1 // SPDX-License-Identifier: GPL-2.0
2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
3
4 #include <linux/mm.h>
5 #include <linux/sched.h>
6 #include <linux/sched/mm.h>
7 #include <linux/sched/coredump.h>
8 #include <linux/mmu_notifier.h>
9 #include <linux/rmap.h>
10 #include <linux/swap.h>
11 #include <linux/mm_inline.h>
12 #include <linux/kthread.h>
13 #include <linux/khugepaged.h>
14 #include <linux/freezer.h>
15 #include <linux/mman.h>
16 #include <linux/hashtable.h>
17 #include <linux/userfaultfd_k.h>
18 #include <linux/page_idle.h>
19 #include <linux/swapops.h>
20 #include <linux/shmem_fs.h>
21
22 #include <asm/tlb.h>
23 #include <asm/pgalloc.h>
24 #include "internal.h"
25
26 enum scan_result {
27 SCAN_FAIL,
28 SCAN_SUCCEED,
29 SCAN_PMD_NULL,
30 SCAN_EXCEED_NONE_PTE,
31 SCAN_EXCEED_SWAP_PTE,
32 SCAN_EXCEED_SHARED_PTE,
33 SCAN_PTE_NON_PRESENT,
34 SCAN_PTE_UFFD_WP,
35 SCAN_PAGE_RO,
36 SCAN_LACK_REFERENCED_PAGE,
37 SCAN_PAGE_NULL,
38 SCAN_SCAN_ABORT,
39 SCAN_PAGE_COUNT,
40 SCAN_PAGE_LRU,
41 SCAN_PAGE_LOCK,
42 SCAN_PAGE_ANON,
43 SCAN_PAGE_COMPOUND,
44 SCAN_ANY_PROCESS,
45 SCAN_VMA_NULL,
46 SCAN_VMA_CHECK,
47 SCAN_ADDRESS_RANGE,
48 SCAN_SWAP_CACHE_PAGE,
49 SCAN_DEL_PAGE_LRU,
50 SCAN_ALLOC_HUGE_PAGE_FAIL,
51 SCAN_CGROUP_CHARGE_FAIL,
52 SCAN_TRUNCATED,
53 SCAN_PAGE_HAS_PRIVATE,
54 };
55
56 #define CREATE_TRACE_POINTS
57 #include <trace/events/huge_memory.h>
58
59 static struct task_struct *khugepaged_thread __read_mostly;
60 static DEFINE_MUTEX(khugepaged_mutex);
61
62 /* default scan 8*512 pte (or vmas) every 30 second */
63 static unsigned int khugepaged_pages_to_scan __read_mostly;
64 static unsigned int khugepaged_pages_collapsed;
65 static unsigned int khugepaged_full_scans;
66 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
67 /* during fragmentation poll the hugepage allocator once every minute */
68 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
69 static unsigned long khugepaged_sleep_expire;
70 static DEFINE_SPINLOCK(khugepaged_mm_lock);
71 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
72 /*
73 * default collapse hugepages if there is at least one pte mapped like
74 * it would have happened if the vma was large enough during page
75 * fault.
76 */
77 static unsigned int khugepaged_max_ptes_none __read_mostly;
78 static unsigned int khugepaged_max_ptes_swap __read_mostly;
79 static unsigned int khugepaged_max_ptes_shared __read_mostly;
80
81 #define MM_SLOTS_HASH_BITS 10
82 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
83
84 static struct kmem_cache *mm_slot_cache __read_mostly;
85
86 #define MAX_PTE_MAPPED_THP 8
87
88 /**
89 * struct mm_slot - hash lookup from mm to mm_slot
90 * @hash: hash collision list
91 * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head
92 * @mm: the mm that this information is valid for
93 */
94 struct mm_slot {
95 struct hlist_node hash;
96 struct list_head mm_node;
97 struct mm_struct *mm;
98
99 /* pte-mapped THP in this mm */
100 int nr_pte_mapped_thp;
101 unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP];
102 };
103
104 /**
105 * struct khugepaged_scan - cursor for scanning
106 * @mm_head: the head of the mm list to scan
107 * @mm_slot: the current mm_slot we are scanning
108 * @address: the next address inside that to be scanned
109 *
110 * There is only the one khugepaged_scan instance of this cursor structure.
111 */
112 struct khugepaged_scan {
113 struct list_head mm_head;
114 struct mm_slot *mm_slot;
115 unsigned long address;
116 };
117
118 static struct khugepaged_scan khugepaged_scan = {
119 .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head),
120 };
121
122 #ifdef CONFIG_SYSFS
scan_sleep_millisecs_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)123 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj,
124 struct kobj_attribute *attr,
125 char *buf)
126 {
127 return sprintf(buf, "%u\n", khugepaged_scan_sleep_millisecs);
128 }
129
scan_sleep_millisecs_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)130 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj,
131 struct kobj_attribute *attr,
132 const char *buf, size_t count)
133 {
134 unsigned long msecs;
135 int err;
136
137 err = kstrtoul(buf, 10, &msecs);
138 if (err || msecs > UINT_MAX)
139 return -EINVAL;
140
141 khugepaged_scan_sleep_millisecs = msecs;
142 khugepaged_sleep_expire = 0;
143 wake_up_interruptible(&khugepaged_wait);
144
145 return count;
146 }
147 static struct kobj_attribute scan_sleep_millisecs_attr =
148 __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show,
149 scan_sleep_millisecs_store);
150
alloc_sleep_millisecs_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)151 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj,
152 struct kobj_attribute *attr,
153 char *buf)
154 {
155 return sprintf(buf, "%u\n", khugepaged_alloc_sleep_millisecs);
156 }
157
alloc_sleep_millisecs_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)158 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj,
159 struct kobj_attribute *attr,
160 const char *buf, size_t count)
161 {
162 unsigned long msecs;
163 int err;
164
165 err = kstrtoul(buf, 10, &msecs);
166 if (err || msecs > UINT_MAX)
167 return -EINVAL;
168
169 khugepaged_alloc_sleep_millisecs = msecs;
170 khugepaged_sleep_expire = 0;
171 wake_up_interruptible(&khugepaged_wait);
172
173 return count;
174 }
175 static struct kobj_attribute alloc_sleep_millisecs_attr =
176 __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show,
177 alloc_sleep_millisecs_store);
178
pages_to_scan_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)179 static ssize_t pages_to_scan_show(struct kobject *kobj,
180 struct kobj_attribute *attr,
181 char *buf)
182 {
183 return sprintf(buf, "%u\n", khugepaged_pages_to_scan);
184 }
pages_to_scan_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)185 static ssize_t pages_to_scan_store(struct kobject *kobj,
186 struct kobj_attribute *attr,
187 const char *buf, size_t count)
188 {
189 int err;
190 unsigned long pages;
191
192 err = kstrtoul(buf, 10, &pages);
193 if (err || !pages || pages > UINT_MAX)
194 return -EINVAL;
195
196 khugepaged_pages_to_scan = pages;
197
198 return count;
199 }
200 static struct kobj_attribute pages_to_scan_attr =
201 __ATTR(pages_to_scan, 0644, pages_to_scan_show,
202 pages_to_scan_store);
203
pages_collapsed_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)204 static ssize_t pages_collapsed_show(struct kobject *kobj,
205 struct kobj_attribute *attr,
206 char *buf)
207 {
208 return sprintf(buf, "%u\n", khugepaged_pages_collapsed);
209 }
210 static struct kobj_attribute pages_collapsed_attr =
211 __ATTR_RO(pages_collapsed);
212
full_scans_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)213 static ssize_t full_scans_show(struct kobject *kobj,
214 struct kobj_attribute *attr,
215 char *buf)
216 {
217 return sprintf(buf, "%u\n", khugepaged_full_scans);
218 }
219 static struct kobj_attribute full_scans_attr =
220 __ATTR_RO(full_scans);
221
khugepaged_defrag_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)222 static ssize_t khugepaged_defrag_show(struct kobject *kobj,
223 struct kobj_attribute *attr, char *buf)
224 {
225 return single_hugepage_flag_show(kobj, attr, buf,
226 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
227 }
khugepaged_defrag_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)228 static ssize_t khugepaged_defrag_store(struct kobject *kobj,
229 struct kobj_attribute *attr,
230 const char *buf, size_t count)
231 {
232 return single_hugepage_flag_store(kobj, attr, buf, count,
233 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);
234 }
235 static struct kobj_attribute khugepaged_defrag_attr =
236 __ATTR(defrag, 0644, khugepaged_defrag_show,
237 khugepaged_defrag_store);
238
239 /*
240 * max_ptes_none controls if khugepaged should collapse hugepages over
241 * any unmapped ptes in turn potentially increasing the memory
242 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not
243 * reduce the available free memory in the system as it
244 * runs. Increasing max_ptes_none will instead potentially reduce the
245 * free memory in the system during the khugepaged scan.
