Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/mm/huge_memory.c

  1 /*
  2  *  Copyright (C) 2009  Red Hat, Inc.
  3  *
  4  *  This work is licensed under the terms of the GNU GPL, version 2. See
  5  *  the COPYING file in the top-level directory.
  6  */
  7 
  8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9 
 10 #include <linux/mm.h>
 11 #include <linux/sched.h>
 12 #include <linux/highmem.h>
 13 #include <linux/hugetlb.h>
 14 #include <linux/mmu_notifier.h>
 15 #include <linux/rmap.h>
 16 #include <linux/swap.h>
 17 #include <linux/shrinker.h>
 18 #include <linux/mm_inline.h>
 19 #include <linux/swapops.h>
 20 #include <linux/dax.h>
 21 #include <linux/khugepaged.h>
 22 #include <linux/freezer.h>
 23 #include <linux/pfn_t.h>
 24 #include <linux/mman.h>
 25 #include <linux/memremap.h>
 26 #include <linux/pagemap.h>
 27 #include <linux/debugfs.h>
 28 #include <linux/migrate.h>
 29 #include <linux/hashtable.h>
 30 #include <linux/userfaultfd_k.h>
 31 #include <linux/page_idle.h>
 32 #include <linux/shmem_fs.h>
 33 
 34 #include <asm/tlb.h>
 35 #include <asm/pgalloc.h>
 36 #include "internal.h"
 37 
 38 /*
 39  * By default transparent hugepage support is disabled in order that avoid
 40  * to risk increase the memory footprint of applications without a guaranteed
 41  * benefit. When transparent hugepage support is enabled, is for all mappings,
 42  * and khugepaged scans all mappings.
 43  * Defrag is invoked by khugepaged hugepage allocations and by page faults
 44  * for all hugepage allocations.
 45  */
 46 unsigned long transparent_hugepage_flags __read_mostly =
 47 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
 48         (1<<TRANSPARENT_HUGEPAGE_FLAG)|
 49 #endif
 50 #ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
 51         (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
 52 #endif
 53         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
 54         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
 55         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
 56 
 57 static struct shrinker deferred_split_shrinker;
 58 
 59 static atomic_t huge_zero_refcount;
 60 struct page *huge_zero_page __read_mostly;
 61 
 62 static struct page *get_huge_zero_page(void)
 63 {
 64         struct page *zero_page;
 65 retry:
 66         if (likely(atomic_inc_not_zero(&huge_zero_refcount)))
 67                 return READ_ONCE(huge_zero_page);
 68 
 69         zero_page = alloc_pages((GFP_TRANSHUGE | __GFP_ZERO) & ~__GFP_MOVABLE,
 70                         HPAGE_PMD_ORDER);
 71         if (!zero_page) {
 72                 count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED);
 73                 return NULL;
 74         }
 75         count_vm_event(THP_ZERO_PAGE_ALLOC);
 76         preempt_disable();
 77         if (cmpxchg(&huge_zero_page, NULL, zero_page)) {
 78                 preempt_enable();
 79                 __free_pages(zero_page, compound_order(zero_page));
 80                 goto retry;
 81         }
 82 
 83         /* We take additional reference here. It will be put back by shrinker */
 84         atomic_set(&huge_zero_refcount, 2);
 85         preempt_enable();
 86         return READ_ONCE(huge_zero_page);
 87 }
 88 
 89 static void put_huge_zero_page(void)
 90 {
 91         /*
 92          * Counter should never go to zero here. Only shrinker can put
 93          * last reference.
 94          */
 95         BUG_ON(atomic_dec_and_test(&huge_zero_refcount));
 96 }
 97 
 98 struct page *mm_get_huge_zero_page(struct mm_struct *mm)
 99 {
100         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
101                 return READ_ONCE(huge_zero_page);
102 
103         if (!get_huge_zero_page())
104                 return NULL;
105 
106         if (test_and_set_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
107                 put_huge_zero_page();
108 
109         return READ_ONCE(huge_zero_page);
110 }
111 
112 void mm_put_huge_zero_page(struct mm_struct *mm)
113 {
114         if (test_bit(MMF_HUGE_ZERO_PAGE, &mm->flags))
115                 put_huge_zero_page();
116 }
117 
118 static unsigned long shrink_huge_zero_page_count(struct shrinker *shrink,
119                                         struct shrink_control *sc)
120 {
121         /* we can free zero page only if last reference remains */
122         return atomic_read(&huge_zero_refcount) == 1 ? HPAGE_PMD_NR : 0;
123 }
124 
125 static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
126                                        struct shrink_control *sc)
127 {
128         if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
129                 struct page *zero_page = xchg(&huge_zero_page, NULL);
130                 BUG_ON(zero_page == NULL);
131                 __free_pages(zero_page, compound_order(zero_page));
132                 return HPAGE_PMD_NR;
133         }
134 
135         return 0;
136 }
137 
138 static struct shrinker huge_zero_page_shrinker = {
139         .count_objects = shrink_huge_zero_page_count,
140         .scan_objects = shrink_huge_zero_page_scan,
141         .seeks = DEFAULT_SEEKS,
142 };
143 
144 #ifdef CONFIG_SYSFS
145 
146 static ssize_t triple_flag_store(struct kobject *kobj,
147                                  struct kobj_attribute *attr,
148                                  const char *buf, size_t count,
149                                  enum transparent_hugepage_flag enabled,
150                                  enum transparent_hugepage_flag deferred,
151                                  enum transparent_hugepage_flag req_madv)
152 {
153         if (!memcmp("defer", buf,
154                     min(sizeof("defer")-1, count))) {
155                 if (enabled == deferred)
156                         return -EINVAL;
157                 clear_bit(enabled, &transparent_hugepage_flags);
158                 clear_bit(req_madv, &transparent_hugepage_flags);
159                 set_bit(deferred, &transparent_hugepage_flags);
160         } else if (!memcmp("always", buf,
161                     min(sizeof("always")-1, count))) {
162                 clear_bit(deferred, &transparent_hugepage_flags);
163                 clear_bit(req_madv, &transparent_hugepage_flags);
164                 set_bit(enabled, &transparent_hugepage_flags);
165         } else if (!memcmp("madvise", buf,
166                            min(sizeof("madvise")-1, count))) {
167                 clear_bit(enabled, &transparent_hugepage_flags);
168                 clear_bit(deferred, &transparent_hugepage_flags);
169                 set_bit(req_madv, &transparent_hugepage_flags);
170         } else if (!memcmp("never", buf,
171                            min(sizeof("never")-1, count))) {
172                 clear_bit(enabled, &transparent_hugepage_flags);
173                 clear_bit(req_madv, &transparent_hugepage_flags);
174                 clear_bit(deferred, &transparent_hugepage_flags);
175         } else
176                 return -EINVAL;
177 
178         return count;
179 }
180 
181 static ssize_t enabled_show(struct kobject *kobj,
182                             struct kobj_attribute *attr, char *buf)
183 {
184         if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
185                 return sprintf(buf, "[always] madvise never\n");
186         else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags))
187                 return sprintf(buf, "always [madvise] never\n");
188         else
189                 return sprintf(buf, "always madvise [never]\n");
190 }
191 
192 static ssize_t enabled_store(struct kobject *kobj,
193                              struct kobj_attribute *attr,
194                              const char *buf, size_t count)
195 {
196         ssize_t ret;
197 
198         ret = triple_flag_store(kobj, attr, buf, count,
199                                 TRANSPARENT_HUGEPAGE_FLAG,
200                                 TRANSPARENT_HUGEPAGE_FLAG,
201                                 TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
202 
203         if (ret > 0) {
204                 int err = start_stop_khugepaged();
205                 if (err)
206                         ret = err;
207         }
208 
209         return ret;
210 }
211 static struct kobj_attribute enabled_attr =
212         __ATTR(enabled, 0644, enabled_show, enabled_store);
213 
214 ssize_t single_hugepage_flag_show(struct kobject *kobj,
215                                 struct kobj_attribute *attr, char *buf,
216                                 enum transparent_hugepage_flag flag)
217 {
218         return sprintf(buf, "%d\n",
219                        !!test_bit(flag, &transparent_hugepage_flags));
220 }
221 
222 ssize_t single_hugepage_flag_store(struct kobject *kobj,
223                                  struct kobj_attribute *attr,
224                                  const char *buf, size_t count,
225                                  enum transparent_hugepage_flag flag)
226 {
227         unsigned long value;
228         int ret;
229 
230         ret = kstrtoul(buf, 10, &value);
231         if (ret < 0)
232                 return ret;
233         if (value > 1)
234                 return -EINVAL;
235 
236         if (value)
237                 set_bit(flag, &transparent_hugepage_flags);
238         else
239                 clear_bit(flag, &transparent_hugepage_flags);
240 
241         return count;
242 }
243 
244 /*
245  * Currently defrag only disables __GFP_NOWAIT for allocation. A blind
246  * __GFP_REPEAT is too aggressive, it's never worth swapping tons of
247  * memory just to allocate one more hugepage.
