1 // SPDX-License-Identifier: GPL-2.0 2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 3 4 #include <linux/mm.h> 5 #include <linux/sched.h> 6 #include <linux/sched/mm.h> 7 #include <linux/sched/coredump.h> 8 #include <linux/mmu_notifier.h> 9 #include <linux/rmap.h> 10 #include <linux/swap.h> 11 #include <linux/mm_inline.h> 12 #include <linux/kthread.h> 13 #include <linux/khugepaged.h> 14 #include <linux/freezer.h> 15 #include <linux/mman.h> 16 #include <linux/hashtable.h> 17 #include <linux/userfaultfd_k.h> 18 #include <linux/page_idle.h> 19 #include <linux/swapops.h> 20 #include <linux/shmem_fs.h> 21 22 #include <asm/tlb.h> 23 #include <asm/pgalloc.h> 24 #include "internal.h" 25 26 enum scan_result { 27 SCAN_FAIL, 28 SCAN_SUCCEED, 29 SCAN_PMD_NULL, 30 SCAN_EXCEED_NONE_PTE, 31 SCAN_EXCEED_SWAP_PTE, 32 SCAN_EXCEED_SHARED_PTE, 33 SCAN_PTE_NON_PRESENT, 34 SCAN_PTE_UFFD_WP, 35 SCAN_PAGE_RO, 36 SCAN_LACK_REFERENCED_PAGE, 37 SCAN_PAGE_NULL, 38 SCAN_SCAN_ABORT, 39 SCAN_PAGE_COUNT, 40 SCAN_PAGE_LRU, 41 SCAN_PAGE_LOCK, 42 SCAN_PAGE_ANON, 43 SCAN_PAGE_COMPOUND, 44 SCAN_ANY_PROCESS, 45 SCAN_VMA_NULL, 46 SCAN_VMA_CHECK, 47 SCAN_ADDRESS_RANGE, 48 SCAN_SWAP_CACHE_PAGE, 49 SCAN_DEL_PAGE_LRU, 50 SCAN_ALLOC_HUGE_PAGE_FAIL, 51 SCAN_CGROUP_CHARGE_FAIL, 52 SCAN_TRUNCATED, 53 SCAN_PAGE_HAS_PRIVATE, 54 }; 55 56 #define CREATE_TRACE_POINTS 57 #include <trace/events/huge_memory.h> 58 59 static struct task_struct *khugepaged_thread __read_mostly; 60 static DEFINE_MUTEX(khugepaged_mutex); 61 62 /* default scan 8*512 pte (or vmas) every 30 second */ 63 static unsigned int khugepaged_pages_to_scan __read_mostly; 64 static unsigned int khugepaged_pages_collapsed; 65 static unsigned int khugepaged_full_scans; 66 static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000; 67 /* during fragmentation poll the hugepage allocator once every minute */ 68 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000; 69 static unsigned long khugepaged_sleep_expire; 70 static DEFINE_SPINLOCK(khugepaged_mm_lock); 71 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait); 72 /* 73 * default collapse hugepages if there is at least one pte mapped like 74 * it would have happened if the vma was large enough during page 75 * fault. 76 */ 77 static unsigned int khugepaged_max_ptes_none __read_mostly; 78 static unsigned int khugepaged_max_ptes_swap __read_mostly; 79 static unsigned int khugepaged_max_ptes_shared __read_mostly; 80 81 #define MM_SLOTS_HASH_BITS 10 82 static __read_mostly DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); 83 84 static struct kmem_cache *mm_slot_cache __read_mostly; 85 86 #define MAX_PTE_MAPPED_THP 8 87 88 /** 89 * struct mm_slot - hash lookup from mm to mm_slot 90 * @hash: hash collision list 91 * @mm_node: khugepaged scan list headed in khugepaged_scan.mm_head 92 * @mm: the mm that this information is valid for 93 * @nr_pte_mapped_thp: number of pte mapped THP 94 * @pte_mapped_thp: address array corresponding pte mapped THP 95 */ 96 struct mm_slot { 97 struct hlist_node hash; 98 struct list_head mm_node; 99 struct mm_struct *mm; 100 101 /* pte-mapped THP in this mm */ 102 int nr_pte_mapped_thp; 103 unsigned long pte_mapped_thp[MAX_PTE_MAPPED_THP]; 104 }; 105 106 /** 107 * struct khugepaged_scan - cursor for scanning 108 * @mm_head: the head of the mm list to scan 109 * @mm_slot: the current mm_slot we are scanning 110 * @address: the next address inside that to be scanned 111 * 112 * There is only the one khugepaged_scan instance of this cursor structure. 113 */ 114 struct khugepaged_scan { 115 struct list_head mm_head; 116 struct mm_slot *mm_slot; 117 unsigned long address; 118 }; 119 120 static struct khugepaged_scan khugepaged_scan = { 121 .mm_head = LIST_HEAD_INIT(khugepaged_scan.mm_head), 122 }; 123 124 #ifdef CONFIG_SYSFS 125 static ssize_t scan_sleep_millisecs_show(struct kobject *kobj, 126 struct kobj_attribute *attr, 127 char *buf) 128 { 129 return sysfs_emit(buf, "%u\n", khugepaged_scan_sleep_millisecs); 130 } 131 132 static ssize_t scan_sleep_millisecs_store(struct kobject *kobj, 133 struct kobj_attribute *attr, 134 const char *buf, size_t count) 135 { 136 unsigned int msecs; 137 int err; 138 139 err = kstrtouint(buf, 10, &msecs); 140 if (err) 141 return -EINVAL; 142 143 khugepaged_scan_sleep_millisecs = msecs; 144 khugepaged_sleep_expire = 0; 145 wake_up_interruptible(&khugepaged_wait); 146 147 return count; 148 } 149 static struct kobj_attribute scan_sleep_millisecs_attr = 150 __ATTR(scan_sleep_millisecs, 0644, scan_sleep_millisecs_show, 151 scan_sleep_millisecs_store); 152 153 static ssize_t alloc_sleep_millisecs_show(struct kobject *kobj, 154 struct kobj_attribute *attr, 155 char *buf) 156 { 157 return sysfs_emit(buf, "%u\n", khugepaged_alloc_sleep_millisecs); 158 } 159 160 static ssize_t alloc_sleep_millisecs_store(struct kobject *kobj, 161 struct kobj_attribute *attr, 162 const char *buf, size_t count) 163 { 164 unsigned int msecs; 165 int err; 166 167 err = kstrtouint(buf, 10, &msecs); 168 if (err) 169 return -EINVAL; 170 171 khugepaged_alloc_sleep_millisecs = msecs; 172 khugepaged_sleep_expire = 0; 173 wake_up_interruptible(&khugepaged_wait); 174 175 return count; 176 } 177 static struct kobj_attribute alloc_sleep_millisecs_attr = 178 __ATTR(alloc_sleep_millisecs, 0644, alloc_sleep_millisecs_show, 179 alloc_sleep_millisecs_store); 180 181 static ssize_t pages_to_scan_show(struct kobject *kobj, 182 struct kobj_attribute *attr, 183 char *buf) 184 { 185 return sysfs_emit(buf, "%u\n", khugepaged_pages_to_scan); 186 } 187 static ssize_t pages_to_scan_store(struct kobject *kobj, 188 struct kobj_attribute *attr, 189 const char *buf, size_t count) 190 { 191 unsigned int pages; 192 int err; 193 194 err = kstrtouint(buf, 10, &pages); 195 if (err || !pages) 196 return -EINVAL; 197 198 khugepaged_pages_to_scan = pages; 199 200 return count; 201 } 202 static struct kobj_attribute pages_to_scan_attr = 203 __ATTR(pages_to_scan, 0644, pages_to_scan_show, 204 pages_to_scan_store); 205 206 static ssize_t pages_collapsed_show(struct kobject *kobj, 207 struct kobj_attribute *attr, 208 char *buf) 209 { 210 return sysfs_emit(buf, "%u\n", khugepaged_pages_collapsed); 211 } 212 static struct kobj_attribute pages_collapsed_attr = 213 __ATTR_RO(pages_collapsed); 214 215 static ssize_t full_scans_show(struct kobject *kobj, 216 struct kobj_attribute *attr, 217 char *buf) 218 { 219 return sysfs_emit(buf, "%u\n", khugepaged_full_scans); 220 } 221 static struct kobj_attribute full_scans_attr = 222 __ATTR_RO(full_scans); 223 224 static ssize_t khugepaged_defrag_show(struct kobject *kobj, 225 struct kobj_attribute *attr, char *buf) 226 { 227 return single_hugepage_flag_show(kobj, attr, buf, 228 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG); 229 } 230 static ssize_t khugepaged_defrag_store(struct kobject *kobj, 231 struct kobj_attribute *attr, 232 const char *buf, size_t count) 233 { 234 return single_hugepage_flag_store(kobj, attr, buf, count, 235 TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG); 236 } 237 static struct kobj_attribute khugepaged_defrag_attr = 238 __ATTR(defrag, 0644, khugepaged_defrag_show, 239 khugepaged_defrag_store); 240 241 /* 242 * max_ptes_none controls if khugepaged should collapse hugepages over 243 * any unmapped ptes in turn potentially increasing the memory 244 * footprint of the vmas. When max_ptes_none is 0 khugepaged will not 245 * reduce the available free memory in the system as it 246 * runs. Increasing max_ptes_none will instead potentially reduce the 247 * free memory in the system during the khugepaged scan. 248 */ 249 static ssize_t khugepaged_max_ptes_none_show(struct kobject *kobj, 250 struct kobj_attribute *attr, 251 char *buf) 252 { 253 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_none); 254 } 255 static ssize_t khugepaged_max_ptes_none_store(struct kobject *kobj, 256 struct kobj_attribute *attr, 257 const char *buf, size_t count) 258 { 259 int err; 260 unsigned long max_ptes_none; 261 262 err = kstrtoul(buf, 10, &max_ptes_none); 263 if (err || max_ptes_none > HPAGE_PMD_NR-1) 264 return -EINVAL; 265 266 khugepaged_max_ptes_none = max_ptes_none; 267 268 return count; 269 } 270 static struct kobj_attribute khugepaged_max_ptes_none_attr = 271 __ATTR(max_ptes_none, 0644, khugepaged_max_ptes_none_show, 272 