma->root->rwsem to
1558 		 * serialize against split_huge_page*.
1559 		 */
1560 		pmdp_splitting_flush(vma, address, pmd);
1561 		ret = 1;
1562 	}
1563 	spin_unlock(&mm->page_table_lock);
1564 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1565 
1566 	return ret;
1567 }
1568 
1569 static void __split_huge_page_refcount(struct page *page,
1570 				       struct list_head *list)
1571 {
1572 	int i;
1573 	struct zone *zone = page_zone(page);
1574 	struct lruvec *lruvec;
1575 	int tail_count = 0;
1576 
1577 	/* prevent PageLRU to go away from under us, and freeze lru stats */
1578 	spin_lock_irq(&zone->lru_lock);
1579 	lruvec = mem_cgroup_page_lruvec(page, zone);
1580 
1581 	compound_lock(page);
1582 	/* complete memcg works before add pages to LRU */
1583 	mem_cgroup_split_huge_fixup(page);
1584 
1585 	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1586 		struct page *page_tail = page + i;
1587 
1588 		/* tail_page->_mapcount cannot change */
1589 		BUG_ON(page_mapcount(page_tail) < 0);
1590 		tail_count += page_mapcount(page_tail);
1591 		/* check for overflow */
1592 		BUG_ON(tail_count < 0);
1593 		BUG_ON(atomic_read(&page_tail->_count) != 0);
1594 		/*
1595 		 * tail_page->_count is zero and not changing from
1596 		 * under us. But get_page_unless_zero() may be running
1597 		 * from under us on the tail_page. If we used
1598 		 * atomic_set() below instead of atomic_add(), we
1599 		 * would then run atomic_set() concurrently with
1600 		 * get_page_unless_zero(), and atomic_set() is
1601 		 * implemented in C not using locked ops. spin_unlock
1602 		 * on x86 sometime uses locked ops because of PPro
1603 		 * errata 66, 92, so unless somebody can guarantee
1604 		 * atomic_set() here would be safe on all archs (and
1605 		 * not only on x86), it's safer to use atomic_add().
1606 		 */
1607 		atomic_add(page_mapcount(page) + page_mapcount(page_tail) + 1,
1608 			   &page_tail->_count);
1609 
1610 		/* after clearing PageTail the gup refcount can be released */
1611 		smp_mb();
1612 
1613 		/*
1614 		 * retain hwpoison flag of the poisoned tail page:
1615 		 *   fix for the unsuitable process killed on Guest Machine(KVM)
1616 		 *   by the memory-failure.
1617 		 */
1618 		page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP | __PG_HWPOISON;
1619 		page_tail->flags |= (page->flags &
1620 				     ((1L << PG_referenced) |
1621 				      (1L << PG_swapbacked) |
1622 				      (1L << PG_mlocked) |
1623 				      (1L << PG_uptodate) |
1624 				      (1L << PG_active) |
1625 				      (1L << PG_unevictable)));
1626 		page_tail->flags |= (1L << PG_dirty);
1627 
1628 		/* clear PageTail before overwriting first_page */
1629 		smp_wmb();
1630 
1631 		/*
1632 		 * __split_huge_page_splitting() already set the
1633 		 * splitting bit in all pmd that could map this
1634 		 * hugepage, that will ensure no CPU can alter the
1635 		 * mapcount on the head page. The mapcount is only
1636 		 * accounted in the head page and it has to be
1637 		 * transferred to all tail pages in the below code. So
1638 		 * for this code to be safe, the split the mapcount
1639 		 * can't change. But that doesn't mean userland can't
1640 		 * keep changing and reading the page contents while
1641 		 * we transfer the mapcount, so the pmd splitting
1642 		 * status is achieved setting a reserved bit in the
1643 		 * pmd, not by clearing the present bit.
1644 		*/
1645 		page_tail->_mapcount = page->_mapcount;
1646 
1647 		BUG_ON(page_tail->mapping);
1648 		page_tail->mapping = page->mapping;
1649 
1650 		page_tail->index = page->index + i;
1651 		page_nid_xchg_last(page_tail, page_nid_last(page));
1652 
1653 		BUG_ON(!PageAnon(page_tail));
1654 		BUG_ON(!PageUptodate(page_tail));
1655 		BUG_ON(!PageDirty(page_tail));
1656 		BUG_ON(!PageSwapBacked(page_tail));
1657 
1658 		lru_add_page_tail(page, page_tail, lruvec, list);
1659 	}
1660 	atomic_sub(tail_count, &page->_count);
1661 	BUG_ON(atomic_read(&page->_count) <= 0);
1662 
1663 	__mod_zone_page_state(zone, NR_ANON_TRANSPARENT_HUGEPAGES, -1);
1664 	__mod_zone_page_state(zone, NR_ANON_PAGES, HPAGE_PMD_NR);
1665 
1666 	ClearPageCompound(page);
1667 	compound_unlock(page);
1668 	spin_unlock_irq(&zone->lru_lock);
1669 
1670 	for (i = 1; i < HPAGE_PMD_NR; i++) {
1671 		struct page *page_tail = page + i;
1672 		BUG_ON(page_count(page_tail) <= 0);
1673 		/*
1674 		 * Tail pages may be freed if there wasn't any mapping
1675 		 * like if add_to_swap() is running on a lru page that
1676 		 * had its mapping zapped. And freeing these pages
1677 		 * requires taking the lru_lock so we do the put_page
1678 		 * of the tail pages after the split is complete.
1679 		 */
1680 		put_page(page_tail);
1681 	}
1682 
1683 	/*
1684 	 * Only the head page (now become a regular page) is required
1685 	 * to be pinned by the caller.
