linux/mm/rmap.c
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   1/*
   2 * mm/rmap.c - physical to virtual reverse mappings
   3 *
   4 * Copyright 2001, Rik van Riel <riel@conectiva.com.br>
   5 * Released under the General Public License (GPL).
   6 *
   7 * Simple, low overhead reverse mapping scheme.
   8 * Please try to keep this thing as modular as possible.
   9 *
  10 * Provides methods for unmapping each kind of mapped page:
  11 * the anon methods track anonymous pages, and
  12 * the file methods track pages belonging to an inode.
  13 *
  14 * Original design by Rik van Riel <riel@conectiva.com.br> 2001
  15 * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
  16 * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
  17 * Contributions by Hugh Dickins 2003, 2004
  18 */
  19
  20/*
  21 * Lock ordering in mm:
  22 *
  23 * inode->i_mutex       (while writing or truncating, not reading or faulting)
  24 *   mm->mmap_sem
  25 *     page->flags PG_locked (lock_page)
  26 *       mapping->i_mmap_mutex
  27 *         anon_vma->rwsem
  28 *           mm->page_table_lock or pte_lock
  29 *             zone->lru_lock (in mark_page_accessed, isolate_lru_page)
  30 *             swap_lock (in swap_duplicate, swap_info_get)
  31 *               mmlist_lock (in mmput, drain_mmlist and others)
  32 *               mapping->private_lock (in __set_page_dirty_buffers)
  33 *               inode->i_lock (in set_page_dirty's __mark_inode_dirty)
  34 *               bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
  35 *                 sb_lock (within inode_lock in fs/fs-writeback.c)
  36 *                 mapping->tree_lock (widely used, in set_page_dirty,
  37 *                           in arch-dependent flush_dcache_mmap_lock,
  38 *                           within bdi.wb->list_lock in __sync_single_inode)
  39 *
  40 * anon_vma->rwsem,mapping->i_mutex      (memory_failure, collect_procs_anon)
  41 *   ->tasklist_lock
  42 *     pte map lock
  43 */
  44
  45#include <linux/mm.h>
  46#include <linux/pagemap.h>
  47#include <linux/swap.h>
  48#include <linux/swapops.h>
  49#include <linux/slab.h>
  50#include <linux/init.h>
  51#include <linux/ksm.h>
  52#include <linux/rmap.h>
  53#include <linux/rcupdate.h>
  54#include <linux/export.h>
  55#include <linux/memcontrol.h>
  56#include <linux/mmu_notifier.h>
  57#include <linux/migrate.h>
  58#include <linux/hugetlb.h>
  59#include <linux/backing-dev.h>
  60
  61#include <asm/tlbflush.h>
  62
  63#include "internal.h"
  64
  65static struct kmem_cache *anon_vma_cachep;
  66static struct kmem_cache *anon_vma_chain_cachep;
  67
  68static inline struct anon_vma *anon_vma_alloc(void)
  69{
  70        struct anon_vma *anon_vma;
  71
  72        anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
  73        if (anon_vma) {
  74                atomic_set(&anon_vma->refcount, 1);
  75                /*
  76                 * Initialise the anon_vma root to point to itself. If called
  77                 * from fork, the root will be reset to the parents anon_vma.
  78                 */
  79                anon_vma->root = anon_vma;
  80        }
  81
  82        return anon_vma;
  83}
  84
  85static inline void anon_vma_free(struct anon_vma *anon_vma)
  86{
  87        VM_BUG_ON(atomic_read(&anon_vma->refcount));
  88
  89        /*
  90         * Synchronize against page_lock_anon_vma_read() such that
  91         * we can safely hold the lock without the anon_vma getting
  92         * freed.
  93         *
  94         * Relies on the full mb implied by the atomic_dec_and_test() from
  95         * put_anon_vma() against the acquire barrier implied by
  96         * down_read_trylock() from page_lock_anon_vma_read(). This orders:
  97         *
  98         * page_lock_anon_vma_read()    VS      put_anon_vma()
  99         *   down_read_trylock()                  atomic_dec_and_test()
 100         *   LOCK                                 MB
 101         *   atomic_read()                        rwsem_is_locked()
 102         *
 103         * LOCK should suffice since the actual taking of the lock must
 104         * happen _before_ what follows.