khugepaged_max_ptes_none_store); 273 274 static ssize_t khugepaged_max_ptes_swap_show(struct kobject *kobj, 275 struct kobj_attribute *attr, 276 char *buf) 277 { 278 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_swap); 279 } 280 281 static ssize_t khugepaged_max_ptes_swap_store(struct kobject *kobj, 282 struct kobj_attribute *attr, 283 const char *buf, size_t count) 284 { 285 int err; 286 unsigned long max_ptes_swap; 287 288 err = kstrtoul(buf, 10, &max_ptes_swap); 289 if (err || max_ptes_swap > HPAGE_PMD_NR-1) 290 return -EINVAL; 291 292 khugepaged_max_ptes_swap = max_ptes_swap; 293 294 return count; 295 } 296 297 static struct kobj_attribute khugepaged_max_ptes_swap_attr = 298 __ATTR(max_ptes_swap, 0644, khugepaged_max_ptes_swap_show, 299 khugepaged_max_ptes_swap_store); 300 301 static ssize_t khugepaged_max_ptes_shared_show(struct kobject *kobj, 302 struct kobj_attribute *attr, 303 char *buf) 304 { 305 return sysfs_emit(buf, "%u\n", khugepaged_max_ptes_shared); 306 } 307 308 static ssize_t khugepaged_max_ptes_shared_store(struct kobject *kobj, 309 struct kobj_attribute *attr, 310 const char *buf, size_t count) 311 { 312 int err; 313 unsigned long max_ptes_shared; 314 315 err = kstrtoul(buf, 10, &max_ptes_shared); 316 if (err || max_ptes_shared > HPAGE_PMD_NR-1) 317 return -EINVAL; 318 319 khugepaged_max_ptes_shared = max_ptes_shared; 320 321 return count; 322 } 323 324 static struct kobj_attribute khugepaged_max_ptes_shared_attr = 325 __ATTR(max_ptes_shared, 0644, khugepaged_max_ptes_shared_show, 326 khugepaged_max_ptes_shared_store); 327 328 static struct attribute *khugepaged_attr[] = { 329 &khugepaged_defrag_attr.attr, 330 &khugepaged_max_ptes_none_attr.attr, 331 &khugepaged_max_ptes_swap_attr.attr, 332 &khugepaged_max_ptes_shared_attr.attr, 333 &pages_to_scan_attr.attr, 334 &pages_collapsed_attr.attr, 335 &full_scans_attr.attr, 336 &scan_sleep_millisecs_attr.attr, 337 &alloc_sleep_millisecs_attr.attr, 338 NULL, 339 }; 340 341 struct attribute_group khugepaged_attr_group = { 342 .attrs = khugepaged_attr, 343 .name = "khugepaged", 344 }; 345 #endif /* CONFIG_SYSFS */ 346 347 int hugepage_madvise(struct vm_area_struct *vma, 348 unsigned long *vm_flags, int advice) 349 { 350 switch (advice) { 351 case MADV_HUGEPAGE: 352 #ifdef CONFIG_S390 353 /* 354 * qemu blindly sets MADV_HUGEPAGE on all allocations, but s390 355 * can't handle this properly after s390_enable_sie, so we simply 356 * ignore the madvise to prevent qemu from causing a SIGSEGV. 357 */ 358 if (mm_has_pgste(vma->vm_mm)) 359 return 0; 360 #endif 361 *vm_flags &= ~VM_NOHUGEPAGE; 362 *vm_flags |= VM_HUGEPAGE; 363 /* 364 * If the vma become good for khugepaged to scan, 365 * register it here without waiting a page fault that 366 * may not happen any time soon. 367 */ 368 if (!(*vm_flags & VM_NO_KHUGEPAGED) && 369 khugepaged_enter_vma_merge(vma, *vm_flags)) 370 return -ENOMEM; 371 break; 372 case MADV_NOHUGEPAGE: 373 *vm_flags &= ~VM_HUGEPAGE; 374 *vm_flags |= VM_NOHUGEPAGE; 375 /* 376 * Setting VM_NOHUGEPAGE will prevent khugepaged from scanning 377 * this vma even if we leave the mm registered in khugepaged if 378 * it got registered before VM_NOHUGEPAGE was set. 379 */ 380 break; 381 } 382 383 return 0; 384 } 385 386 int __init khugepaged_init(void) 387 { 388 mm_slot_cache = kmem_cache_create("khugepaged_mm_slot", 389 sizeof(struct mm_slot), 390 __alignof__(struct mm_slot), 0, NULL); 391 if (!mm_slot_cache) 392 return -ENOMEM; 393 394 khugepaged_pages_to_scan = HPAGE_PMD_NR * 8; 395 khugepaged_max_ptes_none = HPAGE_PMD_NR - 1; 396 khugepaged_max_ptes_swap = HPAGE_PMD_NR / 8; 397 khugepaged_max_ptes_shared = HPAGE_PMD_NR / 2; 398 399 return 0; 400 } 401 402 void __init khugepaged_destroy(void) 403 { 404 kmem_cache_destroy(mm_slot_cache); 405 } 406 407 static inline struct mm_slot *alloc_mm_slot(void) 408 { 409 if (!mm_slot_cache) /* initialization failed */ 410 return NULL; 411 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); 412 } 413 414 static inline void free_mm_slot(struct mm_slot *mm_slot) 415 { 416 kmem_cache_free(mm_slot_cache, mm_slot); 417 } 418 419 static struct mm_slot *get_mm_slot(struct mm_struct *mm) 420 { 421 struct mm_slot *mm_slot; 422 423 hash_for_each_possible(mm_slots_hash, mm_slot, hash, (unsigned long)mm) 424 if (mm == mm_slot->mm) 425 return mm_slot; 426 427 return NULL; 428 } 429 430 static void insert_to_mm_slots_hash(struct mm_struct *mm, 431 struct mm_slot *mm_slot) 432 { 433 mm_slot->mm = mm; 434 hash_add(mm_slots_hash, &mm_slot->hash, (long)mm); 435 } 436 437 static inline int khugepaged_test_exit(struct mm_struct *mm) 438 { 439 return atomic_read(&mm->mm_users) == 0; 440 } 441 442 static bool hugepage_vma_check(struct vm_area_struct *vma, 443 unsigned long vm_flags) 444 { 445 /* Explicitly disabled through madvise. */ 446 if ((vm_flags & VM_NOHUGEPAGE) || 447 test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) 448 return false; 449 450 /* Enabled via shmem mount options or sysfs settings. */ 451 if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) { 452 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, 453 HPAGE_PMD_NR); 454 } 455 456 /* THP settings require madvise. */ 457 if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always()) 458 return false; 459 460 /* Read-only file mappings need to be aligned for THP to work. */ 461 if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file && 462 (vm_flags & VM_DENYWRITE)) { 463 return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff, 464 HPAGE_PMD_NR); 465 } 466 467 if (!vma->anon_vma || vma->vm_ops) 468 return false; 469 if (vma_is_temporary_stack(vma)) 470 return false; 471 return !(vm_flags & VM_NO_KHUGEPAGED); 472 } 473 474 int __khugepaged_enter(struct mm_struct *mm) 475 { 476 struct mm_slot *mm_slot; 477 int wakeup; 478 479 mm_slot = alloc_mm_slot(); 480 if (!mm_slot) 481 return -ENOMEM; 482 483 /* __khugepaged_exit() must not run from under us */ 484 VM_BUG_ON_MM(atomic_read(&mm->mm_users) == 0, mm); 485 if (unlikely(test_and_set_bit(MMF_VM_HUGEPAGE, &mm->flags))) { 486 free_mm_slot(mm_slot); 487 return 0; 488 } 489 490 spin_lock(&khugepaged_mm_lock); 491 insert_to_mm_slots_hash(mm, mm_slot); 492 /* 493 * Insert just behind the scanning cursor, to let the area settle 494 * down a little. 495 */ 496 wakeup = list_empty(&khugepaged_scan.mm_head); 497 list_add_tail(&mm_slot->mm_node, &khugepaged_scan.mm_head); 498 spin_unlock(&khugepaged_mm_lock); 499 500 mmgrab(mm); 501 if (wakeup) 502 wake_up_interruptible(&khugepaged_wait); 503 504 return 0; 505 } 506 507 int khugepaged_enter_vma_merge(struct vm_area_struct *vma, 508 unsigned long vm_flags) 509 { 510 unsigned long hstart, hend; 511 512 /* 513 * khugepaged only supports read-only files for non-shmem files. 514 * khugepaged does not yet work on special mappings. And 515 * file-private shmem THP is not supported. 516 */ 517 if (!hugepage_vma_check(vma, vm_flags)) 518 return 0; 519 520 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; 521 hend = vma->vm_end & HPAGE_PMD_MASK; 522 if (hstart < hend) 523 return khugepaged_enter(vma, vm_flags); 524 return 0; 525 } 526 527 void __khugepaged_exit(struct mm_struct *mm) 528 { 529 struct mm_slot *mm_slot; 530 int free = 0; 531 532 spin_lock(&khugepaged_mm_lock); 533 mm_slot = get_mm_slot(mm); 534 if (mm_slot && khugepaged_scan.mm_slot != mm_slot) { 535 hash_del(&mm_slot->hash); 536 list_del(&mm_slot->mm_node); 537 free = 1; 538 } 539 spin_unlock(&khugepaged_mm_lock); 540 541 if (free) { 542 clear_bit(MMF_VM_HUGEPAGE, &mm->flags); 543 free_mm_slot(mm_slot); 544 mmdrop(mm); 545 } else if (mm_slot) { 546 /* 547 * This is required to serialize against 548 * khugepaged_test_exit() (which is guaranteed to run 549 * under mmap sem read mode). Stop here (after we 550 * return all pagetables will be destroyed) until 551 * khugepaged has finished working on the pagetables 552 * under the mmap_lock. 553 */ 554 mmap_write_lock(mm); 555 mmap_write_unlock(mm); 556 } 557 } 558 559 static void release_pte_page(struct page *page) 560 { 561 mod_node_page_state(page_pgdat(page), 562 NR_ISOLATED_ANON + page_is_file_lru(page), 563 -compound_nr(page)); 564 unlock_page(page); 565 putback_lru_page(page); 566 } 567 568 static void release_pte_pages(pte_t *pte, pte_t *_pte, 569 struct list_head *compound_pagelist) 570 { 571 struct page *page, *tmp; 572 573 while (--_pte >= pte) { 574 pte_t pteval = *_pte; 575 576 page = pte_page(pteval); 577 if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) && 578 !PageCompound(page)) 579 release_pte_page(page); 580 } 581 582 list_for_each_entry_safe(page, tmp, compound_pagelist, lru) { 583 list_del(&page->lru); 584 release_pte_page(page); 585 } 586 } 587 588 static bool is_refcount_suitable(struct page *page) 589 { 590 int expected_refcount; 591 592 expected_refcount = total_mapcount(page); 593 if (PageSwapCache(page)) 594 expected_refcount += compound_nr(page); 595 596 return page_count(page) == expected_refcount; 597 } 598 599 static int __collapse_huge_page_isolate(struct vm_area_struct *vma, 600 unsigned long address, 601 pte_t *pte, 602 struct list_head *compound_pagelist) 603 { 604 struct page *page = NULL; 605 pte_t *_pte; 606 int none_or_zero = 0, shared = 0, result = 0, referenced = 0; 607 bool writable = false; 608 609 for (_pte = pte; _pte < pte+HPAGE_PMD_NR; 610 _pte++, address += PAGE_SIZE) { 611 pte_t pteval = *_pte; 612 if (pte_none(pteval) || (pte_present(pteval) && 613 is_zero_pfn(pte_pfn(pteval)))) { 614 if (!userfaultfd_armed(vma) && 615 ++none_or_zero <= khugepaged_max_ptes_none) { 616 continue; 617 } else { 618 result = SCAN_EXCEED_NONE_PTE; 619 goto out; 620 } 621 } 622 if (!pte_present(pteval)) { 623 result = SCAN_PTE_NON_PRESENT; 624 goto out; 625 } 626 page = vm_normal_page(vma, address, pteval); 627 if (unlikely(!page)) { 628 result = SCAN_PAGE_NULL; 629 goto out; 630 } 631 632 VM_BUG_ON_PAGE(!PageAnon(page), page); 633 634 if (page_mapcount(page) > 1 && 635 ++shared > khugepaged_max_ptes_shared) { 636 result = SCAN_EXCEED_SHARED_PTE; 637 goto out; 638 } 639 640 if (PageCompound(page)) { 641 struct page *p; 642 page = compound_head(page); 643 644 /* 645 * Check if we have dealt with the compound page 646 * already 647 */ 648 list_for_each_entry(p, compound_pagelist, lru) { 649 if (page == p) 650 goto next; 651 } 652 } 653 654 /* 655 * We can do it before isolate_lru_page because the 656 * page can't be freed from under us. NOTE: PG_lock 657 * is needed to serialize against split_huge_page 658 * when invoked from the VM. 659 */ 660 if (!trylock_page(page)) { 661 result = SCAN_PAGE_LOCK; 662 goto out; 663 } 664 665 /* 666 * Check if the page has any GUP (or other external) pins. 667 * 668 * The page table that maps the page has been already unlinked 669 * from the page table tree and this process cannot get 670 * an additinal pin on the page. 671 * 672 * New pins can come later if the page is shared across fork, 673 * but not from this process. The other process cannot write to 674 * the page, only trigger CoW. 675 */ 676 if (!is_refcount_suitable(page)) { 677 unlock_page(page); 678 result = SCAN_PAGE_COUNT; 679 goto out; 680 } 681 if (!pte_write(pteval) && PageSwapCache(page) && 682 !reuse_swap_page(page, NULL)) { 683 /* 684 * Page is in the swap cache and cannot be re-used. 685 * It cannot be collapsed into a THP. 686 */ 687 unlock_page(page); 688 result = SCAN_SWAP_CACHE_PAGE; 689 goto out; 690 } 691 692 /* 693 * Isolate the page to avoid collapsing an hugepage 694 * currently in use by the VM. 695 */ 696 if (isolate_lru_page(page)) { 697 unlock_page(page); 698 result = SCAN_DEL_PAGE_LRU; 699 goto out; 700 } 701 mod_node_page_state(page_pgdat(page), 702 NR_ISOLATED_ANON + page_is_file_lru(page), 703 compound_nr(page)); 704 VM_BUG_ON_PAGE(!PageLocked(page), page); 705 VM_BUG_ON_PAGE(PageLRU(page), page); 706 707 if (PageCompound(page)) 708 list_add_tail(&page->lru, compound_pagelist); 709 next: 710 /* There should be enough young pte to collapse the page */ 711 if (pte_young(pteval) || 712 page_is_young(page) || PageReferenced(page) || 713 mmu_notifier_test_young(vma->vm_mm, address)) 714 referenced++; 715 716 if (pte_write(pteval)) 717 writable = true; 718 } 719 if (likely(writable)) { 720 if (likely(referenced)) { 721 result = SCAN_SUCCEED; 722 trace_mm_collapse_huge_page_isolate(page, none_or_zero, 723 referenced, writable, result); 724 return 1; 725 } 726 } else { 727 result = SCAN_PAGE_RO; 728 } 729 730 out: 731 release_pte_pages(pte, _pte, compound_pagelist); 732 trace_mm_collapse_huge_page_isolate(page, none_or_zero, 733 referenced, writable, result); 734 return 0; 735 } 736 737 static void __collapse_huge_page_copy(pte_t *pte, struct page *page, 738 struct vm_area_struct *vma, 739 unsigned long address, 740 spinlock_t *ptl, 741 struct list_head *compound_pagelist) 742 { 743 struct page *src_page, *tmp; 744 pte_t *_pte; 745 for (_pte = pte; _pte < pte + HPAGE_PMD_NR; 746 _pte++, page++, address += PAGE_SIZE) { 747 pte_t pteval = *_pte; 748 749 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { 750 clear_user_highpage(page, address); 751 add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); 752 if (is_zero_pfn(pte_pfn(pteval))) { 753 /* 754 * ptl mostly unnecessary. 755 */ 756 spin_lock(ptl); 757 /* 758 * paravirt calls inside pte_clear here are 759 * superfluous. 760 */ 761 pte_clear(vma->vm_mm, address, _pte); 762 spin_unlock(ptl); 763 } 764 } else { 765 src_page = pte_page(pteval); 766 copy_user_highpage(page, src_page, address, vma); 767 if (!PageCompound(src_page)) 768 release_pte_page(src_page); 769 /* 770 * ptl mostly unnecessary, but preempt has to 771 * be disabled to update the per-cpu stats 772 * inside page_remove_rmap(). 773 */ 774 spin_lock(ptl); 775 /* 776 * paravirt calls inside pte_clear here are 777 * superfluous. 778 */ 779 pte_clear(vma->vm_mm, address, _pte); 780 page_remove_rmap(src_page, false); 781 spin_unlock(ptl); 782 free_page_and_swap_cache(src_page); 783 } 784 } 785 786 list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) { 787 list_del(&src_page->lru); 788 release_pte_page(src_page); 789 } 790 } 791 792 static void khugepaged_alloc_sleep(void) 793 { 794 DEFINE_WAIT(wait); 795 796 add_wait_queue(&khugepaged_wait, &wait); 797 freezable_schedule_timeout_interruptible( 798 msecs_to_jiffies(khugepaged_alloc_sleep_millisecs)); 799 remove_wait_queue(&khugepaged_wait, &wait); 800 } 801 802 static int khugepaged_node_load[MAX_NUMNODES]; 803 804 static bool khugepaged_scan_abort(int nid) 805 { 806 int i; 807 808 /* 809 * If node_reclaim_mode is disabled, then no extra effort is made to 810 * allocate memory locally. 811 */ 812 if (!node_reclaim_mode) 813 return false; 814 815 /* If there is a count for this node already, it must be acceptable */ 816 if (khugepaged_node_load[nid]) 817 return false; 818 819 for (i = 0; i < MAX_NUMNODES; i++) { 820 if (!khugepaged_node_load[i]) 821 continue; 822 if (node_distance(nid, i) > node_reclaim_distance) 823 return true; 824 } 825 return false; 826 } 827 828 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */ 829 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void) 830 { 831 return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT; 832 } 833 834 #ifdef CONFIG_NUMA 835 static int khugepaged_find_target_node(void) 836 { 837 static int last_khugepaged_target_node = NUMA_NO_NODE; 838 int nid, target_node = 0, max_value = 0; 839 840 /* find first node with max normal pages hit */ 841 for (nid = 0; nid < MAX_NUMNODES; nid++) 842 if (khugepaged_node_load[nid] > max_value) { 843 max_value = khugepaged_node_load[nid]; 844 target_node = nid; 845 } 846 847 /* do some balance if several nodes have the same hit record */ 848 if (target_node <= last_khugepaged_target_node) 849 for (nid = last_khugepaged_target_node + 1; nid < MAX_NUMNODES; 850 nid++) 851 if (max_value == khugepaged_node_load[nid]) { 852 target_node = nid; 853 break; 854 } 855 856 last_khugepaged_target_node = target_node; 857 return target_node; 858 } 859 860 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait) 861 { 862 if (IS_ERR(*hpage)) { 863 if (!*wait) 864 return false; 865 866 *wait = false; 867 *hpage = NULL; 868 khugepaged_alloc_sleep(); 869 } else if (*hpage) { 870 put_page(*hpage); 871 *hpage = NULL; 872 } 873 874 return true; 875 } 876 877 static struct page * 878 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node) 879 { 880 VM_BUG_ON_PAGE(*hpage, *hpage); 881 882 *hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER); 883 if (unlikely(!