248  */
249 static ssize_t defrag_show(struct kobject *kobj,
250                            struct kobj_attribute *attr, char *buf)
251 {
252         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
253                 return sprintf(buf, "[always] defer madvise never\n");
254         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
255                 return sprintf(buf, "always [defer] madvise never\n");
256         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags))
257                 return sprintf(buf, "always defer [madvise] never\n");
258         else
259                 return sprintf(buf, "always defer madvise [never]\n");
260 
261 }
262 static ssize_t defrag_store(struct kobject *kobj,
263                             struct kobj_attribute *attr,
264                             const char *buf, size_t count)
265 {
266         return triple_flag_store(kobj, attr, buf, count,
267                                  TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
268                                  TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
269                                  TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG);
270 }
271 static struct kobj_attribute defrag_attr =
272         __ATTR(defrag, 0644, defrag_show, defrag_store);
273 
274 static ssize_t use_zero_page_show(struct kobject *kobj,
275                 struct kobj_attribute *attr, char *buf)
276 {
277         return single_hugepage_flag_show(kobj, attr, buf,
278                                 TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
279 }
280 static ssize_t use_zero_page_store(struct kobject *kobj,
281                 struct kobj_attribute *attr, const char *buf, size_t count)
282 {
283         return single_hugepage_flag_store(kobj, attr, buf, count,
284                                  TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
285 }
286 static struct kobj_attribute use_zero_page_attr =
287         __ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
288 
289 static ssize_t hpage_pmd_size_show(struct kobject *kobj,
290                 struct kobj_attribute *attr, char *buf)
291 {
292         return sprintf(buf, "%lu\n", HPAGE_PMD_SIZE);
293 }
294 static struct kobj_attribute hpage_pmd_size_attr =
295         __ATTR_RO(hpage_pmd_size);
296 
297 #ifdef CONFIG_DEBUG_VM
298 static ssize_t debug_cow_show(struct kobject *kobj,
299                                 struct kobj_attribute *attr, char *buf)
300 {
301         return single_hugepage_flag_show(kobj, attr, buf,
302                                 TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
303 }
304 static ssize_t debug_cow_store(struct kobject *kobj,
305                                struct kobj_attribute *attr,
306                                const char *buf, size_t count)
307 {
308         return single_hugepage_flag_store(kobj, attr, buf, count,
309                                  TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG);
310 }
311 static struct kobj_attribute debug_cow_attr =
312         __ATTR(debug_cow, 0644, debug_cow_show, debug_cow_store);
313 #endif /* CONFIG_DEBUG_VM */
314 
315 static struct attribute *hugepage_attr[] = {
316         &enabled_attr.attr,
317         &defrag_attr.attr,
318         &use_zero_page_attr.attr,
319         &hpage_pmd_size_attr.attr,
320 #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
321         &shmem_enabled_attr.attr,
322 #endif
323 #ifdef CONFIG_DEBUG_VM
324         &debug_cow_attr.attr,
325 #endif
326         NULL,
327 };
328 
329 static struct attribute_group hugepage_attr_group = {
330         .attrs = hugepage_attr,
331 };
332 
333 static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
334 {
335         int err;
336 
337         *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
338         if (unlikely(!*hugepage_kobj)) {
339                 pr_err("failed to create transparent hugepage kobject\n");
340                 return -ENOMEM;
341         }
342 
343         err = sysfs_create_group(*hugepage_kobj, &hugepage_attr_group);
344         if (err) {
345                 pr_err("failed to register transparent hugepage group\n");
346                 goto delete_obj;
347         }
348 
349         err = sysfs_create_group(*hugepage_kobj, &khugepaged_attr_group);
350         if (err) {
351                 pr_err("failed to register transparent hugepage group\n");
352                 goto remove_hp_group;
353         }
354 
355         return 0;
356 
357 remove_hp_group:
358         sysfs_remove_group(*hugepage_kobj, &hugepage_attr_group);
359 delete_obj:
360         kobject_put(*hugepage_kobj);
361         return err;
362 }
363 
364 static void __init hugepage_exit_sysfs(struct kobject *hugepage_kobj)
365 {
366         sysfs_remove_group(hugepage_kobj, &khugepaged_attr_group);
367         sysfs_remove_group(hugepage_kobj, &hugepage_attr_group);
368         kobject_put(hugepage_kobj);
369 }
370 #else
371 static inline int hugepage_init_sysfs(struct kobject **hugepage_kobj)
372 {
373         return 0;
374 }
375 
376 static inline void hugepage_exit_sysfs(struct kobject *hugepage_kobj)
377 {
378 }
379 #endif /* CONFIG_SYSFS */
380 
381 static int __init hugepage_init(void)
382 {
383         int err;
384         struct kobject *hugepage_kobj;
385 
386         if (!has_transparent_hugepage()) {
387                 transparent_hugepage_flags = 0;
388                 return -EINVAL;
389         }
390 
391         /*
392          * hugepages can't be allocated by the buddy allocator
393          */
394         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER >= MAX_ORDER);
395         /*
396          * we use page->mapping and page->index in second tail page
397          * as list_head: assuming THP order >= 2
398          */
399         MAYBE_BUILD_BUG_ON(HPAGE_PMD_ORDER < 2);
400 
401         err = hugepage_init_sysfs(&hugepage_kobj);
402         if (err)
403                 goto err_sysfs;
404 
405         err = khugepaged_init();
406         if (err)
407                 goto err_slab;
408 
409         err = register_shrinker(&huge_zero_page_shrinker);
410         if (err)
411                 goto err_hzp_shrinker;
412         err = register_shrinker(&deferred_split_shrinker);
413         if (err)
414                 goto err_split_shrinker;
415 
416         /*
417          * By default disable transparent hugepages on smaller systems,
418          * where the extra memory used could hurt more than TLB overhead
419          * is likely to save.  The admin can still enable it through /sys.
420          */
421         if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
422                 transparent_hugepage_flags = 0;
423                 return 0;
424         }
425 
426         err = start_stop_khugepaged();
427         if (err)
428                 goto err_khugepaged;
429 
430         return 0;
431 err_khugepaged:
432         unregister_shrinker(&deferred_split_shrinker);
433 err_split_shrinker:
434         unregister_shrinker(&huge_zero_page_shrinker);
435 err_hzp_shrinker:
436         khugepaged_destroy();
437 err_slab:
438         hugepage_exit_sysfs(hugepage_kobj);
439 err_sysfs:
440         return err;
441 }
442 subsys_initcall(hugepage_init);
443 
444 static int __init setup_transparent_hugepage(char *str)
445 {
446         int ret = 0;
447         if (!str)
448                 goto out;
449         if (!strcmp(str, "always")) {
450                 set_bit(TRANSPARENT_HUGEPAGE_FLAG,
451                         &transparent_hugepage_flags);
452                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
453                           &transparent_hugepage_flags);
454                 ret = 1;
455         } else if (!strcmp(str, "madvise")) {
456                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
457                           &transparent_hugepage_flags);
458                 set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
459                         &transparent_hugepage_flags);
460                 ret = 1;
461         } else if (!strcmp(str, "never")) {
462                 clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
463                           &transparent_hugepage_flags);
464                 clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
465                           &transparent_hugepage_flags);
466                 ret = 1;
467         }
468 out:
469         if (!ret)
470                 pr_warn("transparent_hugepage= cannot parse, ignored\n");
471         return ret;
472 }
473 __setup("transparent_hugepage=", setup_transparent_hugepage);
474 
475 pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
476 {
477         if (likely(vma->vm_flags & VM_WRITE))
478                 pmd = pmd_mkwrite(pmd);
479         return pmd;
480 }
481 
482 static inline struct list_head *page_deferred_list(struct page *page)
483 {
484         /*
485          * ->lru in the tail pages is occupied by compound_head.
486          * Let's use ->mapping + ->index in the second tail page as list_head.
487          */
488         return (struct list_head *)&page[2].mapping;
489 }
490 
491 void prep_transhuge_page(struct page *page)
492 {
493         /*
494          * we use page->mapping and page->indexlru in second tail page
495          * as list_head: assuming THP order >= 2
496          */
497 
498         INIT_LIST_HEAD(page_deferred_list(page));
499         set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
500 }
501 
502 unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len,
503                 loff_t off, unsigned long flags, unsigned long size)
504 {
505         unsigned long addr;
506         loff_t off_end = off + len;
507         loff_t off_align = round_up(off, size);
508         unsigned long len_pad;
509 
510         if (off_end <= off_align || (off_end - off_align) < size)
511                 return 0;
512 
513         len_pad = len + size;
514         if (len_pad < len || (off + len_pad) < off)
515                 return 0;
516 
517         addr = current->mm->get_unmapped_area(filp, 0, len_pad,
518                                               off >> PAGE_SHIFT, flags);
519         if (IS_ERR_VALUE(addr))
520                 return 0;
521 
522         addr += (off - addr) & (size - 1);
523         return addr;
524 }
525 
526 unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
527                 unsigned long len, unsigned long pgoff, unsigned long flags)
528 {
529         loff_t off = (loff_t)pgoff << PAGE_SHIFT;
530 
531         if (addr)
532                 goto out;
533         if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
534                 goto out;
535 
536         addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE);
537         if (addr)
538                 return addr;
539 
540  out:
541         return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
542 }
543 EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
544 
545 static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
546                 gfp_t gfp)
547 {
548         struct vm_area_struct *vma = vmf->vma;
549         struct mem_cgroup *memcg;
550         pgtable_t pgtable;
551         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
552 
553         VM_BUG_ON_PAGE(!PageCompound(page), page);
554 
555         if (mem_cgroup_try_charge(page, vma->vm_mm, gfp, &memcg, true)) {
556                 put_page(page);
557                 count_vm_event(THP_FAULT_FALLBACK);
558                 return VM_FAULT_FALLBACK;
559         }
560 
561         pgtable = pte_alloc_one(vma->vm_mm, haddr);
562         if (unlikely(!pgtable)) {
563                 mem_cgroup_cancel_charge(page, memcg, true);
564                 put_page(page);
565                 return VM_FAULT_OOM;
566         }
567 
568         clear_huge_page(page, haddr, HPAGE_PMD_NR);
569         /*
570          * The memory barrier inside __SetPageUptodate makes sure that
571          * clear_huge_page writes become visible before the set_pmd_at()
572          * write.