246 */
khugepaged_max_ptes_none_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)247 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj,
248 struct kobj_attribute *attr,
249 char *buf)
250 {
251 return sprintf(buf, "%u\n", khugepaged_max_ptes_none);
252 }
khugepaged_max_ptes_none_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)253 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj,
254 struct kobj_attribute *attr,
255 const char *buf, size_t count)
256 {
257 int err;
258 unsigned long max_ptes_none;
259
260 err = kstrtoul(buf, 10, &max_ptes_none);
261 if (err || max_ptes_none > HPAGE_PMD_NR-1)
262 return -EINVAL;
263
264 khugepaged_max_ptes_none = max_ptes_none;
265
266 return count;
267 }
268 static struct kobj_attribute khugepaged_max_ptes_none_attr =
269 __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show,
270 khugepaged_max_ptes_none_store);
271
khugepaged_max_ptes_swap_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)272 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj,
273 struct kobj_attribute *attr,
274 char *buf)
275 {
276 return sprintf(buf, "%u\n", khugepaged_max_ptes_swap);
277 }
278
khugepaged_max_ptes_swap_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)279 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj,
280 struct kobj_attribute *attr,
281 const char *buf, size_t count)
282 {
283 int err;
284 unsigned long max_ptes_swap;
285
286 err = kstrtoul(buf, 10, &max_ptes_swap);
287 if (err || max_ptes_swap > HPAGE_PMD_NR-1)
288 return -EINVAL;
289
290 khugepaged_max_ptes_swap = max_ptes_swap;
291
292 return count;
293 }
294
295 static struct kobj_attribute khugepaged_max_ptes_swap_attr =
296 __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show,
297 khugepaged_max_ptes_swap_store);
298
khugepaged_max_ptes_shared_show(struct kobject * kobj,struct kobj_attribute * attr,char * buf)299 static ssize_t khugepaged_max_ptes_shared_show(struct kobject *kobj,
300 struct kobj_attribute *attr,
301 char *buf)
302 {
303 return sprintf(buf, "%u\n", khugepaged_max_ptes_shared);
304 }
305
khugepaged_max_ptes_shared_store(struct kobject * kobj,struct kobj_attribute * attr,const char * buf,size_t count)306 static ssize_t khugepaged_max_ptes_shared_store(struct kobject *kobj,
307 struct kobj_attribute *attr,
308 const char *buf, size_t count)
309 {
310 int err;
311 unsigned long max_ptes_shared;
312
313 err = kstrtoul(buf, 10, &max_ptes_shared);
314 if (err || max_ptes_shared > HPAGE_PMD_NR-1)
315 return -EINVAL;
316
317 khugepaged_max_ptes_shared = max_ptes_shared;
318
319 return count;
320 }
321
322 static struct kobj_attribute khugepaged_max_ptes_shared_attr =
323 __ATTR(max_ptes_shared, 0644, khugepaged_max_ptes_shared_show,
324 khugepaged_max_ptes_shared_store);
325
326 static struct attribute *khugepaged_attr[] = {
327 &khugepaged_defrag_attr.attr,
328 &khugepaged_max_ptes_none_attr.attr,
329 &khugepaged_max_ptes_swap_attr.attr,
330 &khugepaged_max_ptes_shared_attr.attr,
331 &pages_to_scan_attr.attr,
332 &pages_collapsed_attr.attr,
333 &full_scans_attr.attr,
334 &scan_sleep_millisecs_attr.attr,
335 &alloc_sleep_millisecs_attr.attr,
336 NULL,
337 };
338
339 struct attribute_group khugepaged_attr_group = {
340 .attrs = khugepaged_attr,
341 .name = "khugepaged",
342 };
343 #endif /* CONFIG_SYSFS */
344
hugepage_madvise(struct vm_area_struct * vma,unsigned long * vm_flags,int advice)345 int hugepage_madvise(struct vm_area_struct *vma,
346 unsigned long *vm_flags, int advice)
347 {
348 switch (advice) {
349 case MADV_HUGEPAGE:
350 #ifdef CONFIG_S390
351 /*
352 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390
353 * can't handle this properly after s390_enable_sie, so we simply
354 * ignore the madvise to prevent qemu from causing a SIGSEGV.
355 */
356 if (mm_has_pgste(vma->vm_mm))
357 return 0;
358 #endif
359 *vm_flags &= ~VM_NOHUGEPAGE;
360 *vm_flags |= VM_HUGEPAGE;
361 /*
362 * If the vma become good for khugepaged to scan,
363 * register it here without waiting a page fault that
364 * may not happen any time soon.
365 */
366 if (!(*vm_flags & VM_NO_KHUGEPAGED) &&
367 khugepaged_enter_vma_merge(vma, *vm_flags))
368 return -ENOMEM;
369 break;
370 case MADV_NOHUGEPAGE:
371 *vm_flags &= ~VM_HUGEPAGE;
372 *vm_flags |= VM_NOHUGEPAGE;
373 /*
374 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning
375 * this vma even if we leave the mm registered in khugepaged if
376 * it got registered before VM_NOHUGEPAGE was set.
377 */
378 break;
379 }
380
381 return 0;
382 }
383
khugepaged_init(void)384 int __init khugepaged_init(void)
385 {
386 mm_slot_cache = kmem_cache_create("khugepaged_mm_slot",
387 sizeof(struct mm_slot),
388 __alignof__(struct mm_slot), 0, NULL);
389 if (!mm_slot_cache)
390 return -ENOMEM;
391
392 khugepaged_pages_to_scan = HPAGE_PMD_NR * 8;
393 khugepaged_max_ptes_none = HPAGE_PMD_NR - 1;
394 khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8;
395 khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2;
396
397 return 0;
398 }
399
khugepaged_destroy(void)400 void __init khugepaged_destroy(void)
401 {
402 kmem_cache_destroy(mm_slot_cache);
403 }
404
alloc_mm_slot(void)405 static inline struct mm_slot *alloc_mm_slot(void)
406 {
407 if (!mm_slot_cache) /* initialization failed */
408 return NULL;
409 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
410 }
411
free_mm_slot(struct mm_slot * mm_slot)412 static inline void free_mm_slot(struct mm_slot *mm_slot)
413 {
414 kmem_cache_free(mm_slot_cache, mm_slot);
415 }
416
get_mm_slot(struct mm_struct * mm)417 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
418 {
419 struct mm_slot *mm_slot;
420
421 hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm)
422 if (mm == mm_slot->mm)
423 return mm_slot;
424
425 return NULL;
426 }
427
insert_to_mm_slots_hash(struct mm_struct * mm,struct mm_slot * mm_slot)428 static void insert_to_mm_slots_hash(struct mm_struct *mm,
429 struct mm_slot *mm_slot)
430 {
431 mm_slot->mm = mm;
432 hash_add(mm_slots_hash, &mm_slot->hash, (long)mm);
433 }
434
khugepaged_test_exit(struct mm_struct * mm)435 static inline int khugepaged_test_exit(struct mm_struct *mm)
436 {
437 return atomic_read(&mm->mm_users) == 0;
438 }
439
hugepage_vma_check(struct vm_area_struct * vma,unsigned long vm_flags)440 static bool hugepage_vma_check(struct vm_area_struct *vma,
441 unsigned long vm_flags)
442 {
443 if ((!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
444 (vm_flags & VM_NOHUGEPAGE) ||
445 test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
446 return false;
447
448 if (shmem_file(vma->vm_file) ||
449 (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
450 vma->vm_file &&
451 (vm_flags & VM_DENYWRITE))) {
452 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
453 HPAGE_PMD_NR);
454 }
455 if (!vma->anon_vma || vma->vm_ops)
456 return false;
457 if (vma_is_temporary_stack(vma))
458 return false;
459 return !(vm_flags & VM_NO_KHUGEPAGED);
460 }
461
__khugepaged_enter(struct mm_struct * mm)462 int __khugepaged_enter(struct mm_struct *mm)
463 {
464 struct mm_slot *mm_slot;
465 int wakeup;
466
467 mm_slot = alloc_mm_slot();
468 if (!mm_slot)
469 return -ENOMEM;
470
471 /* __khugepaged_exit() must not run from under us */
472 VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm);
473 if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) {
474 free_mm_slot(mm_slot);
475 return 0;
476 }
477
478 spin_lock(&khugepaged_mm_lock);
479 insert_to_mm_slots_hash(mm, mm_slot);
480 /*
481 * Insert just behind the scanning cursor, to let the area settle
482 * down a little.
483 */
484 wakeup = list_empty(&khugepaged_scan.mm_head);
485 list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head);
486 spin_unlock(&khugepaged_mm_lock);
487
488 mmgrab(mm);
489 if (wakeup)
490 wake_up_interruptible(&khugepaged_wait);
491
492 return 0;
493 }
494
khugepaged_enter_vma_merge(struct vm_area_struct * vma,unsigned long vm_flags)495 int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
496 unsigned long vm_flags)
497 {
498 unsigned long hstart, hend;
499
500 /*
501 * khugepaged only supports read-only files for non-shmem files.
502 * khugepaged does not yet work on special mappings. And
503 * file-private shmem THP is not supported.
504 */
505 if (!hugepage_vma_check(vma, vm_flags))
506 return 0;
507
508 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
509 hend = vma->vm_end & HPAGE_PMD_MASK;
510 if (hstart < hend)
511 return khugepaged_enter(vma, vm_flags);
512 return 0;
513 }
514
__khugepaged_exit(struct mm_struct * mm)515 void __khugepaged_exit(struct mm_struct *mm)
516 {
517 struct mm_slot *mm_slot;
518 int free = 0;
519
520 spin_lock(&khugepaged_mm_lock);
521 mm_slot = get_mm_slot(mm);
522 if (mm_slot && khugepaged_scan.mm_slot != mm_slot) {
523 hash_del(&mm_slot->hash);
524 list_del(&mm_slot->mm_node);
525 free = 1;
526 }
527 spin_unlock(&khugepaged_mm_lock);
528
529 if (free) {
530 clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
531 free_mm_slot(mm_slot);
532 mmdrop(mm);
533 } else if (mm_slot) {
534 /*
535 * This is required to serialize against
536 * khugepaged_test_exit() (which is guaranteed to run
537 * under mmap sem read mode). Stop here (after we
538 * return all pagetables will be destroyed) until
539 * khugepaged has finished working on the pagetables
540 * under the mmap_lock.