*hpage)) { 884 count_vm_event(THP_COLLAPSE_ALLOC_FAILED); 885 *hpage = ERR_PTR(-ENOMEM); 886 return NULL; 887 } 888 889 prep_transhuge_page(*hpage); 890 count_vm_event(THP_COLLAPSE_ALLOC); 891 return *hpage; 892 } 893 #else 894 static int khugepaged_find_target_node(void) 895 { 896 return 0; 897 } 898 899 static inline struct page *alloc_khugepaged_hugepage(void) 900 { 901 struct page *page; 902 903 page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(), 904 HPAGE_PMD_ORDER); 905 if (page) 906 prep_transhuge_page(page); 907 return page; 908 } 909 910 static struct page *khugepaged_alloc_hugepage(bool *wait) 911 { 912 struct page *hpage; 913 914 do { 915 hpage = alloc_khugepaged_hugepage(); 916 if (!hpage) { 917 count_vm_event(THP_COLLAPSE_ALLOC_FAILED); 918 if (!*wait) 919 return NULL; 920 921 *wait = false; 922 khugepaged_alloc_sleep(); 923 } else 924 count_vm_event(THP_COLLAPSE_ALLOC); 925 } while (unlikely(!hpage) && likely(khugepaged_enabled())); 926 927 return hpage; 928 } 929 930 static bool khugepaged_prealloc_page(struct page **hpage, bool *wait) 931 { 932 /* 933 * If the hpage allocated earlier was briefly exposed in page cache 934 * before collapse_file() failed, it is possible that racing lookups 935 * have not yet completed, and would then be unpleasantly surprised by 936 * finding the hpage reused for the same mapping at a different offset. 937 * Just release the previous allocation if there is any danger of that. 938 */ 939 if (*hpage && page_count(*hpage) > 1) { 940 put_page(*hpage); 941 *hpage = NULL; 942 } 943 944 if (!*hpage) 945 *hpage = khugepaged_alloc_hugepage(wait); 946 947 if (unlikely(!*hpage)) 948 return false; 949 950 return true; 951 } 952 953 static struct page * 954 khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node) 955 { 956 VM_BUG_ON(!*hpage); 957 958 return *hpage; 959 } 960 #endif 961 962 /* 963 * If mmap_lock temporarily dropped, revalidate vma 964 * before taking mmap_lock. 965 * Return 0 if succeeds, otherwise return none-zero 966 * value (scan code). 967 */ 968 969 static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, 970 struct vm_area_struct **vmap) 971 { 972 struct vm_area_struct *vma; 973 unsigned long hstart, hend; 974 975 if (unlikely(khugepaged_test_exit(mm))) 976 return SCAN_ANY_PROCESS; 977 978 *vmap = vma = find_vma(mm, address); 979 if (!vma) 980 return SCAN_VMA_NULL; 981 982 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; 983 hend = vma->vm_end & HPAGE_PMD_MASK; 984 if (address < hstart || address + HPAGE_PMD_SIZE > hend) 985 return SCAN_ADDRESS_RANGE; 986 if (!hugepage_vma_check(vma, vma->vm_flags)) 987 return SCAN_VMA_CHECK; 988 /* Anon VMA expected */ 989 if (!vma->anon_vma || vma->vm_ops) 990 return SCAN_VMA_CHECK; 991 return 0; 992 } 993 994 /* 995 * Bring missing pages in from swap, to complete THP collapse. 996 * Only done if khugepaged_scan_pmd believes it is worthwhile. 997 * 998 * Called and returns without pte mapped or spinlocks held, 999 * but with mmap_lock held to protect against vma changes. 1000 */ 1001 1002 static bool __collapse_huge_page_swapin(struct mm_struct *mm, 1003 struct vm_area_struct *vma, 1004 unsigned long haddr, pmd_t *pmd, 1005 int referenced) 1006 { 1007 int swapped_in = 0; 1008 vm_fault_t ret = 0; 1009 unsigned long address, end = haddr + (HPAGE_PMD_NR * PAGE_SIZE); 1010 1011 for (address = haddr; address < end; address += PAGE_SIZE) { 1012 struct vm_fault vmf = { 1013 .vma = vma, 1014 .address = address, 1015 .pgoff = linear_page_index(vma, haddr), 1016 .flags = FAULT_FLAG_ALLOW_RETRY, 1017 .pmd = pmd, 1018 }; 1019 1020 vmf.pte = pte_offset_map(pmd, address); 1021 vmf.orig_pte = *vmf.pte; 1022 if (!is_swap_pte(vmf.orig_pte)) { 1023 pte_unmap(vmf.pte); 1024 continue; 1025 } 1026 swapped_in++; 1027 ret = do_swap_page(&vmf); 1028 1029 /* do_swap_page returns VM_FAULT_RETRY with released mmap_lock */ 1030 if (ret & VM_FAULT_RETRY) { 1031 mmap_read_lock(mm); 1032 if (hugepage_vma_revalidate(mm, haddr, &vma)) { 1033 /* vma is no longer available, don't continue to swapin */ 1034 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); 1035 return false; 1036 } 1037 /* check if the pmd is still valid */ 1038 if (mm_find_pmd(mm, haddr) != pmd) { 1039 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); 1040 return false; 1041 } 1042 } 1043 if (ret & VM_FAULT_ERROR) { 1044 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0); 1045 return false; 1046 } 1047 } 1048 1049 /* Drain LRU add pagevec to remove extra pin on the swapped in pages */ 1050 if (swapped_in) 1051 lru_add_drain(); 1052 1053 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1); 1054 return true; 1055 } 1056 1057 static void collapse_huge_page(struct mm_struct *mm, 1058 unsigned long address, 1059 struct page **hpage, 1060 int node, int referenced, int unmapped) 1061 { 1062 LIST_HEAD(compound_pagelist); 1063 pmd_t *pmd, _pmd; 1064 pte_t *pte; 1065 pgtable_t pgtable; 1066 struct page *new_page; 1067 spinlock_t *pmd_ptl, *pte_ptl; 1068 int isolated = 0, result = 0; 1069 struct vm_area_struct *vma; 1070 struct mmu_notifier_range range; 1071 gfp_t gfp; 1072 1073 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 1074 1075 /* Only allocate from the target node */ 1076 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE; 1077 1078 /* 1079 * Before allocating the hugepage, release the mmap_lock read lock. 1080 * The allocation can take potentially a long time if it involves 1081 * sync compaction, and we do not need to hold the mmap_lock during 1082 * that. We will recheck the vma after taking it again in write mode. 1083 */ 1084 mmap_read_unlock(mm); 1085 new_page = khugepaged_alloc_page(hpage, gfp, node); 1086 if (!new_page) { 1087 result = SCAN_ALLOC_HUGE_PAGE_FAIL; 1088 goto out_nolock; 1089 } 1090 1091 if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) { 1092 result = SCAN_CGROUP_CHARGE_FAIL; 1093 goto out_nolock; 1094 } 1095 count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC); 1096 1097 mmap_read_lock(mm); 1098 result = hugepage_vma_revalidate(mm, address, &vma); 1099 if (result) { 1100 mmap_read_unlock(mm); 1101 goto out_nolock; 1102 } 1103 1104 pmd = mm_find_pmd(mm, address); 1105 if (!pmd) { 1106 result = SCAN_PMD_NULL; 1107 mmap_read_unlock(mm); 1108 goto out_nolock; 1109 } 1110 1111 /* 1112 * __collapse_huge_page_swapin always returns with mmap_lock locked. 1113 * If it fails, we release mmap_lock and jump out_nolock. 1114 * Continuing to collapse causes inconsistency. 1115 */ 1116 if (unmapped && !__collapse_huge_page_swapin(mm, vma, address, 1117 pmd, referenced)) { 1118 mmap_read_unlock(mm); 1119 goto out_nolock; 1120 } 1121 1122 mmap_read_unlock(mm); 1123 /* 1124 * Prevent all access to pagetables with the exception of 1125 * gup_fast later handled by the ptep_clear_flush and the VM 1126 * handled by the anon_vma lock + PG_lock. 1127 */ 1128 mmap_write_lock(mm); 1129 result = hugepage_vma_revalidate(mm, address, &vma); 1130 if (result) 1131 goto out; 1132 /* check if the pmd is still valid */ 1133 if (mm_find_pmd(mm, address) != pmd) 1134 goto out; 1135 1136 anon_vma_lock_write(vma->anon_vma); 1137 1138 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, 1139 address, address + HPAGE_PMD_SIZE); 1140 mmu_notifier_invalidate_range_start(&range); 1141 1142 pte = pte_offset_map(pmd, address); 1143 pte_ptl = pte_lockptr(mm, pmd); 1144 1145 pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */ 1146 /* 1147 * After this gup_fast can't run anymore. This also removes 1148 * any huge TLB entry from the CPU so we won't allow 1149 * huge and small TLB entries for the same virtual address 1150 * to avoid the risk of CPU bugs in that area. 1151 */ 1152 _pmd = pmdp_collapse_flush(vma, address, pmd); 1153 spin_unlock(pmd_ptl); 1154 mmu_notifier_invalidate_range_end(&range); 1155 1156 spin_lock(pte_ptl); 1157 isolated = __collapse_huge_page_isolate(vma, address, pte, 1158 &compound_pagelist); 1159 spin_unlock(pte_ptl); 1160 1161 if (unlikely(!isolated)) { 1162 pte_unmap(pte); 1163 spin_lock(pmd_ptl); 1164 BUG_ON(!pmd_none(*pmd)); 1165 /* 1166 * We can only use set_pmd_at when establishing 1167 * hugepmds and never for establishing regular pmds that 1168 * points to regular pagetables. Use pmd_populate for that 1169 */ 1170 pmd_populate(mm, pmd, pmd_pgtable(_pmd)); 1171 spin_unlock(pmd_ptl); 1172 anon_vma_unlock_write(vma->anon_vma); 1173 result = SCAN_FAIL; 1174 goto out; 1175 } 1176 1177 /* 1178 * All pages are isolated and locked so anon_vma rmap 1179 * can't run anymore. 