1 /* 2 * Memory merging support. 3 * 4 * This code enables dynamic sharing of identical pages found in different 5 * memory areas, even if they are not shared by fork() 6 * 7 * Copyright (C) 2008-2009 Red Hat, Inc. 8 * Authors: 9 * Izik Eidus 10 * Andrea Arcangeli 11 * Chris Wright 12 * Hugh Dickins 13 * 14 * This work is licensed under the terms of the GNU GPL, version 2. 15 */ 16 17 #include <linux/errno.h> 18 #include <linux/mm.h> 19 #include <linux/fs.h> 20 #include <linux/mman.h> 21 #include <linux/sched.h> 22 #include <linux/rwsem.h> 23 #include <linux/pagemap.h> 24 #include <linux/rmap.h> 25 #include <linux/spinlock.h> 26 #include <linux/jhash.h> 27 #include <linux/delay.h> 28 #include <linux/kthread.h> 29 #include <linux/wait.h> 30 #include <linux/slab.h> 31 #include <linux/rbtree.h> 32 #include <linux/memory.h> 33 #include <linux/mmu_notifier.h> 34 #include <linux/swap.h> 35 #include <linux/ksm.h> 36 #include <linux/hash.h> 37 #include <linux/freezer.h> 38 #include <linux/oom.h> 39 40 #include <asm/tlbflush.h> 41 #include "internal.h" 42 43 /* 44 * A few notes about the KSM scanning process, 45 * to make it easier to understand the data structures below: 46 * 47 * In order to reduce excessive scanning, KSM sorts the memory pages by their 48 * contents into a data structure that holds pointers to the pages' locations. 49 * 50 * Since the contents of the pages may change at any moment, KSM cannot just 51 * insert the pages into a normal sorted tree and expect it to find anything. 52 * Therefore KSM uses two data structures - the stable and the unstable tree. 53 * 54 * The stable tree holds pointers to all the merged pages (ksm pages), sorted 55 * by their contents. Because each such page is write-protected, searching on 56 * this tree is fully assured to be working (except when pages are unmapped), 57 * and therefore this tree is called the stable tree. 58 * 59 * In addition to the stable tree, KSM uses a second data structure called the 60 * unstable tree: this tree holds pointers to pages which have been found to 61 * be "unchanged for a period of time". The unstable tree sorts these pages 62 * by their contents, but since they are not write-protected, KSM cannot rely 63 * upon the unstable tree to work correctly - the unstable tree is liable to 64 * be corrupted as its contents are modified, and so it is called unstable. 65 * 66 * KSM solves this problem by several techniques: 67 * 68 * 1) The unstable tree is flushed every time KSM completes scanning all 69 * memory areas, and then the tree is rebuilt again from the beginning. 70 * 2) KSM will only insert into the unstable tree, pages whose hash value 71 * has not changed since the previous scan of all memory areas. 72 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the 73 * colors of the nodes and not on their contents, assuring that even when 74 * the tree gets "corrupted" it won't get out of balance, so scanning time 75 * remains the same (also, searching and inserting nodes in an rbtree uses 76 * the same algorithm, so we have no overhead when we flush and rebuild). 77 * 4) KSM never flushes the stable tree, which means that even if it were to 78 * take 10 attempts to find a page in the unstable tree, once it is found, 79 * it is secured in the stable tree. (When we scan a new page, we first 80 * compare it against the stable tree, and then against the unstable tree.) 81 */ 82 83 /** 84 * struct mm_slot - ksm information per mm that is being scanned 85 * @link: link to the mm_slots hash list 86 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head 87 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items 88 * @mm: the mm that this information is valid for 89 */ 90 struct mm_slot { 91 struct hlist_node link; 92 struct list_head mm_list; 93 struct rmap_item *rmap_list; 94 struct mm_struct *mm; 95 }; 96 97 /** 98 * struct ksm_scan - cursor for scanning 99 * @mm_slot: the current mm_slot we are scanning 100 * @address: the next address inside that to be scanned 101 * @rmap_list: link to the next rmap to be scanned in the rmap_list 102 * @seqnr: count of completed full scans (needed when removing unstable node) 103 * 104 * There is only the one ksm_scan instance of this cursor structure. 105 */ 106 struct ksm_scan { 107 struct mm_slot *mm_slot; 108 unsigned long address; 109 struct rmap_item **rmap_list; 110 unsigned long seqnr; 111 }; 112 113 /** 114 * struct stable_node - node of the stable rbtree 115 * @node: rb node of this ksm page in the stable tree 116 * @hlist: hlist head of rmap_items using this ksm page 117 * @kpfn: page frame number of this ksm page 118 */ 119 struct stable_node { 120 struct rb_node node; 121 struct hlist_head hlist; 122 unsigned long kpfn; 123 }; 124 125 /** 126 * struct rmap_item - reverse mapping item for virtual addresses 127 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list 128 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree 129 * @mm: the memory structure this rmap_item is pointing into 130 * @address: the virtual address this rmap_item tracks (+ flags in low bits) 131 * @oldchecksum: previous checksum of the page at that virtual address 132 * @node: rb node of this rmap_item in the unstable tree 133 * @head: pointer to stable_node heading this list in the stable tree 134 * @hlist: link into hlist of rmap_items hanging off that stable_node 135 */ 136 struct rmap_item { 137 struct rmap_item *rmap_list; 138 struct anon_vma *anon_vma; /* when stable */ 139 struct mm_struct *mm; 140 unsigned long address; /* + low bits used for flags below */ 141 unsigned int oldchecksum; /* when unstable */ 142 union { 143 struct rb_node node; /* when node of unstable tree */ 144 struct { /* when listed from stable tree */ 145 struct stable_node *head; 146 struct hlist_node hlist; 147 }; 148 }; 149 }; 150 151 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ 152 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */ 153 #define STABLE_FLAG 0x200 /* is listed from the stable tree */ 154 155 /* The stable and unstable tree heads */ 156 static struct rb_root root_stable_tree = RB_ROOT; 157 static struct rb_root root_unstable_tree = RB_ROOT; 158 159 #define MM_SLOTS_HASH_SHIFT 10 160 #define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT) 161 static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS]; 162 163 static struct mm_slot ksm_mm_head = { 164 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), 165 }; 166 static struct ksm_scan ksm_scan = { 167 .mm_slot = &ksm_mm_head, 168 }; 169 170 static struct kmem_cache *rmap_item_cache; 171 static struct kmem_cache *stable_node_cache; 172 static struct kmem_cache *mm_slot_cache; 173 174 /* The number of nodes in the stable tree */ 175 static unsigned long ksm_pages_shared; 176 177 /* The number of page slots additionally sharing those nodes */ 178 static unsigned long ksm_pages_sharing; 179 180 /* The number of nodes in the unstable tree */ 181 static unsigned long ksm_pages_unshared; 182 183 /* The number of rmap_items in use: to calculate pages_volatile */ 184 static unsigned long ksm_rmap_items; 185 186 /* Number of pages ksmd should scan in one batch */ 187 static unsigned int ksm_thread_pages_to_scan = 100; 188 189 /* Milliseconds ksmd should sleep between batches */ 190 static unsigned int ksm_thread_sleep_millisecs = 20; 191 192 #define KSM_RUN_STOP 0 193 #define KSM_RUN_MERGE 1 194 #define KSM_RUN_UNMERGE 2 195 static unsigned int ksm_run = KSM_RUN_STOP; 196 197 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); 198 static DEFINE_MUTEX(ksm_thread_mutex); 199 static DEFINE_SPINLOCK(ksm_mmlist_lock); 200 201 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ 202 sizeof(struct __struct), __alignof__(struct __struct),\ 