Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 1 | /* |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 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 Red Hat, Inc. |
| 8 | * Authors: |
| 9 | * Izik Eidus |
| 10 | * Andrea Arcangeli |
| 11 | * Chris Wright |
| 12 | * |
| 13 | * This work is licensed under the terms of the GNU GPL, version 2. |
Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 14 | */ |
| 15 | |
| 16 | #include <linux/errno.h> |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 17 | #include <linux/mm.h> |
| 18 | #include <linux/fs.h> |
Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 19 | #include <linux/mman.h> |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 20 | #include <linux/sched.h> |
| 21 | #include <linux/rwsem.h> |
| 22 | #include <linux/pagemap.h> |
| 23 | #include <linux/rmap.h> |
| 24 | #include <linux/spinlock.h> |
| 25 | #include <linux/jhash.h> |
| 26 | #include <linux/delay.h> |
| 27 | #include <linux/kthread.h> |
| 28 | #include <linux/wait.h> |
| 29 | #include <linux/slab.h> |
| 30 | #include <linux/rbtree.h> |
| 31 | #include <linux/mmu_notifier.h> |
Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 32 | #include <linux/ksm.h> |
| 33 | |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 34 | #include <asm/tlbflush.h> |
| 35 | |
| 36 | /* |
| 37 | * A few notes about the KSM scanning process, |
| 38 | * to make it easier to understand the data structures below: |
| 39 | * |
| 40 | * In order to reduce excessive scanning, KSM sorts the memory pages by their |
| 41 | * contents into a data structure that holds pointers to the pages' locations. |
| 42 | * |
| 43 | * Since the contents of the pages may change at any moment, KSM cannot just |
| 44 | * insert the pages into a normal sorted tree and expect it to find anything. |
| 45 | * Therefore KSM uses two data structures - the stable and the unstable tree. |
| 46 | * |
| 47 | * The stable tree holds pointers to all the merged pages (ksm pages), sorted |
| 48 | * by their contents. Because each such page is write-protected, searching on |
| 49 | * this tree is fully assured to be working (except when pages are unmapped), |
| 50 | * and therefore this tree is called the stable tree. |
| 51 | * |
| 52 | * In addition to the stable tree, KSM uses a second data structure called the |
| 53 | * unstable tree: this tree holds pointers to pages which have been found to |
| 54 | * be "unchanged for a period of time". The unstable tree sorts these pages |
| 55 | * by their contents, but since they are not write-protected, KSM cannot rely |
| 56 | * upon the unstable tree to work correctly - the unstable tree is liable to |
| 57 | * be corrupted as its contents are modified, and so it is called unstable. |
| 58 | * |
| 59 | * KSM solves this problem by several techniques: |
| 60 | * |
| 61 | * 1) The unstable tree is flushed every time KSM completes scanning all |
| 62 | * memory areas, and then the tree is rebuilt again from the beginning. |
| 63 | * 2) KSM will only insert into the unstable tree, pages whose hash value |
| 64 | * has not changed since the previous scan of all memory areas. |
| 65 | * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the |
| 66 | * colors of the nodes and not on their contents, assuring that even when |
| 67 | * the tree gets "corrupted" it won't get out of balance, so scanning time |
| 68 | * remains the same (also, searching and inserting nodes in an rbtree uses |
| 69 | * the same algorithm, so we have no overhead when we flush and rebuild). |
| 70 | * 4) KSM never flushes the stable tree, which means that even if it were to |
| 71 | * take 10 attempts to find a page in the unstable tree, once it is found, |
| 72 | * it is secured in the stable tree. (When we scan a new page, we first |
| 73 | * compare it against the stable tree, and then against the unstable tree.) |
| 74 | */ |
| 75 | |
| 76 | /** |
| 77 | * struct mm_slot - ksm information per mm that is being scanned |
| 78 | * @link: link to the mm_slots hash list |
| 79 | * @mm_list: link into the mm_slots list, rooted in ksm_mm_head |
| 80 | * @rmap_list: head for this mm_slot's list of rmap_items |
| 81 | * @mm: the mm that this information is valid for |
| 82 | */ |
| 83 | struct mm_slot { |
| 84 | struct hlist_node link; |
| 85 | struct list_head mm_list; |
| 86 | struct list_head rmap_list; |
| 87 | struct mm_struct *mm; |
| 88 | }; |
| 89 | |
| 90 | /** |
| 91 | * struct ksm_scan - cursor for scanning |
| 92 | * @mm_slot: the current mm_slot we are scanning |
| 93 | * @address: the next address inside that to be scanned |
| 94 | * @rmap_item: the current rmap that we are scanning inside the rmap_list |
| 95 | * @seqnr: count of completed full scans (needed when removing unstable node) |
| 96 | * |
| 97 | * There is only the one ksm_scan instance of this cursor structure. |
| 98 | */ |
| 99 | struct ksm_scan { |
| 100 | struct mm_slot *mm_slot; |
| 101 | unsigned long address; |
| 102 | struct rmap_item *rmap_item; |
| 103 | unsigned long seqnr; |
| 104 | }; |
| 105 | |
| 106 | /** |
| 107 | * struct rmap_item - reverse mapping item for virtual addresses |
| 108 | * @link: link into mm_slot's rmap_list (rmap_list is per mm) |
| 109 | * @mm: the memory structure this rmap_item is pointing into |
| 110 | * @address: the virtual address this rmap_item tracks (+ flags in low bits) |
| 111 | * @oldchecksum: previous checksum of the page at that virtual address |
| 112 | * @node: rb_node of this rmap_item in either unstable or stable tree |
| 113 | * @next: next rmap_item hanging off the same node of the stable tree |
| 114 | * @prev: previous rmap_item hanging off the same node of the stable tree |
| 115 | */ |
| 116 | struct rmap_item { |
| 117 | struct list_head link; |
| 118 | struct mm_struct *mm; |
| 119 | unsigned long address; /* + low bits used for flags below */ |
| 120 | union { |
| 121 | unsigned int oldchecksum; /* when unstable */ |
| 122 | struct rmap_item *next; /* when stable */ |
| 123 | }; |
| 124 | union { |
| 125 | struct rb_node node; /* when tree node */ |
| 126 | struct rmap_item *prev; /* in stable list */ |
| 127 | }; |
| 128 | }; |
| 129 | |
| 130 | #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ |
| 131 | #define NODE_FLAG 0x100 /* is a node of unstable or stable tree */ |
| 132 | #define STABLE_FLAG 0x200 /* is a node or list item of stable tree */ |
| 133 | |
| 134 | /* The stable and unstable tree heads */ |
| 135 | static struct rb_root root_stable_tree = RB_ROOT; |
| 136 | static struct rb_root root_unstable_tree = RB_ROOT; |
| 137 | |
| 138 | #define MM_SLOTS_HASH_HEADS 1024 |
| 139 | static struct hlist_head *mm_slots_hash; |
| 140 | |
| 141 | static struct mm_slot ksm_mm_head = { |
| 142 | .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), |
| 143 | }; |