573          */
574         __SetPageUptodate(page);
575 
576         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
577         if (unlikely(!pmd_none(*vmf->pmd))) {
578                 spin_unlock(vmf->ptl);
579                 mem_cgroup_cancel_charge(page, memcg, true);
580                 put_page(page);
581                 pte_free(vma->vm_mm, pgtable);
582         } else {
583                 pmd_t entry;
584 
585                 /* Deliver the page fault to userland */
586                 if (userfaultfd_missing(vma)) {
587                         int ret;
588 
589                         spin_unlock(vmf->ptl);
590                         mem_cgroup_cancel_charge(page, memcg, true);
591                         put_page(page);
592                         pte_free(vma->vm_mm, pgtable);
593                         ret = handle_userfault(vmf, VM_UFFD_MISSING);
594                         VM_BUG_ON(ret & VM_FAULT_FALLBACK);
595                         return ret;
596                 }
597 
598                 entry = mk_huge_pmd(page, vma->vm_page_prot);
599                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
600                 page_add_new_anon_rmap(page, vma, haddr, true);
601                 mem_cgroup_commit_charge(page, memcg, false, true);
602                 lru_cache_add_active_or_unevictable(page, vma);
603                 pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
604                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
605                 add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
606                 atomic_long_inc(&vma->vm_mm->nr_ptes);
607                 spin_unlock(vmf->ptl);
608                 count_vm_event(THP_FAULT_ALLOC);
609         }
610 
611         return 0;
612 }
613 
614 /*
615  * If THP defrag is set to always then directly reclaim/compact as necessary
616  * If set to defer then do only background reclaim/compact and defer to khugepaged
617  * If set to madvise and the VMA is flagged then directly reclaim/compact
618  * When direct reclaim/compact is allowed, don't retry except for flagged VMA's
619  */
620 static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
621 {
622         bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
623 
624         if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
625                                 &transparent_hugepage_flags) && vma_madvised)
626                 return GFP_TRANSHUGE;
627         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
628                                                 &transparent_hugepage_flags))
629                 return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
630         else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
631                                                 &transparent_hugepage_flags))
632                 return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
633 
634         return GFP_TRANSHUGE_LIGHT;
635 }
636 
637 /* Caller must hold page table lock. */
638 static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
639                 struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
640                 struct page *zero_page)
641 {
642         pmd_t entry;
643         if (!pmd_none(*pmd))
644                 return false;
645         entry = mk_pmd(zero_page, vma->vm_page_prot);
646         entry = pmd_mkhuge(entry);
647         if (pgtable)
648                 pgtable_trans_huge_deposit(mm, pmd, pgtable);
649         set_pmd_at(mm, haddr, pmd, entry);
650         atomic_long_inc(&mm->nr_ptes);
651         return true;
652 }
653 
654 int do_huge_pmd_anonymous_page(struct vm_fault *vmf)
655 {
656         struct vm_area_struct *vma = vmf->vma;
657         gfp_t gfp;
658         struct page *page;
659         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
660 
661         if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
662                 return VM_FAULT_FALLBACK;
663         if (unlikely(anon_vma_prepare(vma)))
664                 return VM_FAULT_OOM;
665         if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
666                 return VM_FAULT_OOM;
667         if (!(vmf->flags & FAULT_FLAG_WRITE) &&
668                         !mm_forbids_zeropage(vma->vm_mm) &&
669                         transparent_hugepage_use_zero_page()) {
670                 pgtable_t pgtable;
671                 struct page *zero_page;
672                 bool set;
673                 int ret;
674                 pgtable = pte_alloc_one(vma->vm_mm, haddr);
675                 if (unlikely(!pgtable))
676                         return VM_FAULT_OOM;
677                 zero_page = mm_get_huge_zero_page(vma->vm_mm);
678                 if (unlikely(!zero_page)) {
679                         pte_free(vma->vm_mm, pgtable);
680                         count_vm_event(THP_FAULT_FALLBACK);
681                         return VM_FAULT_FALLBACK;
682                 }
683                 vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
684                 ret = 0;
685                 set = false;
686                 if (pmd_none(*vmf->pmd)) {
687                         if (userfaultfd_missing(vma)) {
688                                 spin_unlock(vmf->ptl);
689                                 ret = handle_userfault(vmf, VM_UFFD_MISSING);
690                                 VM_BUG_ON(ret & VM_FAULT_FALLBACK);
691                         } else {
692                                 set_huge_zero_page(pgtable, vma->vm_mm, vma,
693                                                    haddr, vmf->pmd, zero_page);
694                                 spin_unlock(vmf->ptl);
695                                 set = true;
696                         }
697                 } else
698                         spin_unlock(vmf->ptl);
699                 if (!set)
700                         pte_free(vma->vm_mm, pgtable);
701                 return ret;
702         }
703         gfp = alloc_hugepage_direct_gfpmask(vma);
704         page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
705         if (unlikely(!page)) {
706                 count_vm_event(THP_FAULT_FALLBACK);
707                 return VM_FAULT_FALLBACK;
708         }
709         prep_transhuge_page(page);
710         return __do_huge_pmd_anonymous_page(vmf, page, gfp);
711 }
712 
713 static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
714                 pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write)
715 {
716         struct mm_struct *mm = vma->vm_mm;
717         pmd_t entry;
718         spinlock_t *ptl;
719 
720         ptl = pmd_lock(mm, pmd);
721         entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
722         if (pfn_t_devmap(pfn))
723                 entry = pmd_mkdevmap(entry);
724         if (write) {
725                 entry = pmd_mkyoung(pmd_mkdirty(entry));
726                 entry = maybe_pmd_mkwrite(entry, vma);
727         }
728         set_pmd_at(mm, addr, pmd, entry);
729         update_mmu_cache_pmd(vma, addr, pmd);
730         spin_unlock(ptl);
731 }
732 
733 int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
734                         pmd_t *pmd, pfn_t pfn, bool write)
735 {
736         pgprot_t pgprot = vma->vm_page_prot;
737         /*
738          * If we had pmd_special, we could avoid all these restrictions,
739          * but we need to be consistent with PTEs and architectures that
740          * can't support a 'special' bit.
741          */
742         BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
743         BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
744                                                 (VM_PFNMAP|VM_MIXEDMAP));
745         BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
746         BUG_ON(!pfn_t_devmap(pfn));
747 
748         if (addr < vma->vm_start || addr >= vma->vm_end)
749                 return VM_FAULT_SIGBUS;
750 
751         track_pfn_insert(vma, &pgprot, pfn);
752 
753         insert_pfn_pmd(vma, addr, pmd, pfn, pgprot, write);
754         return VM_FAULT_NOPAGE;
755 }
756 EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);
757 
758 static void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
759                 pmd_t *pmd)
760 {
761         pmd_t _pmd;
762 
763         /*
764          * We should set the dirty bit only for FOLL_WRITE but for now
765          * the dirty bit in the pmd is meaningless.  And if the dirty
766          * bit will become meaningful and we'll only set it with
767          * FOLL_WRITE, an atomic set_bit will be required on the pmd to
768          * set the young bit, instead of the current set_pmd_at.
769          */
770         _pmd = pmd_mkyoung(pmd_mkdirty(*pmd));
771         if (pmdp_set_access_flags(vma, addr & HPAGE_PMD_MASK,
772                                 pmd, _pmd,  1))
773                 update_mmu_cache_pmd(vma, addr, pmd);
774 }
775 
776 struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
777                 pmd_t *pmd, int flags)
778 {
779         unsigned long pfn = pmd_pfn(*pmd);
780         struct mm_struct *mm = vma->vm_mm;
781         struct dev_pagemap *pgmap;
782         struct page *page;
783 
784         assert_spin_locked(pmd_lockptr(mm, pmd));
785 
786         /*
787          * When we COW a devmap PMD entry, we split it into PTEs, so we should
788          * not be in this function with `flags & FOLL_COW` set.
789          */
790         WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set");
791 
792         if (flags & FOLL_WRITE && !pmd_write(*pmd))
793                 return NULL;
794 
795         if (pmd_present(*pmd) && pmd_devmap(*pmd))
796                 /* pass */;
797         else
798                 return NULL;
799 
800         if (flags & FOLL_TOUCH)
801                 touch_pmd(vma, addr, pmd);
802 
803         /*
804          * device mapped pages can only be returned if the
805          * caller will manage the page reference count.
806          */
807         if (!(flags & FOLL_GET))
808                 return ERR_PTR(-EEXIST);
809 
810         pfn += (addr & ~PMD_MASK) >> PAGE_SHIFT;
811         pgmap = get_dev_pagemap(pfn, NULL);
812         if (!pgmap)
813                 return ERR_PTR(-EFAULT);
814         page = pfn_to_page(pfn);
815         get_page(page);
816         put_dev_pagemap(pgmap);
817 
818         return page;
819 }
820 
821 int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
822                   pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
823                   struct vm_area_struct *vma)
824 {
825         spinlock_t *dst_ptl, *src_ptl;
826         struct page *src_page;
827         pmd_t pmd;
828         pgtable_t pgtable = NULL;
829         int ret = -ENOMEM;
830 
831         /* Skip if can be re-fill on fault */
832         if (!vma_is_anonymous(vma))
833                 return 0;
834 
835         pgtable = pte_alloc_one(dst_mm, addr);
836         if (unlikely(!pgtable))
837                 goto out;
838 
839         dst_ptl = pmd_lock(dst_mm, dst_pmd);
840         src_ptl = pmd_lockptr(src_mm, src_pmd);
841         spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
842 
843         ret = -EAGAIN;
844         pmd = *src_pmd;
845         if (unlikely(!pmd_trans_huge(pmd))) {
846                 pte_free(dst_mm, pgtable);
847                 goto out_unlock;
848         }
849         /*
850          * When page table lock is held, the huge zero pmd should not be
851          * under splitting since we don't split the page itself, only pmd to
852          * a page table.
853          */
854         if (is_huge_zero_pmd(pmd)) {
855                 struct page *zero_page;
856                 /*
857                  * get_huge_zero_page() will never allocate a new page here,
858                  * since we already have a zero page to copy. It just takes a
859                  * reference.