203 (__flags), NULL) 204 205 static int __init ksm_slab_init(void) 206 { 207 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); 208 if (!rmap_item_cache) 209 goto out; 210 211 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); 212 if (!stable_node_cache) 213 goto out_free1; 214 215 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); 216 if (!mm_slot_cache) 217 goto out_free2; 218 219 return 0; 220 221 out_free2: 222 kmem_cache_destroy(stable_node_cache); 223 out_free1: 224 kmem_cache_destroy(rmap_item_cache); 225 out: 226 return -ENOMEM; 227 } 228 229 static void __init ksm_slab_free(void) 230 { 231 kmem_cache_destroy(mm_slot_cache); 232 kmem_cache_destroy(stable_node_cache); 233 kmem_cache_destroy(rmap_item_cache); 234 mm_slot_cache = NULL; 235 } 236 237 static inline struct rmap_item *alloc_rmap_item(void) 238 { 239 struct rmap_item *rmap_item; 240 241 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL); 242 if (rmap_item) 243 ksm_rmap_items++; 244 return rmap_item; 245 } 246 247 static inline void free_rmap_item(struct rmap_item *rmap_item) 248 { 249 ksm_rmap_items--; 250 rmap_item->mm = NULL; /* debug safety */ 251 kmem_cache_free(rmap_item_cache, rmap_item); 252 } 253 254 static inline struct stable_node *alloc_stable_node(void) 255 { 256 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL); 257 } 258 259 static inline void free_stable_node(struct stable_node *stable_node) 260 { 261 kmem_cache_free(stable_node_cache, stable_node); 262 } 263 264 static inline struct mm_slot *alloc_mm_slot(void) 265 { 266 if (!mm_slot_cache) /* initialization failed */ 267 return NULL; 268 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); 269 } 270 271 static inline void free_mm_slot(struct mm_slot *mm_slot) 272 { 273 kmem_cache_free(mm_slot_cache, mm_slot); 274 } 275 276 static struct mm_slot *get_mm_slot(struct mm_struct *mm) 277 { 278 struct mm_slot *mm_slot; 279 struct hlist_head *bucket; 280 struct hlist_node *node; 281 282 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)]; 283 hlist_for_each_entry(mm_slot, node, bucket, link) { 284 if (mm == mm_slot->mm) 285 return mm_slot; 286 } 287 return NULL; 288 } 289 290 static void insert_to_mm_slots_hash(struct mm_struct *mm, 291 struct mm_slot *mm_slot) 292 { 293 struct hlist_head *bucket; 294 295 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)]; 296 mm_slot->mm = mm; 297 hlist_add_head(&mm_slot->link, bucket); 298 } 299 300 static inline int in_stable_tree(struct rmap_item *rmap_item) 301 { 302 return rmap_item->address & STABLE_FLAG; 303 } 304 305 /* 306 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's 307 * page tables after it has passed through ksm_exit() - which, if necessary, 308 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set 309 * a special flag: they can just back out as soon as mm_users goes to zero. 310 * ksm_test_exit() is used throughout to make this test for exit: in some 311 * places for correctness, in some places just to avoid unnecessary work. 312 */ 313 static inline bool ksm_test_exit(struct mm_struct *mm) 314 { 315 return atomic_read(&mm->mm_users) == 0; 316 } 317 318 /* 319 * We use break_ksm to break COW on a ksm page: it's a stripped down 320 * 321 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1) 322 * put_page(page); 323 * 324 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, 325 * in case the application has unmapped and remapped mm,addr meanwhile. 326 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP 327 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. 328 */ 329 static int break_ksm(struct vm_area_struct *vma, unsigned long addr) 330 { 331 struct page *page; 332 int ret = 0; 333 334 do { 335 cond_resched(); 336 page = follow_page(vma, addr, FOLL_GET); 337 if (IS_ERR_OR_NULL(page)) 338 break; 339 if (PageKsm(page)) 340 ret = handle_mm_fault(vma->vm_mm, vma, addr, 341 FAULT_FLAG_WRITE); 342 else 343 ret = VM_FAULT_WRITE; 344 put_page(page); 345 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM))); 346 /* 347 * We must loop because handle_mm_fault() may back out if there's 348 * any difficulty e.g. if pte accessed bit gets updated concurrently. 349 * 350 * VM_FAULT_WRITE is what we have been hoping for: it indicates that 351 * COW has been broken, even if the vma does not permit VM_WRITE; 352 * but note that a concurrent fault might break PageKsm for us. 353 * 354 * VM_FAULT_SIGBUS could occur if we race with truncation of the 355 * backing file, which also invalidates anonymous pages: that's 356 * okay, that truncation will have unmapped the PageKsm for us. 357 * 358 * VM_FAULT_OOM: at the time of writing (late July 2009), setting 359 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the 360 * current task has TIF_MEMDIE set, and will be OOM killed on return 361 * to user; and ksmd, having no mm, would never be chosen for that. 362 * 363 * But if the mm is in a limited mem_cgroup, then the fault may fail 364 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and 365 * even ksmd can fail in this way - though it's usually breaking ksm 366 * just to undo a merge it made a moment before, so unlikely to oom. 367 * 368 * That's a pity: we might therefore have more kernel pages allocated 369 * than we're counting as nodes in the stable tree; but ksm_do_scan 370 * will retry to break_cow on each pass, so should recover the page 371 * in due course. The important thing is to not let VM_MERGEABLE 372 * be cleared while any such pages might remain in the area. 373 */ 374 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; 375 } 376 377 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm, 378 unsigned long addr) 379 { 380 struct vm_area_struct *vma; 381 if (ksm_test_exit(mm)) 382 return NULL; 383 vma = find_vma(mm, addr); 384 if (!vma || vma->vm_start > addr) 385 return NULL; 386 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) 387 return NULL; 388 return vma; 389 } 390 391 static void break_cow(struct rmap_item *rmap_item) 392 { 393 struct mm_struct *mm = rmap_item->mm; 394 unsigned long addr = rmap_item->address; 395 struct vm_area_struct *vma; 396 397 /* 398 * It is not an accident that whenever we want to break COW 399 * to undo, we also need to drop a reference to the anon_vma. 400 */ 401 put_anon_vma(rmap_item->anon_vma); 402 403 down_read(&mm->mmap_sem); 404 vma = find_mergeable_vma(mm, addr); 405 if (vma) 406 break_ksm(vma, addr); 407 up_read(&mm->mmap_sem); 408 } 409 410 static struct page *page_trans_compound_anon(struct page *page) 411 { 412 if (PageTransCompound(page)) { 413 struct page *head = compound_trans_head(page); 414 /* 415 * head may actually be splitted and freed from under 416 * us but it's ok here. 417 */ 418 if (PageAnon(head)) 419 return head; 420 } 421 return NULL; 422 } 423 424 static struct page *get_mergeable_page(struct rmap_item *rmap_item) 425 { 426 struct mm_struct *mm = rmap_item->mm; 427 unsigned long addr = rmap_item->address; 428 struct vm_area_struct *vma; 429 struct page *page; 430 431 down_read(&mm->mmap_sem); 432 vma = find_mergeable_vma(mm, addr); 433 if (!vma) 434 goto out; 435 436 page = follow_page(vma, addr, FOLL_GET); 437 if (IS_ERR_OR_NULL(page)) 438 goto out; 439 if (PageAnon(page) || page_trans_compound_anon(page)) { 440 flush_anon_page(vma, page, addr); 441 flush_dcache_page(page); 442 } else { 443 put_page(page); 444 out: page = NULL; 445 } 446 up_read(&mm->mmap_sem); 447 return page; 448 } 449 450 static void remove_node_from_stable_tree(struct stable_node *stable_node) 451 { 452 struct rmap_item *rmap_item; 453 struct hlist_node *hlist; 454 455 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { 456 if (rmap_item->hlist.next) 457 ksm_pages_sharing--; 458 else 459 ksm_pages_shared--; 