| 144 | static struct ksm_scan ksm_scan = { |
| 145 | .mm_slot = &ksm_mm_head, |
| 146 | }; |
| 147 | |
| 148 | static struct kmem_cache *rmap_item_cache; |
| 149 | static struct kmem_cache *mm_slot_cache; |
| 150 | |
| 151 | /* The number of nodes in the stable tree */ |
| 152 | static unsigned long ksm_kernel_pages_allocated; |
| 153 | |
| 154 | /* The number of page slots sharing those nodes */ |
| 155 | static unsigned long ksm_pages_shared; |
| 156 | |
| 157 | /* Limit on the number of unswappable pages used */ |
| 158 | static unsigned long ksm_max_kernel_pages; |
| 159 | |
| 160 | /* Number of pages ksmd should scan in one batch */ |
| 161 | static unsigned int ksm_thread_pages_to_scan; |
| 162 | |
| 163 | /* Milliseconds ksmd should sleep between batches */ |
| 164 | static unsigned int ksm_thread_sleep_millisecs; |
| 165 | |
| 166 | #define KSM_RUN_STOP 0 |
| 167 | #define KSM_RUN_MERGE 1 |
| 168 | #define KSM_RUN_UNMERGE 2 |
| 169 | static unsigned int ksm_run; |
| 170 | |
| 171 | static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); |
| 172 | static DEFINE_MUTEX(ksm_thread_mutex); |
| 173 | static DEFINE_SPINLOCK(ksm_mmlist_lock); |
| 174 | |
| 175 | #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ |
| 176 | sizeof(struct __struct), __alignof__(struct __struct),\ |
| 177 | (__flags), NULL) |
| 178 | |
| 179 | static int __init ksm_slab_init(void) |
| 180 | { |
| 181 | rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); |
| 182 | if (!rmap_item_cache) |
| 183 | goto out; |
| 184 | |
| 185 | mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); |
| 186 | if (!mm_slot_cache) |
| 187 | goto out_free; |
| 188 | |
| 189 | return 0; |
| 190 | |
| 191 | out_free: |
| 192 | kmem_cache_destroy(rmap_item_cache); |
| 193 | out: |
| 194 | return -ENOMEM; |
| 195 | } |
| 196 | |
| 197 | static void __init ksm_slab_free(void) |
| 198 | { |
| 199 | kmem_cache_destroy(mm_slot_cache); |
| 200 | kmem_cache_destroy(rmap_item_cache); |
| 201 | mm_slot_cache = NULL; |
| 202 | } |
| 203 | |
| 204 | static inline struct rmap_item *alloc_rmap_item(void) |
| 205 | { |
| 206 | return kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL); |
| 207 | } |
| 208 | |
| 209 | static inline void free_rmap_item(struct rmap_item *rmap_item) |
| 210 | { |
| 211 | rmap_item->mm = NULL; /* debug safety */ |
| 212 | kmem_cache_free(rmap_item_cache, rmap_item); |
| 213 | } |
| 214 | |
| 215 | static inline struct mm_slot *alloc_mm_slot(void) |
| 216 | { |
| 217 | if (!mm_slot_cache) /* initialization failed */ |
| 218 | return NULL; |
| 219 | return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); |
| 220 | } |
| 221 | |
| 222 | static inline void free_mm_slot(struct mm_slot *mm_slot) |
| 223 | { |
| 224 | kmem_cache_free(mm_slot_cache, mm_slot); |
| 225 | } |
| 226 | |
| 227 | static int __init mm_slots_hash_init(void) |
| 228 | { |
| 229 | mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head), |
| 230 | GFP_KERNEL); |
| 231 | if (!mm_slots_hash) |
| 232 | return -ENOMEM; |
| 233 | return 0; |
| 234 | } |
| 235 | |
| 236 | static void __init mm_slots_hash_free(void) |
| 237 | { |
| 238 | kfree(mm_slots_hash); |
| 239 | } |
| 240 | |
| 241 | static struct mm_slot *get_mm_slot(struct mm_struct *mm) |
| 242 | { |
| 243 | struct mm_slot *mm_slot; |
| 244 | struct hlist_head *bucket; |
| 245 | struct hlist_node *node; |
| 246 | |
| 247 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) |
| 248 | % MM_SLOTS_HASH_HEADS]; |
| 249 | hlist_for_each_entry(mm_slot, node, bucket, link) { |
| 250 | if (mm == mm_slot->mm) |
| 251 | return mm_slot; |
| 252 | } |
| 253 | return NULL; |
| 254 | } |
| 255 | |
| 256 | static void insert_to_mm_slots_hash(struct mm_struct *mm, |
| 257 | struct mm_slot *mm_slot) |
| 258 | { |
| 259 | struct hlist_head *bucket; |
| 260 | |
| 261 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) |
| 262 | % MM_SLOTS_HASH_HEADS]; |
| 263 | mm_slot->mm = mm; |
| 264 | INIT_LIST_HEAD(&mm_slot->rmap_list); |
| 265 | hlist_add_head(&mm_slot->link, bucket); |
| 266 | } |
| 267 | |
| 268 | static inline int in_stable_tree(struct rmap_item *rmap_item) |
| 269 | { |
| 270 | return rmap_item->address & STABLE_FLAG; |
| 271 | } |
| 272 | |
| 273 | /* |
| 274 | * We use break_ksm to break COW on a ksm page: it's a stripped down |
| 275 | * |
| 276 | * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1) |
| 277 | * put_page(page); |
| 278 | * |
| 279 | * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, |
| 280 | * in case the application has unmapped and remapped mm,addr meanwhile. |
| 281 | * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP |
| 282 | * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. |
| 283 | */ |
| 284 | static void break_ksm(struct vm_area_struct *vma, unsigned long addr) |
| 285 | { |
| 286 | struct page *page; |
| 287 | int ret; |
| 288 | |
| 289 | do { |
| 290 | cond_resched(); |
| 291 | page = follow_page(vma, addr, FOLL_GET); |
| 292 | if (!page) |
| 293 | break; |
| 294 | if (PageKsm(page)) |
| 295 | ret = handle_mm_fault(vma->vm_mm, vma, addr, |
| 296 | FAULT_FLAG_WRITE); |
| 297 | else |
| 298 | ret = VM_FAULT_WRITE; |
| 299 | put_page(page); |
| 300 | } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS))); |
| 301 | |
| 302 | /* Which leaves us looping there if VM_FAULT_OOM: hmmm... */ |
| 303 | } |
| 304 | |
| 305 | static void __break_cow(struct mm_struct *mm, unsigned long addr) |
| 306 | { |
| 307 | struct vm_area_struct *vma; |
| 308 | |
| 309 | vma = find_vma(mm, addr); |
| 310 | if (!vma || vma->vm_start > addr) |
| 311 | return; |
| 312 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
| 313 | return; |
| 314 | break_ksm(vma, addr); |
| 315 | } |
| 316 | |
| 317 | static void break_cow(struct mm_struct *mm, unsigned long addr) |
| 318 | { |
| 319 | down_read(&mm->mmap_sem); |
| 320 | __break_cow(mm, addr); |
| 321 | up_read(&mm->mmap_sem); |
| 322 | } |
| 323 | |
| 324 | static struct page *get_mergeable_page(struct rmap_item *rmap_item) |
| 325 | { |
| 326 | struct mm_struct *mm = rmap_item->mm; |
| 327 | unsigned long addr = rmap_item->address; |
| 328 | struct vm_area_struct *vma; |
| 329 | struct page *page; |
| 330 | |
| 331 | down_read(&mm->mmap_sem); |
| 332 | vma = find_vma(mm, addr); |
| 333 | if (!vma || vma->vm_start > addr) |
| 334 | goto out; |
| 335 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
| 336 | goto out; |
| 337 | |
| 338 | page = follow_page(vma, addr, FOLL_GET); |
| 339 | if (!page) |
| 340 | goto out; |
| 341 | if (PageAnon(page)) { |
| 342 | flush_anon_page(vma, page, addr); |
| 343 | flush_dcache_page(page); |
| 344 | } else { |
| 345 | put_page(page); |
| 346 | out: page = NULL; |
| 347 | } |
| 348 | up_read(&mm->mmap_sem); |
| 349 | return page; |
| 350 | } |
| 351 | |
| 352 | /* |
| 353 | * get_ksm_page: checks if the page at the virtual address in rmap_item |