 105         */
 106        if (rwsem_is_locked(&anon_vma->root->rwsem)) {
 107                anon_vma_lock_write(anon_vma);
 108                anon_vma_unlock_write(anon_vma);
 109        }
 110
 111        kmem_cache_free(anon_vma_cachep, anon_vma);
 112}
 113
 114static inline struct anon_vma_chain *anon_vma_chain_alloc(gfp_t gfp)
 115{
 116        return kmem_cache_alloc(anon_vma_chain_cachep, gfp);
 117}
 118
 119static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
 120{
 121        kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
 122}
 123
 124static void anon_vma_chain_link(struct vm_area_struct *vma,
 125                                struct anon_vma_chain *avc,
 126                                struct anon_vma *anon_vma)
 127{
 128        avc->vma = vma;
 129        avc->anon_vma = anon_vma;
 130        list_add(&avc->same_vma, &vma->anon_vma_chain);
 131        anon_vma_interval_tree_insert(avc, &anon_vma->rb_root);
 132}
 133
 134/**
 135 * anon_vma_prepare - attach an anon_vma to a memory region
 136 * @vma: the memory region in question
 137 *
 138 * This makes sure the memory mapping described by 'vma' has
 139 * an 'anon_vma' attached to it, so that we can associate the
 140 * anonymous pages mapped into it with that anon_vma.
 141 *
 142 * The common case will be that we already have one, but if
 143 * not we either need to find an adjacent mapping that we
 144 * can re-use the anon_vma from (very common when the only
 145 * reason for splitting a vma has been mprotect()), or we
 146 * allocate a new one.
 147 *
 148 * Anon-vma allocations are very subtle, because we may have
 149 * optimistically looked up an anon_vma in page_lock_anon_vma_read()
 150 * and that may actually touch the spinlock even in the newly
 151 * allocated vma (it depends on RCU to make sure that the
 152 * anon_vma isn't actually destroyed).
 153 *
 154 * As a result, we need to do proper anon_vma locking even
 155 * for the new allocation. At the same time, we do not want
 156 * to do any locking for the common case of already having
 157 * an anon_vma.
 158 *
 159 * This must be called with the mmap_sem held for reading.
 160 */
 161int anon_vma_prepare(struct vm_area_struct *vma)
 162{
 163        struct anon_vma *anon_vma = vma->anon_vma;
 164        struct anon_vma_chain *avc;
 165
 166        might_sleep();
 167        if (unlikely(!anon_vma)) {
 168                struct mm_struct *mm = vma->vm_mm;
 169                struct anon_vma *allocated;
 170
 171                avc = anon_vma_chain_alloc(GFP_KERNEL);
 172                if (!avc)
 173                        goto out_enomem;
 174
 175                anon_vma = find_mergeable_anon_vma(vma);
 176                allocated = NULL;
 177                if (!anon_vma) {
 178                        anon_vma = anon_vma_alloc();
 179                        if (unlikely(!anon_vma))
 180                                goto out_enomem_free_avc;
 181                        allocated = anon_vma;
 182                }
 183
 184                anon_vma_lock_write(anon_vma);
 185                /* page_table_lock to protect against threads */
 186                spin_lock(&mm->page_table_lock);
 187                if (likely(!vma->anon_vma)) {
 188                        vma->anon_vma = anon_vma;
 189                        anon_vma_chain_link(vma, avc, anon_vma);
 190                        allocated = NULL;
 191                        avc = NULL;
 192                }
 193                spin_unlock(&mm->page_table_lock);
 194                anon_vma_unlock_write(anon_vma);
 195
 196                if (unlikely(allocated))
 197                        put_anon_vma(allocated);
 198                if (unlikely(avc))
 199                        anon_vma_chain_free(avc);
 200        }
 201        return 0;
 202
 203 out_enomem_free_avc:
 204        anon_vma_chain_free(avc);
 205 out_enomem:
 206        return -ENOMEM;
 207}
 208
 209/*
 210 * This is a useful helper function for locking the anon_vma root as
 211 * we traverse the vma->anon_vma_chain, looping over anon_vma's that
 212 * have the same vma.