460 put_anon_vma(rmap_item->anon_vma); 461 rmap_item->address &= PAGE_MASK; 462 cond_resched(); 463 } 464 465 rb_erase(&stable_node->node, &root_stable_tree); 466 free_stable_node(stable_node); 467 } 468 469 /* 470 * get_ksm_page: checks if the page indicated by the stable node 471 * is still its ksm page, despite having held no reference to it. 472 * In which case we can trust the content of the page, and it 473 * returns the gotten page; but if the page has now been zapped, 474 * remove the stale node from the stable tree and return NULL. 475 * 476 * You would expect the stable_node to hold a reference to the ksm page. 477 * But if it increments the page's count, swapping out has to wait for 478 * ksmd to come around again before it can free the page, which may take 479 * seconds or even minutes: much too unresponsive. So instead we use a 480 * "keyhole reference": access to the ksm page from the stable node peeps 481 * out through its keyhole to see if that page still holds the right key, 482 * pointing back to this stable node. This relies on freeing a PageAnon 483 * page to reset its page->mapping to NULL, and relies on no other use of 484 * a page to put something that might look like our key in page->mapping. 485 * 486 * include/linux/pagemap.h page_cache_get_speculative() is a good reference, 487 * but this is different - made simpler by ksm_thread_mutex being held, but 488 * interesting for assuming that no other use of the struct page could ever 489 * put our expected_mapping into page->mapping (or a field of the union which 490 * coincides with page->mapping). The RCU calls are not for KSM at all, but 491 * to keep the page_count protocol described with page_cache_get_speculative. 492 * 493 * Note: it is possible that get_ksm_page() will return NULL one moment, 494 * then page the next, if the page is in between page_freeze_refs() and 495 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page 496 * is on its way to being freed; but it is an anomaly to bear in mind. 497 */ 498 static struct page *get_ksm_page(struct stable_node *stable_node) 499 { 500 struct page *page; 501 void *expected_mapping; 502 503 page = pfn_to_page(stable_node->kpfn); 504 expected_mapping = (void *)stable_node + 505 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM); 506 rcu_read_lock(); 507 if (page->mapping != expected_mapping) 508 goto stale; 509 if (!get_page_unless_zero(page)) 510 goto stale; 511 if (page->mapping != expected_mapping) { 512 put_page(page); 513 goto stale; 514 } 515 rcu_read_unlock(); 516 return page; 517 stale: 518 rcu_read_unlock(); 519 remove_node_from_stable_tree(stable_node); 520 return NULL; 521 } 522 523 /* 524 * Removing rmap_item from stable or unstable tree. 525 * This function will clean the information from the stable/unstable tree. 526 */ 527 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) 528 { 529 if (rmap_item->address & STABLE_FLAG) { 530 struct stable_node *stable_node; 531 struct page *page; 532 533 stable_node = rmap_item->head; 534 page = get_ksm_page(stable_node); 535 if (!page) 536 goto out; 537 538 lock_page(page); 539 hlist_del(&rmap_item->hlist); 540 unlock_page(page); 541 put_page(page); 542 543 if (stable_node->hlist.first) 544 ksm_pages_sharing--; 545 else 546 ksm_pages_shared--; 547 548 put_anon_vma(rmap_item->anon_vma); 549 rmap_item->address &= PAGE_MASK; 550 551 } else if (rmap_item->address & UNSTABLE_FLAG) { 552 unsigned char age; 553 /* 554 * Usually ksmd can and must skip the rb_erase, because 555 * root_unstable_tree was already reset to RB_ROOT. 556 * But be careful when an mm is exiting: do the rb_erase 557 * if this rmap_item was inserted by this scan, rather 558 * than left over from before. 559 */ 560 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); 561 BUG_ON(age > 1); 562 if (!age) 563 rb_erase(&rmap_item->node, &root_unstable_tree); 564 565 ksm_pages_unshared--; 566 rmap_item->address &= PAGE_MASK; 567 } 568 out: 569 cond_resched(); /* we're called from many long loops */ 570 } 571 572 static void remove_trailing_rmap_items(struct mm_slot *mm_slot, 573 struct rmap_item **rmap_list) 574 { 575 while (*rmap_list) { 576 struct rmap_item *rmap_item = *rmap_list; 577 *rmap_list = rmap_item->rmap_list; 578 remove_rmap_item_from_tree(rmap_item); 579 free_rmap_item(rmap_item); 580 } 581 } 582 583 /* 584 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather 585 * than check every pte of a given vma, the locking doesn't quite work for 586 * that - an rmap_item is assigned to the stable tree after inserting ksm 587 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing 588 * rmap_items from parent to child at fork time (so as not to waste time 589 * if exit comes before the next scan reaches it). 590 * 591 * Similarly, although we'd like to remove rmap_items (so updating counts 592 * and freeing memory) when unmerging an area, it's easier to leave that 593 * to the next pass of ksmd - consider, for example, how ksmd might be 594 * in cmp_and_merge_page on one of the rmap_items we would be removing. 595 */ 596 static int unmerge_ksm_pages(struct vm_area_struct *vma, 597 unsigned long start, unsigned long end) 598 { 599 unsigned long addr; 600 int err = 0; 601 602 for (addr = start; addr < end && !err; addr += PAGE_SIZE) { 603 if (ksm_test_exit(vma->vm_mm)) 604 break; 605 if (signal_pending(current)) 606 err = -ERESTARTSYS; 607 else 608 err = break_ksm(vma, addr); 609 } 610 return err; 611 } 612 613 #ifdef CONFIG_SYSFS 614 /* 615 * Only called through the sysfs control interface: 616 */ 617 static int unmerge_and_remove_all_rmap_items(void) 618 { 619 struct mm_slot *mm_slot; 620 struct mm_struct *mm; 621 struct vm_area_struct *vma; 622 int err = 0; 623 624 spin_lock(&ksm_mmlist_lock); 625 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next, 626 struct mm_slot, mm_list); 627 spin_unlock(&ksm_mmlist_lock); 628 629 for (mm_slot = ksm_scan.mm_slot; 630 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { 631 mm = mm_slot->mm; 632 down_read(&mm->mmap_sem); 633 for (vma = mm->mmap; vma; vma = vma->vm_next) { 634 if (ksm_test_exit(mm)) 635 break; 636 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) 637 continue; 638 err = unmerge_ksm_pages(vma, 639 vma->vm_start, vma->vm_end); 640 if (err) 641 goto error; 642 } 643 644 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list); 645 646 spin_lock(&ksm_mmlist_lock); 647 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next, 648 struct mm_slot, mm_list); 649 if (ksm_test_exit(mm)) { 650 hlist_del(&mm_slot->link); 651 list_del(&mm_slot->mm_list); 652 spin_unlock(&ksm_mmlist_lock); 653 654 free_mm_slot(mm_slot); 655 clear_bit(MMF_VM_MERGEABLE, &mm->flags); 656 up_read(&mm->mmap_sem); 657 mmdrop(mm); 658 } else { 659 spin_unlock(&ksm_mmlist_lock); 660 up_read(&mm->mmap_sem); 661 } 662 } 663 664 ksm_scan.seqnr = 0; 665 return 0; 666 667 error: 668 up_read(&mm->mmap_sem); 669 spin_lock(&ksm_mmlist_lock); 670 ksm_scan.mm_slot = &ksm_mm_head; 671 spin_unlock(&ksm_mmlist_lock); 672 return err; 673 } 674 #endif /* CONFIG_SYSFS */ 675 676 static u32 calc_checksum(struct page *page) 677 { 678 u32 checksum; 679 void *addr = kmap_atomic(page); 680 checksum = jhash2(addr, PAGE_SIZE / 4, 17); 681 kunmap_atomic(addr); 682 return checksum; 683 } 684 685 static int memcmp_pages(struct page *page1, struct page *page2) 686 { 687 char *addr1, *addr2; 688 int ret; 689 690 addr1 = kmap_atomic(page1); 691 addr2 = kmap_atomic(page2); 692 ret = memcmp(addr1, addr2, PAGE_SIZE); 693 kunmap_atomic(addr2); 694 kunmap_atomic(addr1); 695 return ret; 696 } 697 698 static inline int pages_identical(struct page *page1, struct page *page2) 699 { 700 return !memcmp_pages(page1, page2); 701 } 702 703 static int write_protect_page(struct vm_area_struct *vma, struct page *page, 704 pte_t *orig_pte) 705 { 706 struct mm_struct *mm = vma->vm_mm; 707 unsigned long addr; 708 pte_t *ptep; 709 spinlock_t *ptl; 710 int swapped; 711 int err = -EFAULT; 712 unsigned long mmun_start; /* For mmu_notifiers */ 713 unsigned long mmun_end; /* For mmu_notifiers */ 714 715 addr = page_address_in_vma(page, vma); 716 if (addr == -EFAULT) 717 goto out; 718 719 BUG_ON(PageTransCompound(page)); 720 721 mmun_start = addr; 722 mmun_end = addr + PAGE_SIZE; 723 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); 724 725 ptep = page_check_address(page, mm, addr, &ptl, 0); 726 if (!ptep) 727 goto out_mn; 728 729 if (pte_write(*ptep) || pte_dirty(*ptep)) { 730 pte_t entry; 731 732 swapped = PageSwapCache(page); 733 flush_cache_page(vma, addr, page_to_pfn(page)); 734 /* 735 * Ok this is tricky, when get_user_pages_fast() run it doesn't 736 * take any lock, therefore the check that we are going to make 737 * with the pagecount against the mapcount is racey and 738 * O_DIRECT can happen right after the check. 