860                  */
861                 zero_page = mm_get_huge_zero_page(dst_mm);
862                 set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
863                                 zero_page);
864                 ret = 0;
865                 goto out_unlock;
866         }
867 
868         src_page = pmd_page(pmd);
869         VM_BUG_ON_PAGE(!PageHead(src_page), src_page);
870         get_page(src_page);
871         page_dup_rmap(src_page, true);
872         add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR);
873         atomic_long_inc(&dst_mm->nr_ptes);
874         pgtable_trans_huge_deposit(dst_mm, dst_pmd, pgtable);
875 
876         pmdp_set_wrprotect(src_mm, addr, src_pmd);
877         pmd = pmd_mkold(pmd_wrprotect(pmd));
878         set_pmd_at(dst_mm, addr, dst_pmd, pmd);
879 
880         ret = 0;
881 out_unlock:
882         spin_unlock(src_ptl);
883         spin_unlock(dst_ptl);
884 out:
885         return ret;
886 }
887 
888 void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
889 {
890         pmd_t entry;
891         unsigned long haddr;
892         bool write = vmf->flags & FAULT_FLAG_WRITE;
893 
894         vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
895         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
896                 goto unlock;
897 
898         entry = pmd_mkyoung(orig_pmd);
899         if (write)
900                 entry = pmd_mkdirty(entry);
901         haddr = vmf->address & HPAGE_PMD_MASK;
902         if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write))
903                 update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd);
904 
905 unlock:
906         spin_unlock(vmf->ptl);
907 }
908 
909 static int do_huge_pmd_wp_page_fallback(struct vm_fault *vmf, pmd_t orig_pmd,
910                 struct page *page)
911 {
912         struct vm_area_struct *vma = vmf->vma;
913         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
914         struct mem_cgroup *memcg;
915         pgtable_t pgtable;
916         pmd_t _pmd;
917         int ret = 0, i;
918         struct page **pages;
919         unsigned long mmun_start;       /* For mmu_notifiers */
920         unsigned long mmun_end;         /* For mmu_notifiers */
921 
922         pages = kmalloc(sizeof(struct page *) * HPAGE_PMD_NR,
923                         GFP_KERNEL);
924         if (unlikely(!pages)) {
925                 ret |= VM_FAULT_OOM;
926                 goto out;
927         }
928 
929         for (i = 0; i < HPAGE_PMD_NR; i++) {
930                 pages[i] = alloc_page_vma_node(GFP_HIGHUSER_MOVABLE, vma,
931                                                vmf->address, page_to_nid(page));
932                 if (unlikely(!pages[i] ||
933                              mem_cgroup_try_charge(pages[i], vma->vm_mm,
934                                      GFP_KERNEL, &memcg, false))) {
935                         if (pages[i])
936                                 put_page(pages[i]);
937                         while (--i >= 0) {
938                                 memcg = (void *)page_private(pages[i]);
939                                 set_page_private(pages[i], 0);
940                                 mem_cgroup_cancel_charge(pages[i], memcg,
941                                                 false);
942                                 put_page(pages[i]);
943                         }
944                         kfree(pages);
945                         ret |= VM_FAULT_OOM;
946                         goto out;
947                 }
948                 set_page_private(pages[i], (unsigned long)memcg);
949         }
950 
951         for (i = 0; i < HPAGE_PMD_NR; i++) {
952                 copy_user_highpage(pages[i], page + i,
953                                    haddr + PAGE_SIZE * i, vma);
954                 __SetPageUptodate(pages[i]);
955                 cond_resched();
956         }
957 
958         mmun_start = haddr;
959         mmun_end   = haddr + HPAGE_PMD_SIZE;
960         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
961 
962         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
963         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
964                 goto out_free_pages;
965         VM_BUG_ON_PAGE(!PageHead(page), page);
966 
967         pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
968         /* leave pmd empty until pte is filled */
969 
970         pgtable = pgtable_trans_huge_withdraw(vma->vm_mm, vmf->pmd);
971         pmd_populate(vma->vm_mm, &_pmd, pgtable);
972 
973         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
974                 pte_t entry;
975                 entry = mk_pte(pages[i], vma->vm_page_prot);
976                 entry = maybe_mkwrite(pte_mkdirty(entry), vma);
977                 memcg = (void *)page_private(pages[i]);
978                 set_page_private(pages[i], 0);
979                 page_add_new_anon_rmap(pages[i], vmf->vma, haddr, false);
980                 mem_cgroup_commit_charge(pages[i], memcg, false, false);
981                 lru_cache_add_active_or_unevictable(pages[i], vma);
982                 vmf->pte = pte_offset_map(&_pmd, haddr);
983                 VM_BUG_ON(!pte_none(*vmf->pte));
984                 set_pte_at(vma->vm_mm, haddr, vmf->pte, entry);
985                 pte_unmap(vmf->pte);
986         }
987         kfree(pages);
988 
989         smp_wmb(); /* make pte visible before pmd */
990         pmd_populate(vma->vm_mm, vmf->pmd, pgtable);
991         page_remove_rmap(page, true);
992         spin_unlock(vmf->ptl);
993 
994         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
995 
996         ret |= VM_FAULT_WRITE;
997         put_page(page);
998 
999 out:
1000         return ret;
1001 
1002 out_free_pages:
1003         spin_unlock(vmf->ptl);
1004         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1005         for (i = 0; i < HPAGE_PMD_NR; i++) {
1006                 memcg = (void *)page_private(pages[i]);
1007                 set_page_private(pages[i], 0);
1008                 mem_cgroup_cancel_charge(pages[i], memcg, false);
1009                 put_page(pages[i]);
1010         }
1011         kfree(pages);
1012         goto out;
1013 }
1014 
1015 int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
1016 {
1017         struct vm_area_struct *vma = vmf->vma;
1018         struct page *page = NULL, *new_page;
1019         struct mem_cgroup *memcg;
1020         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1021         unsigned long mmun_start;       /* For mmu_notifiers */
1022         unsigned long mmun_end;         /* For mmu_notifiers */
1023         gfp_t huge_gfp;                 /* for allocation and charge */
1024         int ret = 0;
1025 
1026         vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
1027         VM_BUG_ON_VMA(!vma->anon_vma, vma);
1028         if (is_huge_zero_pmd(orig_pmd))
1029                 goto alloc;
1030         spin_lock(vmf->ptl);
1031         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
1032                 goto out_unlock;
1033 
1034         page = pmd_page(orig_pmd);
1035         VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page);
1036         /*
1037          * We can only reuse the page if nobody else maps the huge page or it's
1038          * part.
1039          */
1040         if (page_trans_huge_mapcount(page, NULL) == 1) {
1041                 pmd_t entry;
1042                 entry = pmd_mkyoung(orig_pmd);
1043                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1044                 if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry,  1))
1045                         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1046                 ret |= VM_FAULT_WRITE;
1047                 goto out_unlock;
1048         }
1049         get_page(page);
1050         spin_unlock(vmf->ptl);
1051 alloc:
1052         if (transparent_hugepage_enabled(vma) &&
1053             !transparent_hugepage_debug_cow()) {
1054                 huge_gfp = alloc_hugepage_direct_gfpmask(vma);
1055                 new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
1056         } else
1057                 new_page = NULL;
1058 
1059         if (likely(new_page)) {
1060                 prep_transhuge_page(new_page);
1061         } else {
1062                 if (!page) {
1063                         split_huge_pmd(vma, vmf->pmd, vmf->address);
1064                         ret |= VM_FAULT_FALLBACK;
1065                 } else {
1066                         ret = do_huge_pmd_wp_page_fallback(vmf, orig_pmd, page);
1067                         if (ret & VM_FAULT_OOM) {
1068                                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1069                                 ret |= VM_FAULT_FALLBACK;
1070                         }
1071                         put_page(page);
1072                 }
1073                 count_vm_event(THP_FAULT_FALLBACK);
1074                 goto out;
1075         }
1076 
1077         if (unlikely(mem_cgroup_try_charge(new_page, vma->vm_mm,
1078                                         huge_gfp, &memcg, true))) {
1079                 put_page(new_page);
1080                 split_huge_pmd(vma, vmf->pmd, vmf->address);
1081                 if (page)
1082                         put_page(page);
1083                 ret |= VM_FAULT_FALLBACK;
1084                 count_vm_event(THP_FAULT_FALLBACK);
1085                 goto out;
1086         }
1087 
1088         count_vm_event(THP_FAULT_ALLOC);
1089 
1090         if (!page)
1091                 clear_huge_page(new_page, haddr, HPAGE_PMD_NR);
1092         else
1093                 copy_user_huge_page(new_page, page, haddr, vma, HPAGE_PMD_NR);
1094         __SetPageUptodate(new_page);
1095 
1096         mmun_start = haddr;
1097         mmun_end   = haddr + HPAGE_PMD_SIZE;
1098         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
1099 
1100         spin_lock(vmf->ptl);
1101         if (page)
1102                 put_page(page);
1103         if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
1104                 spin_unlock(vmf->ptl);
1105                 mem_cgroup_cancel_charge(new_page, memcg, true);
1106                 put_page(new_page);
1107                 goto out_mn;
1108         } else {
1109                 pmd_t entry;
1110                 entry = mk_huge_pmd(new_page, vma->vm_page_prot);
1111                 entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
1112                 pmdp_huge_clear_flush_notify(vma, haddr, vmf->pmd);
1113                 page_add_new_anon_rmap(new_page, vma, haddr, true);
1114                 mem_cgroup_commit_charge(new_page, memcg, false, true);
1115                 lru_cache_add_active_or_unevictable(new_page, vma);
1116                 set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
1117                 update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1118                 if (!page) {
1119                         add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
1120                 } else {
1121                         VM_BUG_ON_PAGE(!PageHead(page), page);
1122                         page_remove_rmap(page, true);
1123                         put_page(page);
1124                 }
1125                 ret |= VM_FAULT_WRITE;
1126         }
1127         spin_unlock(vmf->ptl);
1128 out_mn:
1129         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
1130 out:
1131         return ret;
1132 out_unlock:
1133         spin_unlock(vmf->ptl);
1134         return ret;
1135 }
1136 
1137 /*
1138  * FOLL_FORCE can write to even unwritable pmd's, but only
1139  * after we've gone through a COW cycle and they are dirty.
1140  */
1141 static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
1142 {
1143         return pmd_write(pmd) ||
1144                ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
1145 }
1146 
1147 struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
1148                                    unsigned long addr,
1149                                    pmd_t *pmd,
1150                                    unsigned int flags)
1151 {
1152         struct mm_struct *mm = vma->vm_mm;
1153         struct page *page = NULL;
1154 
1155         assert_spin_locked(pmd_lockptr(mm, pmd));
1156 
1157         if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
1158                 goto out;
1159 
1160         /* Avoid dumping huge zero page */
1161         if ((flags & FOLL_DUMP) && is_huge_zero_pmd(*pmd))
1162                 return ERR_PTR(-EFAULT);
1163 
1164         /* Full NUMA hinting faults to serialise migration in fault paths */
1165         if ((flags & FOLL_NUMA) && pmd_protnone(*pmd))
1166                 goto out;
1167 
1168         page = pmd_page(*pmd);
1169         VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
1170         if (flags & FOLL_TOUCH)
1171                 touch_pmd(vma, addr, pmd);
1172         if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
1173                 /*
1174                  * We don't mlock() pte-mapped THPs. This way we can avoid
1175                  * leaking mlocked pages into non-VM_LOCKED VMAs.
1176                  *
1177                  * For anon THP:
1178                  *
1179                  * In most cases the pmd is the only mapping of the page as we
1180                  * break COW for the mlock() -- see gup_flags |= FOLL_WRITE for
1181                  * writable private mappings in populate_vma_page_range().
1182                  *
1183                  * The only scenario when we have the page shared here is if we
1184                  * mlocking read-only mapping shared over fork(). We skip
1185                  * mlocking such pages.
1186                  *
1187                  * For file THP:
1188                  *
1189                  * We can expect PageDoubleMap() to be stable under page lock:
1190                  * for file pages we set it in page_add_file_rmap(), which
1191                  * requires page to be locked.
1192                  */
1193 
1194                 if (PageAnon(page) && compound_mapcount(page) != 1)
1195                         goto skip_mlock;
1196                 if (PageDoubleMap(page) || !page->mapping)
1197                         goto skip_mlock;
1198                 if (!trylock_page(page))
1199                         goto skip_mlock;
1200                 lru_add_drain();
1201                 if (page->mapping && !PageDoubleMap(page))
1202                         mlock_vma_page(page);
1203                 unlock_page(page);
1204         }
1205 skip_mlock:
1206         page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
1207         VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
1208         if (flags & FOLL_GET)
1209                 get_page(page);
1210 
1211 out:
1212         return page;
1213 }
1214 
1215 /* NUMA hinting page fault entry point for trans huge pmds */
1216 int do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t pmd)
1217 {
1218         struct vm_area_struct *vma = vmf->vma;
1219         struct anon_vma *anon_vma = NULL;
1220         struct page *page;
1221         unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
1222         int page_nid = -1, this_nid = numa_node_id();
1223         int target_nid, last_cpupid = -1;
1224         bool page_locked;
1225         bool migrated = false;
1226         bool was_writable;
1227         int flags = 0;
1228 
1229         vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
1230         if (unlikely(!pmd_same(pmd, *vmf->pmd)))
1231                 goto out_unlock;
1232 
1233         /*
1234          * If there are potential migrations, wait for completion and retry
1235          * without disrupting NUMA hinting information. Do not relock and
1236          * check_same as the page may no longer be mapped.