541 */
542 mmap_write_lock(mm);
543 mmap_write_unlock(mm);
544 }
545 }
546
release_pte_page(struct page * page)547 static void release_pte_page(struct page *page)
548 {
549 mod_node_page_state(page_pgdat(page),
550 NR_ISOLATED_ANON + page_is_file_lru(page),
551 -compound_nr(page));
552 unlock_page(page);
553 putback_lru_page(page);
554 }
555
release_pte_pages(pte_t * pte,pte_t * _pte,struct list_head * compound_pagelist)556 static void release_pte_pages(pte_t *pte, pte_t *_pte,
557 struct list_head *compound_pagelist)
558 {
559 struct page *page, *tmp;
560
561 while (--_pte >= pte) {
562 pte_t pteval = *_pte;
563
564 page = pte_page(pteval);
565 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
566 !PageCompound(page))
567 release_pte_page(page);
568 }
569
570 list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
571 list_del(&page->lru);
572 release_pte_page(page);
573 }
574 }
575
is_refcount_suitable(struct page * page)576 static bool is_refcount_suitable(struct page *page)
577 {
578 int expected_refcount;
579
580 expected_refcount = total_mapcount(page);
581 if (PageSwapCache(page))
582 expected_refcount += compound_nr(page);
583
584 return page_count(page) == expected_refcount;
585 }
586
__collapse_huge_page_isolate(struct vm_area_struct * vma,unsigned long address,pte_t * pte,struct list_head * compound_pagelist)587 static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
588 unsigned long address,
589 pte_t *pte,
590 struct list_head *compound_pagelist)
591 {
592 struct page *page = NULL;
593 pte_t *_pte;
594 int none_or_zero = 0, shared = 0, result = 0, referenced = 0;
595 bool writable = false;
596
597 for (_pte = pte; _pte < pte+HPAGE_PMD_NR;
598 _pte++, address += PAGE_SIZE) {
599 pte_t pteval = *_pte;
600 if (pte_none(pteval) || (pte_present(pteval) &&
601 is_zero_pfn(pte_pfn(pteval)))) {
602 if (!userfaultfd_armed(vma) &&
603 ++none_or_zero <= khugepaged_max_ptes_none) {
604 continue;
605 } else {
606 result = SCAN_EXCEED_NONE_PTE;
607 goto out;
608 }
609 }
610 if (!pte_present(pteval)) {
611 result = SCAN_PTE_NON_PRESENT;
612 goto out;
613 }
614 page = vm_normal_page(vma, address, pteval);
615 if (unlikely(!page)) {
616 result = SCAN_PAGE_NULL;
617 goto out;
618 }
619
620 VM_BUG_ON_PAGE(!PageAnon(page), page);
621
622 if (page_mapcount(page) > 1 &&
623 ++shared > khugepaged_max_ptes_shared) {
624 result = SCAN_EXCEED_SHARED_PTE;
625 goto out;
626 }
627
628 if (PageCompound(page)) {
629 struct page *p;
630 page = compound_head(page);
631
632 /*
633 * Check if we have dealt with the compound page
634 * already
635 */
636 list_for_each_entry(p, compound_pagelist, lru) {
637 if (page == p)
638 goto next;
639 }
640 }
641
642 /*
643 * We can do it before isolate_lru_page because the
644 * page can't be freed from under us. NOTE: PG_lock
645 * is needed to serialize against split_huge_page
646 * when invoked from the VM.
647 */
648 if (!trylock_page(page)) {
649 result = SCAN_PAGE_LOCK;
650 goto out;
651 }
652
653 /*
654 * Check if the page has any GUP (or other external) pins.
655 *
656 * The page table that maps the page has been already unlinked
657 * from the page table tree and this process cannot get
658 * an additinal pin on the page.
659 *
660 * New pins can come later if the page is shared across fork,
661 * but not from this process. The other process cannot write to
662 * the page, only trigger CoW.
663 */
664 if (!is_refcount_suitable(page)) {
665 unlock_page(page);
666 result = SCAN_PAGE_COUNT;
667 goto out;
668 }
669 if (!pte_write(pteval) && PageSwapCache(page) &&
670 !reuse_swap_page(page, NULL)) {
671 /*
672 * Page is in the swap cache and cannot be re-used.
673 * It cannot be collapsed into a THP.
674 */
675 unlock_page(page);
676 result = SCAN_SWAP_CACHE_PAGE;
677 goto out;
678 }
679
680 /*
681 * Isolate the page to avoid collapsing an hugepage
682 * currently in use by the VM.
683 */
684 if (isolate_lru_page(page)) {
685 unlock_page(page);
686 result = SCAN_DEL_PAGE_LRU;
687 goto out;
688 }
689 mod_node_page_state(page_pgdat(page),
690 NR_ISOLATED_ANON + page_is_file_lru(page),
691 compound_nr(page));
692 VM_BUG_ON_PAGE(!PageLocked(page), page);
693 VM_BUG_ON_PAGE(PageLRU(page), page);
694
695 if (PageCompound(page))
696 list_add_tail(&page->lru, compound_pagelist);
697 next:
698 /* There should be enough young pte to collapse the page */
699 if (pte_young(pteval) ||
700 page_is_young(page) || PageReferenced(page) ||
701 mmu_notifier_test_young(vma->vm_mm, address))
702 referenced++;
703
704 if (pte_write(pteval))
705 writable = true;
706 }
707 if (likely(writable)) {
708 if (likely(referenced)) {
709 result = SCAN_SUCCEED;
710 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
711 referenced, writable, result);
712 return 1;
713 }
714 } else {
715 result = SCAN_PAGE_RO;
716 }
717
718 out:
719 release_pte_pages(pte, _pte, compound_pagelist);
720 trace_mm_collapse_huge_page_isolate(page, none_or_zero,
721 referenced, writable, result);
722 return 0;
723 }
724
__collapse_huge_page_copy(pte_t * pte,struct page * page,struct vm_area_struct * vma,unsigned long address,spinlock_t * ptl,struct list_head * compound_pagelist)725 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
726 struct vm_area_struct *vma,
727 unsigned long address,
728 spinlock_t *ptl,
729 struct list_head *compound_pagelist)
730 {
731 struct page *src_page, *tmp;
732 pte_t *_pte;
733 for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
734 _pte++, page++, address += PAGE_SIZE) {
735 pte_t pteval = *_pte;
736
737 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
738 clear_user_highpage(page, address);
739 add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1);
740 if (is_zero_pfn(pte_pfn(pteval))) {
741 /*
742 * ptl mostly unnecessary.
743 */
744 spin_lock(ptl);
745 /*
746 * paravirt calls inside pte_clear here are
747 * superfluous.
748 */
749 pte_clear(vma->vm_mm, address, _pte);
750 spin_unlock(ptl);
751 }
752 } else {
753 src_page = pte_page(pteval);
754 copy_user_highpage(page, src_page, address, vma);
755 if (!PageCompound(src_page))
756 release_pte_page(src_page);
757 /*
758 * ptl mostly unnecessary, but preempt has to
759 * be disabled to update the per-cpu stats
760 * inside page_remove_rmap().
761 */
762 spin_lock(ptl);
763 /*
764 * paravirt calls inside pte_clear here are
765 * superfluous.
766 */
767 pte_clear(vma->vm_mm, address, _pte);
768 page_remove_rmap(src_page, false);
769 spin_unlock(ptl);
770 free_page_and_swap_cache(src_page);
771 }
772 }
773
774 list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
775 list_del(&src_page->lru);
776 release_pte_page(src_page);
777 }
778 }
779
khugepaged_alloc_sleep(void)780 static void khugepaged_alloc_sleep(void)
781 {
782 DEFINE_WAIT(wait);
783
784 add_wait_queue(&khugepaged_wait, &wait);
785 freezable_schedule_timeout_interruptible(
786 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs));
787 remove_wait_queue(&khugepaged_wait, &wait);
788 }
789
790 static int khugepaged_node_load[MAX_NUMNODES];
791
khugepaged_scan_abort(int nid)792 static bool khugepaged_scan_abort(int nid)
793 {
794 int i;
795
796 /*
797 * If node_reclaim_mode is disabled, then no extra effort is made to
798 * allocate memory locally.
799 */
800 if (!node_reclaim_mode)
801 return false;
802
803 /* If there is a count for this node already, it must be acceptable */
804 if (khugepaged_node_load[nid])
805 return false;
806
807 for (i = 0; i < MAX_NUMNODES; i++) {
808 if (!khugepaged_node_load[i])
809 continue;
810 if (node_distance(nid, i) > node_reclaim_distance)
811 return true;
812 }
813 return false;
814 }
815
816 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
alloc_hugepage_khugepaged_gfpmask(void)817 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
818 {
819 return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
820 }
821
822 #ifdef CONFIG_NUMA
khugepaged_find_target_node(void)823 static int khugepaged_find_target_node(void)
824 {
825 static int last_khugepaged_target_node = NUMA_NO_NODE;
826 int nid, target_node = 0, max_value = 0;
827
828 /* find first node with max normal pages hit */
829 for (nid = 0; nid < MAX_NUMNODES; nid++)
830 if (khugepaged_node_load[nid] > max_value) {
831 max_value = khugepaged_node_load[nid];
832 target_node = nid;
833 }
834
835 /* do some balance if several nodes have the same hit record */
836 if (target_node <= last_khugepaged_target_node)
837 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES;
838 nid++)
839 if (max_value == khugepaged_node_load[nid]) {
840 target_node = nid;
841 break;
842 }
843
844 last_khugepaged_target_node = target_node;
845 return target_node;
846 }
847
khugepaged_prealloc_page(struct page ** hpage,bool * wait)848 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
849 {
850 if (IS_ERR(*hpage)) {
851 if (!*wait)
852 return false;
853
854 *wait = false;
855 *hpage = NULL;
856 khugepaged_alloc_sleep();
857 } else if (*hpage) {
858 put_page(*hpage);
859 *hpage = NULL;
860 }
861
862 return true;
863 }
864
865 static struct page *
khugepaged_alloc_page(struct page ** hpage,gfp_t gfp,int node)866 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
867 {
868 VM_BUG_ON_PAGE(*hpage, *hpage);
869
870 *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
871 if (unlikely(!*hpage)) {
872 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
873 *hpage = ERR_PTR(-ENOMEM);
874 return NULL;
875 }
876
877 prep_transhuge_page(*hpage);
878 count_vm_event(THP_COLLAPSE_ALLOC);
879 return *hpage;
880 }
881 #else
khugepaged_find_target_node(void)882 static int khugepaged_find_target_node(void)
883 {
884 return 0;
885 }
886
alloc_khugepaged_hugepage(void)887 static inline struct page *alloc_khugepaged_hugepage(void)
888 {
889 struct page *page;
890
891 page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
892 HPAGE_PMD_ORDER);
893 if (page)
894 prep_transhuge_page(page);
895 return page;
896 }
897
khugepaged_alloc_hugepage(bool * wait)898 static struct page *khugepaged_alloc_hugepage(bool *wait)
899 {
900 struct page *hpage;
901
902 do {
903 hpage = alloc_khugepaged_hugepage();
904 if (!hpage) {
905 count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
906 if (!*wait)
907 return NULL;
908
909 *wait = false;
910 khugepaged_alloc_sleep();
911 } else
912 count_vm_event(THP_COLLAPSE_ALLOC);
913 } while (unlikely(!hpage) && likely(khugepaged_enabled()));
914
915 return hpage;
916 }
917
khugepaged_prealloc_page(struct page ** hpage,bool * wait)918 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait)
919 {
920 /*
921 * If the hpage allocated earlier was briefly exposed in page cache
922 * before collapse_file() failed, it is possible that racing lookups
923 * have not yet completed, and would then be unpleasantly surprised by
924 * finding the hpage reused for the same mapping at a different offset.