739 * So we clear the pte and flush the tlb before the check 740 * this assure us that no O_DIRECT can happen after the check 741 * or in the middle of the check. 742 */ 743 entry = ptep_clear_flush(vma, addr, ptep); 744 /* 745 * Check that no O_DIRECT or similar I/O is in progress on the 746 * page 747 */ 748 if (page_mapcount(page) + 1 + swapped != page_count(page)) { 749 set_pte_at(mm, addr, ptep, entry); 750 goto out_unlock; 751 } 752 if (pte_dirty(entry)) 753 set_page_dirty(page); 754 entry = pte_mkclean(pte_wrprotect(entry)); 755 set_pte_at_notify(mm, addr, ptep, entry); 756 } 757 *orig_pte = *ptep; 758 err = 0; 759 760 out_unlock: 761 pte_unmap_unlock(ptep, ptl); 762 out_mn: 763 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); 764 out: 765 return err; 766 } 767 768 /** 769 * replace_page - replace page in vma by new ksm page 770 * @vma: vma that holds the pte pointing to page 771 * @page: the page we are replacing by kpage 772 * @kpage: the ksm page we replace page by 773 * @orig_pte: the original value of the pte 774 * 775 * Returns 0 on success, -EFAULT on failure. 776 */ 777 static int replace_page(struct vm_area_struct *vma, struct page *page, 778 struct page *kpage, pte_t orig_pte) 779 { 780 struct mm_struct *mm = vma->vm_mm; 781 pmd_t *pmd; 782 pte_t *ptep; 783 spinlock_t *ptl; 784 unsigned long addr; 785 int err = -EFAULT; 786 unsigned long mmun_start; /* For mmu_notifiers */ 787 unsigned long mmun_end; /* For mmu_notifiers */ 788 789 addr = page_address_in_vma(page, vma); 790 if (addr == -EFAULT) 791 goto out; 792 793 pmd = mm_find_pmd(mm, addr); 794 if (!pmd) 795 goto out; 796 BUG_ON(pmd_trans_huge(*pmd)); 797 798 mmun_start = addr; 799 mmun_end = addr + PAGE_SIZE; 800 mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end); 801 802 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); 803 if (!pte_same(*ptep, orig_pte)) { 804 pte_unmap_unlock(ptep, ptl); 805 goto out_mn; 806 } 807 808 get_page(kpage); 809 page_add_anon_rmap(kpage, vma, addr); 810 811 flush_cache_page(vma, addr, pte_pfn(*ptep)); 812 ptep_clear_flush(vma, addr, ptep); 813 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot)); 814 815 page_remove_rmap(page); 816 if (!page_mapped(page)) 817 try_to_free_swap(page); 818 put_page(page); 819 820 pte_unmap_unlock(ptep, ptl); 821 err = 0; 822 out_mn: 823 mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); 824 out: 825 return err; 826 } 827 828 static int page_trans_compound_anon_split(struct page *page) 829 { 830 int ret = 0; 831 struct page *transhuge_head = page_trans_compound_anon(page); 832 if (transhuge_head) { 833 /* Get the reference on the head to split it. */ 834 if (get_page_unless_zero(transhuge_head)) { 835 /* 836 * Recheck we got the reference while the head 837 * was still anonymous. 838 */ 839 if (PageAnon(transhuge_head)) 840 ret = split_huge_page(transhuge_head); 841 else 842 /* 843 * Retry later if split_huge_page run 844 * from under us. 845 */ 846 ret = 1; 847 put_page(transhuge_head); 848 } else 849 /* Retry later if split_huge_page run from under us. */ 850 ret = 1; 851 } 852 return ret; 853 } 854 855 /* 856 * try_to_merge_one_page - take two pages and merge them into one 857 * @vma: the vma that holds the pte pointing to page 858 * @page: the PageAnon page that we want to replace with kpage 859 * @kpage: the PageKsm page that we want to map instead of page, 860 * or NULL the first time when we want to use page as kpage. 861 * 862 * This function returns 0 if the pages were merged, -EFAULT otherwise. 863 */ 864 static int try_to_merge_one_page(struct vm_area_struct *vma, 865 struct page *page, struct page *kpage) 866 { 867 pte_t orig_pte = __pte(0); 868 int err = -EFAULT; 869 870 if (page == kpage) /* ksm page forked */ 871 return 0; 872 873 if (!(vma->vm_flags & VM_MERGEABLE)) 874 goto out; 875 if (PageTransCompound(page) && page_trans_compound_anon_split(page)) 876 goto out; 877 BUG_ON(PageTransCompound(page)); 878 if (!PageAnon(page)) 879 goto out; 880 881 /* 882 * We need the page lock to read a stable PageSwapCache in 883 * write_protect_page(). We use trylock_page() instead of 884 * lock_page() because we don't want to wait here - we 885 * prefer to continue scanning and merging different pages, 886 * then come back to this page when it is unlocked. 887 */ 888 if (!trylock_page(page)) 889 goto out; 890 /* 891 * If this anonymous page is mapped only here, its pte may need 892 * to be write-protected. If it's mapped elsewhere, all of its 893 * ptes are necessarily already write-protected. But in either 894 * case, we need to lock and check page_count is not raised. 895 */ 896 if (write_protect_page(vma, page, &orig_pte) == 0) { 897 if (!kpage) { 898 /* 899 * While we hold page lock, upgrade page from 900 * PageAnon+anon_vma to PageKsm+NULL stable_node: 901 * stable_tree_insert() will update stable_node. 902 */ 903 set_page_stable_node(page, NULL); 904 mark_page_accessed(page); 905 err = 0; 906 } else if (pages_identical(page, kpage)) 907 err = replace_page(vma, page, kpage, orig_pte); 908 } 909 910 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) { 911 munlock_vma_page(page); 912 if (!PageMlocked(kpage)) { 913 unlock_page(page); 914 lock_page(kpage); 915 mlock_vma_page(kpage); 916 page = kpage; /* for final unlock */ 917 } 918 } 919 920 unlock_page(page); 921 out: 922 return err; 923 } 924 925 /* 926 * try_to_merge_with_ksm_page - like try_to_merge_two_pages, 927 * but no new kernel page is allocated: kpage must already be a ksm page. 928 * 929 * This function returns 0 if the pages were merged, -EFAULT otherwise. 930 */ 931 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, 932 struct page *page, struct page *kpage) 933 { 934 struct mm_struct *mm = rmap_item->mm; 935 struct vm_area_struct *vma; 936 int err = -EFAULT; 937 938 down_read(&mm->mmap_sem); 939 if (ksm_test_exit(mm)) 940 goto out; 941 vma = find_vma(mm, rmap_item->address); 942 if (!vma || vma->vm_start > rmap_item->address) 943 goto out; 944 945 err = try_to_merge_one_page(vma, page, kpage); 946 if (err) 947 goto out; 948 949 /* Must get reference to anon_vma while still holding mmap_sem */ 950 rmap_item->anon_vma = vma->anon_vma; 951 get_anon_vma(vma->anon_vma); 952 out: 953 up_read(&mm->mmap_sem); 954 return err; 955 } 956 957 /* 958 * try_to_merge_two_pages - take two identical pages and prepare them 959 * to be merged into one page. 960 * 961 * This function returns the kpage if we successfully merged two identical 962 * pages into one ksm page, NULL otherwise. 