| 354 | * is still PageKsm, in which case we can trust the content of the page, |
| 355 | * and it returns the gotten page; but NULL if the page has been zapped. |
| 356 | */ |
| 357 | static struct page *get_ksm_page(struct rmap_item *rmap_item) |
| 358 | { |
| 359 | struct page *page; |
| 360 | |
| 361 | page = get_mergeable_page(rmap_item); |
| 362 | if (page && !PageKsm(page)) { |
| 363 | put_page(page); |
| 364 | page = NULL; |
| 365 | } |
| 366 | return page; |
| 367 | } |
| 368 | |
| 369 | /* |
| 370 | * Removing rmap_item from stable or unstable tree. |
| 371 | * This function will clean the information from the stable/unstable tree. |
| 372 | */ |
| 373 | static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) |
| 374 | { |
| 375 | if (in_stable_tree(rmap_item)) { |
| 376 | struct rmap_item *next_item = rmap_item->next; |
| 377 | |
| 378 | if (rmap_item->address & NODE_FLAG) { |
| 379 | if (next_item) { |
| 380 | rb_replace_node(&rmap_item->node, |
| 381 | &next_item->node, |
| 382 | &root_stable_tree); |
| 383 | next_item->address |= NODE_FLAG; |
| 384 | } else { |
| 385 | rb_erase(&rmap_item->node, &root_stable_tree); |
| 386 | ksm_kernel_pages_allocated--; |
| 387 | } |
| 388 | } else { |
| 389 | struct rmap_item *prev_item = rmap_item->prev; |
| 390 | |
| 391 | BUG_ON(prev_item->next != rmap_item); |
| 392 | prev_item->next = next_item; |
| 393 | if (next_item) { |
| 394 | BUG_ON(next_item->prev != rmap_item); |
| 395 | next_item->prev = rmap_item->prev; |
| 396 | } |
| 397 | } |
| 398 | |
| 399 | rmap_item->next = NULL; |
| 400 | ksm_pages_shared--; |
| 401 | |
| 402 | } else if (rmap_item->address & NODE_FLAG) { |
| 403 | unsigned char age; |
| 404 | /* |
| 405 | * ksm_thread can and must skip the rb_erase, because |
| 406 | * root_unstable_tree was already reset to RB_ROOT. |
| 407 | * But __ksm_exit has to be careful: do the rb_erase |
| 408 | * if it's interrupting a scan, and this rmap_item was |
| 409 | * inserted by this scan rather than left from before. |
| 410 | * |
| 411 | * Because of the case in which remove_mm_from_lists |
| 412 | * increments seqnr before removing rmaps, unstable_nr |
| 413 | * may even be 2 behind seqnr, but should never be |
| 414 | * further behind. Yes, I did have trouble with this! |
| 415 | */ |
| 416 | age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); |
| 417 | BUG_ON(age > 2); |
| 418 | if (!age) |
| 419 | rb_erase(&rmap_item->node, &root_unstable_tree); |
| 420 | } |
| 421 | |
| 422 | rmap_item->address &= PAGE_MASK; |
| 423 | |
| 424 | cond_resched(); /* we're called from many long loops */ |
| 425 | } |
| 426 | |
| 427 | static void remove_all_slot_rmap_items(struct mm_slot *mm_slot) |
| 428 | { |
| 429 | struct rmap_item *rmap_item, *node; |
| 430 | |
| 431 | list_for_each_entry_safe(rmap_item, node, &mm_slot->rmap_list, link) { |
| 432 | remove_rmap_item_from_tree(rmap_item); |
| 433 | list_del(&rmap_item->link); |
| 434 | free_rmap_item(rmap_item); |
| 435 | } |
| 436 | } |
| 437 | |
| 438 | static void remove_trailing_rmap_items(struct mm_slot *mm_slot, |
| 439 | struct list_head *cur) |
| 440 | { |
| 441 | struct rmap_item *rmap_item; |
| 442 | |
| 443 | while (cur != &mm_slot->rmap_list) { |
| 444 | rmap_item = list_entry(cur, struct rmap_item, link); |
| 445 | cur = cur->next; |
| 446 | remove_rmap_item_from_tree(rmap_item); |
| 447 | list_del(&rmap_item->link); |
| 448 | free_rmap_item(rmap_item); |
| 449 | } |
| 450 | } |
| 451 | |
| 452 | /* |
| 453 | * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather |
| 454 | * than check every pte of a given vma, the locking doesn't quite work for |
| 455 | * that - an rmap_item is assigned to the stable tree after inserting ksm |
| 456 | * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing |
| 457 | * rmap_items from parent to child at fork time (so as not to waste time |
| 458 | * if exit comes before the next scan reaches it). |
| 459 | */ |
| 460 | static void unmerge_ksm_pages(struct vm_area_struct *vma, |
| 461 | unsigned long start, unsigned long end) |
| 462 | { |
| 463 | unsigned long addr; |
| 464 | |
| 465 | for (addr = start; addr < end; addr += PAGE_SIZE) |
| 466 | break_ksm(vma, addr); |
| 467 | } |
| 468 | |
| 469 | static void unmerge_and_remove_all_rmap_items(void) |
| 470 | { |
| 471 | struct mm_slot *mm_slot; |
| 472 | struct mm_struct *mm; |
| 473 | struct vm_area_struct *vma; |
| 474 | |
| 475 | list_for_each_entry(mm_slot, &ksm_mm_head.mm_list, mm_list) { |
| 476 | mm = mm_slot->mm; |
| 477 | down_read(&mm->mmap_sem); |
| 478 | for (vma = mm->mmap; vma; vma = vma->vm_next) { |
| 479 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
| 480 | continue; |
| 481 | unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end); |
| 482 | } |
| 483 | remove_all_slot_rmap_items(mm_slot); |
| 484 | up_read(&mm->mmap_sem); |
| 485 | } |
| 486 | |
| 487 | spin_lock(&ksm_mmlist_lock); |
| 488 | if (ksm_scan.mm_slot != &ksm_mm_head) { |
| 489 | ksm_scan.mm_slot = &ksm_mm_head; |
| 490 | ksm_scan.seqnr++; |
| 491 | } |
| 492 | spin_unlock(&ksm_mmlist_lock); |
| 493 | } |
| 494 | |
| 495 | static void remove_mm_from_lists(struct mm_struct *mm) |
| 496 | { |
| 497 | struct mm_slot *mm_slot; |
| 498 | |
| 499 | spin_lock(&ksm_mmlist_lock); |
| 500 | mm_slot = get_mm_slot(mm); |
| 501 | |
| 502 | /* |
| 503 | * This mm_slot is always at the scanning cursor when we're |
| 504 | * called from scan_get_next_rmap_item; but it's a special |
| 505 | * case when we're called from __ksm_exit. |
| 506 | */ |
| 507 | if (ksm_scan.mm_slot == mm_slot) { |
| 508 | ksm_scan.mm_slot = list_entry( |
| 509 | mm_slot->mm_list.next, struct mm_slot, mm_list); |
| 510 | ksm_scan.address = 0; |
| 511 | ksm_scan.rmap_item = list_entry( |
| 512 | &ksm_scan.mm_slot->rmap_list, struct rmap_item, link); |
| 513 | if (ksm_scan.mm_slot == &ksm_mm_head) |
| 514 | ksm_scan.seqnr++; |
| 515 | } |
| 516 | |
| 517 | hlist_del(&mm_slot->link); |
| 518 | list_del(&mm_slot->mm_list); |
| 519 | spin_unlock(&ksm_mmlist_lock); |
| 520 | |
| 521 | remove_all_slot_rmap_items(mm_slot); |
| 522 | free_mm_slot(mm_slot); |
| 523 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); |
| 524 | } |
| 525 | |
| 526 | static u32 calc_checksum(struct page *page) |
| 527 | { |
| 528 | u32 checksum; |
| 529 | void *addr = kmap_atomic(page, KM_USER0); |
| 530 | checksum = jhash2(addr, PAGE_SIZE / 4, 17); |
| 531 | kunmap_atomic(addr, KM_USER0); |
| 532 | return checksum; |
| 533 | } |
| 534 | |
| 535 | static int memcmp_pages(struct page *page1, struct page *page2) |
| 536 | { |
| 537 | char *addr1, *addr2; |
| 538 | int ret; |
| 539 | |
| 540 | addr1 = kmap_atomic(page1, KM_USER0); |
| 541 | addr2 = kmap_atomic(page2, KM_USER1); |
| 542 | ret = memcmp(addr1, addr2, PAGE_SIZE); |
| 543 | kunmap_atomic(addr2, KM_USER1); |