1686 	 */
1687 	BUG_ON(page_count(page) <= 0);
1688 }
1689 
1690 static int __split_huge_page_map(struct page *page,
1691 				 struct vm_area_struct *vma,
1692 				 unsigned long address)
1693 {
1694 	struct mm_struct *mm = vma->vm_mm;
1695 	pmd_t *pmd, _pmd;
1696 	int ret = 0, i;
1697 	pgtable_t pgtable;
1698 	unsigned long haddr;
1699 
1700 	spin_lock(&mm->page_table_lock);
1701 	pmd = page_check_address_pmd(page, mm, address,
1702 				     PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG);
1703 	if (pmd) {
1704 		pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1705 		pmd_populate(mm, &_pmd, pgtable);
1706 
1707 		haddr = address;
1708 		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1709 			pte_t *pte, entry;
1710 			BUG_ON(PageCompound(page+i));
1711 			entry = mk_pte(page + i, vma->vm_page_prot);
1712 			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
1713 			if (!pmd_write(*pmd))
1714 				entry = pte_wrprotect(entry);
1715 			else
1716 				BUG_ON(page_mapcount(page) != 1);
1717 			if (!pmd_young(*pmd))
1718 				entry = pte_mkold(entry);
1719 			if (pmd_numa(*pmd))
1720 				entry = pte_mknuma(entry);
1721 			pte = pte_offset_map(&_pmd, haddr);
1722 			BUG_ON(!pte_none(*pte));
1723 			set_pte_at(mm, haddr, pte, entry);
1724 			pte_unmap(pte);
1725 		}
1726 
1727 		smp_wmb(); /* make pte visible before pmd */
1728 		/*
1729 		 * Up to this point the pmd is present and huge and
1730 		 * userland has the whole access to the hugepage
1731 		 * during the split (which happens in place). If we
1732 		 * overwrite the pmd with the not-huge version
1733 		 * pointing to the pte here (which of course we could
1734 		 * if all CPUs were bug free), userland could trigger
1735 		 * a small page size TLB miss on the small sized TLB
1736 		 * while the hugepage TLB entry is still established
1737 		 * in the huge TLB. Some CPU doesn't like that. See
1738 		 * http://support.amd.com/us/Processor_TechDocs/41322.pdf,
1739 		 * Erratum 383 on page 93. Intel should be safe but is
1740 		 * also warns that it's only safe if the permission
1741 		 * and cache attributes of the two entries loaded in
1742 		 * the two TLB is identical (which should be the case
1743 		 * here). But it is generally safer to never allow
1744 		 * small and huge TLB entries for the same virtual
1745 		 * address to be loaded simultaneously. So instead of
1746 		 * doing "pmd_populate(); flush_tlb_range();" we first
1747 		 * mark the current pmd notpresent (atomically because
1748 		 * here the pmd_trans_huge and pmd_trans_splitting
1749 		 * must remain set at all times on the pmd until the
1750 		 * split is complete for this pmd), then we flush the
1751 		 * SMP TLB and finally we write the non-huge version
1752 		 * of the pmd entry with pmd_populate.
1753 		 */
1754 		pmdp_invalidate(vma, address, pmd);
1755 		pmd_populate(mm, pmd, pgtable);
1756 		ret = 1;
1757 	}
1758 	spin_unlock(&mm->page_table_lock);
1759 
1760 	return ret;
1761 }
1762 
1763 /* must be called with anon_vma->root->rwsem held */
1764 static void __split_huge_page(struct page *page,
1765 			      struct anon_vma *anon_vma,
1766 			      struct list_head *list)
1767 {
1768 	int mapcount, mapcount2;
1769 	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1770 	struct anon_vma_chain *avc;
1771 
1772 	BUG_ON(!PageHead(page));
1773 	BUG_ON(PageTail(page));
1774 
1775 	mapcount = 0;
1776 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1777 		struct vm_area_struct *vma = avc->vma;
1778 		unsigned long addr = vma_address(page, vma);
1779 		BUG_ON(is_vma_temporary_stack(vma));
1780 		mapcount += __split_huge_page_splitting(page, vma, addr);
1781 	}
1782 	/*
1783 	 * It is critical that new vmas are added to the tail of the
1784 	 * anon_vma list. This guarantes that if copy_huge_pmd() runs
1785 	 * and establishes a child pmd before
1786 	 * __split_huge_page_splitting() freezes the parent pmd (so if
1787 	 * we fail to prevent copy_huge_pmd() from running until the
1788 	 * whole __split_huge_page() is complete), we will still see
1789 	 * the newly established pmd of the child later during the
1790 	 * walk, to be able to set it as pmd_trans_splitting too.
1791 	 */
1792 	if (mapcount != page_mapcount(page))
1793 		printk(KERN_ERR "mapcount %d page_mapcount %d\n",
1794 		       mapcount, page_mapcount(page));
1795 	BUG_ON(mapcount != page_mapcount(page));
1796 
1797 	__split_huge_page_refcount(page, list);
1798 
1799 	mapcount2 = 0;
1800 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1801 		struct vm_area_struct *vma = avc->vma;
1802 		unsigned long addr = vma_address(page, vma);
1803 		BUG_ON(is_vma_temporary_stack(vma));
1804 		mapcount2 += __split_huge_page_map(page, vma, addr);
1805 	}
1806 	if (mapcount != mapcount2)
1807 		printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount %d\n",
1808 		       mapcount, mapcount2, page_mapcount(page));
1809 	BUG_ON(mapcount != mapcount2);
1810 }
1811 
1812 /*
1813  * Split a hugepage into normal pages. This doesn't change the position of head
1814  * page. If @list is null, tail pages will be added to LRU list, otherwise, to
1815  * @list. Both head page and tail pages will inherit mapping, flags, and so on
1816  * from the hugepage.
1817  * Return 0 if the hugepage is split successfully otherwise return 1.
1818  */
1819 int split_huge_page_to_list(struct page *page, struct list_head *list)
1820 {
1821 	struct anon_vma *anon_vma;
1822 	int ret = 1;
1823 
1824 	BUG_ON(is_huge_zero_page(page));
1825 	BUG_ON(!PageAnon(page));
1826 
1827 	/*
1828 	 * The caller does not necessarily hold an mmap_sem that would prevent
1829 	 * the anon_vma disappearing so we first we take a reference to it
1830 	 * and then lock the anon_vma for write. This is similar to
1831 	 * page_lock_anon_vma_read except the write lock is taken to serialise
1832 	 * against parallel split or collapse operations.