 213 *
 214 * Such anon_vma's should have the same root, so you'd expect to see
 215 * just a single mutex_lock for the whole traversal.
 216 */
 217static inline struct anon_vma *lock_anon_vma_root(struct anon_vma *root, struct anon_vma *anon_vma)
 218{
 219        struct anon_vma *new_root = anon_vma->root;
 220        if (new_root != root) {
 221                if (WARN_ON_ONCE(root))
 222                        up_write(&root->rwsem);
 223                root = new_root;
 224                down_write(&root->rwsem);
 225        }
 226        return root;
 227}
 228
 229static inline void unlock_anon_vma_root(struct anon_vma *root)
 230{
 231        if (root)
 232                up_write(&root->rwsem);
 233}
 234
 235/*
 236 * Attach the anon_vmas from src to dst.
 237 * Returns 0 on success, -ENOMEM on failure.
 238 */
 239int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 240{
 241        struct anon_vma_chain *avc, *pavc;
 242        struct anon_vma *root = NULL;
 243
 244        list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
 245                struct anon_vma *anon_vma;
 246
 247                avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
 248                if (unlikely(!avc)) {
 249                        unlock_anon_vma_root(root);
 250                        root = NULL;
 251                        avc = anon_vma_chain_alloc(GFP_KERNEL);
 252                        if (!avc)
 253                                goto enomem_failure;
 254                }
 255                anon_vma = pavc->anon_vma;
 256                root = lock_anon_vma_root(root, anon_vma);
 257                anon_vma_chain_link(dst, avc, anon_vma);
 258        }
 259        unlock_anon_vma_root(root);
 260        return 0;
 261
 262 enomem_failure:
 263        unlink_anon_vmas(dst);
 264        return -ENOMEM;
 265}
 266
 267/*
 268 * Attach vma to its own anon_vma, as well as to the anon_vmas that
 269 * the corresponding VMA in the parent process is attached to.
 270 * Returns 0 on success, non-zero on failure.
 271 */
 272int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
 273{
 274        struct anon_vma_chain *avc;
 275        struct anon_vma *anon_vma;
 276
 277        /* Don't bother if the parent process has no anon_vma here. */
 278        if (!pvma->anon_vma)
 279                return 0;
 280
 281        /*
 282         * First, attach the new VMA to the parent VMA's anon_vmas,
 283         * so rmap can find non-COWed pages in child processes.
 284         */
 285        if (anon_vma_clone(vma, pvma))
 286                return -ENOMEM;
 287
 288        /* Then add our own anon_vma. */
 289        anon_vma = anon_vma_alloc();
 290        if (!anon_vma)
 291                goto out_error;
 292        avc = anon_vma_chain_alloc(GFP_KERNEL);
 293        if (!avc)
 294                goto out_error_free_anon_vma;
 295
 296        /*
 297         * The root anon_vma's spinlock is the lock actually used when we
 298         * lock any of the anon_vmas in this anon_vma tree.
 299         */
 300        anon_vma->root = pvma->anon_vma->root;
 301        /*
 302         * With refcounts, an anon_vma can stay around longer than the
 303         * process it belongs to. The root anon_vma needs to be pinned until
 304         * this anon_vma is freed, because the lock lives in the root.
 305         */
 306        get_anon_vma(anon_vma->root);
 307        /* Mark this anon_vma as the one where our new (COWed) pages go. */
 308        vma->anon_vma = anon_vma;
 309        anon_vma_lock_write(anon_vma);
 310        anon_vma_chain_link(vma, avc, anon_vma);
 311        anon_vma_unlock_write(anon_vma);
 312
 313        return 0;
 314
 315 out_error_free_anon_vma:
 316        put_anon_vma(anon_vma);
 317 out_error:
 318        unlink_anon_vmas(vma);
 319        return -ENOMEM;
 320}
 321
 322void unlink_anon_vmas(struct vm_area_struct *vma)
 323{
 324        struct anon_vma_chain *avc, *next;
 325        struct anon_vma *root = NULL;
 326
 327        /*
 328         * Unlink each anon_vma chained to the VMA.  This list is ordered
 329         * from newest to oldest, ensuring the root anon_vma gets freed last.