| 544 | kunmap_atomic(addr1, KM_USER0); |
| 545 | return ret; |
| 546 | } |
| 547 | |
| 548 | static inline int pages_identical(struct page *page1, struct page *page2) |
| 549 | { |
| 550 | return !memcmp_pages(page1, page2); |
| 551 | } |
| 552 | |
| 553 | static int write_protect_page(struct vm_area_struct *vma, struct page *page, |
| 554 | pte_t *orig_pte) |
| 555 | { |
| 556 | struct mm_struct *mm = vma->vm_mm; |
| 557 | unsigned long addr; |
| 558 | pte_t *ptep; |
| 559 | spinlock_t *ptl; |
| 560 | int swapped; |
| 561 | int err = -EFAULT; |
| 562 | |
| 563 | addr = page_address_in_vma(page, vma); |
| 564 | if (addr == -EFAULT) |
| 565 | goto out; |
| 566 | |
| 567 | ptep = page_check_address(page, mm, addr, &ptl, 0); |
| 568 | if (!ptep) |
| 569 | goto out; |
| 570 | |
| 571 | if (pte_write(*ptep)) { |
| 572 | pte_t entry; |
| 573 | |
| 574 | swapped = PageSwapCache(page); |
| 575 | flush_cache_page(vma, addr, page_to_pfn(page)); |
| 576 | /* |
| 577 | * Ok this is tricky, when get_user_pages_fast() run it doesnt |
| 578 | * take any lock, therefore the check that we are going to make |
| 579 | * with the pagecount against the mapcount is racey and |
| 580 | * O_DIRECT can happen right after the check. |
| 581 | * So we clear the pte and flush the tlb before the check |
| 582 | * this assure us that no O_DIRECT can happen after the check |
| 583 | * or in the middle of the check. |
| 584 | */ |
| 585 | entry = ptep_clear_flush(vma, addr, ptep); |
| 586 | /* |
| 587 | * Check that no O_DIRECT or similar I/O is in progress on the |
| 588 | * page |
| 589 | */ |
| 590 | if ((page_mapcount(page) + 2 + swapped) != page_count(page)) { |
| 591 | set_pte_at_notify(mm, addr, ptep, entry); |
| 592 | goto out_unlock; |
| 593 | } |
| 594 | entry = pte_wrprotect(entry); |
| 595 | set_pte_at_notify(mm, addr, ptep, entry); |
| 596 | } |
| 597 | *orig_pte = *ptep; |
| 598 | err = 0; |
| 599 | |
| 600 | out_unlock: |
| 601 | pte_unmap_unlock(ptep, ptl); |
| 602 | out: |
| 603 | return err; |
| 604 | } |
| 605 | |
| 606 | /** |
| 607 | * replace_page - replace page in vma by new ksm page |
| 608 | * @vma: vma that holds the pte pointing to oldpage |
| 609 | * @oldpage: the page we are replacing by newpage |
| 610 | * @newpage: the ksm page we replace oldpage by |
| 611 | * @orig_pte: the original value of the pte |
| 612 | * |
| 613 | * Returns 0 on success, -EFAULT on failure. |
| 614 | */ |
| 615 | static int replace_page(struct vm_area_struct *vma, struct page *oldpage, |
| 616 | struct page *newpage, pte_t orig_pte) |
| 617 | { |
| 618 | struct mm_struct *mm = vma->vm_mm; |
| 619 | pgd_t *pgd; |
| 620 | pud_t *pud; |
| 621 | pmd_t *pmd; |
| 622 | pte_t *ptep; |
| 623 | spinlock_t *ptl; |
| 624 | unsigned long addr; |
| 625 | pgprot_t prot; |
| 626 | int err = -EFAULT; |
| 627 | |
| 628 | prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE); |
| 629 | |
| 630 | addr = page_address_in_vma(oldpage, vma); |
| 631 | if (addr == -EFAULT) |
| 632 | goto out; |
| 633 | |
| 634 | pgd = pgd_offset(mm, addr); |
| 635 | if (!pgd_present(*pgd)) |
| 636 | goto out; |
| 637 | |
| 638 | pud = pud_offset(pgd, addr); |
| 639 | if (!pud_present(*pud)) |
| 640 | goto out; |
| 641 | |
| 642 | pmd = pmd_offset(pud, addr); |
| 643 | if (!pmd_present(*pmd)) |
| 644 | goto out; |
| 645 | |
| 646 | ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); |
| 647 | if (!pte_same(*ptep, orig_pte)) { |
| 648 | pte_unmap_unlock(ptep, ptl); |
| 649 | goto out; |
| 650 | } |
| 651 | |
| 652 | get_page(newpage); |
| 653 | page_add_ksm_rmap(newpage); |
| 654 | |
| 655 | flush_cache_page(vma, addr, pte_pfn(*ptep)); |
| 656 | ptep_clear_flush(vma, addr, ptep); |
| 657 | set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot)); |
| 658 | |
| 659 | page_remove_rmap(oldpage); |
| 660 | put_page(oldpage); |
| 661 | |
| 662 | pte_unmap_unlock(ptep, ptl); |
| 663 | err = 0; |
| 664 | out: |
| 665 | return err; |
| 666 | } |
| 667 | |
| 668 | /* |
| 669 | * try_to_merge_one_page - take two pages and merge them into one |
| 670 | * @vma: the vma that hold the pte pointing into oldpage |
| 671 | * @oldpage: the page that we want to replace with newpage |
| 672 | * @newpage: the page that we want to map instead of oldpage |
| 673 | * |
| 674 | * Note: |
| 675 | * oldpage should be a PageAnon page, while newpage should be a PageKsm page, |
| 676 | * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm. |
| 677 | * |
| 678 | * This function returns 0 if the pages were merged, -EFAULT otherwise. |
| 679 | */ |
| 680 | static int try_to_merge_one_page(struct vm_area_struct *vma, |
| 681 | struct page *oldpage, |
| 682 | struct page *newpage) |
| 683 | { |
| 684 | pte_t orig_pte = __pte(0); |
| 685 | int err = -EFAULT; |
| 686 | |
| 687 | if (!(vma->vm_flags & VM_MERGEABLE)) |
| 688 | goto out; |
| 689 | |
| 690 | if (!PageAnon(oldpage)) |
| 691 | goto out; |
| 692 | |
| 693 | get_page(newpage); |
| 694 | get_page(oldpage); |
| 695 | |
| 696 | /* |
| 697 | * We need the page lock to read a stable PageSwapCache in |
| 698 | * write_protect_page(). We use trylock_page() instead of |
| 699 | * lock_page() because we don't want to wait here - we |
| 700 | * prefer to continue scanning and merging different pages, |
| 701 | * then come back to this page when it is unlocked. |
| 702 | */ |
| 703 | if (!trylock_page(oldpage)) |
| 704 | goto out_putpage; |
| 705 | /* |
| 706 | * If this anonymous page is mapped only here, its pte may need |
| 707 | * to be write-protected. If it's mapped elsewhere, all of its |
| 708 | * ptes are necessarily already write-protected. But in either |
| 709 | * case, we need to lock and check page_count is not raised. |
| 710 | */ |
| 711 | if (write_protect_page(vma, oldpage, &orig_pte)) { |
| 712 | unlock_page(oldpage); |
| 713 | goto out_putpage; |
| 714 | } |
| 715 | unlock_page(oldpage); |
| 716 | |
| 717 | if (pages_identical(oldpage, newpage)) |
| 718 | err = replace_page(vma, oldpage, newpage, orig_pte); |
| 719 | |
| 720 | out_putpage: |
| 721 | put_page(oldpage); |
| 722 | put_page(newpage); |
| 723 | out: |
| 724 | return err; |
| 725 | } |
| 726 | |
| 727 | /* |
| 728 | * try_to_merge_two_pages - take two identical pages and prepare them |
| 729 | * to be merged into one page. |
| 730 | * |
| 731 | * This function returns 0 if we successfully mapped two identical pages |
| 732 | * into one page, -EFAULT otherwise. |
| 733 | * |
| 734 | * Note that this function allocates a new kernel page: if one of the pages |
| 735 | * is already a ksm page, try_to_merge_with_ksm_page should be used. |
| 736 | */ |
| 737 | static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1, |
| 738 | struct page *page1, struct mm_struct *mm2, |
| 739 | unsigned long addr2, struct page *page2) |
| 740 | { |
| 741 | struct vm_area_struct *vma; |