1833 	 */
1834 	anon_vma = page_get_anon_vma(page);
1835 	if (!anon_vma)
1836 		goto out;
1837 	anon_vma_lock_write(anon_vma);
1838 
1839 	ret = 0;
1840 	if (!PageCompound(page))
1841 		goto out_unlock;
1842 
1843 	BUG_ON(!PageSwapBacked(page));
1844 	__split_huge_page(page, anon_vma, list);
1845 	count_vm_event(THP_SPLIT);
1846 
1847 	BUG_ON(PageCompound(page));
1848 out_unlock:
1849 	anon_vma_unlock_write(anon_vma);
1850 	put_anon_vma(anon_vma);
1851 out:
1852 	return ret;
1853 }
1854 
1855 #define VM_NO_THP (VM_SPECIAL|VM_MIXEDMAP|VM_HUGETLB|VM_SHARED|VM_MAYSHARE)
1856 
1857 int hugepage_madvise(struct vm_area_struct *vma,
1858 		     unsigned long *vm_flags, int advice)
1859 {
1860 	struct mm_struct *mm = vma->vm_mm;
1861 
1862 	switch (advice) {
1863 	case MADV_HUGEPAGE:
1864 		/*
1865 		 * Be somewhat over-protective like KSM for now!
1866 		 */
1867 		if (*vm_flags & (VM_HUGEPAGE | VM_NO_THP))
1868 			return -EINVAL;
1869 		if (mm->def_flags & VM_NOHUGEPAGE)
1870 			return -EINVAL;
1871 		*vm_flags &= ~VM_NOHUGEPAGE;
1872 		*vm_flags |= VM_HUGEPAGE;
1873 		/*
1874 		 * If the vma become good for khugepaged to scan,
1875 		 * register it here without waiting a page fault that
1876 		 * may not happen any time soon.
1877 		 */
1878 		if (unlikely(khugepaged_enter_vma_merge(vma)))
1879 			return -ENOMEM;
1880 		break;
1881 	case MADV_NOHUGEPAGE:
1882 		/*
1883 		 * Be somewhat over-protective like KSM for now!
1884 		 */
1885 		if (*vm_flags & (VM_NOHUGEPAGE | VM_NO_THP))
1886 			return -EINVAL;
1887 		*vm_flags &= ~VM_HUGEPAGE;
1888 		*vm_flags |= VM_NOHUGEPAGE;
1889 		/*
1890 		 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
1891 		 * this vma even if we leave the mm registered in khugepaged if
1892 		 * it got registered before VM_NOHUGEPAGE was set.
1893 		 */
1894 		break;
1895 	}
1896 
1897 	return 0;
1898 }
1899 
1900 static int __init khugepaged_slab_init(void)
1901 {
1902 	mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
1903 					  sizeof(struct mm_slot),
1904 					  __alignof__(struct mm_slot), 0, NULL);
1905 	if (!mm_slot_cache)
1906 		return -ENOMEM;
1907 
1908 	return 0;
1909 }
1910 
1911 static inline struct mm_slot *alloc_mm_slot(void)
1912 {
1913 	if (!mm_slot_cache)	/* initialization failed */
1914 		return NULL;
1915 	return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
1916 }
1917 
1918 static inline void free_mm_slot(struct mm_slot *mm_slot)
1919 {
1920 	kmem_cache_free(mm_slot_cache, mm_slot);
1921 }
1922 
1923 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
1924 {
1925 	struct mm_slot *mm_slot;
1926 
1927 	hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
1928 		if (mm == mm_slot->mm)
1929 			return mm_slot;
1930 
1931 	return NULL;
1932 }
1933 
1934 static void insert_to_mm_slots_hash(struct mm_struct *mm,
1935 				    struct mm_slot *mm_slot)
1936 {
1937 	mm_slot->mm = mm;
1938 	hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
1939 }
1940 
1941 static inline int khugepaged_test_exit(struct mm_struct *mm)
1942 {
1943 	return atomic_read(&mm->mm_users) == 0;
1944 }
1945 
1946 int __khugepaged_enter(struct mm_struct *mm)
1947 {
1948 	struct mm_slot *mm_slot;
1949 	int wakeup;
1950 
1951 	mm_slot = alloc_mm_slot();
1952 	if (!mm_slot)
1953 		return -ENOMEM;
1954 
1955 	/* __khugepaged_exit() must not run from under us */
1956 	VM_BUG_ON(khugepaged_test_exit(mm));
1957 	if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
1958 		free_mm_slot(mm_slot);
1959 		return 0;
1960 	}
1961 
1962 	spin_lock(&khugepaged_mm_lock);
1963 	insert_to_mm_slots_hash(mm, mm_slot);
1964 	/*
1965 	 * Insert just behind the scanning cursor, to let the area settle
1966 	 * down a little.
1967 	 */
1968 	wakeup = list_empty(&khugepaged_scan.mm_head);
1969 	list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
1970 	spin_unlock(&khugepaged_mm_lock);
1971 
1972 	atomic_inc(&mm->mm_count);
1973 	if (wakeup)
1974 		wake_up_interruptible(&khugepaged_wait);
1975 
1976 	return 0;
1977 }
1978 
1979 int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
1980 {
1981 	unsigned long hstart, hend;
1982 	if (!vma->anon_vma)
1983 		/*
1984 		 * Not yet faulted in so we will register later in the
1985 		 * page fault if needed.