925 * Just release the previous allocation if there is any danger of that.
926 */
927 if (*hpage && page_count(*hpage) > 1) {
928 put_page(*hpage);
929 *hpage = NULL;
930 }
931
932 if (!*hpage)
933 *hpage = khugepaged_alloc_hugepage(wait);
934
935 if (unlikely(!*hpage))
936 return false;
937
938 return true;
939 }
940
941 static struct page *
khugepaged_alloc_page(struct page ** hpage,gfp_t gfp,int node)942 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
943 {
944 VM_BUG_ON(!*hpage);
945
946 return *hpage;
947 }
948 #endif
949
950 /*
951 * If mmap_lock temporarily dropped, revalidate vma
952 * before taking mmap_lock.
953 * Return 0 if succeeds, otherwise return none-zero
954 * value (scan code).
955 */
956
hugepage_vma_revalidate(struct mm_struct * mm,unsigned long address,struct vm_area_struct ** vmap)957 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
958 struct vm_area_struct **vmap)
959 {
960 struct vm_area_struct *vma;
961 unsigned long hstart, hend;
962
963 if (unlikely(khugepaged_test_exit(mm)))
964 return SCAN_ANY_PROCESS;
965
966 *vmap = vma = find_vma(mm, address);
967 if (!vma)
968 return SCAN_VMA_NULL;
969
970 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
971 hend = vma->vm_end & HPAGE_PMD_MASK;
972 if (address < hstart || address + HPAGE_PMD_SIZE > hend)
973 return SCAN_ADDRESS_RANGE;
974 if (!hugepage_vma_check(vma, vma->vm_flags))
975 return SCAN_VMA_CHECK;
976 /* Anon VMA expected */
977 if (!vma->anon_vma || vma->vm_ops)
978 return SCAN_VMA_CHECK;
979 return 0;
980 }
981
982 /*
983 * Bring missing pages in from swap, to complete THP collapse.
984 * Only done if khugepaged_scan_pmd believes it is worthwhile.
985 *
986 * Called and returns without pte mapped or spinlocks held,
987 * but with mmap_lock held to protect against vma changes.
988 */
989
__collapse_huge_page_swapin(struct mm_struct * mm,struct vm_area_struct * vma,unsigned long address,pmd_t * pmd,int referenced)990 static bool __collapse_huge_page_swapin(struct mm_struct *mm,
991 struct vm_area_struct *vma,
992 unsigned long address, pmd_t *pmd,
993 int referenced)
994 {
995 int swapped_in = 0;
996 vm_fault_t ret = 0;
997 struct vm_fault vmf = {
998 .vma = vma,
999 .address = address,
1000 .flags = FAULT_FLAG_ALLOW_RETRY,
1001 .pmd = pmd,
1002 .pgoff = linear_page_index(vma, address),
1003 };
1004
1005 vmf.pte = pte_offset_map(pmd, address);
1006 for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
1007 vmf.pte++, vmf.address += PAGE_SIZE) {
1008 vmf.orig_pte = *vmf.pte;
1009 if (!is_swap_pte(vmf.orig_pte))
1010 continue;
1011 swapped_in++;
1012 ret = do_swap_page(&vmf);
1013
1014 /* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */
1015 if (ret & VM_FAULT_RETRY) {
1016 mmap_read_lock(mm);
1017 if (hugepage_vma_revalidate(mm, address, &vmf.vma)) {
1018 /* vma is no longer available, don't continue to swapin */
1019 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1020 return false;
1021 }
1022 /* check if the pmd is still valid */
1023 if (mm_find_pmd(mm, address) != pmd) {
1024 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1025 return false;
1026 }
1027 }
1028 if (ret & VM_FAULT_ERROR) {
1029 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
1030 return false;
1031 }
1032 /* pte is unmapped now, we need to map it */
1033 vmf.pte = pte_offset_map(pmd, vmf.address);
1034 }
1035 vmf.pte--;
1036 pte_unmap(vmf.pte);
1037
1038 /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
1039 if (swapped_in)
1040 lru_add_drain();
1041
1042 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
1043 return true;
1044 }
1045
collapse_huge_page(struct mm_struct * mm,unsigned long address,struct page ** hpage,int node,int referenced,int unmapped)1046 static void collapse_huge_page(struct mm_struct *mm,
1047 unsigned long address,
1048 struct page **hpage,
1049 int node, int referenced, int unmapped)
1050 {
1051 LIST_HEAD(compound_pagelist);
1052 pmd_t *pmd, _pmd;
1053 pte_t *pte;
1054 pgtable_t pgtable;
1055 struct page *new_page;
1056 spinlock_t *pmd_ptl, *pte_ptl;
1057 int isolated = 0, result = 0;
1058 struct vm_area_struct *vma;
1059 struct mmu_notifier_range range;
1060 gfp_t gfp;
1061
1062 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1063
1064 /* Only allocate from the target node */
1065 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1066
1067 /*
1068 * Before allocating the hugepage, release the mmap_lock read lock.
1069 * The allocation can take potentially a long time if it involves
1070 * sync compaction, and we do not need to hold the mmap_lock during
1071 * that. We will recheck the vma after taking it again in write mode.
1072 */
1073 mmap_read_unlock(mm);
1074 new_page = khugepaged_alloc_page(hpage, gfp, node);
1075 if (!new_page) {
1076 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1077 goto out_nolock;
1078 }
1079
1080 if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
1081 result = SCAN_CGROUP_CHARGE_FAIL;
1082 goto out_nolock;
1083 }
1084 count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
1085
1086 mmap_read_lock(mm);
1087 result = hugepage_vma_revalidate(mm, address, &vma);
1088 if (result) {
1089 mmap_read_unlock(mm);
1090 goto out_nolock;
1091 }
1092
1093 pmd = mm_find_pmd(mm, address);
1094 if (!pmd) {
1095 result = SCAN_PMD_NULL;
1096 mmap_read_unlock(mm);
1097 goto out_nolock;
1098 }
1099
1100 /*
1101 * __collapse_huge_page_swapin always returns with mmap_lock locked.
1102 * If it fails, we release mmap_lock and jump out_nolock.
1103 * Continuing to collapse causes inconsistency.
1104 */
1105 if (unmapped && !__collapse_huge_page_swapin(mm, vma, address,
1106 pmd, referenced)) {
1107 mmap_read_unlock(mm);
1108 goto out_nolock;
1109 }
1110
1111 mmap_read_unlock(mm);
1112 /*
1113 * Prevent all access to pagetables with the exception of
1114 * gup_fast later handled by the ptep_clear_flush and the VM
1115 * handled by the anon_vma lock + PG_lock.
1116 */
1117 mmap_write_lock(mm);
1118 result = hugepage_vma_revalidate(mm, address, &vma);
1119 if (result)
1120 goto out;
1121 /* check if the pmd is still valid */
1122 if (mm_find_pmd(mm, address) != pmd)
1123 goto out;
1124
1125 anon_vma_lock_write(vma->anon_vma);
1126
1127 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,
1128 address, address + HPAGE_PMD_SIZE);
1129 mmu_notifier_invalidate_range_start(&range);
1130
1131 pte = pte_offset_map(pmd, address);
1132 pte_ptl = pte_lockptr(mm, pmd);
1133
1134 pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */
1135 /*
1136 * After this gup_fast can't run anymore. This also removes
1137 * any huge TLB entry from the CPU so we won't allow
1138 * huge and small TLB entries for the same virtual address
1139 * to avoid the risk of CPU bugs in that area.
1140 */
1141 _pmd = pmdp_collapse_flush(vma, address, pmd);
1142 spin_unlock(pmd_ptl);
1143 mmu_notifier_invalidate_range_end(&range);
1144
1145 spin_lock(pte_ptl);
1146 isolated = __collapse_huge_page_isolate(vma, address, pte,
1147 &compound_pagelist);
1148 spin_unlock(pte_ptl);
1149
1150 if (unlikely(!isolated)) {
1151 pte_unmap(pte);
1152 spin_lock(pmd_ptl);
1153 BUG_ON(!pmd_none(*pmd));
1154 /*
1155 * We can only use set_pmd_at when establishing
1156 * hugepmds and never for establishing regular pmds that
1157 * points to regular pagetables. Use pmd_populate for that
1158 */
1159 pmd_populate(mm, pmd, pmd_pgtable(_pmd));
1160 spin_unlock(pmd_ptl);
1161 anon_vma_unlock_write(vma->anon_vma);
1162 result = SCAN_FAIL;
1163 goto out;
1164 }
1165
1166 /*
1167 * All pages are isolated and locked so anon_vma rmap
1168 * can't run anymore.
1169 */
1170 anon_vma_unlock_write(vma->anon_vma);
1171
1172 __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
1173 &compound_pagelist);
1174 pte_unmap(pte);
1175 __SetPageUptodate(new_page);
1176 pgtable = pmd_pgtable(_pmd);
1177
1178 _pmd = mk_huge_pmd(new_page, vma->vm_page_prot);
1179 _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma);
1180
1181 /*
1182 * spin_lock() below is not the equivalent of smp_wmb(), so
1183 * this is needed to avoid the copy_huge_page writes to become
1184 * visible after the set_pmd_at() write.