 330         */
 331        list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
 332                struct anon_vma *anon_vma = avc->anon_vma;
 333
 334                root = lock_anon_vma_root(root, anon_vma);
 335                anon_vma_interval_tree_remove(avc, &anon_vma->rb_root);
 336
 337                /*
 338                 * Leave empty anon_vmas on the list - we'll need
 339                 * to free them outside the lock.
 340                 */
 341                if (RB_EMPTY_ROOT(&anon_vma->rb_root))
 342                        continue;
 343
 344                list_del(&avc->same_vma);
 345                anon_vma_chain_free(avc);
 346        }
 347        unlock_anon_vma_root(root);
 348
 349        /*
 350         * Iterate the list once more, it now only contains empty and unlinked
 351         * anon_vmas, destroy them. Could not do before due to __put_anon_vma()
 352         * needing to write-acquire the anon_vma->root->rwsem.
 353         */
 354        list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
 355                struct anon_vma *anon_vma = avc->anon_vma;
 356
 357                put_anon_vma(anon_vma);
 358
 359                list_del(&avc->same_vma);
 360                anon_vma_chain_free(avc);
 361        }
 362}
 363
 364static void anon_vma_ctor(void *data)
 365{
 366        struct anon_vma *anon_vma = data;
 367
 368        init_rwsem(&anon_vma->rwsem);
 369        atomic_set(&anon_vma->refcount, 0);
 370        anon_vma->rb_root = RB_ROOT;
 371}
 372
 373void __init anon_vma_init(void)
 374{
 375        anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
 376                        0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
 377        anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
 378}
 379
 380/*
 381 * Getting a lock on a stable anon_vma from a page off the LRU is tricky!
 382 *
 383 * Since there is no serialization what so ever against page_remove_rmap()
 384 * the best this function can do is return a locked anon_vma that might
 385 * have been relevant to this page.
 386 *
 387 * The page might have been remapped to a different anon_vma or the anon_vma
 388 * returned may already be freed (and even reused).
 389 *
 390 * In case it was remapped to a different anon_vma, the new anon_vma will be a
 391 * child of the old anon_vma, and the anon_vma lifetime rules will therefore
 392 * ensure that any anon_vma obtained from the page will still be valid for as
 393 * long as we observe page_mapped() [ hence all those page_mapped() tests ].
 394 *
 395 * All users of this function must be very careful when walking the anon_vma
 396 * chain and verify that the page in question is indeed mapped in it
 397 * [ something equivalent to page_mapped_in_vma() ].
 398 *
 399 * Since anon_vma's slab is DESTROY_BY_RCU and we know from page_remove_rmap()
 400 * that the anon_vma pointer from page->mapping is valid if there is a
 401 * mapcount, we can dereference the anon_vma after observing those.
 402 */
 403struct anon_vma *page_get_anon_vma(struct page *page)
 404{
 405        struct anon_vma *anon_vma = NULL;
 406        unsigned long anon_mapping;
 407
 408        rcu_read_lock();
 409        anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
 410        if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
 411                goto out;
 412        if (!page_mapped(page))
 413                goto out;
 414
 415        anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
 416        if (!atomic_inc_not_zero(&anon_vma->refcount)) {
 417                anon_vma = NULL;
 418                goto out;
 419        }
 420
 421        /*
 422         * If this page is still mapped, then its anon_vma cannot have been
 423         * freed.  But if it has been unmapped, we have no security against the
 424         * anon_vma structure being freed and reused (for another anon_vma:
 425         * SLAB_DESTROY_BY_RCU guarantees that - so the atomic_inc_not_zero()
 426         * above cannot corrupt).
 427         */
 428        if (!page_mapped(page)) {
 429                put_anon_vma(anon_vma);
 430                anon_vma = NULL;
 431        }
 432out:
 433        rcu_read_unlock();
 434
 435        return anon_vma;
 436}
 437
 438/*
 439 * Similar to page_get_anon_vma() except it locks the anon_vma.
 440 *
 441 * Its a little more complex as it tries to keep the fast path to a single
 442 * atomic op -- the trylock. If we fail the trylock, we fall back to getting a
 443 * reference like with page_get_anon_vma() and then block on the mutex.