1237          */
1238         if (unlikely(pmd_trans_migrating(*vmf->pmd))) {
1239                 page = pmd_page(*vmf->pmd);
1240                 spin_unlock(vmf->ptl);
1241                 wait_on_page_locked(page);
1242                 goto out;
1243         }
1244 
1245         page = pmd_page(pmd);
1246         BUG_ON(is_huge_zero_page(page));
1247         page_nid = page_to_nid(page);
1248         last_cpupid = page_cpupid_last(page);
1249         count_vm_numa_event(NUMA_HINT_FAULTS);
1250         if (page_nid == this_nid) {
1251                 count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);
1252                 flags |= TNF_FAULT_LOCAL;
1253         }
1254 
1255         /* See similar comment in do_numa_page for explanation */
1256         if (!pmd_write(pmd))
1257                 flags |= TNF_NO_GROUP;
1258 
1259         /*
1260          * Acquire the page lock to serialise THP migrations but avoid dropping
1261          * page_table_lock if at all possible
1262          */
1263         page_locked = trylock_page(page);
1264         target_nid = mpol_misplaced(page, vma, haddr);
1265         if (target_nid == -1) {
1266                 /* If the page was locked, there are no parallel migrations */
1267                 if (page_locked)
1268                         goto clear_pmdnuma;
1269         }
1270 
1271         /* Migration could have started since the pmd_trans_migrating check */
1272         if (!page_locked) {
1273                 spin_unlock(vmf->ptl);
1274                 wait_on_page_locked(page);
1275                 page_nid = -1;
1276                 goto out;
1277         }
1278 
1279         /*
1280          * Page is misplaced. Page lock serialises migrations. Acquire anon_vma
1281          * to serialises splits
1282          */
1283         get_page(page);
1284         spin_unlock(vmf->ptl);
1285         anon_vma = page_lock_anon_vma_read(page);
1286 
1287         /* Confirm the PMD did not change while page_table_lock was released */
1288         spin_lock(vmf->ptl);
1289         if (unlikely(!pmd_same(pmd, *vmf->pmd))) {
1290                 unlock_page(page);
1291                 put_page(page);
1292                 page_nid = -1;
1293                 goto out_unlock;
1294         }
1295 
1296         /* Bail if we fail to protect against THP splits for any reason */
1297         if (unlikely(!anon_vma)) {
1298                 put_page(page);
1299                 page_nid = -1;
1300                 goto clear_pmdnuma;
1301         }
1302 
1303         /*
1304          * Migrate the THP to the requested node, returns with page unlocked
1305          * and access rights restored.
1306          */
1307         spin_unlock(vmf->ptl);
1308         migrated = migrate_misplaced_transhuge_page(vma->vm_mm, vma,
1309                                 vmf->pmd, pmd, vmf->address, page, target_nid);
1310         if (migrated) {
1311                 flags |= TNF_MIGRATED;
1312                 page_nid = target_nid;
1313         } else
1314                 flags |= TNF_MIGRATE_FAIL;
1315 
1316         goto out;
1317 clear_pmdnuma:
1318         BUG_ON(!PageLocked(page));
1319         was_writable = pmd_write(pmd);
1320         pmd = pmd_modify(pmd, vma->vm_page_prot);
1321         pmd = pmd_mkyoung(pmd);
1322         if (was_writable)
1323                 pmd = pmd_mkwrite(pmd);
1324         set_pmd_at(vma->vm_mm, haddr, vmf->pmd, pmd);
1325         update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
1326         unlock_page(page);
1327 out_unlock:
1328         spin_unlock(vmf->ptl);
1329 
1330 out:
1331         if (anon_vma)
1332                 page_unlock_anon_vma_read(anon_vma);
1333 
1334         if (page_nid != -1)
1335                 task_numa_fault(last_cpupid, page_nid, HPAGE_PMD_NR,
1336                                 vmf->flags);
1337 
1338         return 0;
1339 }
1340 
1341 /*
1342  * Return true if we do MADV_FREE successfully on entire pmd page.
1343  * Otherwise, return false.
1344  */
1345 bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1346                 pmd_t *pmd, unsigned long addr, unsigned long next)
1347 {
1348         spinlock_t *ptl;
1349         pmd_t orig_pmd;
1350         struct page *page;
1351         struct mm_struct *mm = tlb->mm;
1352         bool ret = false;
1353 
1354         tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
1355 
1356         ptl = pmd_trans_huge_lock(pmd, vma);
1357         if (!ptl)
1358                 goto out_unlocked;
1359 
1360         orig_pmd = *pmd;
1361         if (is_huge_zero_pmd(orig_pmd))
1362                 goto out;
1363 
1364         page = pmd_page(orig_pmd);
1365         /*
1366          * If other processes are mapping this page, we couldn't discard
1367          * the page unless they all do MADV_FREE so let's skip the page.
1368          */
1369         if (page_mapcount(page) != 1)
1370                 goto out;
1371 
1372         if (!trylock_page(page))
1373                 goto out;
1374 
1375         /*
1376          * If user want to discard part-pages of THP, split it so MADV_FREE
1377          * will deactivate only them.
1378          */
1379         if (next - addr != HPAGE_PMD_SIZE) {
1380                 get_page(page);
1381                 spin_unlock(ptl);
1382                 split_huge_page(page);
1383                 put_page(page);
1384                 unlock_page(page);
1385                 goto out_unlocked;
1386         }
1387 
1388         if (PageDirty(page))
1389                 ClearPageDirty(page);
1390         unlock_page(page);
1391 
1392         if (PageActive(page))
1393                 deactivate_page(page);
1394 
1395         if (pmd_young(orig_pmd) || pmd_dirty(orig_pmd)) {
1396                 orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1397                         tlb->fullmm);
1398                 orig_pmd = pmd_mkold(orig_pmd);
1399                 orig_pmd = pmd_mkclean(orig_pmd);
1400 
1401                 set_pmd_at(mm, addr, pmd, orig_pmd);
1402                 tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1403         }
1404         ret = true;
1405 out:
1406         spin_unlock(ptl);
1407 out_unlocked:
1408         return ret;
1409 }
1410 
1411 static inline void zap_deposited_table(struct mm_struct *mm, pmd_t *pmd)
1412 {
1413         pgtable_t pgtable;
1414 
1415         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1416         pte_free(mm, pgtable);
1417         atomic_long_dec(&mm->nr_ptes);
1418 }
1419 
1420 int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
1421                  pmd_t *pmd, unsigned long addr)
1422 {
1423         pmd_t orig_pmd;
1424         spinlock_t *ptl;
1425 
1426         tlb_remove_check_page_size_change(tlb, HPAGE_PMD_SIZE);
1427 
1428         ptl = __pmd_trans_huge_lock(pmd, vma);
1429         if (!ptl)
1430                 return 0;
1431         /*
1432          * For architectures like ppc64 we look at deposited pgtable
1433          * when calling pmdp_huge_get_and_clear. So do the
1434          * pgtable_trans_huge_withdraw after finishing pmdp related
1435          * operations.
1436          */
1437         orig_pmd = pmdp_huge_get_and_clear_full(tlb->mm, addr, pmd,
1438                         tlb->fullmm);
1439         tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
1440         if (vma_is_dax(vma)) {
1441                 spin_unlock(ptl);
1442                 if (is_huge_zero_pmd(orig_pmd))
1443                         tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1444         } else if (is_huge_zero_pmd(orig_pmd)) {
1445                 pte_free(tlb->mm, pgtable_trans_huge_withdraw(tlb->mm, pmd));
1446                 atomic_long_dec(&tlb->mm->nr_ptes);
1447                 spin_unlock(ptl);
1448                 tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
1449         } else {
1450                 struct page *page = pmd_page(orig_pmd);
1451                 page_remove_rmap(page, true);
1452                 VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
1453                 VM_BUG_ON_PAGE(!PageHead(page), page);
1454                 if (PageAnon(page)) {
1455                         pgtable_t pgtable;
1456                         pgtable = pgtable_trans_huge_withdraw(tlb->mm, pmd);
1457                         pte_free(tlb->mm, pgtable);
1458                         atomic_long_dec(&tlb->mm->nr_ptes);
1459                         add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
1460                 } else {
1461                         if (arch_needs_pgtable_deposit())
1462                                 zap_deposited_table(tlb->mm, pmd);
1463                         add_mm_counter(tlb->mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1464                 }
1465                 spin_unlock(ptl);
1466                 tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
1467         }
1468         return 1;
1469 }
1470 
1471 #ifndef pmd_move_must_withdraw
1472 static inline int pmd_move_must_withdraw(spinlock_t *new_pmd_ptl,
1473                                          spinlock_t *old_pmd_ptl,
1474                                          struct vm_area_struct *vma)
1475 {
1476         /*
1477          * With split pmd lock we also need to move preallocated
1478          * PTE page table if new_pmd is on different PMD page table.
1479          *
1480          * We also don't deposit and withdraw tables for file pages.
1481          */
1482         return (new_pmd_ptl != old_pmd_ptl) && vma_is_anonymous(vma);
1483 }
1484 #endif
1485 
1486 bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
1487                   unsigned long new_addr, unsigned long old_end,
1488                   pmd_t *old_pmd, pmd_t *new_pmd, bool *need_flush)
1489 {
1490         spinlock_t *old_ptl, *new_ptl;
1491         pmd_t pmd;
1492         struct mm_struct *mm = vma->vm_mm;
1493         bool force_flush = false;
1494 
1495         if ((old_addr & ~HPAGE_PMD_MASK) ||
1496             (new_addr & ~HPAGE_PMD_MASK) ||
1497             old_end - old_addr < HPAGE_PMD_SIZE)
1498                 return false;
1499 
1500         /*
1501          * The destination pmd shouldn't be established, free_pgtables()
1502          * should have release it.
1503          */
1504         if (WARN_ON(!pmd_none(*new_pmd))) {
1505                 VM_BUG_ON(pmd_trans_huge(*new_pmd));
1506                 return false;
1507         }
1508 
1509         /*
1510          * We don't have to worry about the ordering of src and dst
1511          * ptlocks because exclusive mmap_sem prevents deadlock.