963 * 964 * Note that this function upgrades page to ksm page: if one of the pages 965 * is already a ksm page, try_to_merge_with_ksm_page should be used. 966 */ 967 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, 968 struct page *page, 969 struct rmap_item *tree_rmap_item, 970 struct page *tree_page) 971 { 972 int err; 973 974 err = try_to_merge_with_ksm_page(rmap_item, page, NULL); 975 if (!err) { 976 err = try_to_merge_with_ksm_page(tree_rmap_item, 977 tree_page, page); 978 /* 979 * If that fails, we have a ksm page with only one pte 980 * pointing to it: so break it. 981 */ 982 if (err) 983 break_cow(rmap_item); 984 } 985 return err ? NULL : page; 986 } 987 988 /* 989 * stable_tree_search - search for page inside the stable tree 990 * 991 * This function checks if there is a page inside the stable tree 992 * with identical content to the page that we are scanning right now. 993 * 994 * This function returns the stable tree node of identical content if found, 995 * NULL otherwise. 996 */ 997 static struct page *stable_tree_search(struct page *page) 998 { 999 struct rb_node *node = root_stable_tree.rb_node; 1000 struct stable_node *stable_node; 1001 1002 stable_node = page_stable_node(page); 1003 if (stable_node) { /* ksm page forked */ 1004 get_page(page); 1005 return page; 1006 } 1007 1008 while (node) { 1009 struct page *tree_page; 1010 int ret; 1011 1012 cond_resched(); 1013 stable_node = rb_entry(node, struct stable_node, node); 1014 tree_page = get_ksm_page(stable_node); 1015 if (!tree_page) 1016 return NULL; 1017 1018 ret = memcmp_pages(page, tree_page); 1019 1020 if (ret < 0) { 1021 put_page(tree_page); 1022 node = node->rb_left; 1023 } else if (ret > 0) { 1024 put_page(tree_page); 1025 node = node->rb_right; 1026 } else 1027 return tree_page; 1028 } 1029 1030 return NULL; 1031 } 1032 1033 /* 1034 * stable_tree_insert - insert rmap_item pointing to new ksm page 1035 * into the stable tree. 1036 * 1037 * This function returns the stable tree node just allocated on success, 1038 * NULL otherwise. 1039 */ 1040 static struct stable_node *stable_tree_insert(struct page *kpage) 1041 { 1042 struct rb_node **new = &root_stable_tree.rb_node; 1043 struct rb_node *parent = NULL; 1044 struct stable_node *stable_node; 1045 1046 while (*new) { 1047 struct page *tree_page; 1048 int ret; 1049 1050 cond_resched(); 1051 stable_node = rb_entry(*new, struct stable_node, node); 1052 tree_page = get_ksm_page(stable_node); 1053 if (!tree_page) 1054 return NULL; 1055 1056 ret = memcmp_pages(kpage, tree_page); 1057 put_page(tree_page); 1058 1059 parent = *new; 1060 if (ret < 0) 1061 new = &parent->rb_left; 1062 else if (ret > 0) 1063 new = &parent->rb_right; 1064 else { 1065 /* 1066 * It is not a bug that stable_tree_search() didn't 1067 * find this node: because at that time our page was 1068 * not yet write-protected, so may have changed since. 1069 */ 1070 return NULL; 1071 } 1072 } 1073 1074 stable_node = alloc_stable_node(); 1075 if (!stable_node) 1076 return NULL; 1077 1078 rb_link_node(&stable_node->node, parent, new); 1079 rb_insert_color(&stable_node->node, &root_stable_tree); 1080 1081 INIT_HLIST_HEAD(&stable_node->hlist); 1082 1083 stable_node->kpfn = page_to_pfn(kpage); 1084 set_page_stable_node(kpage, stable_node); 1085 1086 return stable_node; 1087 } 1088 1089 /* 1090 * unstable_tree_search_insert - search for identical page, 1091 * else insert rmap_item into the unstable tree. 1092 * 1093 * This function searches for a page in the unstable tree identical to the 1094 * page currently being scanned; and if no identical page is found in the 1095 * tree, we insert rmap_item as a new object into the unstable tree. 1096 * 1097 * This function returns pointer to rmap_item found to be identical 1098 * to the currently scanned page, NULL otherwise. 1099 * 1100 * This function does both searching and inserting, because they share 1101 * the same walking algorithm in an rbtree. 1102 */ 1103 static 1104 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, 1105 struct page *page, 1106 struct page **tree_pagep) 1107 1108 { 1109 struct rb_node **new = &root_unstable_tree.rb_node; 1110 struct rb_node *parent = NULL; 1111 1112 while (*new) { 1113 struct rmap_item *tree_rmap_item; 1114 struct page *tree_page; 1115 int ret; 1116 1117 cond_resched(); 1118 tree_rmap_item = rb_entry(*new, struct rmap_item, node); 1119 tree_page = get_mergeable_page(tree_rmap_item); 1120 if (IS_ERR_OR_NULL(tree_page)) 1121 return NULL; 1122 1123 /* 1124 * Don't substitute a ksm page for a forked page. 1125 */ 1126 if (page == tree_page) { 1127 put_page(tree_page); 1128 return NULL; 1129 } 1130 1131 ret = memcmp_pages(page, tree_page); 1132 1133 parent = *new; 1134 if (ret < 0) { 1135 put_page(tree_page); 1136 new = &parent->rb_left; 1137 } else if (ret > 0) { 1138 put_page(tree_page); 1139 new = &parent->rb_right; 1140 } else { 1141 *tree_pagep = tree_page; 1142 return tree_rmap_item; 1143 } 1144 } 1145 1146 rmap_item->address |= UNSTABLE_FLAG; 1147 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); 1148 rb_link_node(&rmap_item->node, parent, new); 1149 rb_insert_color(&rmap_item->node, &root_unstable_tree); 1150 1151 ksm_pages_unshared++; 1152 return NULL; 1153 } 1154 1155 /* 1156 * stable_tree_append - add another rmap_item to the linked list of 1157 * rmap_items hanging off a given node of the stable tree, all sharing 1158 * the same ksm page. 1159 */ 1160 static void stable_tree_append(struct rmap_item *rmap_item, 1161 struct stable_node *stable_node) 1162 { 1163 rmap_item->head = stable_node; 1164 rmap_item->address |= STABLE_FLAG; 1165 hlist_add_head(&rmap_item->hlist, &stable_node->hlist); 1166 1167 if (rmap_item->hlist.next) 1168 ksm_pages_sharing++; 1169 else 1170 ksm_pages_shared++; 1171 } 1172 1173 /* 1174 * cmp_and_merge_page - first see if page can be merged into the stable tree; 1175 * if not, compare checksum to previous and if it's the same, see if page can 1176 * be inserted into the unstable tree, or merged with a page already there and 1177 * both transferred to the stable tree. 1178 * 1179 * @page: the page that we are searching identical page to. 1180 * @rmap_item: the reverse mapping into the virtual address of this page 1181 */ 1182 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) 1183 { 1184 struct rmap_item *tree_rmap_item; 1185 struct page *tree_page = NULL; 1186 struct stable_node *stable_node; 1187 struct page *kpage; 1188 unsigned int checksum; 1189 int err; 1190 1191 remove_rmap_item_from_tree(rmap_item); 1192 1193 /* We first start with searching the page inside the stable tree */ 1194 kpage = stable_tree_search(page); 1195 if (kpage) { 1196 err = try_to_merge_with_ksm_page(rmap_item, page, kpage); 1197 if (!err) { 1198 /* 1199 * The page was successfully merged: 1200 * add its rmap_item to the stable tree. 1201 */ 1202 lock_page(kpage); 1203 stable_tree_append(rmap_item, page_stable_node(kpage)); 1204 unlock_page(kpage); 1205 } 1206 put_page(kpage); 1207 return; 1208 } 1209 1210 /* 1211 * If the hash value of the page has changed from the last time 1212 * we calculated it, this page is changing frequently: therefore we 1213 * don't want to insert it in the unstable tree, and we don't want 1214 * to waste our time searching for something identical to it there. 