1180 */ 1181 anon_vma_unlock_write(vma->anon_vma); 1182 1183 __collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl, 1184 &compound_pagelist); 1185 pte_unmap(pte); 1186 __SetPageUptodate(new_page); 1187 pgtable = pmd_pgtable(_pmd); 1188 1189 _pmd = mk_huge_pmd(new_page, vma->vm_page_prot); 1190 _pmd = maybe_pmd_mkwrite(pmd_mkdirty(_pmd), vma); 1191 1192 /* 1193 * spin_lock() below is not the equivalent of smp_wmb(), so 1194 * this is needed to avoid the copy_huge_page writes to become 1195 * visible after the set_pmd_at() write. 1196 */ 1197 smp_wmb(); 1198 1199 spin_lock(pmd_ptl); 1200 BUG_ON(!pmd_none(*pmd)); 1201 page_add_new_anon_rmap(new_page, vma, address, true); 1202 lru_cache_add_inactive_or_unevictable(new_page, vma); 1203 pgtable_trans_huge_deposit(mm, pmd, pgtable); 1204 set_pmd_at(mm, address, pmd, _pmd); 1205 update_mmu_cache_pmd(vma, address, pmd); 1206 spin_unlock(pmd_ptl); 1207 1208 *hpage = NULL; 1209 1210 khugepaged_pages_collapsed++; 1211 result = SCAN_SUCCEED; 1212 out_up_write: 1213 mmap_write_unlock(mm); 1214 out_nolock: 1215 if (!IS_ERR_OR_NULL(*hpage)) 1216 mem_cgroup_uncharge(*hpage); 1217 trace_mm_collapse_huge_page(mm, isolated, result); 1218 return; 1219 out: 1220 goto out_up_write; 1221 } 1222 1223 static int khugepaged_scan_pmd(struct mm_struct *mm, 1224 struct vm_area_struct *vma, 1225 unsigned long address, 1226 struct page **hpage) 1227 { 1228 pmd_t *pmd; 1229 pte_t *pte, *_pte; 1230 int ret = 0, result = 0, referenced = 0; 1231 int none_or_zero = 0, shared = 0; 1232 struct page *page = NULL; 1233 unsigned long _address; 1234 spinlock_t *ptl; 1235 int node = NUMA_NO_NODE, unmapped = 0; 1236 bool writable = false; 1237 1238 VM_BUG_ON(address & ~HPAGE_PMD_MASK); 1239 1240 pmd = mm_find_pmd(mm, address); 1241 if (!pmd) { 1242 result = SCAN_PMD_NULL; 1243 goto out; 1244 } 1245 1246 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load)); 1247 pte = pte_offset_map_lock(mm, pmd, address, &ptl); 1248 for (_address = address, _pte = pte; _pte < pte+HPAGE_PMD_NR; 1249 _pte++, _address += PAGE_SIZE) { 1250 pte_t pteval = *_pte; 1251 if (is_swap_pte(pteval)) { 1252 if (++unmapped <= khugepaged_max_ptes_swap) { 1253 /* 1254 * Always be strict with uffd-wp 1255 * enabled swap entries. Please see 1256 * comment below for pte_uffd_wp(). 1257 */ 1258 if (pte_swp_uffd_wp(pteval)) { 1259 result = SCAN_PTE_UFFD_WP; 1260 goto out_unmap; 1261 } 1262 continue; 1263 } else { 1264 result = SCAN_EXCEED_SWAP_PTE; 1265 goto out_unmap; 1266 } 1267 } 1268 if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { 1269 if (!userfaultfd_armed(vma) && 1270 ++none_or_zero <= khugepaged_max_ptes_none) { 1271 continue; 1272 } else { 1273 result = SCAN_EXCEED_NONE_PTE; 1274 goto out_unmap; 1275 } 1276 } 1277 if (!pte_present(pteval)) { 1278 result = SCAN_PTE_NON_PRESENT; 1279 goto out_unmap; 1280 } 1281 if (pte_uffd_wp(pteval)) { 1282 /* 1283 * Don't collapse the page if any of the small 1284 * PTEs are armed with uffd write protection. 1285 * Here we can also mark the new huge pmd as 1286 * write protected if any of the small ones is 1287 * marked but that could bring unknown 1288 * userfault messages that falls outside of 1289 * the registered range. So, just be simple. 1290 */ 1291 result = SCAN_PTE_UFFD_WP; 1292 goto out_unmap; 1293 } 1294 if (pte_write(pteval)) 1295 writable = true; 1296 1297 page = vm_normal_page(vma, _address, pteval); 1298 if (unlikely(!page)) { 1299 result = SCAN_PAGE_NULL; 1300 goto out_unmap; 1301 } 1302 1303 if (page_mapcount(page) > 1 && 1304 ++shared > khugepaged_max_ptes_shared) { 1305 result = SCAN_EXCEED_SHARED_PTE; 1306 goto out_unmap; 1307 } 1308 1309 page = compound_head(page); 1310 1311 /* 1312 * Record which node the original page is from and save this 1313 * information to khugepaged_node_load[]. 1314 * Khupaged will allocate hugepage from the node has the max 1315 * hit record. 1316 */ 1317 node = page_to_nid(page); 1318 if (khugepaged_scan_abort(node)) { 1319 result = SCAN_SCAN_ABORT; 1320 goto out_unmap; 1321 } 1322 khugepaged_node_load[node]++; 1323 if (!PageLRU(page)) { 1324 result = SCAN_PAGE_LRU; 1325 goto out_unmap; 1326 } 1327 if (PageLocked(page)) { 1328 result = SCAN_PAGE_LOCK; 1329 goto out_unmap; 1330 } 1331 if (!PageAnon(page)) { 1332 result = SCAN_PAGE_ANON; 1333 goto out_unmap; 1334 } 1335 1336 /* 1337 * Check if the page has any GUP (or other external) pins. 1338 * 1339 * Here the check is racy it may see totmal_mapcount > refcount 1340 * in some cases. 1341 * For example, one process with one forked child process. 1342 * The parent has the PMD split due to MADV_DONTNEED, then 1343 * the child is trying unmap the whole PMD, but khugepaged 1344 * may be scanning the parent between the child has 1345 * PageDoubleMap flag cleared and dec the mapcount. So 1346 * khugepaged may see total_mapcount > refcount. 1347 * 1348 * But such case is ephemeral we could always retry collapse 1349 * later. However it may report false positive if the page 1350 * has excessive GUP pins (i.e. 512). Anyway the same check 1351 * will be done again later the risk seems low. 1352 */ 1353 if (!is_refcount_suitable(page)) { 1354 result = SCAN_PAGE_COUNT; 1355 goto out_unmap; 1356 } 1357 if (pte_young(pteval) || 1358 page_is_young(page) || PageReferenced(page) || 1359 mmu_notifier_test_young(vma->vm_mm, address)) 1360 referenced++; 1361 } 1362 if (!writable) { 1363 result = SCAN_PAGE_RO; 1364 } else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) { 1365 result = SCAN_LACK_REFERENCED_PAGE; 1366 } else { 1367 result = SCAN_SUCCEED; 1368 ret = 1; 1369 } 1370 out_unmap: 1371 pte_unmap_unlock(pte, ptl); 1372 if (ret) { 1373 node = khugepaged_find_target_node(); 1374 /* collapse_huge_page will return with the mmap_lock released */ 1375 collapse_huge_page(mm, address, hpage, node, 1376 referenced, unmapped); 1377 } 1378 out: 1379 trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced, 1380 none_or_zero, result, unmapped); 1381 return ret; 1382 } 1383 1384 static void collect_mm_slot(struct mm_slot *mm_slot) 1385 { 1386 struct mm_struct *mm = mm_slot->mm; 1387 1388 lockdep_assert_held(&khugepaged_mm_lock); 1389 1390 if (khugepaged_test_exit(mm)) { 1391 /* free mm_slot */ 1392 hash_del(&mm_slot->hash); 1393 list_del(&mm_slot->mm_node); 1394 1395 /* 1396 * Not strictly needed because the mm exited already. 1397 * 1398 * clear_bit(MMF_VM_HUGEPAGE, &mm->flags); 1399 */ 1400 1401 /* khugepaged_mm_lock actually not necessary for the below */ 1402 free_mm_slot(mm_slot); 1403 mmdrop(mm); 1404 } 1405 } 1406 1407 #ifdef CONFIG_SHMEM 1408 /* 1409 * Notify khugepaged that given addr of the mm is pte-mapped THP. Then 1410 * khugepaged should try to collapse the page table. 1411 */ 1412 static int khugepaged_add_pte_mapped_thp(struct mm_struct *mm, 1413 unsigned long addr) 1414 { 1415 struct mm_slot *mm_slot; 1416 1417 VM_BUG_ON(addr & ~HPAGE_PMD_MASK); 1418 1419 spin_lock(&khugepaged_mm_lock); 1420 mm_slot = get_mm_slot(mm); 1421 if (likely(mm_slot && mm_slot->nr_pte_mapped_thp < MAX_PTE_MAPPED_THP)) 1422 mm_slot->pte_mapped_thp[mm_slot->nr_pte_mapped_thp++] = addr; 1423 spin_unlock(&khugepaged_mm_lock); 1424 return 0; 1425 } 1426 1427 /** 1428 * collapse_pte_mapped_thp - Try to collapse a pte-mapped THP for mm at 1429 * address haddr. 1430 * 1431 * @mm: process address space where collapse happens 1432 * @addr: THP collapse address 1433 * 1434 * This function checks whether all the PTEs in the PMD are pointing to the 1435 * right THP. If so, retract the page table so the THP can refault in with 1436 * as pmd-mapped. 