1512          */
1513         old_ptl = __pmd_trans_huge_lock(old_pmd, vma);
1514         if (old_ptl) {
1515                 new_ptl = pmd_lockptr(mm, new_pmd);
1516                 if (new_ptl != old_ptl)
1517                         spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
1518                 pmd = pmdp_huge_get_and_clear(mm, old_addr, old_pmd);
1519                 if (pmd_present(pmd) && pmd_dirty(pmd))
1520                         force_flush = true;
1521                 VM_BUG_ON(!pmd_none(*new_pmd));
1522 
1523                 if (pmd_move_must_withdraw(new_ptl, old_ptl, vma)) {
1524                         pgtable_t pgtable;
1525                         pgtable = pgtable_trans_huge_withdraw(mm, old_pmd);
1526                         pgtable_trans_huge_deposit(mm, new_pmd, pgtable);
1527                 }
1528                 set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
1529                 if (new_ptl != old_ptl)
1530                         spin_unlock(new_ptl);
1531                 if (force_flush)
1532                         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
1533                 else
1534                         *need_flush = true;
1535                 spin_unlock(old_ptl);
1536                 return true;
1537         }
1538         return false;
1539 }
1540 
1541 /*
1542  * Returns
1543  *  - 0 if PMD could not be locked
1544  *  - 1 if PMD was locked but protections unchange and TLB flush unnecessary
1545  *  - HPAGE_PMD_NR is protections changed and TLB flush necessary
1546  */
1547 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1548                 unsigned long addr, pgprot_t newprot, int prot_numa)
1549 {
1550         struct mm_struct *mm = vma->vm_mm;
1551         spinlock_t *ptl;
1552         int ret = 0;
1553 
1554         ptl = __pmd_trans_huge_lock(pmd, vma);
1555         if (ptl) {
1556                 pmd_t entry;
1557                 bool preserve_write = prot_numa && pmd_write(*pmd);
1558                 ret = 1;
1559 
1560                 /*
1561                  * Avoid trapping faults against the zero page. The read-only
1562                  * data is likely to be read-cached on the local CPU and
1563                  * local/remote hits to the zero page are not interesting.
1564                  */
1565                 if (prot_numa && is_huge_zero_pmd(*pmd)) {
1566                         spin_unlock(ptl);
1567                         return ret;
1568                 }
1569 
1570                 if (!prot_numa || !pmd_protnone(*pmd)) {
1571                         entry = pmdp_huge_get_and_clear_notify(mm, addr, pmd);
1572                         entry = pmd_modify(entry, newprot);
1573                         if (preserve_write)
1574                                 entry = pmd_mkwrite(entry);
1575                         ret = HPAGE_PMD_NR;
1576                         set_pmd_at(mm, addr, pmd, entry);
1577                         BUG_ON(vma_is_anonymous(vma) && !preserve_write &&
1578                                         pmd_write(entry));
1579                 }
1580                 spin_unlock(ptl);
1581         }
1582 
1583         return ret;
1584 }
1585 
1586 /*
1587  * Returns page table lock pointer if a given pmd maps a thp, NULL otherwise.
1588  *
1589  * Note that if it returns page table lock pointer, this routine returns without
1590  * unlocking page table lock. So callers must unlock it.
1591  */
1592 spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
1593 {
1594         spinlock_t *ptl;
1595         ptl = pmd_lock(vma->vm_mm, pmd);
1596         if (likely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
1597                 return ptl;
1598         spin_unlock(ptl);
1599         return NULL;
1600 }
1601 
1602 static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
1603                 unsigned long haddr, pmd_t *pmd)
1604 {
1605         struct mm_struct *mm = vma->vm_mm;
1606         pgtable_t pgtable;
1607         pmd_t _pmd;
1608         int i;
1609 
1610         /* leave pmd empty until pte is filled */
1611         pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1612 
1613         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1614         pmd_populate(mm, &_pmd, pgtable);
1615 
1616         for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
1617                 pte_t *pte, entry;
1618                 entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
1619                 entry = pte_mkspecial(entry);
1620                 pte = pte_offset_map(&_pmd, haddr);
1621                 VM_BUG_ON(!pte_none(*pte));
1622                 set_pte_at(mm, haddr, pte, entry);
1623                 pte_unmap(pte);
1624         }
1625         smp_wmb(); /* make pte visible before pmd */
1626         pmd_populate(mm, pmd, pgtable);
1627 }
1628 
1629 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
1630                 unsigned long haddr, bool freeze)
1631 {
1632         struct mm_struct *mm = vma->vm_mm;
1633         struct page *page;
1634         pgtable_t pgtable;
1635         pmd_t _pmd;
1636         bool young, write, dirty, soft_dirty;
1637         unsigned long addr;
1638         int i;
1639 
1640         VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
1641         VM_BUG_ON_VMA(vma->vm_start > haddr, vma);
1642         VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma);
1643         VM_BUG_ON(!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd));
1644 
1645         count_vm_event(THP_SPLIT_PMD);
1646 
1647         if (!vma_is_anonymous(vma)) {
1648                 _pmd = pmdp_huge_clear_flush_notify(vma, haddr, pmd);
1649                 /*
1650                  * We are going to unmap this huge page. So
1651                  * just go ahead and zap it
1652                  */
1653                 if (arch_needs_pgtable_deposit())
1654                         zap_deposited_table(mm, pmd);
1655                 if (vma_is_dax(vma))
1656                         return;
1657                 page = pmd_page(_pmd);
1658                 if (!PageReferenced(page) && pmd_young(_pmd))
1659                         SetPageReferenced(page);
1660                 page_remove_rmap(page, true);
1661                 put_page(page);
1662                 add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
1663                 return;
1664         } else if (is_huge_zero_pmd(*pmd)) {
1665                 return __split_huge_zero_page_pmd(vma, haddr, pmd);
1666         }
1667 
1668         page = pmd_page(*pmd);
1669         VM_BUG_ON_PAGE(!page_count(page), page);
1670         page_ref_add(page, HPAGE_PMD_NR - 1);
1671         write = pmd_write(*pmd);
1672         young = pmd_young(*pmd);
1673         dirty = pmd_dirty(*pmd);
1674         soft_dirty = pmd_soft_dirty(*pmd);
1675 
1676         pmdp_huge_split_prepare(vma, haddr, pmd);
1677         pgtable = pgtable_trans_huge_withdraw(mm, pmd);
1678         pmd_populate(mm, &_pmd, pgtable);
1679 
1680         for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
1681                 pte_t entry, *pte;
1682                 /*
1683                  * Note that NUMA hinting access restrictions are not
1684                  * transferred to avoid any possibility of altering
1685                  * permissions across VMAs.
1686                  */
1687                 if (freeze) {
1688                         swp_entry_t swp_entry;
1689                         swp_entry = make_migration_entry(page + i, write);
1690                         entry = swp_entry_to_pte(swp_entry);
1691                         if (soft_dirty)
1692                                 entry = pte_swp_mksoft_dirty(entry);
1693                 } else {
1694                         entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
1695                         entry = maybe_mkwrite(entry, vma);
1696                         if (!write)
1697                                 entry = pte_wrprotect(entry);
1698                         if (!young)
1699                                 entry = pte_mkold(entry);
1700                         if (soft_dirty)
1701                                 entry = pte_mksoft_dirty(entry);
1702                 }
1703                 if (dirty)
1704                         SetPageDirty(page + i);
1705                 pte = pte_offset_map(&_pmd, addr);
1706                 BUG_ON(!pte_none(*pte));
1707                 set_pte_at(mm, addr, pte, entry);
1708                 atomic_inc(&page[i]._mapcount);
1709                 pte_unmap(pte);
1710         }
1711 
1712         /*
1713          * Set PG_double_map before dropping compound_mapcount to avoid
1714          * false-negative page_mapped().
1715          */
1716         if (compound_mapcount(page) > 1 && !TestSetPageDoubleMap(page)) {
1717                 for (i = 0; i < HPAGE_PMD_NR; i++)
1718                         atomic_inc(&page[i]._mapcount);
1719         }
1720 
1721         if (atomic_add_negative(-1, compound_mapcount_ptr(page))) {
1722                 /* Last compound_mapcount is gone. */
1723                 __dec_node_page_state(page, NR_ANON_THPS);
1724                 if (TestClearPageDoubleMap(page)) {
1725                         /* No need in mapcount reference anymore */
1726                         for (i = 0; i < HPAGE_PMD_NR; i++)
1727                                 atomic_dec(&page[i]._mapcount);
1728                 }
1729         }
1730 
1731         smp_wmb(); /* make pte visible before pmd */
1732         /*
1733          * Up to this point the pmd is present and huge and userland has the
1734          * whole access to the hugepage during the split (which happens in
1735          * place). If we overwrite the pmd with the not-huge version pointing
1736          * to the pte here (which of course we could if all CPUs were bug
1737          * free), userland could trigger a small page size TLB miss on the
1738          * small sized TLB while the hugepage TLB entry is still established in
1739          * the huge TLB. Some CPU doesn't like that.
1740          * See http://support.amd.com/us/Processor_TechDocs/41322.pdf, Erratum
1741          * 383 on page 93. Intel should be safe but is also warns that it's
1742          * only safe if the permission and cache attributes of the two entries
1743          * loaded in the two TLB is identical (which should be the case here).
1744          * But it is generally safer to never allow small and huge TLB entries
1745          * for the same virtual address to be loaded simultaneously. So instead
1746          * of doing "pmd_populate(); flush_pmd_tlb_range();" we first mark the
1747          * current pmd notpresent (atomically because here the pmd_trans_huge
1748          * and pmd_trans_splitting must remain set at all times on the pmd
1749          * until the split is complete for this pmd), then we flush the SMP TLB
1750          * and finally we write the non-huge version of the pmd entry with
1751          * pmd_populate.
1752          */
1753         pmdp_invalidate(vma, haddr, pmd);
1754         pmd_populate(mm, pmd, pgtable);
1755 
1756         if (freeze) {
1757                 for (i = 0; i < HPAGE_PMD_NR; i++) {
1758                         page_remove_rmap(page + i, false);
1759                         put_page(page + i);
1760                 }
1761         }
1762 }
1763 
1764 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
1765                 unsigned long address, bool freeze, struct page *page)
1766 {
1767         spinlock_t *ptl;
1768         struct mm_struct *mm = vma->vm_mm;
1769         unsigned long haddr = address & HPAGE_PMD_MASK;
1770 
1771         mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
1772         ptl = pmd_lock(mm, pmd);
1773 
1774         /*
1775          * If caller asks to setup a migration entries, we need a page to check
1776          * pmd against. Otherwise we can end up replacing wrong page.