| 742 | struct page *kpage; |
| 743 | int err = -EFAULT; |
| 744 | |
| 745 | /* |
| 746 | * The number of nodes in the stable tree |
| 747 | * is the number of kernel pages that we hold. |
| 748 | */ |
| 749 | if (ksm_max_kernel_pages && |
| 750 | ksm_max_kernel_pages <= ksm_kernel_pages_allocated) |
| 751 | return err; |
| 752 | |
| 753 | kpage = alloc_page(GFP_HIGHUSER); |
| 754 | if (!kpage) |
| 755 | return err; |
| 756 | |
| 757 | down_read(&mm1->mmap_sem); |
| 758 | vma = find_vma(mm1, addr1); |
| 759 | if (!vma || vma->vm_start > addr1) { |
| 760 | put_page(kpage); |
| 761 | up_read(&mm1->mmap_sem); |
| 762 | return err; |
| 763 | } |
| 764 | |
| 765 | copy_user_highpage(kpage, page1, addr1, vma); |
| 766 | err = try_to_merge_one_page(vma, page1, kpage); |
| 767 | up_read(&mm1->mmap_sem); |
| 768 | |
| 769 | if (!err) { |
| 770 | down_read(&mm2->mmap_sem); |
| 771 | vma = find_vma(mm2, addr2); |
| 772 | if (!vma || vma->vm_start > addr2) { |
| 773 | put_page(kpage); |
| 774 | up_read(&mm2->mmap_sem); |
| 775 | break_cow(mm1, addr1); |
| 776 | return -EFAULT; |
| 777 | } |
| 778 | |
| 779 | err = try_to_merge_one_page(vma, page2, kpage); |
| 780 | up_read(&mm2->mmap_sem); |
| 781 | |
| 782 | /* |
| 783 | * If the second try_to_merge_one_page failed, we have a |
| 784 | * ksm page with just one pte pointing to it, so break it. |
| 785 | */ |
| 786 | if (err) |
| 787 | break_cow(mm1, addr1); |
| 788 | else |
| 789 | ksm_pages_shared += 2; |
| 790 | } |
| 791 | |
| 792 | put_page(kpage); |
| 793 | return err; |
| 794 | } |
| 795 | |
| 796 | /* |
| 797 | * try_to_merge_with_ksm_page - like try_to_merge_two_pages, |
| 798 | * but no new kernel page is allocated: kpage must already be a ksm page. |
| 799 | */ |
| 800 | static int try_to_merge_with_ksm_page(struct mm_struct *mm1, |
| 801 | unsigned long addr1, |
| 802 | struct page *page1, |
| 803 | struct page *kpage) |
| 804 | { |
| 805 | struct vm_area_struct *vma; |
| 806 | int err = -EFAULT; |
| 807 | |
| 808 | down_read(&mm1->mmap_sem); |
| 809 | vma = find_vma(mm1, addr1); |
| 810 | if (!vma || vma->vm_start > addr1) { |
| 811 | up_read(&mm1->mmap_sem); |
| 812 | return err; |
| 813 | } |
| 814 | |
| 815 | err = try_to_merge_one_page(vma, page1, kpage); |
| 816 | up_read(&mm1->mmap_sem); |
| 817 | |
| 818 | if (!err) |
| 819 | ksm_pages_shared++; |
| 820 | |
| 821 | return err; |
| 822 | } |
| 823 | |
| 824 | /* |
| 825 | * stable_tree_search - search page inside the stable tree |
| 826 | * @page: the page that we are searching identical pages to. |
| 827 | * @page2: pointer into identical page that we are holding inside the stable |
| 828 | * tree that we have found. |
| 829 | * @rmap_item: the reverse mapping item |
| 830 | * |
| 831 | * This function checks if there is a page inside the stable tree |
| 832 | * with identical content to the page that we are scanning right now. |
| 833 | * |
| 834 | * This function return rmap_item pointer to the identical item if found, |
| 835 | * NULL otherwise. |
| 836 | */ |
| 837 | static struct rmap_item *stable_tree_search(struct page *page, |
| 838 | struct page **page2, |
| 839 | struct rmap_item *rmap_item) |
| 840 | { |
| 841 | struct rb_node *node = root_stable_tree.rb_node; |
| 842 | |
| 843 | while (node) { |
| 844 | struct rmap_item *tree_rmap_item, *next_rmap_item; |
| 845 | int ret; |
| 846 | |
| 847 | tree_rmap_item = rb_entry(node, struct rmap_item, node); |
| 848 | while (tree_rmap_item) { |
| 849 | BUG_ON(!in_stable_tree(tree_rmap_item)); |
| 850 | cond_resched(); |
| 851 | page2[0] = get_ksm_page(tree_rmap_item); |
| 852 | if (page2[0]) |
| 853 | break; |
| 854 | next_rmap_item = tree_rmap_item->next; |
| 855 | remove_rmap_item_from_tree(tree_rmap_item); |
| 856 | tree_rmap_item = next_rmap_item; |
| 857 | } |
| 858 | if (!tree_rmap_item) |
| 859 | return NULL; |
| 860 | |
| 861 | ret = memcmp_pages(page, page2[0]); |
| 862 | |
| 863 | if (ret < 0) { |
| 864 | put_page(page2[0]); |
| 865 | node = node->rb_left; |
| 866 | } else if (ret > 0) { |
| 867 | put_page(page2[0]); |
| 868 | node = node->rb_right; |
| 869 | } else { |
| 870 | return tree_rmap_item; |
| 871 | } |
| 872 | } |
| 873 | |
| 874 | return NULL; |
| 875 | } |
| 876 | |
| 877 | /* |
| 878 | * stable_tree_insert - insert rmap_item pointing to new ksm page |
| 879 | * into the stable tree. |
| 880 | * |
| 881 | * @page: the page that we are searching identical page to inside the stable |
| 882 | * tree. |
| 883 | * @rmap_item: pointer to the reverse mapping item. |
| 884 | * |
| 885 | * This function returns rmap_item if success, NULL otherwise. |
| 886 | */ |
| 887 | static struct rmap_item *stable_tree_insert(struct page *page, |
| 888 | struct rmap_item *rmap_item) |
| 889 | { |
| 890 | struct rb_node **new = &root_stable_tree.rb_node; |
| 891 | struct rb_node *parent = NULL; |
| 892 | |
| 893 | while (*new) { |
| 894 | struct rmap_item *tree_rmap_item, *next_rmap_item; |
| 895 | struct page *tree_page; |
| 896 | int ret; |
| 897 | |
| 898 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); |
| 899 | while (tree_rmap_item) { |
| 900 | BUG_ON(!in_stable_tree(tree_rmap_item)); |
| 901 | cond_resched(); |
| 902 | tree_page = get_ksm_page(tree_rmap_item); |
| 903 | if (tree_page) |
| 904 | break; |
| 905 | next_rmap_item = tree_rmap_item->next; |
| 906 | remove_rmap_item_from_tree(tree_rmap_item); |
| 907 | tree_rmap_item = next_rmap_item; |
| 908 | } |
| 909 | if (!tree_rmap_item) |
| 910 | return NULL; |
| 911 | |
| 912 | ret = memcmp_pages(page, tree_page); |
| 913 | put_page(tree_page); |
| 914 | |
| 915 | parent = *new; |
| 916 | if (ret < 0) |
| 917 | new = &parent->rb_left; |
| 918 | else if (ret > 0) |
| 919 | new = &parent->rb_right; |
| 920 | else { |
| 921 | /* |
| 922 | * It is not a bug that stable_tree_search() didn't |
| 923 | * find this node: because at that time our page was |
| 924 | * not yet write-protected, so may have changed since. |
| 925 | */ |
| 926 | return NULL; |
| 927 | } |
| 928 | } |
| 929 | |
| 930 | ksm_kernel_pages_allocated++; |
| 931 | |
| 932 | rmap_item->address |= NODE_FLAG | STABLE_FLAG; |
| 933 | rmap_item->next = NULL; |
| 934 | rb_link_node(&rmap_item->node, parent, new); |
| 935 | rb_insert_color(&rmap_item->node, &root_stable_tree); |
| 936 | |
| 937 | return rmap_item; |
| 938 | } |
| 939 | |
| 940 | /* |
| 941 | * unstable_tree_search_insert - search and insert items into the unstable tree. |
| 942 | * |
| 943 | * @page: the page that we are going to search for identical page or to insert |
| 944 | * into the unstable tree |
| 945 | * @page2: pointer into identical page that was found inside the unstable tree |
| 946 | * @rmap_item: the reverse mapping item of page |
| 947 | * |
| 948 | * This function searches for a page in the unstable tree identical to the |
| 949 | * page currently being scanned; and if no identical page is found in the |