1986 		 */
1987 		return 0;
1988 	if (vma->vm_ops)
1989 		/* khugepaged not yet working on file or special mappings */
1990 		return 0;
1991 	VM_BUG_ON(vma->vm_flags & VM_NO_THP);
1992 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
1993 	hend = vma->vm_end & HPAGE_PMD_MASK;
1994 	if (hstart < hend)
1995 		return khugepaged_enter(vma);
1996 	return 0;
1997 }
1998 
1999 void __khugepaged_exit(struct mm_struct *mm)
2000 {
2001 	struct mm_slot *mm_slot;
2002 	int free = 0;
2003 
2004 	spin_lock(&khugepaged_mm_lock);
2005 	mm_slot = get_mm_slot(mm);
2006 	if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
2007 		hash_del(&mm_slot->hash);
2008 		list_del(&mm_slot->mm_node);
2009 		free = 1;
2010 	}
2011 	spin_unlock(&khugepaged_mm_lock);
2012 
2013 	if (free) {
2014 		clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2015 		free_mm_slot(mm_slot);
2016 		mmdrop(mm);
2017 	} else if (mm_slot) {
2018 		/*
2019 		 * This is required to serialize against
2020 		 * khugepaged_test_exit() (which is guaranteed to run
2021 		 * under mmap sem read mode). Stop here (after we
2022 		 * return all pagetables will be destroyed) until
2023 		 * khugepaged has finished working on the pagetables
2024 		 * under the mmap_sem.
2025 		 */
2026 		down_write(&mm->mmap_sem);
2027 		up_write(&mm->mmap_sem);
2028 	}
2029 }
2030 
2031 static void release_pte_page(struct page *page)
2032 {
2033 	/* 0 stands for page_is_file_cache(page) == false */
2034 	dec_zone_page_state(page, NR_ISOLATED_ANON + 0);
2035 	unlock_page(page);
2036 	putback_lru_page(page);
2037 }
2038 
2039 static void release_pte_pages(pte_t *pte, pte_t *_pte)
2040 {
2041 	while (--_pte >= pte) {
2042 		pte_t pteval = *_pte;
2043 		if (!pte_none(pteval))
2044 			release_pte_page(pte_page(pteval));
2045 	}
2046 }
2047 
2048 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
2049 					unsigned long address,
2050 					pte_t *pte)
2051 {
2052 	struct page *page;
2053 	pte_t *_pte;
2054 	int referenced = 0, none = 0;
2055 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
2056 	     _pte++, address += PAGE_SIZE) {
2057 		pte_t pteval = *_pte;
2058 		if (pte_none(pteval)) {
2059 			if (++none <= khugepaged_max_ptes_none)
2060 				continue;
2061 			else
2062 				goto out;
2063 		}
2064 		if (!pte_present(pteval) || !pte_write(pteval))
2065 			goto out;
2066 		page = vm_normal_page(vma, address, pteval);
2067 		if (unlikely(!page))
2068 			goto out;
2069 
2070 		VM_BUG_ON(PageCompound(page));
2071 		BUG_ON(!PageAnon(page));
2072 		VM_BUG_ON(!PageSwapBacked(page));
2073 
2074 		/* cannot use mapcount: can't collapse if there's a gup pin */
2075 		if (page_count(page) != 1)
2076 			goto out;
2077 		/*
2078 		 * We can do it before isolate_lru_page because the
2079 		 * page can't be freed from under us. NOTE: PG_lock
2080 		 * is needed to serialize against split_huge_page
2081 		 * when invoked from the VM.
2082 		 */
2083 		if (!trylock_page(page))
2084 			goto out;
2085 		/*
2086 		 * Isolate the page to avoid collapsing an hugepage
2087 		 * currently in use by the VM.
2088 		 */
2089 		if (isolate_lru_page(page)) {
2090 			unlock_page(page);
2091 			goto out;
2092 		}
2093 		/* 0 stands for page_is_file_cache(page) == false */
2094 		inc_zone_page_state(page, NR_ISOLATED_ANON + 0);
2095 		VM_BUG_ON(!PageLocked(page));
2096 		VM_BUG_ON(PageLRU(page));
2097 
2098 		/* If there is no mapped pte young don't collapse the page */
2099 		if (pte_young(pteval) || PageReferenced(page) ||
2100 		    mmu_notifier_test_young(vma->vm_mm, address))
2101 			referenced = 1;
2102 	}
2103 	if (likely(referenced))
2104 		return 1;
2105 out:
2106 	release_pte_pages(pte, _pte);
2107 	return 0;
2108 }
2109 
2110 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
2111 				      struct vm_area_struct *vma,
2112 				      unsigned long address,
2113 				      spinlock_t *ptl)
2114 {
2115 	pte_t *_pte;
2116 	for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
2117 		pte_t pteval = *_pte;
2118 		struct page *src_page;
2119 
2120 		if (pte_none(pteval)) {
2121 			clear_user_highpage(page, address);
2122 			add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
2123 		} else {
2124 			src_page = pte_page(pteval);
2125 			copy_user_highpage(page, src_page, address, vma);
2126 			VM_BUG_ON(page_mapcount(src_page) != 1);
2127 			release_pte_page(src_page);
2128 			/*
2129 			 * ptl mostly unnecessary, but preempt has to
2130 			 * be disabled to update the per-cpu stats
2131 			 * inside page_remove_rmap().
2132 			 */
2133 			spin_lock(ptl);
2134 			/*
2135 			 * paravirt calls inside pte_clear here are
2136 			 * superfluous.