 444 */
 445struct anon_vma *page_lock_anon_vma_read(struct page *page)
 446{
 447        struct anon_vma *anon_vma = NULL;
 448        struct anon_vma *root_anon_vma;
 449        unsigned long anon_mapping;
 450
 451        rcu_read_lock();
 452        anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
 453        if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
 454                goto out;
 455        if (!page_mapped(page))
 456                goto out;
 457
 458        anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
 459        root_anon_vma = ACCESS_ONCE(anon_vma->root);
 460        if (down_read_trylock(&root_anon_vma->rwsem)) {
 461                /*
 462                 * If the page is still mapped, then this anon_vma is still
 463                 * its anon_vma, and holding the mutex ensures that it will
 464                 * not go away, see anon_vma_free().
 465                 */
 466                if (!page_mapped(page)) {
 467                        up_read(&root_anon_vma->rwsem);
 468                        anon_vma = NULL;
 469                }
 470                goto out;
 471        }
 472
 473        /* trylock failed, we got to sleep */
 474        if (!atomic_inc_not_zero(&anon_vma->refcount)) {
 475                anon_vma = NULL;
 476                goto out;
 477        }
 478
 479        if (!page_mapped(page)) {
 480                put_anon_vma(anon_vma);
 481                anon_vma = NULL;
 482                goto out;
 483        }
 484
 485        /* we pinned the anon_vma, its safe to sleep */
 486        rcu_read_unlock();
 487        anon_vma_lock_read(anon_vma);
 488
 489        if (atomic_dec_and_test(&anon_vma->refcount)) {
 490                /*
 491                 * Oops, we held the last refcount, release the lock
 492                 * and bail -- can't simply use put_anon_vma() because
 493                 * we'll deadlock on the anon_vma_lock_write() recursion.
 494                 */
 495                anon_vma_unlock_read(anon_vma);
 496                __put_anon_vma(anon_vma);
 497                anon_vma = NULL;
 498        }
 499
 500        return anon_vma;
 501
 502out:
 503        rcu_read_unlock();
 504        return anon_vma;
 505}
 506
 507void page_unlock_anon_vma_read(struct anon_vma *anon_vma)
 508{
 509        anon_vma_unlock_read(anon_vma);
 510}
 511
 512/*
 513 * At what user virtual address is page expected in @vma?
 514 */
 515static inline unsigned long
 516__vma_address(struct page *page, struct vm_area_struct *vma)
 517{
 518        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 519
 520        if (unlikely(is_vm_hugetlb_page(vma)))
 521                pgoff = page->index << huge_page_order(page_hstate(page));
 522
 523        return vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
 524}
 525
 526inline unsigned long
 527vma_address(struct page *page, struct vm_area_struct *vma)
 528{
 529        unsigned long address = __vma_address(page, vma);
 530
 531        /* page should be within @vma mapping range */
 532        VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
 533
 534        return address;
 535}
 536
 537/*
 538 * At what user virtual address is page expected in vma?
 539 * Caller should check the page is actually part of the vma.
 540 */
 541unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 542{
 543        unsigned long address;
 544        if (PageAnon(page)) {
 545                struct anon_vma *page__anon_vma = page_anon_vma(page);
 546                /*
 547                 * Note: swapoff's unuse_vma() is more efficient with this
 548                 * check, and needs it to match anon_vma when KSM is active.
 549                 */
 550                if (!vma->anon_vma || !page__anon_vma ||
 551                    vma->anon_vma->root != page__anon_vma->root)
 552                        return -EFAULT;
 553        } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
 554                if (!vma->vm_file ||
 555                    vma->vm_file->f_mapping != page->mapping)
 556                        return -EFAULT;
 557        } else
 558                return -EFAULT;
 559        address = __vma_address(page, vma);
 560        if (unlikely(address < vma->vm_start || address >= vma->vm_end))
 561                return -EFAULT;
 562        return address;
 563}
 564
 565pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address)
 566{
 567        pgd_t *pgd;
 568        pud_t *pud;
 569        pmd_t *pmd = NULL;
 570
 571        pgd = pgd_offset(mm, address);
 572        if (!pgd_present(*pgd))
 573                goto out;
 574
 575        pud = pud_offset(pgd, address);
 576        if (!pud_present(*pud))
 577                goto out;
 578
 579        pmd = pmd_offset(pud, address);
 580        if (!pmd_present(*pmd))
 581                pmd = NULL;
 582out:
 583        return pmd;
 584}
 585
 586/*
 587 * Check that @page is mapped at @address into @mm.