1215 */ 1216 checksum = calc_checksum(page); 1217 if (rmap_item->oldchecksum != checksum) { 1218 rmap_item->oldchecksum = checksum; 1219 return; 1220 } 1221 1222 tree_rmap_item = 1223 unstable_tree_search_insert(rmap_item, page, &tree_page); 1224 if (tree_rmap_item) { 1225 kpage = try_to_merge_two_pages(rmap_item, page, 1226 tree_rmap_item, tree_page); 1227 put_page(tree_page); 1228 /* 1229 * As soon as we merge this page, we want to remove the 1230 * rmap_item of the page we have merged with from the unstable 1231 * tree, and insert it instead as new node in the stable tree. 1232 */ 1233 if (kpage) { 1234 remove_rmap_item_from_tree(tree_rmap_item); 1235 1236 lock_page(kpage); 1237 stable_node = stable_tree_insert(kpage); 1238 if (stable_node) { 1239 stable_tree_append(tree_rmap_item, stable_node); 1240 stable_tree_append(rmap_item, stable_node); 1241 } 1242 unlock_page(kpage); 1243 1244 /* 1245 * If we fail to insert the page into the stable tree, 1246 * we will have 2 virtual addresses that are pointing 1247 * to a ksm page left outside the stable tree, 1248 * in which case we need to break_cow on both. 1249 */ 1250 if (!stable_node) { 1251 break_cow(tree_rmap_item); 1252 break_cow(rmap_item); 1253 } 1254 } 1255 } 1256 } 1257 1258 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, 1259 struct rmap_item **rmap_list, 1260 unsigned long addr) 1261 { 1262 struct rmap_item *rmap_item; 1263 1264 while (*rmap_list) { 1265 rmap_item = *rmap_list; 1266 if ((rmap_item->address & PAGE_MASK) == addr) 1267 return rmap_item; 1268 if (rmap_item->address > addr) 1269 break; 1270 *rmap_list = rmap_item->rmap_list; 1271 remove_rmap_item_from_tree(rmap_item); 1272 free_rmap_item(rmap_item); 1273 } 1274 1275 rmap_item = alloc_rmap_item(); 1276 if (rmap_item) { 1277 /* It has already been zeroed */ 1278 rmap_item->mm = mm_slot->mm; 1279 rmap_item->address = addr; 1280 rmap_item->rmap_list = *rmap_list; 1281 *rmap_list = rmap_item; 1282 } 1283 return rmap_item; 1284 } 1285 1286 static struct rmap_item *scan_get_next_rmap_item(struct page **page) 1287 { 1288 struct mm_struct *mm; 1289 struct mm_slot *slot; 1290 struct vm_area_struct *vma; 1291 struct rmap_item *rmap_item; 1292 1293 if (list_empty(&ksm_mm_head.mm_list)) 1294 return NULL; 1295 1296 slot = ksm_scan.mm_slot; 1297 if (slot == &ksm_mm_head) { 1298 /* 1299 * A number of pages can hang around indefinitely on per-cpu 1300 * pagevecs, raised page count preventing write_protect_page 1301 * from merging them. Though it doesn't really matter much, 1302 * it is puzzling to see some stuck in pages_volatile until 1303 * other activity jostles them out, and they also prevented 1304 * LTP's KSM test from succeeding deterministically; so drain 1305 * them here (here rather than on entry to ksm_do_scan(), 1306 * so we don't IPI too often when pages_to_scan is set low). 1307 */ 1308 lru_add_drain_all(); 1309 1310 root_unstable_tree = RB_ROOT; 1311 1312 spin_lock(&ksm_mmlist_lock); 1313 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); 1314 ksm_scan.mm_slot = slot; 1315 spin_unlock(&ksm_mmlist_lock); 1316 /* 1317 * Although we tested list_empty() above, a racing __ksm_exit 1318 * of the last mm on the list may have removed it since then. 1319 */ 1320 if (slot == &ksm_mm_head) 1321 return NULL; 1322 next_mm: 1323 ksm_scan.address = 0; 1324 ksm_scan.rmap_list = &slot->rmap_list; 1325 } 1326 1327 mm = slot->mm; 1328 down_read(&mm->mmap_sem); 1329 if (ksm_test_exit(mm)) 1330 vma = NULL; 1331 else 1332 vma = find_vma(mm, ksm_scan.address); 1333 1334 for (; vma; vma = vma->vm_next) { 1335 if (!(vma->vm_flags & VM_MERGEABLE)) 1336 continue; 1337 if (ksm_scan.address < vma->vm_start) 1338 ksm_scan.address = vma->vm_start; 1339 if (!vma->anon_vma) 1340 ksm_scan.address = vma->vm_end; 1341 1342 while (ksm_scan.address < vma->vm_end) { 1343 if (ksm_test_exit(mm)) 1344 break; 1345 *page = follow_page(vma, ksm_scan.address, FOLL_GET); 1346 if (IS_ERR_OR_NULL(*page)) { 1347 ksm_scan.address += PAGE_SIZE; 1348 cond_resched(); 1349 continue; 1350 } 1351 if (PageAnon(*page) || 1352 page_trans_compound_anon(*page)) { 1353 flush_anon_page(vma, *page, ksm_scan.address); 1354 flush_dcache_page(*page); 1355 rmap_item = get_next_rmap_item(slot, 1356 ksm_scan.rmap_list, ksm_scan.address); 1357 if (rmap_item) { 1358 ksm_scan.rmap_list = 1359 &rmap_item->rmap_list; 1360 ksm_scan.address += PAGE_SIZE; 1361 } else 1362 put_page(*page); 1363 up_read(&mm->mmap_sem); 1364 return rmap_item; 1365 } 1366 put_page(*page); 1367 ksm_scan.address += PAGE_SIZE; 1368 cond_resched(); 1369 } 1370 } 1371 1372 if (ksm_test_exit(mm)) { 1373 ksm_scan.address = 0; 1374 ksm_scan.rmap_list = &slot->rmap_list; 1375 } 1376 /* 1377 * Nuke all the rmap_items that are above this current rmap: 1378 * because there were no VM_MERGEABLE vmas with such addresses. 1379 */ 1380 remove_trailing_rmap_items(slot, ksm_scan.rmap_list); 1381 1382 spin_lock(&ksm_mmlist_lock); 1383 ksm_scan.mm_slot = list_entry(slot->mm_list.next, 1384 struct mm_slot, mm_list); 1385 if (ksm_scan.address == 0) { 1386 /* 1387 * We've completed a full scan of all vmas, holding mmap_sem 1388 * throughout, and found no VM_MERGEABLE: so do the same as 1389 * __ksm_exit does to remove this mm from all our lists now. 1390 * This applies either when cleaning up after __ksm_exit 1391 * (but beware: we can reach here even before __ksm_exit), 1392 * or when all VM_MERGEABLE areas have been unmapped (and 1393 * mmap_sem then protects against race with MADV_MERGEABLE). 1394 */ 1395 hlist_del(&slot->link); 1396 list_del(&slot->mm_list); 1397 spin_unlock(&ksm_mmlist_lock); 1398 1399 free_mm_slot(slot); 1400 clear_bit(MMF_VM_MERGEABLE, &mm->flags); 1401 up_read(&mm->mmap_sem); 1402 mmdrop(mm); 1403 } else { 1404 spin_unlock(&ksm_mmlist_lock); 1405 up_read(&mm->mmap_sem); 1406 } 1407 1408 /* Repeat until we've completed scanning the whole list */ 1409 slot = ksm_scan.mm_slot; 1410 if (slot != &ksm_mm_head) 1411 goto next_mm; 1412 1413 ksm_scan.seqnr++; 1414 return NULL; 1415 } 1416 1417 /** 1418 * ksm_do_scan - the ksm scanner main worker function. 1419 * @scan_npages - number of pages we want to scan before we return. 1420 */ 1421 static void ksm_do_scan(unsigned int scan_npages) 1422 { 1423 struct rmap_item *rmap_item; 1424 struct page *uninitialized_var(page); 1425 1426 while (scan_npages-- && likely(!freezing(current))) { 1427 cond_resched(); 1428 rmap_item = scan_get_next_rmap_item(&page); 1429 if (!rmap_item) 1430 return; 1431 if (!PageKsm(page) || !in_stable_tree(rmap_item)) 1432 cmp_and_merge_page(page, rmap_item); 1433 put_page(page); 1434 } 1435 } 1436 1437 static int ksmd_should_run(void) 1438 { 1439 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); 1440 } 1441 1442 static int ksm_scan_thread(void *nothing) 1443 { 1444 set_freezable(); 1445 set_user_nice(current, 5); 1446 1447 while (!kthread_should_stop()) { 1448 mutex_lock(&ksm_thread_mutex); 1449 if (ksmd_should_run()) 1450 ksm_do_scan(ksm_thread_pages_to_scan); 1451 mutex_unlock(&ksm_thread_mutex); 1452 1453 try_to_freeze(); 1454 1455 if (ksmd_should_run()) { 1456 schedule_timeout_interruptible( 1457 msecs_to_jiffies(ksm_thread_sleep_millisecs)); 1458 } else { 1459 wait_event_freezable(ksm_thread_wait, 1460 ksmd_should_run() || kthread_should_stop()); 1461 } 1462 } 1463 return 0; 1464 } 1465 1466 int ksm_madvise(struct vm_area_struct *vma, unsigned long start, 1467 unsigned long end, int advice, unsigned long *vm_flags) 1468 { 1469 struct mm_struct *mm = vma->vm_mm; 1470 int err; 1471 1472 switch (advice) { 1473 case MADV_MERGEABLE: 1474 /* 1475 * Be somewhat over-protective for now! 1476 */ 1477 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | 1478 VM_PFNMAP | VM_IO | VM_DONTEXPAND | 1479 VM_HUGETLB | VM_NONLINEAR | VM_MIXEDMAP)) 1480 return 0; /* just ignore the advice */ 1481 1482 #ifdef VM_SAO 1483 if (*vm_flags & VM_SAO) 1484 return 0; 1485 #endif 1486 1487 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { 1488 err = __ksm_enter(mm); 1489 if (err) 1490 return err; 1491 } 1492 1493 *vm_flags |= VM_MERGEABLE; 1494 break; 1495 1496 case MADV_UNMERGEABLE: 1497 if (!