| 950 | * tree, we insert rmap_item as a new object into the unstable tree. |
| 951 | * |
| 952 | * This function returns pointer to rmap_item found to be identical |
| 953 | * to the currently scanned page, NULL otherwise. |
| 954 | * |
| 955 | * This function does both searching and inserting, because they share |
| 956 | * the same walking algorithm in an rbtree. |
| 957 | */ |
| 958 | static struct rmap_item *unstable_tree_search_insert(struct page *page, |
| 959 | struct page **page2, |
| 960 | struct rmap_item *rmap_item) |
| 961 | { |
| 962 | struct rb_node **new = &root_unstable_tree.rb_node; |
| 963 | struct rb_node *parent = NULL; |
| 964 | |
| 965 | while (*new) { |
| 966 | struct rmap_item *tree_rmap_item; |
| 967 | int ret; |
| 968 | |
| 969 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); |
| 970 | page2[0] = get_mergeable_page(tree_rmap_item); |
| 971 | if (!page2[0]) |
| 972 | return NULL; |
| 973 | |
| 974 | /* |
| 975 | * Don't substitute an unswappable ksm page |
| 976 | * just for one good swappable forked page. |
| 977 | */ |
| 978 | if (page == page2[0]) { |
| 979 | put_page(page2[0]); |
| 980 | return NULL; |
| 981 | } |
| 982 | |
| 983 | ret = memcmp_pages(page, page2[0]); |
| 984 | |
| 985 | parent = *new; |
| 986 | if (ret < 0) { |
| 987 | put_page(page2[0]); |
| 988 | new = &parent->rb_left; |
| 989 | } else if (ret > 0) { |
| 990 | put_page(page2[0]); |
| 991 | new = &parent->rb_right; |
| 992 | } else { |
| 993 | return tree_rmap_item; |
| 994 | } |
| 995 | } |
| 996 | |
| 997 | rmap_item->address |= NODE_FLAG; |
| 998 | rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); |
| 999 | rb_link_node(&rmap_item->node, parent, new); |
| 1000 | rb_insert_color(&rmap_item->node, &root_unstable_tree); |
| 1001 | |
| 1002 | return NULL; |
| 1003 | } |
| 1004 | |
| 1005 | /* |
| 1006 | * stable_tree_append - add another rmap_item to the linked list of |
| 1007 | * rmap_items hanging off a given node of the stable tree, all sharing |
| 1008 | * the same ksm page. |
| 1009 | */ |
| 1010 | static void stable_tree_append(struct rmap_item *rmap_item, |
| 1011 | struct rmap_item *tree_rmap_item) |
| 1012 | { |
| 1013 | rmap_item->next = tree_rmap_item->next; |
| 1014 | rmap_item->prev = tree_rmap_item; |
| 1015 | |
| 1016 | if (tree_rmap_item->next) |
| 1017 | tree_rmap_item->next->prev = rmap_item; |
| 1018 | |
| 1019 | tree_rmap_item->next = rmap_item; |
| 1020 | rmap_item->address |= STABLE_FLAG; |
| 1021 | } |
| 1022 | |
| 1023 | /* |
| 1024 | * cmp_and_merge_page - take a page computes its hash value and check if there |
| 1025 | * is similar hash value to different page, |
| 1026 | * in case we find that there is similar hash to different page we call to |
| 1027 | * try_to_merge_two_pages(). |
| 1028 | * |
| 1029 | * @page: the page that we are searching identical page to. |
| 1030 | * @rmap_item: the reverse mapping into the virtual address of this page |
| 1031 | */ |
| 1032 | static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) |
| 1033 | { |
| 1034 | struct page *page2[1]; |
| 1035 | struct rmap_item *tree_rmap_item; |
| 1036 | unsigned int checksum; |
| 1037 | int err; |
| 1038 | |
| 1039 | if (in_stable_tree(rmap_item)) |
| 1040 | remove_rmap_item_from_tree(rmap_item); |
| 1041 | |
| 1042 | /* We first start with searching the page inside the stable tree */ |
| 1043 | tree_rmap_item = stable_tree_search(page, page2, rmap_item); |
| 1044 | if (tree_rmap_item) { |
| 1045 | if (page == page2[0]) { /* forked */ |
| 1046 | ksm_pages_shared++; |
| 1047 | err = 0; |
| 1048 | } else |
| 1049 | err = try_to_merge_with_ksm_page(rmap_item->mm, |
| 1050 | rmap_item->address, |
| 1051 | page, page2[0]); |
| 1052 | put_page(page2[0]); |
| 1053 | |
| 1054 | if (!err) { |
| 1055 | /* |
| 1056 | * The page was successfully merged: |
| 1057 | * add its rmap_item to the stable tree. |
| 1058 | */ |
| 1059 | stable_tree_append(rmap_item, tree_rmap_item); |
| 1060 | } |
| 1061 | return; |
| 1062 | } |
| 1063 | |
| 1064 | /* |
| 1065 | * A ksm page might have got here by fork, but its other |
| 1066 | * references have already been removed from the stable tree. |
| 1067 | */ |
| 1068 | if (PageKsm(page)) |
| 1069 | break_cow(rmap_item->mm, rmap_item->address); |
| 1070 | |
| 1071 | /* |
| 1072 | * In case the hash value of the page was changed from the last time we |
| 1073 | * have calculated it, this page to be changed frequely, therefore we |
| 1074 | * don't want to insert it to the unstable tree, and we don't want to |
| 1075 | * waste our time to search if there is something identical to it there. |
| 1076 | */ |
| 1077 | checksum = calc_checksum(page); |
| 1078 | if (rmap_item->oldchecksum != checksum) { |
| 1079 | rmap_item->oldchecksum = checksum; |
| 1080 | return; |
| 1081 | } |
| 1082 | |
| 1083 | tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item); |
| 1084 | if (tree_rmap_item) { |
| 1085 | err = try_to_merge_two_pages(rmap_item->mm, |
| 1086 | rmap_item->address, page, |
| 1087 | tree_rmap_item->mm, |
| 1088 | tree_rmap_item->address, page2[0]); |
| 1089 | /* |
| 1090 | * As soon as we merge this page, we want to remove the |
| 1091 | * rmap_item of the page we have merged with from the unstable |
| 1092 | * tree, and insert it instead as new node in the stable tree. |
| 1093 | */ |
| 1094 | if (!err) { |
| 1095 | rb_erase(&tree_rmap_item->node, &root_unstable_tree); |
| 1096 | tree_rmap_item->address &= ~NODE_FLAG; |
| 1097 | /* |
| 1098 | * If we fail to insert the page into the stable tree, |
| 1099 | * we will have 2 virtual addresses that are pointing |
| 1100 | * to a ksm page left outside the stable tree, |
| 1101 | * in which case we need to break_cow on both. |
| 1102 | */ |
| 1103 | if (stable_tree_insert(page2[0], tree_rmap_item)) |
| 1104 | stable_tree_append(rmap_item, tree_rmap_item); |
| 1105 | else { |
| 1106 | break_cow(tree_rmap_item->mm, |
| 1107 | tree_rmap_item->address); |
| 1108 | break_cow(rmap_item->mm, rmap_item->address); |
| 1109 | ksm_pages_shared -= 2; |
| 1110 | } |
| 1111 | } |
| 1112 | |
| 1113 | put_page(page2[0]); |
| 1114 | } |
| 1115 | } |
| 1116 | |
| 1117 | static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, |
| 1118 | struct list_head *cur, |
| 1119 | unsigned long addr) |
| 1120 | { |
| 1121 | struct rmap_item *rmap_item; |
| 1122 | |
| 1123 | while (cur != &mm_slot->rmap_list) { |
| 1124 | rmap_item = list_entry(cur, struct rmap_item, link); |
| 1125 | if ((rmap_item->address & PAGE_MASK) == addr) { |
| 1126 | if (!in_stable_tree(rmap_item)) |
| 1127 | remove_rmap_item_from_tree(rmap_item); |
| 1128 | return rmap_item; |
| 1129 | } |
| 1130 | if (rmap_item->address > addr) |
| 1131 | break; |
| 1132 | cur = cur->next; |
| 1133 | remove_rmap_item_from_tree(rmap_item); |
| 1134 | list_del(&rmap_item->link); |