1437 */ 1438 void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr) 1439 { 1440 unsigned long haddr = addr & HPAGE_PMD_MASK; 1441 struct vm_area_struct *vma = find_vma(mm, haddr); 1442 struct page *hpage; 1443 pte_t *start_pte, *pte; 1444 pmd_t *pmd, _pmd; 1445 spinlock_t *ptl; 1446 int count = 0; 1447 int i; 1448 1449 if (!vma || !vma->vm_file || 1450 vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE) 1451 return; 1452 1453 /* 1454 * This vm_flags may not have VM_HUGEPAGE if the page was not 1455 * collapsed by this mm. But we can still collapse if the page is 1456 * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check() 1457 * will not fail the vma for missing VM_HUGEPAGE 1458 */ 1459 if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE)) 1460 return; 1461 1462 hpage = find_lock_page(vma->vm_file->f_mapping, 1463 linear_page_index(vma, haddr)); 1464 if (!hpage) 1465 return; 1466 1467 if (!PageHead(hpage)) 1468 goto drop_hpage; 1469 1470 pmd = mm_find_pmd(mm, haddr); 1471 if (!pmd) 1472 goto drop_hpage; 1473 1474 start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl); 1475 1476 /* step 1: check all mapped PTEs are to the right huge page */ 1477 for (i = 0, addr = haddr, pte = start_pte; 1478 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) { 1479 struct page *page; 1480 1481 /* empty pte, skip */ 1482 if (pte_none(*pte)) 1483 continue; 1484 1485 /* page swapped out, abort */ 1486 if (!pte_present(*pte)) 1487 goto abort; 1488 1489 page = vm_normal_page(vma, addr, *pte); 1490 1491 /* 1492 * Note that uprobe, debugger, or MAP_PRIVATE may change the 1493 * page table, but the new page will not be a subpage of hpage. 1494 */ 1495 if (hpage + i != page) 1496 goto abort; 1497 count++; 1498 } 1499 1500 /* step 2: adjust rmap */ 1501 for (i = 0, addr = haddr, pte = start_pte; 1502 i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) { 1503 struct page *page; 1504 1505 if (pte_none(*pte)) 1506 continue; 1507 page = vm_normal_page(vma, addr, *pte); 1508 page_remove_rmap(page, false); 1509 } 1510 1511 pte_unmap_unlock(start_pte, ptl); 1512 1513 /* step 3: set proper refcount and mm_counters. */ 1514 if (count) { 1515 page_ref_sub(hpage, count); 1516 add_mm_counter(vma->vm_mm, mm_counter_file(hpage), -count); 1517 } 1518 1519 /* step 4: collapse pmd */ 1520 ptl = pmd_lock(vma->vm_mm, pmd); 1521 _pmd = pmdp_collapse_flush(vma, haddr, pmd); 1522 spin_unlock(ptl); 1523 mm_dec_nr_ptes(mm); 1524 pte_free(mm, pmd_pgtable(_pmd)); 1525 1526 drop_hpage: 1527 unlock_page(hpage); 1528 put_page(hpage); 1529 return; 1530 1531 abort: 1532 pte_unmap_unlock(start_pte, ptl); 1533 goto drop_hpage; 1534 } 1535 1536 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot) 1537 { 1538 struct mm_struct *mm = mm_slot->mm; 1539 int i; 1540 1541 if (likely(mm_slot->nr_pte_mapped_thp == 0)) 1542 return 0; 1543 1544 if (!mmap_write_trylock(mm)) 1545 return -EBUSY; 1546 1547 if (unlikely(khugepaged_test_exit(mm))) 1548 goto out; 1549 1550 for (i = 0; i < mm_slot->nr_pte_mapped_thp; i++) 1551 collapse_pte_mapped_thp(mm, mm_slot->pte_mapped_thp[i]); 1552 1553 out: 1554 mm_slot->nr_pte_mapped_thp = 0; 1555 mmap_write_unlock(mm); 1556 return 0; 1557 } 1558 1559 static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) 1560 { 1561 struct vm_area_struct *vma; 1562 struct mm_struct *mm; 1563 unsigned long addr; 1564 pmd_t *pmd, _pmd; 1565 1566 i_mmap_lock_write(mapping); 1567 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) { 1568 /* 1569 * Check vma->anon_vma to exclude MAP_PRIVATE mappings that 1570 * got written to. These VMAs are likely not worth investing 1571 * mmap_write_lock(mm) as PMD-mapping is likely to be split 1572 * later. 1573 * 1574 * Not that vma->anon_vma check is racy: it can be set up after 1575 * the check but before we took mmap_lock by the fault path. 1576 * But page lock would prevent establishing any new ptes of the 1577 * page, so we are safe. 1578 * 1579 * An alternative would be drop the check, but check that page 1580 * table is clear before calling pmdp_collapse_flush() under 1581 * ptl. It has higher chance to recover THP for the VMA, but 1582 * has higher cost too. 1583 */ 1584 if (vma->anon_vma) 1585 continue; 1586 addr = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); 1587 if (addr & ~HPAGE_PMD_MASK) 1588 continue; 1589 if (vma->vm_end < addr + HPAGE_PMD_SIZE) 1590 continue; 1591 mm = vma->vm_mm; 1592 pmd = mm_find_pmd(mm, addr); 1593 if (!pmd) 1594 continue; 1595 /* 1596 * We need exclusive mmap_lock to retract page table. 1597 * 1598 * We use trylock due to lock inversion: we need to acquire 1599 * mmap_lock while holding page lock. Fault path does it in 1600 * reverse order. Trylock is a way to avoid deadlock. 1601 */ 1602 if (mmap_write_trylock(mm)) { 1603 if (!khugepaged_test_exit(mm)) { 1604 spinlock_t *ptl = pmd_lock(mm, pmd); 1605 /* assume page table is clear */ 1606 _pmd = pmdp_collapse_flush(vma, addr, pmd); 1607 spin_unlock(ptl); 1608 mm_dec_nr_ptes(mm); 1609 pte_free(mm, pmd_pgtable(_pmd)); 1610 } 1611 mmap_write_unlock(mm); 1612 } else { 1613 /* Try again later */ 1614 khugepaged_add_pte_mapped_thp(mm, addr); 1615 } 1616 } 1617 i_mmap_unlock_write(mapping); 1618 } 1619 1620 /** 1621 * collapse_file - collapse filemap/tmpfs/shmem pages into huge one. 1622 * 1623 * @mm: process address space where collapse happens 1624 * @file: file that collapse on 1625 * @start: collapse start address 1626 * @hpage: new allocated huge page for collapse 1627 * @node: appointed node the new huge page allocate from 1628 * 1629 * Basic scheme is simple, details are more complex: 1630 * - allocate and lock a new huge page; 1631 * - scan page cache replacing old pages with the new one 1632 * + swap/gup in pages if necessary; 1633 * + fill in gaps; 1634 * + keep old pages around in case rollback is required; 1635 * - if replacing succeeds: 1636 * + copy data over; 1637 * + free old pages; 1638 * + unlock huge page; 1639 * - if replacing failed; 1640 * + put all pages back and unfreeze them; 1641 * + restore gaps in the page cache; 1642 * + unlock and free huge page; 1643 */ 1644 static void collapse_file(struct mm_struct *mm, 1645 struct file *file, pgoff_t start, 1646 struct page **hpage, int node) 1647 { 1648 struct address_space *mapping = file->f_mapping; 1649 gfp_t gfp; 1650 struct page *new_page; 1651 pgoff_t index, end = start + HPAGE_PMD_NR; 1652 LIST_HEAD(pagelist); 1653 XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER); 1654 int nr_none = 0, result = SCAN_SUCCEED; 1655 bool is_shmem = shmem_file(file); 1656 int nr; 1657 1658 VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem); 1659 VM_BUG_ON(start & (HPAGE_PMD_NR - 1)); 1660 1661 /* Only allocate from the target node */ 1662 gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE; 1663 1664 new_page = khugepaged_alloc_page(hpage, gfp, node); 1665 if (!new_page) { 1666 result = SCAN_ALLOC_HUGE_PAGE_FAIL; 1667 goto out; 1668 } 1669 1670 if (unlikely(mem_cgroup_charge(new_page, mm, gfp))) { 1671 result = SCAN_CGROUP_CHARGE_FAIL; 1672 goto out; 1673 } 1674 count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC); 1675 1676 /* This will be less messy when we use multi-index entries */ 1677 do { 1678 xas_lock_irq(&xas); 1679 xas_create_range(&xas); 1680 if (!xas_error(&xas)) 1681 break; 1682 xas_unlock_irq(&xas); 1683 if (!xas_nomem(&xas, GFP_KERNEL)) { 1684 result = SCAN_FAIL; 1685 goto out; 1686 } 1687 } while (1); 1688 1689 __SetPageLocked(new_page); 1690 if (is_shmem) 1691 __SetPageSwapBacked(new_page); 1692 new_page->index = start; 1693 new_page->mapping = mapping; 1694 1695 /* 1696 * At this point the new_page is locked and not up-to-date. 1697 * It's safe to insert it into the page cache, because nobody would 1698 * be able to map it or use it in another way until we unlock it. 1699 */ 1700 1701 xas_set(&xas, start); 1702 for (index = start; index < end; index++) { 1703 struct page *page = xas_next(&xas); 1704 1705 VM_BUG_ON(index != xas.xa_index); 1706 if (is_shmem) { 1707 if (!page) { 1708 /* 1709 * Stop if extent has been truncated or 1710 * hole-punched, and is now completely 1711 * empty. 1712 */ 1713 if (index == start) { 1714 if (!xas_next_entry(&xas, end - 1)) { 1715 result = SCAN_TRUNCATED; 1716 goto xa_locked; 1717 } 1718 xas_set(&xas, index); 1719 } 1720 if (!shmem_charge(mapping->host, 1)) { 1721 result = SCAN_FAIL; 1722 goto xa_locked; 1723 } 1724 xas_store(&xas, new_page); 1725 nr_none++; 1726 continue; 1727 } 1728 1729 if (xa_is_value(page) || !PageUptodate(page)) { 1730 xas_unlock_irq(&xas); 1731 /* swap in or instantiate fallocated page */ 1732 if (shmem_getpage(mapping->host, index, &page, 1733 SGP_NOHUGE)) { 1734 result = SCAN_FAIL; 1735 goto xa_unlocked; 1736 } 1737 } else if (trylock_page(page)) { 1738 get_page(page); 1739 xas_unlock_irq(&xas); 1740 } else { 1741 result = SCAN_PAGE_LOCK; 1742 goto xa_locked; 1743 } 1744 } else { /* !is_shmem */ 1745 if (!page || xa_is_value(page)) { 1746 xas_unlock_irq(&xas); 1747 page_cache_sync_readahead(mapping, &file->f_ra, 1748 file, index, 1749 end - index); 1750 /* drain pagevecs to help isolate_lru_page() */ 1751 lru_add_drain(); 1752 page = find_lock_page(mapping, index); 1753 if (unlikely(page == NULL)) { 1754 result = SCAN_FAIL; 1755 goto xa_unlocked; 1756 } 1757 } else if (PageDirty(page)) { 1758 /* 1759 * khugepaged only works on read-only fd, 1760 * so this page is dirty because it hasn't 1761 * been flushed since first write. There 1762 * won't be new dirty pages. 