1777          */
1778         VM_BUG_ON(freeze && !page);
1779         if (page && page != pmd_page(*pmd))
1780                 goto out;
1781 
1782         if (pmd_trans_huge(*pmd)) {
1783                 page = pmd_page(*pmd);
1784                 if (PageMlocked(page))
1785                         clear_page_mlock(page);
1786         } else if (!pmd_devmap(*pmd))
1787                 goto out;
1788         __split_huge_pmd_locked(vma, pmd, haddr, freeze);
1789 out:
1790         spin_unlock(ptl);
1791         mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
1792 }
1793 
1794 void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
1795                 bool freeze, struct page *page)
1796 {
1797         pgd_t *pgd;
1798         pud_t *pud;
1799         pmd_t *pmd;
1800 
1801         pgd = pgd_offset(vma->vm_mm, address);
1802         if (!pgd_present(*pgd))
1803                 return;
1804 
1805         pud = pud_offset(pgd, address);
1806         if (!pud_present(*pud))
1807                 return;
1808 
1809         pmd = pmd_offset(pud, address);
1810 
1811         __split_huge_pmd(vma, pmd, address, freeze, page);
1812 }
1813 
1814 void vma_adjust_trans_huge(struct vm_area_struct *vma,
1815                              unsigned long start,
1816                              unsigned long end,
1817                              long adjust_next)
1818 {
1819         /*
1820          * If the new start address isn't hpage aligned and it could
1821          * previously contain an hugepage: check if we need to split
1822          * an huge pmd.
1823          */
1824         if (start & ~HPAGE_PMD_MASK &&
1825             (start & HPAGE_PMD_MASK) >= vma->vm_start &&
1826             (start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1827                 split_huge_pmd_address(vma, start, false, NULL);
1828 
1829         /*
1830          * If the new end address isn't hpage aligned and it could
1831          * previously contain an hugepage: check if we need to split
1832          * an huge pmd.
1833          */
1834         if (end & ~HPAGE_PMD_MASK &&
1835             (end & HPAGE_PMD_MASK) >= vma->vm_start &&
1836             (end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
1837                 split_huge_pmd_address(vma, end, false, NULL);
1838 
1839         /*
1840          * If we're also updating the vma->vm_next->vm_start, if the new
1841          * vm_next->vm_start isn't page aligned and it could previously
1842          * contain an hugepage: check if we need to split an huge pmd.
1843          */
1844         if (adjust_next > 0) {
1845                 struct vm_area_struct *next = vma->vm_next;
1846                 unsigned long nstart = next->vm_start;
1847                 nstart += adjust_next << PAGE_SHIFT;
1848                 if (nstart & ~HPAGE_PMD_MASK &&
1849                     (nstart & HPAGE_PMD_MASK) >= next->vm_start &&
1850                     (nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
1851                         split_huge_pmd_address(next, nstart, false, NULL);
1852         }
1853 }
1854 
1855 static void freeze_page(struct page *page)
1856 {
1857         enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS |
1858                 TTU_RMAP_LOCKED;
1859         int i, ret;
1860 
1861         VM_BUG_ON_PAGE(!PageHead(page), page);
1862 
1863         if (PageAnon(page))
1864                 ttu_flags |= TTU_MIGRATION;
1865 
1866         /* We only need TTU_SPLIT_HUGE_PMD once */
1867         ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
1868         for (i = 1; !ret && i < HPAGE_PMD_NR; i++) {
1869                 /* Cut short if the page is unmapped */
1870                 if (page_count(page) == 1)
1871                         return;
1872 
1873                 ret = try_to_unmap(page + i, ttu_flags);
1874         }
1875         VM_BUG_ON_PAGE(ret, page + i - 1);
1876 }
1877 
1878 static void unfreeze_page(struct page *page)
1879 {
1880         int i;
1881 
1882         for (i = 0; i < HPAGE_PMD_NR; i++)
1883                 remove_migration_ptes(page + i, page + i, true);
1884 }
1885 
1886 static void __split_huge_page_tail(struct page *head, int tail,
1887                 struct lruvec *lruvec, struct list_head *list)
1888 {
1889         struct page *page_tail = head + tail;
1890 
1891         VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
1892         VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail);
1893 
1894         /*
1895          * tail_page->_refcount is zero and not changing from under us. But
1896          * get_page_unless_zero() may be running from under us on the
1897          * tail_page. If we used atomic_set() below instead of atomic_inc() or
1898          * atomic_add(), we would then run atomic_set() concurrently with
1899          * get_page_unless_zero(), and atomic_set() is implemented in C not
1900          * using locked ops. spin_unlock on x86 sometime uses locked ops
1901          * because of PPro errata 66, 92, so unless somebody can guarantee
1902          * atomic_set() here would be safe on all archs (and not only on x86),
1903          * it's safer to use atomic_inc()/atomic_add().
1904          */
1905         if (PageAnon(head)) {
1906                 page_ref_inc(page_tail);
1907         } else {
1908                 /* Additional pin to radix tree */
1909                 page_ref_add(page_tail, 2);
1910         }
1911 
1912         page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
1913         page_tail->flags |= (head->flags &
1914                         ((1L << PG_referenced) |
1915                          (1L << PG_swapbacked) |
1916                          (1L << PG_mlocked) |
1917                          (1L << PG_uptodate) |
1918                          (1L << PG_active) |
1919                          (1L << PG_locked) |
1920                          (1L << PG_unevictable) |
1921                          (1L << PG_dirty)));
1922 
1923         /*
1924          * After clearing PageTail the gup refcount can be released.
1925          * Page flags also must be visible before we make the page non-compound.
1926          */
1927         smp_wmb();
1928 
1929         clear_compound_head(page_tail);
1930 
1931         if (page_is_young(head))
1932                 set_page_young(page_tail);
1933         if (page_is_idle(head))
1934                 set_page_idle(page_tail);
1935 
1936         /* ->mapping in first tail page is compound_mapcount */
1937         VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
1938                         page_tail);
1939         page_tail->mapping = head->mapping;
1940 
1941         page_tail->index = head->index + tail;
1942         page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
1943         lru_add_page_tail(head, page_tail, lruvec, list);
1944 }
1945 
1946 static void __split_huge_page(struct page *page, struct list_head *list,
1947                 unsigned long flags)
1948 {
1949         struct page *head = compound_head(page);
1950         struct zone *zone = page_zone(head);
1951         struct lruvec *lruvec;
1952         pgoff_t end = -1;
1953         int i;
1954 
1955         lruvec = mem_cgroup_page_lruvec(head, zone->zone_pgdat);
1956 
1957         /* complete memcg works before add pages to LRU */
1958         mem_cgroup_split_huge_fixup(head);
1959 
1960         if (!PageAnon(page))
1961                 end = DIV_ROUND_UP(i_size_read(head->mapping->host), PAGE_SIZE);
1962 
1963         for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
1964                 __split_huge_page_tail(head, i, lruvec, list);
1965                 /* Some pages can be beyond i_size: drop them from page cache */
1966                 if (head[i].index >= end) {
1967                         __ClearPageDirty(head + i);
1968                         __delete_from_page_cache(head + i, NULL);
1969                         if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
1970                                 shmem_uncharge(head->mapping->host, 1);
1971                         put_page(head + i);
1972                 }
1973         }
1974 
1975         ClearPageCompound(head);
1976         /* See comment in __split_huge_page_tail() */
1977         if (PageAnon(head)) {
1978                 page_ref_inc(head);
1979         } else {
1980                 /* Additional pin to radix tree */
1981                 page_ref_add(head, 2);
1982                 spin_unlock(&head->mapping->tree_lock);
1983         }
1984 
1985         spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
1986 
1987         unfreeze_page(head);
1988 
1989         for (i = 0; i < HPAGE_PMD_NR; i++) {
1990                 struct page *subpage = head + i;
1991                 if (subpage == page)
1992                         continue;
1993                 unlock_page(subpage);
1994 
1995                 /*
1996                  * Subpages may be freed if there wasn't any mapping
1997                  * like if add_to_swap() is running on a lru page that
1998                  * had its mapping zapped. And freeing these pages
1999                  * requires taking the lru_lock so we do the put_page
2000                  * of the tail pages after the split is complete.
2001                  */
2002                 put_page(subpage);
2003         }
2004 }
2005 
2006 int total_mapcount(struct page *page)
2007 {
2008         int i, compound, ret;
2009 
2010         VM_BUG_ON_PAGE(PageTail(page), page);
2011 
2012         if (likely(!PageCompound(page)))
2013                 return atomic_read(&page->_mapcount) + 1;
2014 
2015         compound = compound_mapcount(page);
2016         if (PageHuge(page))
2017                 return compound;
2018         ret = compound;
2019         for (i = 0; i < HPAGE_PMD_NR; i++)
2020                 ret += atomic_read(&page[i]._mapcount) + 1;
2021         /* File pages has compound_mapcount included in _mapcount */
2022         if (!PageAnon(page))
2023                 return ret - compound * HPAGE_PMD_NR;
2024         if (PageDoubleMap(page))
2025                 ret -= HPAGE_PMD_NR;
2026         return ret;
2027 }
2028 
2029 /*
2030  * This calculates accurately how many mappings a transparent hugepage
2031  * has (unlike page_mapcount() which isn't fully accurate). This full
2032  * accuracy is primarily needed to know if copy-on-write faults can
2033  * reuse the page and change the mapping to read-write instead of
2034  * copying them. At the same time this returns the total_mapcount too.
2035  *
2036  * The function returns the highest mapcount any one of the subpages
2037  * has. If the return value is one, even if different processes are
2038  * mapping different subpages of the transparent hugepage, they can
2039  * all reuse it, because each process is reusing a different subpage.
2040  *
2041  * The total_mapcount is instead counting all virtual mappings of the
2042  * subpages. If the total_mapcount is equal to "one", it tells the
2043  * caller all mappings belong to the same "mm" and in turn the
2044  * anon_vma of the transparent hugepage can become the vma->anon_vma
2045  * local one as no other process may be mapping any of the subpages.
2046  *
2047  * It would be more accurate to replace page_mapcount() with
2048  * page_trans_huge_mapcount(), however we only use
2049  * page_trans_huge_mapcount() in the copy-on-write faults where we
2050  * need full accuracy to avoid breaking page pinning, because
2051  * page_trans_huge_mapcount() is slower than page_mapcount().
2052  */
2053 int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
2054 {
2055         int i, ret, _total_mapcount, mapcount;
2056 
2057         /* hugetlbfs shouldn't call it */
2058         VM_BUG_ON_PAGE(PageHuge(page), page);
2059 
2060         if (likely(!PageTransCompound(page))) {
2061                 mapcount = atomic_read(&page->_mapcount) + 1;
2062                 if (total_mapcount)
2063                         *total_mapcount = mapcount;
2064                 return mapcount;
2065         }
2066 
2067         page = compound_head(page);
2068 
2069         _total_mapcount = ret = 0;
2070         for (i = 0; i < HPAGE_PMD_NR; i++) {
2071                 mapcount = atomic_read(&page[i]._mapcount) + 1;
2072                 ret = max(ret, mapcount);
2073                 _total_mapcount += mapcount;
2074         }
2075         if (PageDoubleMap(page)) {
2076                 ret -= 1;
2077                 _total_mapcount -= HPAGE_PMD_NR;
2078         }
2079         mapcount = compound_mapcount(page);
2080         ret += mapcount;
2081         _total_mapcount += mapcount;
2082         if (total_mapcount)
2083                 *total_mapcount = _total_mapcount;
2084         return ret;
2085 }
2086 
2087 /*
2088  * This function splits huge page into normal pages. @page can point to any
2089  * subpage of huge page to split. Split doesn't change the position of @page.