2137 			 */
2138 			pte_clear(vma->vm_mm, address, _pte);
2139 			page_remove_rmap(src_page);
2140 			spin_unlock(ptl);
2141 			free_page_and_swap_cache(src_page);
2142 		}
2143 
2144 		address += PAGE_SIZE;
2145 		page++;
2146 	}
2147 }
2148 
2149 static void khugepaged_alloc_sleep(void)
2150 {
2151 	wait_event_freezable_timeout(khugepaged_wait, false,
2152 			msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
2153 }
2154 
2155 #ifdef CONFIG_NUMA
2156 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2157 {
2158 	if (IS_ERR(*hpage)) {
2159 		if (!*wait)
2160 			return false;
2161 
2162 		*wait = false;
2163 		*hpage = NULL;
2164 		khugepaged_alloc_sleep();
2165 	} else if (*hpage) {
2166 		put_page(*hpage);
2167 		*hpage = NULL;
2168 	}
2169 
2170 	return true;
2171 }
2172 
2173 static struct page
2174 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2175 		       struct vm_area_struct *vma, unsigned long address,
2176 		       int node)
2177 {
2178 	VM_BUG_ON(*hpage);
2179 	/*
2180 	 * Allocate the page while the vma is still valid and under
2181 	 * the mmap_sem read mode so there is no memory allocation
2182 	 * later when we take the mmap_sem in write mode. This is more
2183 	 * friendly behavior (OTOH it may actually hide bugs) to
2184 	 * filesystems in userland with daemons allocating memory in
2185 	 * the userland I/O paths.  Allocating memory with the
2186 	 * mmap_sem in read mode is good idea also to allow greater
2187 	 * scalability.
2188 	 */
2189 	*hpage  = alloc_hugepage_vma(khugepaged_defrag(), vma, address,
2190 				      node, __GFP_OTHER_NODE);
2191 
2192 	/*
2193 	 * After allocating the hugepage, release the mmap_sem read lock in
2194 	 * preparation for taking it in write mode.
2195 	 */
2196 	up_read(&mm->mmap_sem);
2197 	if (unlikely(!*hpage)) {
2198 		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2199 		*hpage = ERR_PTR(-ENOMEM);
2200 		return NULL;
2201 	}
2202 
2203 	count_vm_event(THP_COLLAPSE_ALLOC);
2204 	return *hpage;
2205 }
2206 #else
2207 static struct page *khugepaged_alloc_hugepage(bool *wait)
2208 {
2209 	struct page *hpage;
2210 
2211 	do {
2212 		hpage = alloc_hugepage(khugepaged_defrag());
2213 		if (!hpage) {
2214 			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
2215 			if (!*wait)
2216 				return NULL;
2217 
2218 			*wait = false;
2219 			khugepaged_alloc_sleep();
2220 		} else
2221 			count_vm_event(THP_COLLAPSE_ALLOC);
2222 	} while (unlikely(!hpage) && likely(khugepaged_enabled()));
2223 
2224 	return hpage;
2225 }
2226 
2227 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
2228 {
2229 	if (!*hpage)
2230 		*hpage = khugepaged_alloc_hugepage(wait);
2231 
2232 	if (unlikely(!*hpage))
2233 		return false;
2234 
2235 	return true;
2236 }
2237 
2238 static struct page
2239 *khugepaged_alloc_page(struct page **hpage, struct mm_struct *mm,
2240 		       struct vm_area_struct *vma, unsigned long address,
2241 		       int node)
2242 {
2243 	up_read(&mm->mmap_sem);
2244 	VM_BUG_ON(!*hpage);
2245 	return  *hpage;
2246 }
2247 #endif
2248 
2249 static bool hugepage_vma_check(struct vm_area_struct *vma)
2250 {
2251 	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
2252 	    (vma->vm_flags & VM_NOHUGEPAGE))
2253 		return false;
2254 
2255 	if (!vma->anon_vma || vma->vm_ops)
2256 		return false;
2257 	if (is_vma_temporary_stack(vma))
2258 		return false;
2259 	VM_BUG_ON(vma->vm_flags & VM_NO_THP);
2260 	return true;
2261 }
2262 
2263 static void collapse_huge_page(struct mm_struct *mm,
2264 				   unsigned long address,
2265 				   struct page **hpage,
2266 				   struct vm_area_struct *vma,
2267 				   int node)
2268 {
2269 	pmd_t *pmd, _pmd;
2270 	pte_t *pte;
2271 	pgtable_t pgtable;
2272 	struct page *new_page;
2273 	spinlock_t *ptl;
2274 	int isolated;
2275 	unsigned long hstart, hend;
2276 	unsigned long mmun_start;	/* For mmu_notifiers */
2277 	unsigned long mmun_end;		/* For mmu_notifiers */
2278 
2279 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2280 
2281 	/* release the mmap_sem read lock. */
2282 	new_page = khugepaged_alloc_page(hpage, mm, vma, address, node);
2283 	if (!new_page)
2284 		return;
2285 
2286 	if (unlikely(mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL)))
2287 		return;
2288 
2289 	/*
2290 	 * Prevent all access to pagetables with the exception of
2291 	 * gup_fast later hanlded by the ptep_clear_flush and the VM
2292 	 * handled by the anon_vma lock + PG_lock.
2293 	 */
2294 	down_write(&mm->mmap_sem);
2295 	if (unlikely(khugepaged_test_exit(mm)))
2296 		goto out;
2297 
2298 	vma = find_vma(mm, address);
2299 	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2300 	hend = vma->vm_end & HPAGE_PMD_MASK;
2301 	if (address < hstart || address + HPAGE_PMD_SIZE > hend)
2302 		goto out;
2303 	if (!hugepage_vma_check(vma))
2304 		goto out;
2305 	pmd = mm_find_pmd(mm, address);
2306 	if (!pmd)
2307 		goto out;
2308 	if (pmd_trans_huge(*pmd))
2309 		goto out;
2310 
2311 	anon_vma_lock_write(vma->anon_vma);
2312 
2313 	pte = pte_offset_map(pmd, address);
2314 	ptl = pte_lockptr(mm, pmd);
2315 
2316 	mmun_start = address;
2317 	mmun_end   = address + HPAGE_PMD_SIZE;
2318 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2319 	spin_lock(&mm->page_table_lock); /* probably unnecessary */
2320 	/*
2321 	 * After this gup_fast can't run anymore. This also removes
2322 	 * any huge TLB entry from the CPU so we won't allow
2323 	 * huge and small TLB entries for the same virtual address
2324 	 * to avoid the risk of CPU bugs in that area.