1185 */
1186 smp_wmb();
1187
1188 spin_lock(pmd_ptl);
1189 BUG_ON(!pmd_none(*pmd));
1190 page_add_new_anon_rmap(new_page, vma, address, true);
1191 lru_cache_add_inactive_or_unevictable(new_page, vma);
1192 pgtable_trans_huge_deposit(mm, pmd, pgtable);
1193 set_pmd_at(mm, address, pmd, _pmd);
1194 update_mmu_cache_pmd(vma, address, pmd);
1195 spin_unlock(pmd_ptl);
1196
1197 *hpage = NULL;
1198
1199 khugepaged_pages_collapsed++;
1200 result = SCAN_SUCCEED;
1201 out_up_write:
1202 mmap_write_unlock(mm);
1203 out_nolock:
1204 if (!IS_ERR_OR_NULL(*hpage))
1205 mem_cgroup_uncharge(*hpage);
1206 trace_mm_collapse_huge_page(mm, isolated, result);
1207 return;
1208 out:
1209 goto out_up_write;
1210 }
1211
khugepaged_scan_pmd(struct mm_struct * mm,struct vm_area_struct * vma,unsigned long address,struct page ** hpage)1212 static int khugepaged_scan_pmd(struct mm_struct *mm,
1213 struct vm_area_struct *vma,
1214 unsigned long address,
1215 struct page **hpage)
1216 {
1217 pmd_t *pmd;
1218 pte_t *pte, *_pte;
1219 int ret = 0, result = 0, referenced = 0;
1220 int none_or_zero = 0, shared = 0;
1221 struct page *page = NULL;
1222 unsigned long _address;
1223 spinlock_t *ptl;
1224 int node = NUMA_NO_NODE, unmapped = 0;
1225 bool writable = false;
1226
1227 VM_BUG_ON(address & ~HPAGE_PMD_MASK);
1228
1229 pmd = mm_find_pmd(mm, address);
1230 if (!pmd) {
1231 result = SCAN_PMD_NULL;
1232 goto out;
1233 }
1234
1235 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1236 pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1237 for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR;
1238 _pte++, _address += PAGE_SIZE) {
1239 pte_t pteval = *_pte;
1240 if (is_swap_pte(pteval)) {
1241 if (++unmapped <= khugepaged_max_ptes_swap) {
1242 /*
1243 * Always be strict with uffd-wp
1244 * enabled swap entries. Please see
1245 * comment below for pte_uffd_wp().
1246 */
1247 if (pte_swp_uffd_wp(pteval)) {
1248 result = SCAN_PTE_UFFD_WP;
1249 goto out_unmap;
1250 }
1251 continue;
1252 } else {
1253 result = SCAN_EXCEED_SWAP_PTE;
1254 goto out_unmap;
1255 }
1256 }
1257 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
1258 if (!userfaultfd_armed(vma) &&
1259 ++none_or_zero <= khugepaged_max_ptes_none) {
1260 continue;
1261 } else {
1262 result = SCAN_EXCEED_NONE_PTE;
1263 goto out_unmap;
1264 }
1265 }
1266 if (!pte_present(pteval)) {
1267 result = SCAN_PTE_NON_PRESENT;
1268 goto out_unmap;
1269 }
1270 if (pte_uffd_wp(pteval)) {
1271 /*
1272 * Don't collapse the page if any of the small
1273 * PTEs are armed with uffd write protection.
1274 * Here we can also mark the new huge pmd as
1275 * write protected if any of the small ones is
1276 * marked but that could bring uknown
1277 * userfault messages that falls outside of
1278 * the registered range. So, just be simple.
1279 */
1280 result = SCAN_PTE_UFFD_WP;
1281 goto out_unmap;
1282 }
1283 if (pte_write(pteval))
1284 writable = true;
1285
1286 page = vm_normal_page(vma, _address, pteval);
1287 if (unlikely(!page)) {
1288 result = SCAN_PAGE_NULL;
1289 goto out_unmap;
1290 }
1291
1292 if (page_mapcount(page) > 1 &&
1293 ++shared > khugepaged_max_ptes_shared) {
1294 result = SCAN_EXCEED_SHARED_PTE;
1295 goto out_unmap;
1296 }
1297
1298 page = compound_head(page);
1299
1300 /*
1301 * Record which node the original page is from and save this
1302 * information to khugepaged_node_load[].
1303 * Khupaged will allocate hugepage from the node has the max
1304 * hit record.
1305 */
1306 node = page_to_nid(page);
1307 if (khugepaged_scan_abort(node)) {
1308 result = SCAN_SCAN_ABORT;
1309 goto out_unmap;
1310 }
1311 khugepaged_node_load[node]++;
1312 if (!PageLRU(page)) {
1313 result = SCAN_PAGE_LRU;
1314 goto out_unmap;
1315 }
1316 if (PageLocked(page)) {
1317 result = SCAN_PAGE_LOCK;
1318 goto out_unmap;
1319 }
1320 if (!PageAnon(page)) {
1321 result = SCAN_PAGE_ANON;
1322 goto out_unmap;
1323 }
1324
1325 /*
1326 * Check if the page has any GUP (or other external) pins.
1327 *
1328 * Here the check is racy it may see totmal_mapcount > refcount
1329 * in some cases.
1330 * For example, one process with one forked child process.
1331 * The parent has the PMD split due to MADV_DONTNEED, then
1332 * the child is trying unmap the whole PMD, but khugepaged
1333 * may be scanning the parent between the child has
1334 * PageDoubleMap flag cleared and dec the mapcount. So
1335 * khugepaged may see total_mapcount > refcount.
1336 *
1337 * But such case is ephemeral we could always retry collapse
1338 * later. However it may report false positive if the page
1339 * has excessive GUP pins (i.e. 512). Anyway the same check
1340 * will be done again later the risk seems low.
1341 */
1342 if (!is_refcount_suitable(page)) {
1343 result = SCAN_PAGE_COUNT;
1344 goto out_unmap;
1345 }
1346 if (pte_young(pteval) ||
1347 page_is_young(page) || PageReferenced(page) ||
1348 mmu_notifier_test_young(vma->vm_mm, address))
1349 referenced++;
1350 }
1351 if (!writable) {
1352 result = SCAN_PAGE_RO;
1353 } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
1354 result = SCAN_LACK_REFERENCED_PAGE;
1355 } else {
1356 result = SCAN_SUCCEED;
1357 ret = 1;
1358 }
1359 out_unmap:
1360 pte_unmap_unlock(pte, ptl);
1361 if (ret) {
1362 node = khugepaged_find_target_node();
1363 /* collapse_huge_page will return with the mmap_lock released */
1364 collapse_huge_page(mm, address, hpage, node,
1365 referenced, unmapped);
1366 }
1367 out:
1368 trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
1369 none_or_zero, result, unmapped);
1370 return ret;
1371 }
1372
collect_mm_slot(struct mm_slot * mm_slot)1373 static void collect_mm_slot(struct mm_slot *mm_slot)
1374 {
1375 struct mm_struct *mm = mm_slot->mm;
1376
1377 lockdep_assert_held(&khugepaged_mm_lock);
1378
1379 if (khugepaged_test_exit(mm)) {
1380 /* free mm_slot */
1381 hash_del(&mm_slot->hash);
1382 list_del(&mm_slot->mm_node);
1383
1384 /*
1385 * Not strictly needed because the mm exited already.
1386 *
1387 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags);
1388 */
1389
1390 /* khugepaged_mm_lock actually not necessary for the below */
1391 free_mm_slot(mm_slot);
1392 mmdrop(mm);
1393 }
1394 }
1395
1396 #ifdef CONFIG_SHMEM
1397 /*
1398 * Notify khugepaged that given addr of the mm is pte-mapped THP. Then
1399 * khugepaged should try to collapse the page table.
1400 */
khugepaged_add_pte_mapped_thp(struct mm_struct * mm,unsigned long addr)1401 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm,
1402 unsigned long addr)
1403 {
1404 struct mm_slot *mm_slot;
1405
1406 VM_BUG_ON(addr & ~HPAGE_PMD_MASK);
1407
1408 spin_lock(&khugepaged_mm_lock);
1409 mm_slot = get_mm_slot(mm);
1410 if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP))
1411 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr;
1412 spin_unlock(&khugepaged_mm_lock);
1413 return 0;
1414 }
1415
1416 /**
1417 * Try to collapse a pte-mapped THP for mm at address haddr.
1418 *
1419 * This function checks whether all the PTEs in the PMD are pointing to the
1420 * right THP. If so, retract the page table so the THP can refault in with
1421 * as pmd-mapped.
1422 */
collapse_pte_mapped_thp(struct mm_struct * mm,unsigned long addr)1423 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
1424 {
1425 unsigned long haddr = addr & HPAGE_PMD_MASK;
1426 struct vm_area_struct *vma = find_vma(mm, haddr);
1427 struct page *hpage;
1428 pte_t *start_pte, *pte;
1429 pmd_t *pmd, _pmd;
1430 spinlock_t *ptl;
1431 int count = 0;
1432 int i;
1433
1434 if (!vma || !vma->vm_file ||
1435 vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
1436 return;
1437
1438 /*
1439 * This vm_flags may not have VM_HUGEPAGE if the page was not
1440 * collapsed by this mm. But we can still collapse if the page is
1441 * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
1442 * will not fail the vma for missing VM_HUGEPAGE
1443 */
1444 if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
1445 return;
1446
1447 hpage = find_lock_page(vma->vm_file->f_mapping,
1448 linear_page_index(vma, haddr));
1449 if (!hpage)
1450 return;
1451
1452 if (!PageHead(hpage))
1453 goto drop_hpage;
1454
1455 pmd = mm_find_pmd(mm, haddr);
1456 if (!pmd)
1457 goto drop_hpage;
1458
1459 start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
1460
1461 /* step 1: check all mapped PTEs are to the right huge page */
1462 for (i = 0, addr = haddr, pte = start_pte;
1463 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1464 struct page *page;
1465
1466 /* empty pte, skip */
1467 if (pte_none(*pte))
1468 continue;
1469
1470 /* page swapped out, abort */
1471 if (!pte_present(*pte))
1472 goto abort;
1473
1474 page = vm_normal_page(vma, addr, *pte);
1475
1476 /*
1477 * Note that uprobe, debugger, or MAP_PRIVATE may change the
1478 * page table, but the new page will not be a subpage of hpage.