| 1135 | free_rmap_item(rmap_item); |
| 1136 | } |
| 1137 | |
| 1138 | rmap_item = alloc_rmap_item(); |
| 1139 | if (rmap_item) { |
| 1140 | /* It has already been zeroed */ |
| 1141 | rmap_item->mm = mm_slot->mm; |
| 1142 | rmap_item->address = addr; |
| 1143 | list_add_tail(&rmap_item->link, cur); |
| 1144 | } |
| 1145 | return rmap_item; |
| 1146 | } |
| 1147 | |
| 1148 | static struct rmap_item *scan_get_next_rmap_item(struct page **page) |
| 1149 | { |
| 1150 | struct mm_struct *mm; |
| 1151 | struct mm_slot *slot; |
| 1152 | struct vm_area_struct *vma; |
| 1153 | struct rmap_item *rmap_item; |
| 1154 | |
| 1155 | if (list_empty(&ksm_mm_head.mm_list)) |
| 1156 | return NULL; |
| 1157 | |
| 1158 | slot = ksm_scan.mm_slot; |
| 1159 | if (slot == &ksm_mm_head) { |
| 1160 | root_unstable_tree = RB_ROOT; |
| 1161 | |
| 1162 | spin_lock(&ksm_mmlist_lock); |
| 1163 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); |
| 1164 | ksm_scan.mm_slot = slot; |
| 1165 | spin_unlock(&ksm_mmlist_lock); |
| 1166 | next_mm: |
| 1167 | ksm_scan.address = 0; |
| 1168 | ksm_scan.rmap_item = list_entry(&slot->rmap_list, |
| 1169 | struct rmap_item, link); |
| 1170 | } |
| 1171 | |
| 1172 | mm = slot->mm; |
| 1173 | down_read(&mm->mmap_sem); |
| 1174 | for (vma = find_vma(mm, ksm_scan.address); vma; vma = vma->vm_next) { |
| 1175 | if (!(vma->vm_flags & VM_MERGEABLE)) |
| 1176 | continue; |
| 1177 | if (ksm_scan.address < vma->vm_start) |
| 1178 | ksm_scan.address = vma->vm_start; |
| 1179 | if (!vma->anon_vma) |
| 1180 | ksm_scan.address = vma->vm_end; |
| 1181 | |
| 1182 | while (ksm_scan.address < vma->vm_end) { |
| 1183 | *page = follow_page(vma, ksm_scan.address, FOLL_GET); |
| 1184 | if (*page && PageAnon(*page)) { |
| 1185 | flush_anon_page(vma, *page, ksm_scan.address); |
| 1186 | flush_dcache_page(*page); |
| 1187 | rmap_item = get_next_rmap_item(slot, |
| 1188 | ksm_scan.rmap_item->link.next, |
| 1189 | ksm_scan.address); |
| 1190 | if (rmap_item) { |
| 1191 | ksm_scan.rmap_item = rmap_item; |
| 1192 | ksm_scan.address += PAGE_SIZE; |
| 1193 | } else |
| 1194 | put_page(*page); |
| 1195 | up_read(&mm->mmap_sem); |
| 1196 | return rmap_item; |
| 1197 | } |
| 1198 | if (*page) |
| 1199 | put_page(*page); |
| 1200 | ksm_scan.address += PAGE_SIZE; |
| 1201 | cond_resched(); |
| 1202 | } |
| 1203 | } |
| 1204 | |
| 1205 | if (!ksm_scan.address) { |
| 1206 | /* |
| 1207 | * We've completed a full scan of all vmas, holding mmap_sem |
| 1208 | * throughout, and found no VM_MERGEABLE: so do the same as |
| 1209 | * __ksm_exit does to remove this mm from all our lists now. |
| 1210 | */ |
| 1211 | remove_mm_from_lists(mm); |
| 1212 | up_read(&mm->mmap_sem); |
| 1213 | slot = ksm_scan.mm_slot; |
| 1214 | if (slot != &ksm_mm_head) |
| 1215 | goto next_mm; |
| 1216 | return NULL; |
| 1217 | } |
| 1218 | |
| 1219 | /* |
| 1220 | * Nuke all the rmap_items that are above this current rmap: |
| 1221 | * because there were no VM_MERGEABLE vmas with such addresses. |
| 1222 | */ |
| 1223 | remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next); |
| 1224 | up_read(&mm->mmap_sem); |
| 1225 | |
| 1226 | spin_lock(&ksm_mmlist_lock); |
| 1227 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); |
| 1228 | ksm_scan.mm_slot = slot; |
| 1229 | spin_unlock(&ksm_mmlist_lock); |
| 1230 | |
| 1231 | /* Repeat until we've completed scanning the whole list */ |
| 1232 | if (slot != &ksm_mm_head) |
| 1233 | goto next_mm; |
| 1234 | |
| 1235 | /* |
| 1236 | * Bump seqnr here rather than at top, so that __ksm_exit |
| 1237 | * can skip rb_erase on unstable tree until we run again. |
| 1238 | */ |
| 1239 | ksm_scan.seqnr++; |
| 1240 | return NULL; |
| 1241 | } |
| 1242 | |
| 1243 | /** |
| 1244 | * ksm_do_scan - the ksm scanner main worker function. |
| 1245 | * @scan_npages - number of pages we want to scan before we return. |
| 1246 | */ |
| 1247 | static void ksm_do_scan(unsigned int scan_npages) |
| 1248 | { |
| 1249 | struct rmap_item *rmap_item; |
| 1250 | struct page *page; |
| 1251 | |
| 1252 | while (scan_npages--) { |
| 1253 | cond_resched(); |
| 1254 | rmap_item = scan_get_next_rmap_item(&page); |
| 1255 | if (!rmap_item) |
| 1256 | return; |
| 1257 | if (!PageKsm(page) || !in_stable_tree(rmap_item)) |
| 1258 | cmp_and_merge_page(page, rmap_item); |
| 1259 | put_page(page); |
| 1260 | } |
| 1261 | } |
| 1262 | |
| 1263 | static int ksm_scan_thread(void *nothing) |
| 1264 | { |
| 1265 | set_user_nice(current, 0); |
| 1266 | |
| 1267 | while (!kthread_should_stop()) { |
| 1268 | if (ksm_run & KSM_RUN_MERGE) { |
| 1269 | mutex_lock(&ksm_thread_mutex); |
| 1270 | ksm_do_scan(ksm_thread_pages_to_scan); |
| 1271 | mutex_unlock(&ksm_thread_mutex); |
| 1272 | schedule_timeout_interruptible( |
| 1273 | msecs_to_jiffies(ksm_thread_sleep_millisecs)); |
| 1274 | } else { |
| 1275 | wait_event_interruptible(ksm_thread_wait, |
| 1276 | (ksm_run & KSM_RUN_MERGE) || |
| 1277 | kthread_should_stop()); |
| 1278 | } |
| 1279 | } |
| 1280 | return 0; |
| 1281 | } |
| 1282 | |
Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 1283 | int ksm_madvise(struct vm_area_struct *vma, unsigned long start, |
| 1284 | unsigned long end, int advice, unsigned long *vm_flags) |
| 1285 | { |
| 1286 | struct mm_struct *mm = vma->vm_mm; |
| 1287 | |
| 1288 | switch (advice) { |
| 1289 | case MADV_MERGEABLE: |
| 1290 | /* |
| 1291 | * Be somewhat over-protective for now! |
| 1292 | */ |
| 1293 | if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | |
| 1294 | VM_PFNMAP | VM_IO | VM_DONTEXPAND | |
| 1295 | VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE | |
| 1296 | VM_MIXEDMAP | VM_SAO)) |
| 1297 | return 0; /* just ignore the advice */ |
| 1298 | |
| 1299 | if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) |
| 1300 | if (__ksm_enter(mm) < 0) |
| 1301 | return -EAGAIN; |
| 1302 | |
| 1303 | *vm_flags |= VM_MERGEABLE; |
| 1304 | break; |
| 1305 | |
| 1306 | case MADV_UNMERGEABLE: |
| 1307 | if (!(*vm_flags & VM_MERGEABLE)) |
| 1308 | return 0; /* just ignore the advice */ |
| 1309 | |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 1310 | if (vma->anon_vma) |
| 1311 | unmerge_ksm_pages(vma, start, end); |
Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 1312 | |
| 1313 | *vm_flags &= ~VM_MERGEABLE; |
| 1314 | break; |
| 1315 | } |
| 1316 | |
| 1317 | return 0; |
| 1318 | } |
| 1319 | |
| 1320 | int __ksm_enter(struct mm_struct *mm) |
| 1321 | { |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 1322 | struct mm_slot *mm_slot = alloc_mm_slot(); |
| 1323 | if (!mm_slot) |
| 1324 | return -ENOMEM; |
| 1325 | |
| 1326 | spin_lock(&ksm_mmlist_lock); |
| 1327 | insert_to_mm_slots_hash(mm, mm_slot); |
| 1328 | /* |
| 1329 | * Insert just behind the scanning cursor, to let the area settle |
| 1330 | * down a little; when fork is followed by immediate exec, we don't |