2325 	 */
2326 	_pmd = pmdp_clear_flush(vma, address, pmd);
2327 	spin_unlock(&mm->page_table_lock);
2328 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2329 
2330 	spin_lock(ptl);
2331 	isolated = __collapse_huge_page_isolate(vma, address, pte);
2332 	spin_unlock(ptl);
2333 
2334 	if (unlikely(!isolated)) {
2335 		pte_unmap(pte);
2336 		spin_lock(&mm->page_table_lock);
2337 		BUG_ON(!pmd_none(*pmd));
2338 		/*
2339 		 * We can only use set_pmd_at when establishing
2340 		 * hugepmds and never for establishing regular pmds that
2341 		 * points to regular pagetables. Use pmd_populate for that
2342 		 */
2343 		pmd_populate(mm, pmd, pmd_pgtable(_pmd));
2344 		spin_unlock(&mm->page_table_lock);
2345 		anon_vma_unlock_write(vma->anon_vma);
2346 		goto out;
2347 	}
2348 
2349 	/*
2350 	 * All pages are isolated and locked so anon_vma rmap
2351 	 * can't run anymore.
2352 	 */
2353 	anon_vma_unlock_write(vma->anon_vma);
2354 
2355 	__collapse_huge_page_copy(pte, new_page, vma, address, ptl);
2356 	pte_unmap(pte);
2357 	__SetPageUptodate(new_page);
2358 	pgtable = pmd_pgtable(_pmd);
2359 
2360 	_pmd = mk_huge_pmd(new_page, vma);
2361 
2362 	/*
2363 	 * spin_lock() below is not the equivalent of smp_wmb(), so
2364 	 * this is needed to avoid the copy_huge_page writes to become
2365 	 * visible after the set_pmd_at() write.
2366 	 */
2367 	smp_wmb();
2368 
2369 	spin_lock(&mm->page_table_lock);
2370 	BUG_ON(!pmd_none(*pmd));
2371 	page_add_new_anon_rmap(new_page, vma, address);
2372 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
2373 	set_pmd_at(mm, address, pmd, _pmd);
2374 	update_mmu_cache_pmd(vma, address, pmd);
2375 	spin_unlock(&mm->page_table_lock);
2376 
2377 	*hpage = NULL;
2378 
2379 	khugepaged_pages_collapsed++;
2380 out_up_write:
2381 	up_write(&mm->mmap_sem);
2382 	return;
2383 
2384 out:
2385 	mem_cgroup_uncharge_page(new_page);
2386 	goto out_up_write;
2387 }
2388 
2389 static int khugepaged_scan_pmd(struct mm_struct *mm,
2390 			       struct vm_area_struct *vma,
2391 			       unsigned long address,
2392 			       struct page **hpage)
2393 {
2394 	pmd_t *pmd;
2395 	pte_t *pte, *_pte;
2396 	int ret = 0, referenced = 0, none = 0;
2397 	struct page *page;
2398 	unsigned long _address;
2399 	spinlock_t *ptl;
2400 	int node = NUMA_NO_NODE;
2401 
2402 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
2403 
2404 	pmd = mm_find_pmd(mm, address);
2405 	if (!pmd)
2406 		goto out;
2407 	if (pmd_trans_huge(*pmd))
2408 		goto out;
2409 
2410 	pte = pte_offset_map_lock(mm, pmd, address, &ptl);
2411 	for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
2412 	     _pte++, _address += PAGE_SIZE) {
2413 		pte_t pteval = *_pte;
2414 		if (pte_none(pteval)) {
2415 			if (++none <= khugepaged_max_ptes_none)
2416 				continue;
2417 			else
2418 				goto out_unmap;
2419 		}
2420 		if (!pte_present(pteval) || !pte_write(pteval))
2421 			goto out_unmap;
2422 		page = vm_normal_page(vma, _address, pteval);
2423 		if (unlikely(!page))
2424 			goto out_unmap;
2425 		/*
2426 		 * Chose the node of the first page. This could
2427 		 * be more sophisticated and look at more pages,
2428 		 * but isn't for now.
2429 		 */
2430 		if (node == NUMA_NO_NODE)
2431 			node = page_to_nid(page);
2432 		VM_BUG_ON(PageCompound(page));
2433 		if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
2434 			goto out_unmap;
2435 		/* cannot use mapcount: can't collapse if there's a gup pin */
2436 		if (page_count(page) != 1)
2437 			goto out_unmap;
2438 		if (pte_young(pteval) || PageReferenced(page) ||
2439 		    mmu_notifier_test_young(vma->vm_mm, address))
2440 			referenced = 1;
2441 	}
2442 	if (referenced)
2443 		ret = 1;
2444 out_unmap:
2445 	pte_unmap_unlock(pte, ptl);
2446 	if (ret)
2447 		/* collapse_huge_page will return with the mmap_sem released */
2448 		collapse_huge_page(mm, address, hpage, vma, node);
2449 out:
2450 	return ret;
2451 }
2452 
2453 static void collect_mm_slot(struct mm_slot *mm_slot)
2454 {
2455 	struct mm_struct *mm = mm_slot->mm;
2456 
2457 	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2458 
2459 	if (khugepaged_test_exit(mm)) {
2460 		/* free mm_slot */
2461 		hash_del(&mm_slot->hash);
2462 		list_del(&mm_slot->mm_node);
2463 
2464 		/*
2465 		 * Not strictly needed because the mm exited already.