1479 */
1480 if (hpage + i != page)
1481 goto abort;
1482 count++;
1483 }
1484
1485 /* step 2: adjust rmap */
1486 for (i = 0, addr = haddr, pte = start_pte;
1487 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
1488 struct page *page;
1489
1490 if (pte_none(*pte))
1491 continue;
1492 page = vm_normal_page(vma, addr, *pte);
1493 page_remove_rmap(page, false);
1494 }
1495
1496 pte_unmap_unlock(start_pte, ptl);
1497
1498 /* step 3: set proper refcount and mm_counters. */
1499 if (count) {
1500 page_ref_sub(hpage, count);
1501 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count);
1502 }
1503
1504 /* step 4: collapse pmd */
1505 ptl = pmd_lock(vma->vm_mm, pmd);
1506 _pmd = pmdp_collapse_flush(vma, haddr, pmd);
1507 spin_unlock(ptl);
1508 mm_dec_nr_ptes(mm);
1509 pte_free(mm, pmd_pgtable(_pmd));
1510
1511 drop_hpage:
1512 unlock_page(hpage);
1513 put_page(hpage);
1514 return;
1515
1516 abort:
1517 pte_unmap_unlock(start_pte, ptl);
1518 goto drop_hpage;
1519 }
1520
khugepaged_collapse_pte_mapped_thps(struct mm_slot * mm_slot)1521 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
1522 {
1523 struct mm_struct *mm = mm_slot->mm;
1524 int i;
1525
1526 if (likely(mm_slot->nr_pte_mapped_thp == 0))
1527 return 0;
1528
1529 if (!mmap_write_trylock(mm))
1530 return -EBUSY;
1531
1532 if (unlikely(khugepaged_test_exit(mm)))
1533 goto out;
1534
1535 for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++)
1536 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]);
1537
1538 out:
1539 mm_slot->nr_pte_mapped_thp = 0;
1540 mmap_write_unlock(mm);
1541 return 0;
1542 }
1543
retract_page_tables(struct address_space * mapping,pgoff_t pgoff)1544 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
1545 {
1546 struct vm_area_struct *vma;
1547 struct mm_struct *mm;
1548 unsigned long addr;
1549 pmd_t *pmd, _pmd;
1550
1551 i_mmap_lock_write(mapping);
1552 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1553 /*
1554 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that
1555 * got written to. These VMAs are likely not worth investing
1556 * mmap_write_lock(mm) as PMD-mapping is likely to be split
1557 * later.
1558 *
1559 * Not that vma->anon_vma check is racy: it can be set up after
1560 * the check but before we took mmap_lock by the fault path.
1561 * But page lock would prevent establishing any new ptes of the
1562 * page, so we are safe.
1563 *
1564 * An alternative would be drop the check, but check that page
1565 * table is clear before calling pmdp_collapse_flush() under
1566 * ptl. It has higher chance to recover THP for the VMA, but
1567 * has higher cost too.
1568 */
1569 if (vma->anon_vma)
1570 continue;
1571 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
1572 if (addr & ~HPAGE_PMD_MASK)
1573 continue;
1574 if (vma->vm_end < addr + HPAGE_PMD_SIZE)
1575 continue;
1576 mm = vma->vm_mm;
1577 pmd = mm_find_pmd(mm, addr);
1578 if (!pmd)
1579 continue;
1580 /*
1581 * We need exclusive mmap_lock to retract page table.
1582 *
1583 * We use trylock due to lock inversion: we need to acquire
1584 * mmap_lock while holding page lock. Fault path does it in
1585 * reverse order. Trylock is a way to avoid deadlock.
1586 */
1587 if (mmap_write_trylock(mm)) {
1588 if (!khugepaged_test_exit(mm)) {
1589 spinlock_t *ptl = pmd_lock(mm, pmd);
1590 /* assume page table is clear */
1591 _pmd = pmdp_collapse_flush(vma, addr, pmd);
1592 spin_unlock(ptl);
1593 mm_dec_nr_ptes(mm);
1594 pte_free(mm, pmd_pgtable(_pmd));
1595 }
1596 mmap_write_unlock(mm);
1597 } else {
1598 /* Try again later */
1599 khugepaged_add_pte_mapped_thp(mm, addr);
1600 }
1601 }
1602 i_mmap_unlock_write(mapping);
1603 }
1604
1605 /**
1606 * collapse_file - collapse filemap/tmpfs/shmem pages into huge one.
1607 *
1608 * Basic scheme is simple, details are more complex:
1609 * - allocate and lock a new huge page;
1610 * - scan page cache replacing old pages with the new one
1611 * + swap/gup in pages if necessary;
1612 * + fill in gaps;
1613 * + keep old pages around in case rollback is required;
1614 * - if replacing succeeds:
1615 * + copy data over;
1616 * + free old pages;
1617 * + unlock huge page;
1618 * - if replacing failed;
1619 * + put all pages back and unfreeze them;
1620 * + restore gaps in the page cache;
1621 * + unlock and free huge page;
1622 */
collapse_file(struct mm_struct * mm,struct file * file,pgoff_t start,struct page ** hpage,int node)1623 static void collapse_file(struct mm_struct *mm,
1624 struct file *file, pgoff_t start,
1625 struct page **hpage, int node)
1626 {
1627 struct address_space *mapping = file->f_mapping;
1628 gfp_t gfp;
1629 struct page *new_page;
1630 pgoff_t index, end = start + HPAGE_PMD_NR;
1631 LIST_HEAD(pagelist);
1632 XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
1633 int nr_none = 0, result = SCAN_SUCCEED;
1634 bool is_shmem = shmem_file(file);
1635
1636 VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
1637 VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
1638
1639 /* Only allocate from the target node */
1640 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
1641
1642 new_page = khugepaged_alloc_page(hpage, gfp, node);
1643 if (!new_page) {
1644 result = SCAN_ALLOC_HUGE_PAGE_FAIL;
1645 goto out;
1646 }
1647
1648 if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) {
1649 result = SCAN_CGROUP_CHARGE_FAIL;
1650 goto out;
1651 }
1652 count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
1653
1654 /* This will be less messy when we use multi-index entries */
1655 do {
1656 xas_lock_irq(&xas);
1657 xas_create_range(&xas);
1658 if (!xas_error(&xas))
1659 break;
1660 xas_unlock_irq(&xas);
1661 if (!xas_nomem(&xas, GFP_KERNEL)) {
1662 result = SCAN_FAIL;
1663 goto out;
1664 }
1665 } while (1);
1666
1667 __SetPageLocked(new_page);
1668 if (is_shmem)
1669 __SetPageSwapBacked(new_page);
1670 new_page->index = start;
1671 new_page->mapping = mapping;
1672
1673 /*
1674 * At this point the new_page is locked and not up-to-date.
1675 * It's safe to insert it into the page cache, because nobody would
1676 * be able to map it or use it in another way until we unlock it.
1677 */
1678
1679 xas_set(&xas, start);
1680 for (index = start; index < end; index++) {
1681 struct page *page = xas_next(&xas);
1682
1683 VM_BUG_ON(index != xas.xa_index);
1684 if (is_shmem) {
1685 if (!page) {
1686 /*
1687 * Stop if extent has been truncated or
1688 * hole-punched, and is now completely
1689 * empty.
1690 */
1691 if (index == start) {
1692 if (!xas_next_entry(&xas, end - 1)) {
1693 result = SCAN_TRUNCATED;
1694 goto xa_locked;
1695 }
1696 xas_set(&xas, index);
1697 }
1698 if (!shmem_charge(mapping->host, 1)) {
1699 result = SCAN_FAIL;
1700 goto xa_locked;
1701 }
1702 xas_store(&xas, new_page);
1703 nr_none++;
1704 continue;
1705 }
1706
1707 if (xa_is_value(page) || !PageUptodate(page)) {
1708 xas_unlock_irq(&xas);
1709 /* swap in or instantiate fallocated page */
1710 if (shmem_getpage(mapping->host, index, &page,
1711 SGP_NOHUGE)) {
1712 result = SCAN_FAIL;
1713 goto xa_unlocked;
1714 }
1715 } else if (trylock_page(page)) {
1716 get_page(page);
1717 xas_unlock_irq(&xas);
1718 } else {
1719 result = SCAN_PAGE_LOCK;
1720 goto xa_locked;
1721 }
1722 } else { /* !is_shmem */
1723 if (!page || xa_is_value(page)) {
1724 xas_unlock_irq(&xas);
1725 page_cache_sync_readahead(mapping, &file->f_ra,
1726 file, index,
1727 end - index);
1728 /* drain pagevecs to help isolate_lru_page() */
1729 lru_add_drain();
1730 page = find_lock_page(mapping, index);
1731 if (unlikely(page == NULL)) {
1732 result = SCAN_FAIL;
1733 goto xa_unlocked;
1734 }
1735 } else if (PageDirty(page)) {
1736 /*
1737 * khugepaged only works on read-only fd,
1738 * so this page is dirty because it hasn't
1739 * been flushed since first write. There
1740 * won't be new dirty pages.
1741 *
1742 * Trigger async flush here and hope the
1743 * writeback is done when khugepaged
1744 * revisits this page.
1745 *
1746 * This is a one-off situation. We are not
1747 * forcing writeback in loop.