1763 * 1764 * Trigger async flush here and hope the 1765 * writeback is done when khugepaged 1766 * revisits this page. 1767 * 1768 * This is a one-off situation. We are not 1769 * forcing writeback in loop. 1770 */ 1771 xas_unlock_irq(&xas); 1772 filemap_flush(mapping); 1773 result = SCAN_FAIL; 1774 goto xa_unlocked; 1775 } else if (trylock_page(page)) { 1776 get_page(page); 1777 xas_unlock_irq(&xas); 1778 } else { 1779 result = SCAN_PAGE_LOCK; 1780 goto xa_locked; 1781 } 1782 } 1783 1784 /* 1785 * The page must be locked, so we can drop the i_pages lock 1786 * without racing with truncate. 1787 */ 1788 VM_BUG_ON_PAGE(!PageLocked(page), page); 1789 1790 /* make sure the page is up to date */ 1791 if (unlikely(!PageUptodate(page))) { 1792 result = SCAN_FAIL; 1793 goto out_unlock; 1794 } 1795 1796 /* 1797 * If file was truncated then extended, or hole-punched, before 1798 * we locked the first page, then a THP might be there already. 1799 */ 1800 if (PageTransCompound(page)) { 1801 result = SCAN_PAGE_COMPOUND; 1802 goto out_unlock; 1803 } 1804 1805 if (page_mapping(page) != mapping) { 1806 result = SCAN_TRUNCATED; 1807 goto out_unlock; 1808 } 1809 1810 if (!is_shmem && PageDirty(page)) { 1811 /* 1812 * khugepaged only works on read-only fd, so this 1813 * page is dirty because it hasn't been flushed 1814 * since first write. 1815 */ 1816 result = SCAN_FAIL; 1817 goto out_unlock; 1818 } 1819 1820 if (isolate_lru_page(page)) { 1821 result = SCAN_DEL_PAGE_LRU; 1822 goto out_unlock; 1823 } 1824 1825 if (page_has_private(page) && 1826 !try_to_release_page(page, GFP_KERNEL)) { 1827 result = SCAN_PAGE_HAS_PRIVATE; 1828 putback_lru_page(page); 1829 goto out_unlock; 1830 } 1831 1832 if (page_mapped(page)) 1833 unmap_mapping_pages(mapping, index, 1, false); 1834 1835 xas_lock_irq(&xas); 1836 xas_set(&xas, index); 1837 1838 VM_BUG_ON_PAGE(page != xas_load(&xas), page); 1839 VM_BUG_ON_PAGE(page_mapped(page), page); 1840 1841 /* 1842 * The page is expected to have page_count() == 3: 1843 * - we hold a pin on it; 1844 * - one reference from page cache; 1845 * - one from isolate_lru_page; 1846 */ 1847 if (!page_ref_freeze(page, 3)) { 1848 result = SCAN_PAGE_COUNT; 1849 xas_unlock_irq(&xas); 1850 putback_lru_page(page); 1851 goto out_unlock; 1852 } 1853 1854 /* 1855 * Add the page to the list to be able to undo the collapse if 1856 * something go wrong. 1857 */ 1858 list_add_tail(&page->lru, &pagelist); 1859 1860 /* Finally, replace with the new page. */ 1861 xas_store(&xas, new_page); 1862 continue; 1863 out_unlock: 1864 unlock_page(page); 1865 put_page(page); 1866 goto xa_unlocked; 1867 } 1868 nr = thp_nr_pages(new_page); 1869 1870 if (is_shmem) 1871 __mod_lruvec_page_state(new_page, NR_SHMEM_THPS, nr); 1872 else { 1873 __mod_lruvec_page_state(new_page, NR_FILE_THPS, nr); 1874 filemap_nr_thps_inc(mapping); 1875 } 1876 1877 if (nr_none) { 1878 __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none); 1879 if (is_shmem) 1880 __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none); 1881 } 1882 1883 xa_locked: 1884 xas_unlock_irq(&xas); 1885 xa_unlocked: 1886 1887 if (result == SCAN_SUCCEED) { 1888 struct page *page, *tmp; 1889 1890 /* 1891 * Replacing old pages with new one has succeeded, now we 1892 * need to copy the content and free the old pages. 1893 */ 1894 index = start; 1895 list_for_each_entry_safe(page, tmp, &pagelist, lru) { 1896 while (index < page->index) { 1897 clear_highpage(new_page + (index % HPAGE_PMD_NR)); 1898 index++; 1899 } 1900 copy_highpage(new_page + (page->index % HPAGE_PMD_NR), 1901 page); 1902 list_del(&page->lru); 1903 page->mapping = NULL; 1904 page_ref_unfreeze(page, 1); 1905 ClearPageActive(page); 1906 ClearPageUnevictable(page); 1907 unlock_page(page); 1908 put_page(page); 1909 index++; 1910 } 1911 while (index < end) { 1912 clear_highpage(new_page + (index % HPAGE_PMD_NR)); 1913 index++; 1914 } 1915 1916 SetPageUptodate(new_page); 1917 page_ref_add(new_page, HPAGE_PMD_NR - 1); 1918 if (is_shmem) 1919 set_page_dirty(new_page); 1920 lru_cache_add(new_page); 1921 1922 /* 1923 * Remove pte page tables, so we can re-fault the page as huge. 1924 */ 1925 retract_page_tables(mapping, start); 1926 *hpage = NULL; 1927 1928 khugepaged_pages_collapsed++; 1929 } else { 1930 struct page *page; 1931 1932 /* Something went wrong: roll back page cache changes */ 1933 xas_lock_irq(&xas); 1934 mapping->nrpages -= nr_none; 1935 1936 if (is_shmem) 1937 shmem_uncharge(mapping->host, nr_none); 1938 1939 xas_set(&xas, start); 1940 xas_for_each(&xas, page, end - 1) { 1941 page = list_first_entry_or_null(&pagelist, 1942 struct page, lru); 1943 if (!page || xas.xa_index < page->index) { 1944 if (!nr_none) 1945 break; 1946 nr_none--; 1947 /* Put holes back where they were */ 1948 xas_store(&xas, NULL); 1949 continue; 1950 } 1951 1952 VM_BUG_ON_PAGE(page->index != xas.xa_index, page); 1953 1954 /* Unfreeze the page. */ 1955 list_del(&page->lru); 1956 page_ref_unfreeze(page, 2); 1957 xas_store(&xas, page); 1958 xas_pause(&xas); 1959 xas_unlock_irq(&xas); 1960 unlock_page(page); 1961 putback_lru_page(page); 1962 xas_lock_irq(&xas); 1963 } 1964 VM_BUG_ON(nr_none); 1965 xas_unlock_irq(&xas); 1966 1967 new_page->mapping = NULL; 1968 } 1969 1970 unlock_page(new_page); 1971 out: 1972 VM_BUG_ON(!list_empty(&pagelist)); 1973 if (!IS_ERR_OR_NULL(*hpage)) 1974 mem_cgroup_uncharge(*hpage); 1975 /* TODO: tracepoints */ 1976 } 1977 1978 static void khugepaged_scan_file(struct mm_struct *mm, 1979 struct file *file, pgoff_t start, struct page **hpage) 1980 { 1981 struct page *page = NULL; 1982 struct address_space *mapping = file->f_mapping; 1983 XA_STATE(xas, &mapping->i_pages, start); 1984 int present, swap; 1985 int node = NUMA_NO_NODE; 1986 int result = SCAN_SUCCEED; 1987 1988 present = 0; 1989 swap = 0; 1990 memset(khugepaged_node_load, 0, sizeof(khugepaged_node_load)); 1991 rcu_read_lock(); 1992 xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) { 1993 if (xas_retry(&xas, page)) 1994 continue; 1995 1996 if (xa_is_value(page)) { 1997 if (++swap > khugepaged_max_ptes_swap) { 1998 result = SCAN_EXCEED_SWAP_PTE; 1999 break; 2000 } 2001 continue; 2002 } 2003 2004 if (PageTransCompound(page)) { 2005 result = SCAN_PAGE_COMPOUND; 2006 break; 2007 } 2008 2009 node = page_to_nid(page); 2010 if (khugepaged_scan_abort(node)) { 2011 result = SCAN_SCAN_ABORT; 2012 break; 2013 } 2014 khugepaged_node_load[node]++; 2015 2016 if (!PageLRU(page)) { 2017 result = SCAN_PAGE_LRU; 2018 break; 2019 } 2020 2021 if (page_count(page) != 2022 1 + page_mapcount(page) + page_has_private(page)) { 2023 result = SCAN_PAGE_COUNT; 2024 break; 2025 } 2026 2027 /* 2028 * We probably should check if the page is referenced here, but 2029 * nobody would transfer pte_young() to PageReferenced() for us. 2030 * And rmap walk here is just too costly... 