2466 		 *
2467 		 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
2468 		 */
2469 
2470 		/* khugepaged_mm_lock actually not necessary for the below */
2471 		free_mm_slot(mm_slot);
2472 		mmdrop(mm);
2473 	}
2474 }
2475 
2476 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2477 					    struct page **hpage)
2478 	__releases(&khugepaged_mm_lock)
2479 	__acquires(&khugepaged_mm_lock)
2480 {
2481 	struct mm_slot *mm_slot;
2482 	struct mm_struct *mm;
2483 	struct vm_area_struct *vma;
2484 	int progress = 0;
2485 
2486 	VM_BUG_ON(!pages);
2487 	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&khugepaged_mm_lock));
2488 
2489 	if (khugepaged_scan.mm_slot)
2490 		mm_slot = khugepaged_scan.mm_slot;
2491 	else {
2492 		mm_slot = list_entry(khugepaged_scan.mm_head.next,
2493 				     struct mm_slot, mm_node);
2494 		khugepaged_scan.address = 0;
2495 		khugepaged_scan.mm_slot = mm_slot;
2496 	}
2497 	spin_unlock(&khugepaged_mm_lock);
2498 
2499 	mm = mm_slot->mm;
2500 	down_read(&mm->mmap_sem);
2501 	if (unlikely(khugepaged_test_exit(mm)))
2502 		vma = NULL;
2503 	else
2504 		vma = find_vma(mm, khugepaged_scan.address);
2505 
2506 	progress++;
2507 	for (; vma; vma = vma->vm_next) {
2508 		unsigned long hstart, hend;
2509 
2510 		cond_resched();
2511 		if (unlikely(khugepaged_test_exit(mm))) {
2512 			progress++;
2513 			break;
2514 		}
2515 		if (!hugepage_vma_check(vma)) {
2516 skip:
2517 			progress++;
2518 			continue;
2519 		}
2520 		hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2521 		hend = vma->vm_end & HPAGE_PMD_MASK;
2522 		if (hstart >= hend)
2523 			goto skip;
2524 		if (khugepaged_scan.address > hend)
2525 			goto skip;
2526 		if (khugepaged_scan.address < hstart)
2527 			khugepaged_scan.address = hstart;
2528 		VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2529 
2530 		while (khugepaged_scan.address < hend) {
2531 			int ret;
2532 			cond_resched();
2533 			if (unlikely(khugepaged_test_exit(mm)))
2534 				goto breakouterloop;
2535 
2536 			VM_BUG_ON(khugepaged_scan.address < hstart ||
2537 				  khugepaged_scan.address + HPAGE_PMD_SIZE >
2538 				  hend);
2539 			ret = khugepaged_scan_pmd(mm, vma,
2540 						  khugepaged_scan.address,
2541 						  hpage);
2542 			/* move to next address */
2543 			khugepaged_scan.address += HPAGE_PMD_SIZE;
2544 			progress += HPAGE_PMD_NR;
2545 			if (ret)
2546 				/* we released mmap_sem so break loop */
2547 				goto breakouterloop_mmap_sem;
2548 			if (progress >= pages)
2549 				goto breakouterloop;
2550 		}
2551 	}
2552 breakouterloop:
2553 	up_read(&mm->mmap_sem); /* exit_mmap will destroy ptes after this */
2554 breakouterloop_mmap_sem:
2555 
2556 	spin_lock(&khugepaged_mm_lock);
2557 	VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2558 	/*
2559 	 * Release the current mm_slot if this mm is about to die, or
2560 	 * if we scanned all vmas of this mm.
2561 	 */
2562 	if (khugepaged_test_exit(mm) || !vma) {
2563 		/*
2564 		 * Make sure that if mm_users is reaching zero while
2565 		 * khugepaged runs here, khugepaged_exit will find
2566 		 * mm_slot not pointing to the exiting mm.
2567 		 */
2568 		if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2569 			khugepaged_scan.mm_slot = list_entry(
2570 				mm_slot->mm_node.next,
2571 				struct mm_slot, mm_node);
2572 			khugepaged_scan.address = 0;
2573 		} else {
2574 			khugepaged_scan.mm_slot = NULL;
2575 			khugepaged_full_scans++;
2576 		}
2577 
2578 		collect_mm_slot(mm_slot);
2579 	}
2580 
2581 	return progress;
2582 }
2583 
2584 static int khugepaged_has_work(void)
2585 {
2586 	return !list_empty(&khugepaged_scan.mm_head) &&
2587 		khugepaged_enabled();
2588 }
2589 
2590 static int khugepaged_wait_event(void)
2591 {
2592 	return !list_empty(&khugepaged_scan.mm_head) ||
2593 		kthread_should_stop();
2594 }
2595 
2596 static void khugepaged_do_scan(void)
2597 {
2598 	struct page *hpage = NULL;
2599 	unsigned int progress = 0, pass_through_head = 0;
2600 	unsigned int pages = khugepaged_pages_to_scan;
2601 	bool wait = true;
2602 
2603 	barrier(); /* write khugepaged_pages_to_scan to local stack */
2604 
2605 	while (progress < pages) {
2606 		if (!khugepaged_prealloc_page(&hpage, &wait))
2607 			break;
2608 
2609 		cond_resched();
2610 
2611 		if (unlikely(kthread_should_stop() || freezing(current)))
2612 			break;
2613 
2614 		spin_lock(&khugepaged_mm_lock);
2615 		if (!khugepaged_scan.mm_slot)
2616 			pass_through_head++;
2617 		if (khugepaged_has_work() &&
2618 		    pass_through_head < 2)
2619 			progress += khugepaged_scan_mm_slot(pages - progress,
2620 							    &hpage);
2621 		else
2622 			progress = pages;
2623 		spin_unlock(&khugepaged_mm_lock);
2624 	}
2625 
2626 	if (!IS_ERR_OR_NULL(hpage))
2627 		put_page(hpage);
2628 }
2629 
2630 static void khugepaged_wait_work(void)
2631 {
2632 	try_to_freeze();
2633 
2634 	if (khugepaged_has_work()) {
2635 		if (!khugepaged_scan_sleep_millisecs)
2636 			return;
2637 
2638 		wait_event_freezable_timeout(khugepaged_wait,
2639 					     kthread_should_stop(),
2640 			msecs_to_jiffies(khugepaged_scan_sleep_millisecs));