1748 */
1749 xas_unlock_irq(&xas);
1750 filemap_flush(mapping);
1751 result = SCAN_FAIL;
1752 goto xa_unlocked;
1753 } else if (trylock_page(page)) {
1754 get_page(page);
1755 xas_unlock_irq(&xas);
1756 } else {
1757 result = SCAN_PAGE_LOCK;
1758 goto xa_locked;
1759 }
1760 }
1761
1762 /*
1763 * The page must be locked, so we can drop the i_pages lock
1764 * without racing with truncate.
1765 */
1766 VM_BUG_ON_PAGE(!PageLocked(page), page);
1767
1768 /* make sure the page is up to date */
1769 if (unlikely(!PageUptodate(page))) {
1770 result = SCAN_FAIL;
1771 goto out_unlock;
1772 }
1773
1774 /*
1775 * If file was truncated then extended, or hole-punched, before
1776 * we locked the first page, then a THP might be there already.
1777 */
1778 if (PageTransCompound(page)) {
1779 result = SCAN_PAGE_COMPOUND;
1780 goto out_unlock;
1781 }
1782
1783 if (page_mapping(page) != mapping) {
1784 result = SCAN_TRUNCATED;
1785 goto out_unlock;
1786 }
1787
1788 if (!is_shmem && PageDirty(page)) {
1789 /*
1790 * khugepaged only works on read-only fd, so this
1791 * page is dirty because it hasn't been flushed
1792 * since first write.
1793 */
1794 result = SCAN_FAIL;
1795 goto out_unlock;
1796 }
1797
1798 if (isolate_lru_page(page)) {
1799 result = SCAN_DEL_PAGE_LRU;
1800 goto out_unlock;
1801 }
1802
1803 if (page_has_private(page) &&
1804 !try_to_release_page(page, GFP_KERNEL)) {
1805 result = SCAN_PAGE_HAS_PRIVATE;
1806 putback_lru_page(page);
1807 goto out_unlock;
1808 }
1809
1810 if (page_mapped(page))
1811 unmap_mapping_pages(mapping, index, 1, false);
1812
1813 xas_lock_irq(&xas);
1814 xas_set(&xas, index);
1815
1816 VM_BUG_ON_PAGE(page != xas_load(&xas), page);
1817 VM_BUG_ON_PAGE(page_mapped(page), page);
1818
1819 /*
1820 * The page is expected to have page_count() == 3:
1821 * - we hold a pin on it;
1822 * - one reference from page cache;
1823 * - one from isolate_lru_page;
1824 */
1825 if (!page_ref_freeze(page, 3)) {
1826 result = SCAN_PAGE_COUNT;
1827 xas_unlock_irq(&xas);
1828 putback_lru_page(page);
1829 goto out_unlock;
1830 }
1831
1832 /*
1833 * Add the page to the list to be able to undo the collapse if
1834 * something go wrong.
1835 */
1836 list_add_tail(&page->lru, &pagelist);
1837
1838 /* Finally, replace with the new page. */
1839 xas_store(&xas, new_page);
1840 continue;
1841 out_unlock:
1842 unlock_page(page);
1843 put_page(page);
1844 goto xa_unlocked;
1845 }
1846
1847 if (is_shmem)
1848 __inc_node_page_state(new_page, NR_SHMEM_THPS);
1849 else {
1850 __inc_node_page_state(new_page, NR_FILE_THPS);
1851 filemap_nr_thps_inc(mapping);
1852 }
1853
1854 if (nr_none) {
1855 __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
1856 if (is_shmem)
1857 __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
1858 }
1859
1860 xa_locked:
1861 xas_unlock_irq(&xas);
1862 xa_unlocked:
1863
1864 if (result == SCAN_SUCCEED) {
1865 struct page *page, *tmp;
1866
1867 /*
1868 * Replacing old pages with new one has succeeded, now we
1869 * need to copy the content and free the old pages.
1870 */
1871 index = start;
1872 list_for_each_entry_safe(page, tmp, &pagelist, lru) {
1873 while (index < page->index) {
1874 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1875 index++;
1876 }
1877 copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
1878 page);
1879 list_del(&page->lru);
1880 page->mapping = NULL;
1881 page_ref_unfreeze(page, 1);
1882 ClearPageActive(page);
1883 ClearPageUnevictable(page);
1884 unlock_page(page);
1885 put_page(page);
1886 index++;
1887 }
1888 while (index < end) {
1889 clear_highpage(new_page + (index % HPAGE_PMD_NR));
1890 index++;
1891 }
1892
1893 SetPageUptodate(new_page);
1894 page_ref_add(new_page, HPAGE_PMD_NR - 1);
1895 if (is_shmem)
1896 set_page_dirty(new_page);
1897 lru_cache_add(new_page);
1898
1899 /*
1900 * Remove pte page tables, so we can re-fault the page as huge.
1901 */
1902 retract_page_tables(mapping, start);
1903 *hpage = NULL;
1904
1905 khugepaged_pages_collapsed++;
1906 } else {
1907 struct page *page;
1908
1909 /* Something went wrong: roll back page cache changes */
1910 xas_lock_irq(&xas);
1911 mapping->nrpages -= nr_none;
1912
1913 if (is_shmem)
1914 shmem_uncharge(mapping->host, nr_none);
1915
1916 xas_set(&xas, start);
1917 xas_for_each(&xas, page, end - 1) {
1918 page = list_first_entry_or_null(&pagelist,
1919 struct page, lru);
1920 if (!page || xas.xa_index < page->index) {
1921 if (!nr_none)
1922 break;
1923 nr_none--;
1924 /* Put holes back where they were */
1925 xas_store(&xas, NULL);
1926 continue;
1927 }
1928
1929 VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
1930
1931 /* Unfreeze the page. */
1932 list_del(&page->lru);
1933 page_ref_unfreeze(page, 2);
1934 xas_store(&xas, page);
1935 xas_pause(&xas);
1936 xas_unlock_irq(&xas);
1937 unlock_page(page);
1938 putback_lru_page(page);
1939 xas_lock_irq(&xas);
1940 }
1941 VM_BUG_ON(nr_none);
1942 xas_unlock_irq(&xas);
1943
1944 new_page->mapping = NULL;
1945 }
1946
1947 unlock_page(new_page);
1948 out:
1949 VM_BUG_ON(!list_empty(&pagelist));
1950 if (!IS_ERR_OR_NULL(*hpage))
1951 mem_cgroup_uncharge(*hpage);
1952 /* TODO: tracepoints */
1953 }
1954
khugepaged_scan_file(struct mm_struct * mm,struct file * file,pgoff_t start,struct page ** hpage)1955 static void khugepaged_scan_file(struct mm_struct *mm,
1956 struct file *file, pgoff_t start, struct page **hpage)
1957 {
1958 struct page *page = NULL;
1959 struct address_space *mapping = file->f_mapping;
1960 XA_STATE(xas, &mapping->i_pages, start);
1961 int present, swap;
1962 int node = NUMA_NO_NODE;
1963 int result = SCAN_SUCCEED;
1964
1965 present = 0;
1966 swap = 0;
1967 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load));
1968 rcu_read_lock();
1969 xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) {
1970 if (xas_retry(&xas, page))
1971 continue;
1972
1973 if (xa_is_value(page)) {
1974 if (++swap > khugepaged_max_ptes_swap) {
1975 result = SCAN_EXCEED_SWAP_PTE;
1976 break;
1977 }
1978 continue;
1979 }
1980
1981 if (PageTransCompound(page)) {
1982 result = SCAN_PAGE_COMPOUND;
1983 break;
1984 }
1985
1986 node = page_to_nid(page);
1987 if (khugepaged_scan_abort(node)) {
1988 result = SCAN_SCAN_ABORT;
1989 break;
1990 }
1991 khugepaged_node_load[node]++;
1992
1993 if (!PageLRU(page)) {
1994 result = SCAN_PAGE_LRU;
1995 break;
1996 }
1997
1998 if (page_count(page) !=
1999 1 + page_mapcount(page) + page_has_private(page)) {
2000 result = SCAN_PAGE_COUNT;
2001 break;
2002 }
2003
2004 /*
2005 * We probably should check if the page is referenced here, but
2006 * nobody would transfer pte_young() to PageReferenced() for us.
2007 * And rmap walk here is just too costly...
2008 */
2009
2010 present++;
2011
2012 if (need_resched()) {
2013 xas_pause(&xas);
2014 cond_resched_rcu();
2015 }
2016 }
2017 rcu_read_unlock();
2018
2019 if (result == SCAN_SUCCEED) {
2020 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {
2021 result = SCAN_EXCEED_NONE_PTE;
2022 } else {
2023 node = khugepaged_find_target_node();
2024 collapse_file(mm, file, start, hpage, node);
2025 }
2026 }
2027
2028 /* TODO: tracepoints */
2029 }
2030 #else
khugepaged_scan_file(struct mm_struct * mm,struct file * file,pgoff_t start,struct page ** hpage)2031 static void khugepaged_scan_file(struct mm_struct *mm,
2032 struct file *file, pgoff_t start, struct page **hpage)
2033 {
2034 BUILD_BUG();
2035 }
2036
khugepaged_collapse_pte_mapped_thps(struct mm_slot * mm_slot)2037 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot)
2038 {
2039 return 0;
2040 }
2041 #endif
2042
khugepaged_scan_mm_slot(unsigned int pages,struct page ** hpage)2043 static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
2044 struct page **hpage)
2045 __releases(&khugepaged_mm_lock)
2046 __acquires(&khugepaged_mm_lock)
2047 {
2048 struct mm_slot *mm_slot;
2049 struct mm_struct *mm;
2050 struct vm_area_struct *vma;
2051 int progress = 0;
2052
2053 VM_BUG_ON(!pages);
2054 lockdep_assert_held(&khugepaged_mm_lock);
2055
2056 if (khugepaged_scan.mm_slot)
2057 mm_slot = khugepaged_scan.mm_slot;
2058 else {
2059 mm_slot = list_entry(khugepaged_scan.mm_head.next,
2060 struct mm_slot, mm_node);
2061 khugepaged_scan.address = 0;
2062 khugepaged_scan.mm_slot = mm_slot;
2063 }
2064 spin_unlock(&khugepaged_mm_lock);
2065 khugepaged_collapse_pte_mapped_thps(mm_slot);
2066
2067 mm = mm_slot->mm;
2068 /*
2069 * Don't wait for semaphore (to avoid long wait times). Just move to
2070 * the next mm on the list.