2090  *
2091  * Only caller must hold pin on the @page, otherwise split fails with -EBUSY.
2092  * The huge page must be locked.
2093  *
2094  * If @list is null, tail pages will be added to LRU list, otherwise, to @list.
2095  *
2096  * Both head page and tail pages will inherit mapping, flags, and so on from
2097  * the hugepage.
2098  *
2099  * GUP pin and PG_locked transferred to @page. Rest subpages can be freed if
2100  * they are not mapped.
2101  *
2102  * Returns 0 if the hugepage is split successfully.
2103  * Returns -EBUSY if the page is pinned or if anon_vma disappeared from under
2104  * us.
2105  */
2106 int split_huge_page_to_list(struct page *page, struct list_head *list)
2107 {
2108         struct page *head = compound_head(page);
2109         struct pglist_data *pgdata = NODE_DATA(page_to_nid(head));
2110         struct anon_vma *anon_vma = NULL;
2111         struct address_space *mapping = NULL;
2112         int count, mapcount, extra_pins, ret;
2113         bool mlocked;
2114         unsigned long flags;
2115 
2116         VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
2117         VM_BUG_ON_PAGE(!PageLocked(page), page);
2118         VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
2119         VM_BUG_ON_PAGE(!PageCompound(page), page);
2120 
2121         if (PageAnon(head)) {
2122                 /*
2123                  * The caller does not necessarily hold an mmap_sem that would
2124                  * prevent the anon_vma disappearing so we first we take a
2125                  * reference to it and then lock the anon_vma for write. This
2126                  * is similar to page_lock_anon_vma_read except the write lock
2127                  * is taken to serialise against parallel split or collapse
2128                  * operations.
2129                  */
2130                 anon_vma = page_get_anon_vma(head);
2131                 if (!anon_vma) {
2132                         ret = -EBUSY;
2133                         goto out;
2134                 }
2135                 extra_pins = 0;
2136                 mapping = NULL;
2137                 anon_vma_lock_write(anon_vma);
2138         } else {
2139                 mapping = head->mapping;
2140 
2141                 /* Truncated ? */
2142                 if (!mapping) {
2143                         ret = -EBUSY;
2144                         goto out;
2145                 }
2146 
2147                 /* Addidional pins from radix tree */
2148                 extra_pins = HPAGE_PMD_NR;
2149                 anon_vma = NULL;
2150                 i_mmap_lock_read(mapping);
2151         }
2152 
2153         /*
2154          * Racy check if we can split the page, before freeze_page() will
2155          * split PMDs
2156          */
2157         if (total_mapcount(head) != page_count(head) - extra_pins - 1) {
2158                 ret = -EBUSY;
2159                 goto out_unlock;
2160         }
2161 
2162         mlocked = PageMlocked(page);
2163         freeze_page(head);
2164         VM_BUG_ON_PAGE(compound_mapcount(head), head);
2165 
2166         /* Make sure the page is not on per-CPU pagevec as it takes pin */
2167         if (mlocked)
2168                 lru_add_drain();
2169 
2170         /* prevent PageLRU to go away from under us, and freeze lru stats */
2171         spin_lock_irqsave(zone_lru_lock(page_zone(head)), flags);
2172 
2173         if (mapping) {
2174                 void **pslot;
2175 
2176                 spin_lock(&mapping->tree_lock);
2177                 pslot = radix_tree_lookup_slot(&mapping->page_tree,
2178                                 page_index(head));
2179                 /*
2180                  * Check if the head page is present in radix tree.
2181                  * We assume all tail are present too, if head is there.
2182                  */
2183                 if (radix_tree_deref_slot_protected(pslot,
2184                                         &mapping->tree_lock) != head)
2185                         goto fail;
2186         }
2187 
2188         /* Prevent deferred_split_scan() touching ->_refcount */
2189         spin_lock(&pgdata->split_queue_lock);
2190         count = page_count(head);
2191         mapcount = total_mapcount(head);
2192         if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
2193                 if (!list_empty(page_deferred_list(head))) {
2194                         pgdata->split_queue_len--;
2195                         list_del(page_deferred_list(head));
2196                 }
2197                 if (mapping)
2198                         __dec_node_page_state(page, NR_SHMEM_THPS);
2199                 spin_unlock(&pgdata->split_queue_lock);
2200                 __split_huge_page(page, list, flags);
2201                 ret = 0;
2202         } else {
2203                 if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
2204                         pr_alert("total_mapcount: %u, page_count(): %u\n",
2205                                         mapcount, count);
2206                         if (PageTail(page))
2207                                 dump_page(head, NULL);
2208                         dump_page(page, "total_mapcount(head) > 0");
2209                         BUG();
2210                 }
2211                 spin_unlock(&pgdata->split_queue_lock);
2212 fail:           if (mapping)
2213                         spin_unlock(&mapping->tree_lock);
2214                 spin_unlock_irqrestore(zone_lru_lock(page_zone(head)), flags);
2215                 unfreeze_page(head);
2216                 ret = -EBUSY;
2217         }
2218 
2219 out_unlock:
2220         if (anon_vma) {
2221                 anon_vma_unlock_write(anon_vma);
2222                 put_anon_vma(anon_vma);
2223         }
2224         if (mapping)
2225                 i_mmap_unlock_read(mapping);
2226 out:
2227         count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
2228         return ret;
2229 }
2230 
2231 void free_transhuge_page(struct page *page)
2232 {
2233         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2234         unsigned long flags;
2235 
2236         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2237         if (!list_empty(page_deferred_list(page))) {
2238                 pgdata->split_queue_len--;
2239                 list_del(page_deferred_list(page));
2240         }
2241         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2242         free_compound_page(page);
2243 }
2244 
2245 void deferred_split_huge_page(struct page *page)
2246 {
2247         struct pglist_data *pgdata = NODE_DATA(page_to_nid(page));
2248         unsigned long flags;
2249 
2250         VM_BUG_ON_PAGE(!PageTransHuge(page), page);
2251 
2252         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2253         if (list_empty(page_deferred_list(page))) {
2254                 count_vm_event(THP_DEFERRED_SPLIT_PAGE);
2255                 list_add_tail(page_deferred_list(page), &pgdata->split_queue);
2256                 pgdata->split_queue_len++;
2257         }
2258         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2259 }
2260 
2261 static unsigned long deferred_split_count(struct shrinker *shrink,
2262                 struct shrink_control *sc)
2263 {
2264         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2265         return ACCESS_ONCE(pgdata->split_queue_len);
2266 }
2267 
2268 static unsigned long deferred_split_scan(struct shrinker *shrink,
2269                 struct shrink_control *sc)
2270 {
2271         struct pglist_data *pgdata = NODE_DATA(sc->nid);
2272         unsigned long flags;
2273         LIST_HEAD(list), *pos, *next;
2274         struct page *page;
2275         int split = 0;
2276 
2277         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2278         /* Take pin on all head pages to avoid freeing them under us */
2279         list_for_each_safe(pos, next, &pgdata->split_queue) {
2280                 page = list_entry((void *)pos, struct page, mapping);
2281                 page = compound_head(page);
2282                 if (get_page_unless_zero(page)) {
2283                         list_move(page_deferred_list(page), &list);
2284                 } else {
2285                         /* We lost race with put_compound_page() */
2286                         list_del_init(page_deferred_list(page));
2287                         pgdata->split_queue_len--;
2288                 }
2289                 if (!--sc->nr_to_scan)
2290                         break;
2291         }
2292         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2293 
2294         list_for_each_safe(pos, next, &list) {
2295                 page = list_entry((void *)pos, struct page, mapping);
2296                 lock_page(page);
2297                 /* split_huge_page() removes page from list on success */
2298                 if (!split_huge_page(page))
2299                         split++;
2300                 unlock_page(page);
2301                 put_page(page);
2302         }
2303 
2304         spin_lock_irqsave(&pgdata->split_queue_lock, flags);
2305         list_splice_tail(&list, &pgdata->split_queue);
2306         spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
2307 
2308         /*
2309          * Stop shrinker if we didn't split any page, but the queue is empty.
2310          * This can happen if pages were freed under us.
2311          */
2312         if (!split && list_empty(&pgdata->split_queue))
2313                 return SHRINK_STOP;
2314         return split;
2315 }
2316 
2317 static struct shrinker deferred_split_shrinker = {
2318         .count_objects = deferred_split_count,
2319         .scan_objects = deferred_split_scan,
2320         .seeks = DEFAULT_SEEKS,
2321         .flags = SHRINKER_NUMA_AWARE,
2322 };
2323 
2324 #ifdef CONFIG_DEBUG_FS
2325 static int split_huge_pages_set(void *data, u64 val)
2326 {
2327         struct zone *zone;
2328         struct page *page;
2329         unsigned long pfn, max_zone_pfn;
2330         unsigned long total = 0, split = 0;
2331 
2332         if (val != 1)
2333                 return -EINVAL;
2334 
2335         for_each_populated_zone(zone) {
2336                 max_zone_pfn = zone_end_pfn(zone);
2337                 for (pfn = zone->zone_start_pfn; pfn < max_zone_pfn; pfn++) {
2338                         if (!pfn_valid(pfn))
2339                                 continue;
2340 
2341                         page = pfn_to_page(pfn);
2342                         if (!get_page_unless_zero(page))
2343                                 continue;
2344 
2345                         if (zone != page_zone(page))
2346                                 goto next;
2347 
2348                         if (!PageHead(page) || PageHuge(page) || !PageLRU(page))
2349                                 goto next;
2350 
2351                         total++;
2352                         lock_page(page);
2353                         if (!split_huge_page(page))
2354                                 split++;
2355                         unlock_page(page);
2356 next:
2357                         put_page(page);
2358                 }
2359         }
2360 
2361         pr_info("%lu of %lu THP split\n", split, total);
2362 
2363         return 0;
2364 }
2365 DEFINE_SIMPLE_ATTRIBUTE(split_huge_pages_fops, NULL, split_huge_pages_set,
2366                 "%llu\n");
2367 
2368 static int __init split_huge_pages_debugfs(void)
2369 {
2370         void *ret;
2371 
2372         ret = debugfs_create_file("split_huge_pages", 0200, NULL, NULL,
2373                         &split_huge_pages_fops);
2374         if (!ret)
2375                 pr_warn("Failed to create split_huge_pages in debugfs");
2376         return 0;
2377 }
2378 late_initcall(split_huge_pages_debugfs);
2379 #endif
2380 

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