(*vm_flags & VM_MERGEABLE)) 1498 return 0; /* just ignore the advice */ 1499 1500 if (vma->anon_vma) { 1501 err = unmerge_ksm_pages(vma, start, end); 1502 if (err) 1503 return err; 1504 } 1505 1506 *vm_flags &= ~VM_MERGEABLE; 1507 break; 1508 } 1509 1510 return 0; 1511 } 1512 1513 int __ksm_enter(struct mm_struct *mm) 1514 { 1515 struct mm_slot *mm_slot; 1516 int needs_wakeup; 1517 1518 mm_slot = alloc_mm_slot(); 1519 if (!mm_slot) 1520 return -ENOMEM; 1521 1522 /* Check ksm_run too? Would need tighter locking */ 1523 needs_wakeup = list_empty(&ksm_mm_head.mm_list); 1524 1525 spin_lock(&ksm_mmlist_lock); 1526 insert_to_mm_slots_hash(mm, mm_slot); 1527 /* 1528 * Insert just behind the scanning cursor, to let the area settle 1529 * down a little; when fork is followed by immediate exec, we don't 1530 * want ksmd to waste time setting up and tearing down an rmap_list. 1531 */ 1532 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); 1533 spin_unlock(&ksm_mmlist_lock); 1534 1535 set_bit(MMF_VM_MERGEABLE, &mm->flags); 1536 atomic_inc(&mm->mm_count); 1537 1538 if (needs_wakeup) 1539 wake_up_interruptible(&ksm_thread_wait); 1540 1541 return 0; 1542 } 1543 1544 void __ksm_exit(struct mm_struct *mm) 1545 { 1546 struct mm_slot *mm_slot; 1547 int easy_to_free = 0; 1548 1549 /* 1550 * This process is exiting: if it's straightforward (as is the 1551 * case when ksmd was never running), free mm_slot immediately. 1552 * But if it's at the cursor or has rmap_items linked to it, use 1553 * mmap_sem to synchronize with any break_cows before pagetables 1554 * are freed, and leave the mm_slot on the list for ksmd to free. 1555 * Beware: ksm may already have noticed it exiting and freed the slot. 1556 */ 1557 1558 spin_lock(&ksm_mmlist_lock); 1559 mm_slot = get_mm_slot(mm); 1560 if (mm_slot && ksm_scan.mm_slot != mm_slot) { 1561 if (!mm_slot->rmap_list) { 1562 hlist_del(&mm_slot->link); 1563 list_del(&mm_slot->mm_list); 1564 easy_to_free = 1; 1565 } else { 1566 list_move(&mm_slot->mm_list, 1567 &ksm_scan.mm_slot->mm_list); 1568 } 1569 } 1570 spin_unlock(&ksm_mmlist_lock); 1571 1572 if (easy_to_free) { 1573 free_mm_slot(mm_slot); 1574 clear_bit(MMF_VM_MERGEABLE, &mm->flags); 1575 mmdrop(mm); 1576 } else if (mm_slot) { 1577 down_write(&mm->mmap_sem); 1578 up_write(&mm->mmap_sem); 1579 } 1580 } 1581 1582 struct page *ksm_does_need_to_copy(struct page *page, 1583 struct vm_area_struct *vma, unsigned long address) 1584 { 1585 struct page *new_page; 1586 1587 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); 1588 if (new_page) { 1589 copy_user_highpage(new_page, page, address, vma); 1590 1591 SetPageDirty(new_page); 1592 __SetPageUptodate(new_page); 1593 SetPageSwapBacked(new_page); 1594 __set_page_locked(new_page); 1595 1596 if (!mlocked_vma_newpage(vma, new_page)) 1597 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON); 1598 else 1599 add_page_to_unevictable_list(new_page); 1600 } 1601 1602 return new_page; 1603 } 1604 1605 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg, 1606 unsigned long *vm_flags) 1607 { 1608 struct stable_node *stable_node; 1609 struct rmap_item *rmap_item; 1610 struct hlist_node *hlist; 1611 unsigned int mapcount = page_mapcount(page); 1612 int referenced = 0; 1613 int search_new_forks = 0; 1614 1615 VM_BUG_ON(!PageKsm(page)); 1616 VM_BUG_ON(!PageLocked(page)); 1617 1618 stable_node = page_stable_node(page); 1619 if (!stable_node) 1620 return 0; 1621 again: 1622 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { 1623 struct anon_vma *anon_vma = rmap_item->anon_vma; 1624 struct anon_vma_chain *vmac; 1625 struct vm_area_struct *vma; 1626 1627 anon_vma_lock_read(anon_vma); 1628 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, 1629 0, ULONG_MAX) { 1630 vma = vmac->vma; 1631 if (rmap_item->address < vma->vm_start || 1632 rmap_item->address >= vma->vm_end) 1633 continue; 1634 /* 1635 * Initially we examine only the vma which covers this 1636 * rmap_item; but later, if there is still work to do, 1637 * we examine covering vmas in other mms: in case they 1638 * were forked from the original since ksmd passed. 1639 */ 1640 if ((rmap_item->mm == vma->vm_mm) == search_new_forks) 1641 continue; 1642 1643 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg)) 1644 continue; 1645 1646 referenced += page_referenced_one(page, vma, 1647 rmap_item->address, &mapcount, vm_flags); 1648 if (!search_new_forks || !mapcount) 1649 break; 1650 } 1651 anon_vma_unlock_read(anon_vma); 1652 if (!mapcount) 1653 goto out; 1654 } 1655 if (!search_new_forks++) 1656 goto again; 1657 out: 1658 return referenced; 1659 } 1660 1661 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags) 1662 { 1663 struct stable_node *stable_node; 1664 struct hlist_node *hlist; 1665 struct rmap_item *rmap_item; 1666 int ret = SWAP_AGAIN; 1667 int search_new_forks = 0; 1668 1669 VM_BUG_ON(!PageKsm(page)); 1670 VM_BUG_ON(!PageLocked(page)); 1671 1672 stable_node = page_stable_node(page); 1673 if (!stable_node) 1674 return SWAP_FAIL; 1675 again: 1676 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { 1677 struct anon_vma *anon_vma = rmap_item->anon_vma; 1678 struct anon_vma_chain *vmac; 1679 struct vm_area_struct *vma; 1680 1681 anon_vma_lock_read(anon_vma); 1682 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, 1683 0, ULONG_MAX) { 1684 vma = vmac->vma; 1685 if (rmap_item->address < vma->vm_start || 1686 rmap_item->address >= vma->vm_end) 1687 continue; 1688 /* 1689 * Initially we examine only the vma which covers this 1690 * rmap_item; but later, if there is still work to do, 1691 * we examine covering vmas in other mms: in case they 1692 * were forked from the original since ksmd passed. 1693 */ 1694 if ((rmap_item->mm == vma->vm_mm) == search_new_forks) 1695 continue; 1696 1697 ret = try_to_unmap_one(page, vma, 1698 rmap_item->address, flags); 1699 if (ret != SWAP_AGAIN || !page_mapped(page)) { 1700 anon_vma_unlock_read(anon_vma); 1701 goto out; 1702 } 1703 } 1704 anon_vma_unlock_read(anon_vma); 1705 } 1706 if (!search_new_forks++) 1707 goto again; 1708 out: 1709 return ret; 1710 } 1711 1712 #ifdef CONFIG_MIGRATION 1713 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *, 1714 struct vm_area_struct *, unsigned long, void *), void *arg) 1715 { 1716 struct stable_node *stable_node; 1717 struct hlist_node *hlist; 1718 struct rmap_item *rmap_item; 1719 int ret = SWAP_AGAIN; 1720 int search_new_forks = 0; 1721 1722 VM_BUG_ON(!PageKsm(page)); 1723 VM_BUG_ON(!PageLocked(page)); 1724 1725 stable_node = page_stable_node(page); 1726 if (!stable_node) 1727 return ret; 1728 again: 1729 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { 1730 struct anon_vma *anon_vma = rmap_item->anon_vma; 1731 struct anon_vma_chain *vmac; 1732 struct vm_area_struct *vma; 1733 1734 anon_vma_lock_read(anon_vma); 1735 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, 1736 0, ULONG_MAX) { 1737 vma = vmac->vma; 1738 if (rmap_item->address < vma->vm_start || 1739 rmap_item->address >= vma->vm_end) 1740 continue; 1741 /* 1742 * Initially we examine only the vma which covers this 1743 * rmap_item; but later, if there is still work to do, 1744 * we examine covering vmas in other mms: in case they 1745 * were forked from the original since ksmd passed. 