2071 */
2072 vma = NULL;
2073 if (unlikely(!mmap_read_trylock(mm)))
2074 goto breakouterloop_mmap_lock;
2075 if (likely(!khugepaged_test_exit(mm)))
2076 vma = find_vma(mm, khugepaged_scan.address);
2077
2078 progress++;
2079 for (; vma; vma = vma->vm_next) {
2080 unsigned long hstart, hend;
2081
2082 cond_resched();
2083 if (unlikely(khugepaged_test_exit(mm))) {
2084 progress++;
2085 break;
2086 }
2087 if (!hugepage_vma_check(vma, vma->vm_flags)) {
2088 skip:
2089 progress++;
2090 continue;
2091 }
2092 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
2093 hend = vma->vm_end & HPAGE_PMD_MASK;
2094 if (hstart >= hend)
2095 goto skip;
2096 if (khugepaged_scan.address > hend)
2097 goto skip;
2098 if (khugepaged_scan.address < hstart)
2099 khugepaged_scan.address = hstart;
2100 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK);
2101 if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma))
2102 goto skip;
2103
2104 while (khugepaged_scan.address < hend) {
2105 int ret;
2106 cond_resched();
2107 if (unlikely(khugepaged_test_exit(mm)))
2108 goto breakouterloop;
2109
2110 VM_BUG_ON(khugepaged_scan.address < hstart ||
2111 khugepaged_scan.address + HPAGE_PMD_SIZE >
2112 hend);
2113 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
2114 struct file *file = get_file(vma->vm_file);
2115 pgoff_t pgoff = linear_page_index(vma,
2116 khugepaged_scan.address);
2117
2118 mmap_read_unlock(mm);
2119 ret = 1;
2120 khugepaged_scan_file(mm, file, pgoff, hpage);
2121 fput(file);
2122 } else {
2123 ret = khugepaged_scan_pmd(mm, vma,
2124 khugepaged_scan.address,
2125 hpage);
2126 }
2127 /* move to next address */
2128 khugepaged_scan.address += HPAGE_PMD_SIZE;
2129 progress += HPAGE_PMD_NR;
2130 if (ret)
2131 /* we released mmap_lock so break loop */
2132 goto breakouterloop_mmap_lock;
2133 if (progress >= pages)
2134 goto breakouterloop;
2135 }
2136 }
2137 breakouterloop:
2138 mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */
2139 breakouterloop_mmap_lock:
2140
2141 spin_lock(&khugepaged_mm_lock);
2142 VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot);
2143 /*
2144 * Release the current mm_slot if this mm is about to die, or
2145 * if we scanned all vmas of this mm.
2146 */
2147 if (khugepaged_test_exit(mm) || !vma) {
2148 /*
2149 * Make sure that if mm_users is reaching zero while
2150 * khugepaged runs here, khugepaged_exit will find
2151 * mm_slot not pointing to the exiting mm.
2152 */
2153 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) {
2154 khugepaged_scan.mm_slot = list_entry(
2155 mm_slot->mm_node.next,
2156 struct mm_slot, mm_node);
2157 khugepaged_scan.address = 0;
2158 } else {
2159 khugepaged_scan.mm_slot = NULL;
2160 khugepaged_full_scans++;
2161 }
2162
2163 collect_mm_slot(mm_slot);
2164 }
2165
2166 return progress;
2167 }
2168
khugepaged_has_work(void)2169 static int khugepaged_has_work(void)
2170 {
2171 return !list_empty(&khugepaged_scan.mm_head) &&
2172 khugepaged_enabled();
2173 }
2174
khugepaged_wait_event(void)2175 static int khugepaged_wait_event(void)
2176 {
2177 return !list_empty(&khugepaged_scan.mm_head) ||
2178 kthread_should_stop();
2179 }
2180
khugepaged_do_scan(void)2181 static void khugepaged_do_scan(void)
2182 {
2183 struct page *hpage = NULL;
2184 unsigned int progress = 0, pass_through_head = 0;
2185 unsigned int pages = khugepaged_pages_to_scan;
2186 bool wait = true;
2187
2188 barrier(); /* write khugepaged_pages_to_scan to local stack */
2189
2190 lru_add_drain_all();
2191
2192 while (progress < pages) {
2193 if (!khugepaged_prealloc_page(&hpage, &wait))
2194 break;
2195
2196 cond_resched();
2197
2198 if (unlikely(kthread_should_stop() || try_to_freeze()))
2199 break;
2200
2201 spin_lock(&khugepaged_mm_lock);
2202 if (!khugepaged_scan.mm_slot)
2203 pass_through_head++;
2204 if (khugepaged_has_work() &&
2205 pass_through_head < 2)
2206 progress += khugepaged_scan_mm_slot(pages - progress,
2207 &hpage);
2208 else
2209 progress = pages;
2210 spin_unlock(&khugepaged_mm_lock);
2211 }
2212
2213 if (!IS_ERR_OR_NULL(hpage))
2214 put_page(hpage);
2215 }
2216
khugepaged_should_wakeup(void)2217 static bool khugepaged_should_wakeup(void)
2218 {
2219 return kthread_should_stop() ||
2220 time_after_eq(jiffies, khugepaged_sleep_expire);
2221 }
2222
khugepaged_wait_work(void)2223 static void khugepaged_wait_work(void)
2224 {
2225 if (khugepaged_has_work()) {
2226 const unsigned long scan_sleep_jiffies =
2227 msecs_to_jiffies(khugepaged_scan_sleep_millisecs);
2228
2229 if (!scan_sleep_jiffies)
2230 return;
2231
2232 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies;
2233 wait_event_freezable_timeout(khugepaged_wait,
2234 khugepaged_should_wakeup(),
2235 scan_sleep_jiffies);
2236 return;
2237 }
2238
2239 if (khugepaged_enabled())
2240 wait_event_freezable(khugepaged_wait, khugepaged_wait_event());
2241 }
2242
khugepaged(void * none)2243 static int khugepaged(void *none)
2244 {
2245 struct mm_slot *mm_slot;
2246
2247 set_freezable();
2248 set_user_nice(current, MAX_NICE);
2249
2250 while (!kthread_should_stop()) {
2251 khugepaged_do_scan();
2252 khugepaged_wait_work();
2253 }
2254
2255 spin_lock(&khugepaged_mm_lock);
2256 mm_slot = khugepaged_scan.mm_slot;
2257 khugepaged_scan.mm_slot = NULL;
2258 if (mm_slot)
2259 collect_mm_slot(mm_slot);
2260 spin_unlock(&khugepaged_mm_lock);
2261 return 0;
2262 }
2263
set_recommended_min_free_kbytes(void)2264 static void set_recommended_min_free_kbytes(void)
2265 {
2266 struct zone *zone;
2267 int nr_zones = 0;
2268 unsigned long recommended_min;
2269
2270 for_each_populated_zone(zone) {
2271 /*
2272 * We don't need to worry about fragmentation of
2273 * ZONE_MOVABLE since it only has movable pages.
2274 */
2275 if (zone_idx(zone) > gfp_zone(GFP_USER))
2276 continue;
2277
2278 nr_zones++;
2279 }
2280
2281 /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
2282 recommended_min = pageblock_nr_pages * nr_zones * 2;
2283
2284 /*
2285 * Make sure that on average at least two pageblocks are almost free
2286 * of another type, one for a migratetype to fall back to and a
2287 * second to avoid subsequent fallbacks of other types There are 3
2288 * MIGRATE_TYPES we care about.
2289 */
2290 recommended_min += pageblock_nr_pages * nr_zones *
2291 MIGRATE_PCPTYPES * MIGRATE_PCPTYPES;
2292
2293 /* don't ever allow to reserve more than 5% of the lowmem */
2294 recommended_min = min(recommended_min,
2295 (unsigned long) nr_free_buffer_pages() / 20);
2296 recommended_min <<= (PAGE_SHIFT-10);
2297
2298 if (recommended_min > min_free_kbytes) {
2299 if (user_min_free_kbytes >= 0)
2300 pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
2301 min_free_kbytes, recommended_min);
2302
2303 min_free_kbytes = recommended_min;
2304 }
2305 setup_per_zone_wmarks();
2306 }
2307
start_stop_khugepaged(void)2308 int start_stop_khugepaged(void)
2309 {
2310 int err = 0;
2311
2312 mutex_lock(&khugepaged_mutex);
2313 if (khugepaged_enabled()) {
2314 if (!khugepaged_thread)
2315 khugepaged_thread = kthread_run(khugepaged, NULL,
2316 "khugepaged");
2317 if (IS_ERR(khugepaged_thread)) {
2318 pr_err("khugepaged: kthread_run(khugepaged) failed\n");
2319 err = PTR_ERR(khugepaged_thread);
2320 khugepaged_thread = NULL;
2321 goto fail;
2322 }
2323
2324 if (!list_empty(&khugepaged_scan.mm_head))
2325 wake_up_interruptible(&khugepaged_wait);
2326
2327 set_recommended_min_free_kbytes();
2328 } else if (khugepaged_thread) {
2329 kthread_stop(khugepaged_thread);
2330 khugepaged_thread = NULL;
2331 }
2332 fail:
2333 mutex_unlock(&khugepaged_mutex);
2334 return err;
2335 }
2336
khugepaged_min_free_kbytes_update(void)2337 void khugepaged_min_free_kbytes_update(void)
2338 {
2339 mutex_lock(&khugepaged_mutex);
2340 if (khugepaged_enabled() && khugepaged_thread)
2341 set_recommended_min_free_kbytes();
2342 mutex_unlock(&khugepaged_mutex);
2343 }
2344