2031 */ 2032 2033 present++; 2034 2035 if (need_resched()) { 2036 xas_pause(&xas); 2037 cond_resched_rcu(); 2038 } 2039 } 2040 rcu_read_unlock(); 2041 2042 if (result == SCAN_SUCCEED) { 2043 if (present < HPAGE_PMD_NR - khugepaged_max_ptes_none) { 2044 result = SCAN_EXCEED_NONE_PTE; 2045 } else { 2046 node = khugepaged_find_target_node(); 2047 collapse_file(mm, file, start, hpage, node); 2048 } 2049 } 2050 2051 /* TODO: tracepoints */ 2052 } 2053 #else 2054 static void khugepaged_scan_file(struct mm_struct *mm, 2055 struct file *file, pgoff_t start, struct page **hpage) 2056 { 2057 BUILD_BUG(); 2058 } 2059 2060 static int khugepaged_collapse_pte_mapped_thps(struct mm_slot *mm_slot) 2061 { 2062 return 0; 2063 } 2064 #endif 2065 2066 static unsigned int khugepaged_scan_mm_slot(unsigned int pages, 2067 struct page **hpage) 2068 __releases(&khugepaged_mm_lock) 2069 __acquires(&khugepaged_mm_lock) 2070 { 2071 struct mm_slot *mm_slot; 2072 struct mm_struct *mm; 2073 struct vm_area_struct *vma; 2074 int progress = 0; 2075 2076 VM_BUG_ON(!pages); 2077 lockdep_assert_held(&khugepaged_mm_lock); 2078 2079 if (khugepaged_scan.mm_slot) 2080 mm_slot = khugepaged_scan.mm_slot; 2081 else { 2082 mm_slot = list_entry(khugepaged_scan.mm_head.next, 2083 struct mm_slot, mm_node); 2084 khugepaged_scan.address = 0; 2085 khugepaged_scan.mm_slot = mm_slot; 2086 } 2087 spin_unlock(&khugepaged_mm_lock); 2088 khugepaged_collapse_pte_mapped_thps(mm_slot); 2089 2090 mm = mm_slot->mm; 2091 /* 2092 * Don't wait for semaphore (to avoid long wait times). Just move to 2093 * the next mm on the list. 2094 */ 2095 vma = NULL; 2096 if (unlikely(!mmap_read_trylock(mm))) 2097 goto breakouterloop_mmap_lock; 2098 if (likely(!khugepaged_test_exit(mm))) 2099 vma = find_vma(mm, khugepaged_scan.address); 2100 2101 progress++; 2102 for (; vma; vma = vma->vm_next) { 2103 unsigned long hstart, hend; 2104 2105 cond_resched(); 2106 if (unlikely(khugepaged_test_exit(mm))) { 2107 progress++; 2108 break; 2109 } 2110 if (!hugepage_vma_check(vma, vma->vm_flags)) { 2111 skip: 2112 progress++; 2113 continue; 2114 } 2115 hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK; 2116 hend = vma->vm_end & HPAGE_PMD_MASK; 2117 if (hstart >= hend) 2118 goto skip; 2119 if (khugepaged_scan.address > hend) 2120 goto skip; 2121 if (khugepaged_scan.address < hstart) 2122 khugepaged_scan.address = hstart; 2123 VM_BUG_ON(khugepaged_scan.address & ~HPAGE_PMD_MASK); 2124 if (shmem_file(vma->vm_file) && !shmem_huge_enabled(vma)) 2125 goto skip; 2126 2127 while (khugepaged_scan.address < hend) { 2128 int ret; 2129 cond_resched(); 2130 if (unlikely(khugepaged_test_exit(mm))) 2131 goto breakouterloop; 2132 2133 VM_BUG_ON(khugepaged_scan.address < hstart || 2134 khugepaged_scan.address + HPAGE_PMD_SIZE > 2135 hend); 2136 if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) { 2137 struct file *file = get_file(vma->vm_file); 2138 pgoff_t pgoff = linear_page_index(vma, 2139 khugepaged_scan.address); 2140 2141 mmap_read_unlock(mm); 2142 ret = 1; 2143 khugepaged_scan_file(mm, file, pgoff, hpage); 2144 fput(file); 2145 } else { 2146 ret = khugepaged_scan_pmd(mm, vma, 2147 khugepaged_scan.address, 2148 hpage); 2149 } 2150 /* move to next address */ 2151 khugepaged_scan.address += HPAGE_PMD_SIZE; 2152 progress += HPAGE_PMD_NR; 2153 if (ret) 2154 /* we released mmap_lock so break loop */ 2155 goto breakouterloop_mmap_lock; 2156 if (progress >= pages) 2157 goto breakouterloop; 2158 } 2159 } 2160 breakouterloop: 2161 mmap_read_unlock(mm); /* exit_mmap will destroy ptes after this */ 2162 breakouterloop_mmap_lock: 2163 2164 spin_lock(&khugepaged_mm_lock); 2165 VM_BUG_ON(khugepaged_scan.mm_slot != mm_slot); 2166 /* 2167 * Release the current mm_slot if this mm is about to die, or 2168 * if we scanned all vmas of this mm. 2169 */ 2170 if (khugepaged_test_exit(mm) || !vma) { 2171 /* 2172 * Make sure that if mm_users is reaching zero while 2173 * khugepaged runs here, khugepaged_exit will find 2174 * mm_slot not pointing to the exiting mm. 2175 */ 2176 if (mm_slot->mm_node.next != &khugepaged_scan.mm_head) { 2177 khugepaged_scan.mm_slot = list_entry( 2178 mm_slot->mm_node.next, 2179 struct mm_slot, mm_node); 2180 khugepaged_scan.address = 0; 2181 } else { 2182 khugepaged_scan.mm_slot = NULL; 2183 khugepaged_full_scans++; 2184 } 2185 2186 collect_mm_slot(mm_slot); 2187 } 2188 2189 return progress; 2190 } 2191 2192 static int khugepaged_has_work(void) 2193 { 2194 return !list_empty(&khugepaged_scan.mm_head) && 2195 khugepaged_enabled(); 2196 } 2197 2198 static int khugepaged_wait_event(void) 2199 { 2200 return !list_empty(&khugepaged_scan.mm_head) || 2201 kthread_should_stop(); 2202 } 2203 2204 static void khugepaged_do_scan(void) 2205 { 2206 struct page *hpage = NULL; 2207 unsigned int progress = 0, pass_through_head = 0; 2208 unsigned int pages = khugepaged_pages_to_scan; 2209 bool wait = true; 2210 2211 barrier(); /* write khugepaged_pages_to_scan to local stack */ 2212 2213 lru_add_drain_all(); 2214 2215 while (progress < pages) { 2216 if (!khugepaged_prealloc_page(&hpage, &wait)) 2217 break; 2218 2219 cond_resched(); 2220 2221 if (unlikely(kthread_should_stop() || try_to_freeze())) 2222 break; 2223 2224 spin_lock(&khugepaged_mm_lock); 2225 if (!khugepaged_scan.mm_slot) 2226 pass_through_head++; 2227 if (khugepaged_has_work() && 2228 pass_through_head < 2) 2229 progress += khugepaged_scan_mm_slot(pages - progress, 2230 &hpage); 2231 else 2232 progress = pages; 2233 spin_unlock(&khugepaged_mm_lock); 2234 } 2235 2236 if (!IS_ERR_OR_NULL(hpage)) 2237 put_page(hpage); 2238 } 2239 2240 static bool khugepaged_should_wakeup(void) 2241 { 2242 return kthread_should_stop() || 2243 time_after_eq(jiffies, khugepaged_sleep_expire); 2244 } 2245 2246 static void khugepaged_wait_work(void) 2247 { 2248 if (khugepaged_has_work()) { 2249 const unsigned long scan_sleep_jiffies = 2250 msecs_to_jiffies(khugepaged_scan_sleep_millisecs); 2251 2252 if (!scan_sleep_jiffies) 2253 return; 2254 2255 khugepaged_sleep_expire = jiffies + scan_sleep_jiffies; 2256 wait_event_freezable_timeout(khugepaged_wait, 2257 khugepaged_should_wakeup(), 2258 scan_sleep_jiffies); 2259 return; 2260 } 2261 2262 if (khugepaged_enabled()) 2263 wait_event_freezable(khugepaged_wait, khugepaged_wait_event()); 2264 } 2265 2266 static int khugepaged(void *none) 2267 { 2268 struct mm_slot *mm_slot; 2269 2270 set_freezable(); 2271 set_user_nice(current, MAX_NICE); 2272 2273 while (!kthread_should_stop()) { 2274 khugepaged_do_scan(); 2275 khugepaged_wait_work(); 2276 } 2277 2278 spin_lock(&khugepaged_mm_lock); 2279 mm_slot = khugepaged_scan.mm_slot; 2280 khugepaged_scan.mm_slot = NULL; 2281 if (mm_slot) 2282 collect_mm_slot(mm_slot); 2283 spin_unlock(&khugepaged_mm_lock); 2284 return 0; 2285 } 2286 2287 static void set_recommended_min_free_kbytes(void) 2288 { 2289 struct zone *zone; 2290 int nr_zones = 0; 2291 unsigned long recommended_min; 2292 2293 for_each_populated_zone(zone) { 2294 /* 2295 * We don't need to worry about fragmentation of 2296 * ZONE_MOVABLE since it only has movable pages. 2297 */ 2298 if (zone_idx(zone) > gfp_zone(GFP_USER)) 2299 continue; 2300 2301 nr_zones++; 2302 } 2303 2304 /* Ensure 2 pageblocks are free to assist fragmentation avoidance */ 2305 recommended_min = pageblock_nr_pages * nr_zones * 2; 2306 2307 /* 2308 * Make sure that on average at least two pageblocks are almost free 2309 * of another type, one for a migratetype to fall back to and a 2310 * second to avoid subsequent fallbacks of other types There are 3 2311 * MIGRATE_TYPES we care about. 2312 */ 2313 recommended_min += pageblock_nr_pages * nr_zones * 2314 MIGRATE_PCPTYPES * MIGRATE_PCPTYPES; 2315 2316 /* don't ever allow to reserve more than 5% of the lowmem */ 2317 recommended_min = min(recommended_min, 2318 (unsigned long) nr_free_buffer_pages() / 20); 2319 recommended_min <<= (PAGE_SHIFT-10); 2320 2321 if (recommended_min > min_free_kbytes) { 2322 if (user_min_free_kbytes >= 0) 2323 pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n", 2324 min_free_kbytes, recommended_min); 2325 2326 min_free_kbytes = recommended_min; 2327 } 2328 setup_per_zone_wmarks(); 2329 } 2330 2331 int start_stop_khugepaged(void) 2332 { 2333 int err = 0; 2334 2335 mutex_lock(&khugepaged_mutex); 2336 if (khugepaged_enabled()) { 2337 if (!khugepaged_thread) 2338 khugepaged_thread = kthread_run(khugepaged, NULL, 2339 "khugepaged"); 2340 if (IS_ERR(khugepaged_thread)) { 2341 pr_err("khugepaged: kthread_run(khugepaged) failed\n"); 2342 err = PTR_ERR(khugepaged_thread); 2343 khugepaged_thread = NULL; 2344 goto fail; 2345 } 2346 2347 if (!list_empty(&khugepaged_scan.mm_head)) 2348 wake_up_interruptible(&khugepaged_wait); 2349 2350 set_recommended_min_free_kbytes(); 2351 } else if (khugepaged_thread) { 2352 kthread_stop(khugepaged_thread); 2353 khugepaged_thread = NULL; 2354 } 2355 fail: 2356 mutex_unlock(&khugepaged_mutex); 2357 return err; 2358 } 2359 2360 void khugepaged_min_free_kbytes_update(void) 2361 { 2362 mutex_lock(&khugepaged_mutex); 2363 if (khugepaged_enabled() && khugepaged_thread) 2364 set_recommended_min_free_kbytes(); 2365 mutex_unlock(&khugepaged_mutex); 2366 } 2367