| 1331 | * want ksmd to waste time setting up and tearing down an rmap_list. |
| 1332 | */ |
| 1333 | list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); |
| 1334 | spin_unlock(&ksm_mmlist_lock); |
| 1335 | |
Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 1336 | set_bit(MMF_VM_MERGEABLE, &mm->flags); |
| 1337 | return 0; |
| 1338 | } |
| 1339 | |
| 1340 | void __ksm_exit(struct mm_struct *mm) |
| 1341 | { |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 1342 | /* |
| 1343 | * This process is exiting: doesn't hold and doesn't need mmap_sem; |
| 1344 | * but we do need to exclude ksmd and other exiters while we modify |
| 1345 | * the various lists and trees. |
| 1346 | */ |
| 1347 | mutex_lock(&ksm_thread_mutex); |
| 1348 | remove_mm_from_lists(mm); |
| 1349 | mutex_unlock(&ksm_thread_mutex); |
Hugh Dickins | f8af4da | 2009-09-21 17:01:57 -0700 | [diff] [blame] | 1350 | } |
Izik Eidus | 31dbd01 | 2009-09-21 17:02:03 -0700 | [diff] [blame^] | 1351 | |
| 1352 | #define KSM_ATTR_RO(_name) \ |
| 1353 | static struct kobj_attribute _name##_attr = __ATTR_RO(_name) |
| 1354 | #define KSM_ATTR(_name) \ |
| 1355 | static struct kobj_attribute _name##_attr = \ |
| 1356 | __ATTR(_name, 0644, _name##_show, _name##_store) |
| 1357 | |
| 1358 | static ssize_t sleep_millisecs_show(struct kobject *kobj, |
| 1359 | struct kobj_attribute *attr, char *buf) |
| 1360 | { |
| 1361 | return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); |
| 1362 | } |
| 1363 | |
| 1364 | static ssize_t sleep_millisecs_store(struct kobject *kobj, |
| 1365 | struct kobj_attribute *attr, |
| 1366 | const char *buf, size_t count) |
| 1367 | { |
| 1368 | unsigned long msecs; |
| 1369 | int err; |
| 1370 | |
| 1371 | err = strict_strtoul(buf, 10, &msecs); |
| 1372 | if (err || msecs > UINT_MAX) |
| 1373 | return -EINVAL; |
| 1374 | |
| 1375 | ksm_thread_sleep_millisecs = msecs; |
| 1376 | |
| 1377 | return count; |
| 1378 | } |
| 1379 | KSM_ATTR(sleep_millisecs); |
| 1380 | |
| 1381 | static ssize_t pages_to_scan_show(struct kobject *kobj, |
| 1382 | struct kobj_attribute *attr, char *buf) |
| 1383 | { |
| 1384 | return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); |
| 1385 | } |
| 1386 | |
| 1387 | static ssize_t pages_to_scan_store(struct kobject *kobj, |
| 1388 | struct kobj_attribute *attr, |
| 1389 | const char *buf, size_t count) |
| 1390 | { |
| 1391 | int err; |
| 1392 | unsigned long nr_pages; |
| 1393 | |
| 1394 | err = strict_strtoul(buf, 10, &nr_pages); |
| 1395 | if (err || nr_pages > UINT_MAX) |
| 1396 | return -EINVAL; |
| 1397 | |
| 1398 | ksm_thread_pages_to_scan = nr_pages; |
| 1399 | |
| 1400 | return count; |
| 1401 | } |
| 1402 | KSM_ATTR(pages_to_scan); |
| 1403 | |
| 1404 | static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, |
| 1405 | char *buf) |
| 1406 | { |
| 1407 | return sprintf(buf, "%u\n", ksm_run); |
| 1408 | } |
| 1409 | |
| 1410 | static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, |
| 1411 | const char *buf, size_t count) |
| 1412 | { |
| 1413 | int err; |
| 1414 | unsigned long flags; |
| 1415 | |
| 1416 | err = strict_strtoul(buf, 10, &flags); |
| 1417 | if (err || flags > UINT_MAX) |
| 1418 | return -EINVAL; |
| 1419 | if (flags > KSM_RUN_UNMERGE) |
| 1420 | return -EINVAL; |
| 1421 | |
| 1422 | /* |
| 1423 | * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. |
| 1424 | * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, |
| 1425 | * breaking COW to free the kernel_pages_allocated (but leaves |
| 1426 | * mm_slots on the list for when ksmd may be set running again). |
| 1427 | */ |
| 1428 | |
| 1429 | mutex_lock(&ksm_thread_mutex); |
| 1430 | if (ksm_run != flags) { |
| 1431 | ksm_run = flags; |
| 1432 | if (flags & KSM_RUN_UNMERGE) |
| 1433 | unmerge_and_remove_all_rmap_items(); |
| 1434 | } |
| 1435 | mutex_unlock(&ksm_thread_mutex); |
| 1436 | |
| 1437 | if (flags & KSM_RUN_MERGE) |
| 1438 | wake_up_interruptible(&ksm_thread_wait); |
| 1439 | |
| 1440 | return count; |
| 1441 | } |
| 1442 | KSM_ATTR(run); |
| 1443 | |
| 1444 | static ssize_t pages_shared_show(struct kobject *kobj, |
| 1445 | struct kobj_attribute *attr, char *buf) |
| 1446 | { |
| 1447 | return sprintf(buf, "%lu\n", |
| 1448 | ksm_pages_shared - ksm_kernel_pages_allocated); |
| 1449 | } |
| 1450 | KSM_ATTR_RO(pages_shared); |
| 1451 | |
| 1452 | static ssize_t kernel_pages_allocated_show(struct kobject *kobj, |
| 1453 | struct kobj_attribute *attr, |
| 1454 | char *buf) |
| 1455 | { |
| 1456 | return sprintf(buf, "%lu\n", ksm_kernel_pages_allocated); |
| 1457 | } |
| 1458 | KSM_ATTR_RO(kernel_pages_allocated); |
| 1459 | |
| 1460 | static ssize_t max_kernel_pages_store(struct kobject *kobj, |
| 1461 | struct kobj_attribute *attr, |
| 1462 | const char *buf, size_t count) |
| 1463 | { |
| 1464 | int err; |
| 1465 | unsigned long nr_pages; |
| 1466 | |
| 1467 | err = strict_strtoul(buf, 10, &nr_pages); |
| 1468 | if (err) |
| 1469 | return -EINVAL; |
| 1470 | |
| 1471 | ksm_max_kernel_pages = nr_pages; |
| 1472 | |
| 1473 | return count; |
| 1474 | } |
| 1475 | |
| 1476 | static ssize_t max_kernel_pages_show(struct kobject *kobj, |
| 1477 | struct kobj_attribute *attr, char *buf) |
| 1478 | { |
| 1479 | return sprintf(buf, "%lu\n", ksm_max_kernel_pages); |
| 1480 | } |
| 1481 | KSM_ATTR(max_kernel_pages); |
| 1482 | |
| 1483 | static struct attribute *ksm_attrs[] = { |
| 1484 | &sleep_millisecs_attr.attr, |
| 1485 | &pages_to_scan_attr.attr, |
| 1486 | &run_attr.attr, |
| 1487 | &pages_shared_attr.attr, |
| 1488 | &kernel_pages_allocated_attr.attr, |
| 1489 | &max_kernel_pages_attr.attr, |
| 1490 | NULL, |
| 1491 | }; |
| 1492 | |
| 1493 | static struct attribute_group ksm_attr_group = { |
| 1494 | .attrs = ksm_attrs, |
| 1495 | .name = "ksm", |
| 1496 | }; |
| 1497 | |
| 1498 | static int __init ksm_init(void) |
| 1499 | { |
| 1500 | struct task_struct *ksm_thread; |
| 1501 | int err; |
| 1502 | |
| 1503 | err = ksm_slab_init(); |
| 1504 | if (err) |
| 1505 | goto out; |
| 1506 | |
| 1507 | err = mm_slots_hash_init(); |
| 1508 | if (err) |
| 1509 | goto out_free1; |
| 1510 | |
| 1511 | ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); |
| 1512 | if (IS_ERR(ksm_thread)) { |
| 1513 | printk(KERN_ERR "ksm: creating kthread failed\n"); |
| 1514 | err = PTR_ERR(ksm_thread); |
| 1515 | goto out_free2; |
| 1516 | } |
| 1517 | |
| 1518 | err = sysfs_create_group(mm_kobj, &ksm_attr_group); |
| 1519 | if (err) { |
| 1520 | printk(KERN_ERR "ksm: register sysfs failed\n"); |
| 1521 | goto out_free3; |
| 1522 | } |
| 1523 | |
| 1524 | return 0; |
| 1525 | |
| 1526 | out_free3: |
| 1527 | kthread_stop(ksm_thread); |
| 1528 | out_free2: |
| 1529 | mm_slots_hash_free(); |
| 1530 | out_free1: |
| 1531 | ksm_slab_free(); |
| 1532 | out: |
| 1533 | return err; |
| 1534 | } |
| 1535 | module_init(ksm_init) |