2641 		return;
2642 	}
2643 
2644 	if (khugepaged_enabled())
2645 		wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2646 }
2647 
2648 static int khugepaged(void *none)
2649 {
2650 	struct mm_slot *mm_slot;
2651 
2652 	set_freezable();
2653 	set_user_nice(current, 19);
2654 
2655 	while (!kthread_should_stop()) {
2656 		khugepaged_do_scan();
2657 		khugepaged_wait_work();
2658 	}
2659 
2660 	spin_lock(&khugepaged_mm_lock);
2661 	mm_slot = khugepaged_scan.mm_slot;
2662 	khugepaged_scan.mm_slot = NULL;
2663 	if (mm_slot)
2664 		collect_mm_slot(mm_slot);
2665 	spin_unlock(&khugepaged_mm_lock);
2666 	return 0;
2667 }
2668 
2669 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
2670 		unsigned long haddr, pmd_t *pmd)
2671 {
2672 	struct mm_struct *mm = vma->vm_mm;
2673 	pgtable_t pgtable;
2674 	pmd_t _pmd;
2675 	int i;
2676 
2677 	pmdp_clear_flush(vma, haddr, pmd);
2678 	/* leave pmd empty until pte is filled */
2679 
2680 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
2681 	pmd_populate(mm, &_pmd, pgtable);
2682 
2683 	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
2684 		pte_t *pte, entry;
2685 		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
2686 		entry = pte_mkspecial(entry);
2687 		pte = pte_offset_map(&_pmd, haddr);
2688 		VM_BUG_ON(!pte_none(*pte));
2689 		set_pte_at(mm, haddr, pte, entry);
2690 		pte_unmap(pte);
2691 	}
2692 	smp_wmb(); /* make pte visible before pmd */
2693 	pmd_populate(mm, pmd, pgtable);
2694 	put_huge_zero_page();
2695 }
2696 
2697 void __split_huge_page_pmd(struct vm_area_struct *vma, unsigned long address,
2698 		pmd_t *pmd)
2699 {
2700 	struct page *page;
2701 	struct mm_struct *mm = vma->vm_mm;
2702 	unsigned long haddr = address & HPAGE_PMD_MASK;
2703 	unsigned long mmun_start;	/* For mmu_notifiers */
2704 	unsigned long mmun_end;		/* For mmu_notifiers */
2705 
2706 	BUG_ON(vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE);
2707 
2708 	mmun_start = haddr;
2709 	mmun_end   = haddr + HPAGE_PMD_SIZE;
2710 	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
2711 	spin_lock(&mm->page_table_lock);
2712 	if (unlikely(!pmd_trans_huge(*pmd))) {
2713 		spin_unlock(&mm->page_table_lock);
2714 		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2715 		return;
2716 	}
2717 	if (is_huge_zero_pmd(*pmd)) {
2718 		__split_huge_zero_page_pmd(vma, haddr, pmd);
2719 		spin_unlock(&mm->page_table_lock);
2720 		mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2721 		return;
2722 	}
2723 	page = pmd_page(*pmd);
2724 	VM_BUG_ON(!page_count(page));
2725 	get_page(page);
2726 	spin_unlock(&mm->page_table_lock);
2727 	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
2728 
2729 	split_huge_page(page);
2730 
2731 	put_page(page);
2732 	BUG_ON(pmd_trans_huge(*pmd));
2733 }
2734 
2735 void split_huge_page_pmd_mm(struct mm_struct *mm, unsigned long address,
2736 		pmd_t *pmd)
2737 {
2738 	struct vm_area_struct *vma;
2739 
2740 	vma = find_vma(mm, address);
2741 	BUG_ON(vma == NULL);
2742 	split_huge_page_pmd(vma, address, pmd);
2743 }
2744 
2745 static void split_huge_page_address(struct mm_struct *mm,
2746 				    unsigned long address)
2747 {
2748 	pmd_t *pmd;
2749 
2750 	VM_BUG_ON(!(address & ~HPAGE_PMD_MASK));
2751 
2752 	pmd = mm_find_pmd(mm, address);
2753 	if (!pmd)
2754 		return;
2755 	/*
2756 	 * Caller holds the mmap_sem write mode, so a huge pmd cannot
2757 	 * materialize from under us.
2758 	 */
2759 	split_huge_page_pmd_mm(mm, address, pmd);
2760 }
2761 
2762 void __vma_adjust_trans_huge(struct vm_area_struct *vma,
2763 			     unsigned long start,
2764 			     unsigned long end,
2765 			     long adjust_next)
2766 {
2767 	/*
2768 	 * If the new start address isn't hpage aligned and it could
2769 	 * previously contain an hugepage: check if we need to split
2770 	 * an huge pmd.
2771 	 */
2772 	if (start & ~HPAGE_PMD_MASK &&
2773 	    (start & HPAGE_PMD_MASK) >= vma->vm_start &&
2774 	    (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2775 		split_huge_page_address(vma->vm_mm, start);
2776 
2777 	/*
2778 	 * If the new end address isn't hpage aligned and it could
2779 	 * previously contain an hugepage: check if we need to split
2780 	 * an huge pmd.
2781 	 */
2782 	if (end & ~HPAGE_PMD_MASK &&
2783 	    (end & HPAGE_PMD_MASK) >= vma->vm_start &&
2784 	    (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
2785 		split_huge_page_address(vma->vm_mm, end);
2786 
2787 	/*
2788 	 * If we're also updating the vma->vm_next->vm_start, if the new
2789 	 * vm_next->vm_start isn't page aligned and it could previously
2790 	 * contain an hugepage: check if we need to split an huge pmd.
2791 	 */
2792 	if (adjust_next > 0) {
2793 		struct vm_area_struct *next = vma->vm_next;
2794 		unsigned long nstart = next->vm_start;
2795 		nstart += adjust_next << PAGE_SHIFT;
2796 		if (nstart & ~HPAGE_PMD_MASK &&
2797 		    (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
2798 		    (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
2799 			split_huge_page_address(next->vm_mm, nstart);
2800 	}
2801 }
2802