1746 */ 1747 if ((rmap_item->mm == vma->vm_mm) == search_new_forks) 1748 continue; 1749 1750 ret = rmap_one(page, vma, rmap_item->address, arg); 1751 if (ret != SWAP_AGAIN) { 1752 anon_vma_unlock_read(anon_vma); 1753 goto out; 1754 } 1755 } 1756 anon_vma_unlock_read(anon_vma); 1757 } 1758 if (!search_new_forks++) 1759 goto again; 1760 out: 1761 return ret; 1762 } 1763 1764 void ksm_migrate_page(struct page *newpage, struct page *oldpage) 1765 { 1766 struct stable_node *stable_node; 1767 1768 VM_BUG_ON(!PageLocked(oldpage)); 1769 VM_BUG_ON(!PageLocked(newpage)); 1770 VM_BUG_ON(newpage->mapping != oldpage->mapping); 1771 1772 stable_node = page_stable_node(newpage); 1773 if (stable_node) { 1774 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage)); 1775 stable_node->kpfn = page_to_pfn(newpage); 1776 } 1777 } 1778 #endif /* CONFIG_MIGRATION */ 1779 1780 #ifdef CONFIG_MEMORY_HOTREMOVE 1781 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn, 1782 unsigned long end_pfn) 1783 { 1784 struct rb_node *node; 1785 1786 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) { 1787 struct stable_node *stable_node; 1788 1789 stable_node = rb_entry(node, struct stable_node, node); 1790 if (stable_node->kpfn >= start_pfn && 1791 stable_node->kpfn < end_pfn) 1792 return stable_node; 1793 } 1794 return NULL; 1795 } 1796 1797 static int ksm_memory_callback(struct notifier_block *self, 1798 unsigned long action, void *arg) 1799 { 1800 struct memory_notify *mn = arg; 1801 struct stable_node *stable_node; 1802 1803 switch (action) { 1804 case MEM_GOING_OFFLINE: 1805 /* 1806 * Keep it very simple for now: just lock out ksmd and 1807 * MADV_UNMERGEABLE while any memory is going offline. 1808 * mutex_lock_nested() is necessary because lockdep was alarmed 1809 * that here we take ksm_thread_mutex inside notifier chain 1810 * mutex, and later take notifier chain mutex inside 1811 * ksm_thread_mutex to unlock it. But that's safe because both 1812 * are inside mem_hotplug_mutex. 1813 */ 1814 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING); 1815 break; 1816 1817 case MEM_OFFLINE: 1818 /* 1819 * Most of the work is done by page migration; but there might 1820 * be a few stable_nodes left over, still pointing to struct 1821 * pages which have been offlined: prune those from the tree. 1822 */ 1823 while ((stable_node = ksm_check_stable_tree(mn->start_pfn, 1824 mn->start_pfn + mn->nr_pages)) != NULL) 1825 remove_node_from_stable_tree(stable_node); 1826 /* fallthrough */ 1827 1828 case MEM_CANCEL_OFFLINE: 1829 mutex_unlock(&ksm_thread_mutex); 1830 break; 1831 } 1832 return NOTIFY_OK; 1833 } 1834 #endif /* CONFIG_MEMORY_HOTREMOVE */ 1835 1836 #ifdef CONFIG_SYSFS 1837 /* 1838 * This all compiles without CONFIG_SYSFS, but is a waste of space. 1839 */ 1840 1841 #define KSM_ATTR_RO(_name) \ 1842 static struct kobj_attribute _name##_attr = __ATTR_RO(_name) 1843 #define KSM_ATTR(_name) \ 1844 static struct kobj_attribute _name##_attr = \ 1845 __ATTR(_name, 0644, _name##_show, _name##_store) 1846 1847 static ssize_t sleep_millisecs_show(struct kobject *kobj, 1848 struct kobj_attribute *attr, char *buf) 1849 { 1850 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); 1851 } 1852 1853 static ssize_t sleep_millisecs_store(struct kobject *kobj, 1854 struct kobj_attribute *attr, 1855 const char *buf, size_t count) 1856 { 1857 unsigned long msecs; 1858 int err; 1859 1860 err = strict_strtoul(buf, 10, &msecs); 1861 if (err || msecs > UINT_MAX) 1862 return -EINVAL; 1863 1864 ksm_thread_sleep_millisecs = msecs; 1865 1866 return count; 1867 } 1868 KSM_ATTR(sleep_millisecs); 1869 1870 static ssize_t pages_to_scan_show(struct kobject *kobj, 1871 struct kobj_attribute *attr, char *buf) 1872 { 1873 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); 1874 } 1875 1876 static ssize_t pages_to_scan_store(struct kobject *kobj, 1877 struct kobj_attribute *attr, 1878 const char *buf, size_t count) 1879 { 1880 int err; 1881 unsigned long nr_pages; 1882 1883 err = strict_strtoul(buf, 10, &nr_pages); 1884 if (err || nr_pages > UINT_MAX) 1885 return -EINVAL; 1886 1887 ksm_thread_pages_to_scan = nr_pages; 1888 1889 return count; 1890 } 1891 KSM_ATTR(pages_to_scan); 1892 1893 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, 1894 char *buf) 1895 { 1896 return sprintf(buf, "%u\n", ksm_run); 1897 } 1898 1899 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, 1900 const char *buf, size_t count) 1901 { 1902 int err; 1903 unsigned long flags; 1904 1905 err = strict_strtoul(buf, 10, &flags); 1906 if (err || flags > UINT_MAX) 1907 return -EINVAL; 1908 if (flags > KSM_RUN_UNMERGE) 1909 return -EINVAL; 1910 1911 /* 1912 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. 1913 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, 1914 * breaking COW to free the pages_shared (but leaves mm_slots 1915 * on the list for when ksmd may be set running again). 1916 */ 1917 1918 mutex_lock(&ksm_thread_mutex); 1919 if (ksm_run != flags) { 1920 ksm_run = flags; 1921 if (flags & KSM_RUN_UNMERGE) { 1922 set_current_oom_origin(); 1923 err = unmerge_and_remove_all_rmap_items(); 1924 clear_current_oom_origin(); 1925 if (err) { 1926 ksm_run = KSM_RUN_STOP; 1927 count = err; 1928 } 1929 } 1930 } 1931 mutex_unlock(&ksm_thread_mutex); 1932 1933 if (flags & KSM_RUN_MERGE) 1934 wake_up_interruptible(&ksm_thread_wait); 1935 1936 return count; 1937 } 1938 KSM_ATTR(run); 1939 1940 static ssize_t pages_shared_show(struct kobject *kobj, 1941 struct kobj_attribute *attr, char *buf) 1942 { 1943 return sprintf(buf, "%lu\n", ksm_pages_shared); 1944 } 1945 KSM_ATTR_RO(pages_shared); 1946 1947 static ssize_t pages_sharing_show(struct kobject *kobj, 1948 struct kobj_attribute *attr, char *buf) 1949 { 1950 return sprintf(buf, "%lu\n", ksm_pages_sharing); 1951 } 1952 KSM_ATTR_RO(pages_sharing); 1953 1954 static ssize_t pages_unshared_show(struct kobject *kobj, 1955 struct kobj_attribute *attr, char *buf) 1956 { 1957 return sprintf(buf, "%lu\n", ksm_pages_unshared); 1958 } 1959 KSM_ATTR_RO(pages_unshared); 1960 1961 static ssize_t pages_volatile_show(struct kobject *kobj, 1962 struct kobj_attribute *attr, char *buf) 1963 { 1964 long ksm_pages_volatile; 1965 1966 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared 1967 - ksm_pages_sharing - ksm_pages_unshared; 1968 /* 1969 * It was not worth any locking to calculate that statistic, 1970 * but it might therefore sometimes be negative: conceal that. 1971 */ 1972 if (ksm_pages_volatile < 0) 1973 ksm_pages_volatile = 0; 1974 return sprintf(buf, "%ld\n", ksm_pages_volatile); 1975 } 1976 KSM_ATTR_RO(pages_volatile); 1977 1978 static ssize_t full_scans_show(struct kobject *kobj, 1979 struct kobj_attribute *attr, char *buf) 1980 { 1981 return sprintf(buf, "%lu\n", ksm_scan.seqnr); 1982 } 1983 KSM_ATTR_RO(full_scans); 1984 1985 static struct attribute *ksm_attrs[] = { 1986 &sleep_millisecs_attr.attr, 1987 &pages_to_scan_attr.attr, 1988 &run_attr.attr, 1989 &pages_shared_attr.attr, 1990 &pages_sharing_attr.attr, 1991 &pages_unshared_attr.attr, 1992 &pages_volatile_attr.attr, 1993 &full_scans_attr.attr, 1994 NULL, 1995 }; 1996 1997 static struct attribute_group ksm_attr_group = { 1998 .attrs = ksm_attrs, 1999 .name = "ksm", 2000 }; 2001 #endif /* CONFIG_SYSFS */ 2002 2003 static int __init ksm_init(void) 2004 { 2005 struct task_struct *ksm_thread; 2006 int err; 2007 2008 err = ksm_slab_init(); 2009 if (err) 2010 goto out; 2011 2012 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); 2013 if (IS_ERR(ksm_thread)) { 2014 printk(KERN_ERR "ksm: creating kthread failed\n"); 2015 err = PTR_ERR(ksm_thread); 2016 goto out_free; 2017 } 2018 2019 #ifdef CONFIG_SYSFS 2020 err = sysfs_create_group(mm_kobj, &ksm_attr_group); 2021 if (err) { 2022 printk(KERN_ERR "ksm: register sysfs failed\n"); 2023 kthread_stop(ksm_thread); 2024 goto out_free; 2025 } 2026 #else 2027 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ 2028 2029 #endif /* CONFIG_SYSFS */ 2030 2031 #ifdef CONFIG_MEMORY_HOTREMOVE 2032 /* 2033 * Choose a high priority since the callback takes ksm_thread_mutex: 2034 * later callbacks could only be taking locks which nest within that. 2035 */ 2036 hotplug_memory_notifier(ksm_memory_callback, 100); 2037 #endif 2038 return 0; 2039 2040 out_free: 2041 ksm_slab_free(); 2042 out: 2043 return err; 2044 } 2045 module_init(ksm_init) 2046