 588 *
 589 * If @sync is false, page_check_address may perform a racy check to avoid
 590 * the page table lock when the pte is not present (helpful when reclaiming
 591 * highly shared pages).
 592 *
 593 * On success returns with pte mapped and locked.
 594 */
 595pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
 596                          unsigned long address, spinlock_t **ptlp, int sync)
 597{
 598        pmd_t *pmd;
 599        pte_t *pte;
 600        spinlock_t *ptl;
 601
 602        if (unlikely(PageHuge(page))) {
 603                pte = huge_pte_offset(mm, address);
 604                ptl = &mm->page_table_lock;
 605                goto check;
 606        }
 607
 608        pmd = mm_find_pmd(mm, address);
 609        if (!pmd)
 610                return NULL;
 611
 612        if (pmd_trans_huge(*pmd))
 613                return NULL;
 614
 615        pte = pte_offset_map(pmd, address);
 616        /* Make a quick check before getting the lock */
 617        if (!sync && !pte_present(*pte)) {
 618                pte_unmap(pte);
 619                return NULL;
 620        }
 621
 622        ptl = pte_lockptr(mm, pmd);
 623check:
 624        spin_lock(ptl);
 625        if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
 626                *ptlp = ptl;
 627                return pte;
 628        }
 629        pte_unmap_unlock(pte, ptl);
 630        return NULL;
 631}
 632
 633/**
 634 * page_mapped_in_vma - check whether a page is really mapped in a VMA
 635 * @page: the page to test
 636 * @vma: the VMA to test
 637 *
 638 * Returns 1 if the page is mapped into the page tables of the VMA, 0
 639 * if the page is not mapped into the page tables of this VMA.  Only
 640 * valid for normal file or anonymous VMAs.
 641 */
 642int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
 643{
 644        unsigned long address;
 645        pte_t *pte;
 646        spinlock_t *ptl;
 647
 648        address = __vma_address(page, vma);
 649        if (unlikely(address < vma->vm_start || address >= vma->vm_end))
 650                return 0;
 651        pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
 652        if (!pte)                       /* the page is not in this mm */
 653                return 0;
 654        pte_unmap_unlock(pte, ptl);
 655
 656        return 1;
 657}
 658
 659/*
 660 * Subfunctions of page_referenced: page_referenced_one called
 661 * repeatedly from either page_referenced_anon or page_referenced_file.
 662 */
 663int page_referenced_one(struct page *page, struct vm_area_struct *vma,
 664                        unsigned long address, unsigned int *mapcount,
 665                        unsigned long *vm_flags)
 666{
 667        struct mm_struct *mm = vma->vm_mm;
 668        int referenced = 0;
 669
 670        if (unlikely(PageTransHuge(page))) {
 671                pmd_t *pmd;
 672
 673                spin_lock(&mm->page_table_lock);
 674                /*
 675                 * rmap might return false positives; we must filter
 676                 * these out using page_check_address_pmd().
 677                 */
 678                pmd = page_check_address_pmd(page, mm, address,
 679                                             PAGE_CHECK_ADDRESS_PMD_FLAG);
 680                if (!pmd) {
 681                        spin_unlock(&mm->page_table_lock);
 682                        goto out;
 683                }
 684
 685                if (vma->vm_flags & VM_LOCKED) {
 686                        spin_unlock(&mm->page_table_lock);
 687                        *mapcount = 0;  /* break early from loop */
 688                        *vm_flags |= VM_LOCKED;
 689                        goto out;
 690                }
 691
 692                /* go ahead even if the pmd is pmd_trans_splitting() */
 693                if (pmdp_clear_flush_young_notify(vma, address, pmd))
 694                        referenced++;
 695                spin_unlock(&mm->page_table_lock);
 696        } else {
 697                pte_t *pte;
 698                spinlock_t *ptl;
 699
 700                /*
 701                 * rmap might return false positives; we must filter
 702                 * these out using page_check_address().
 703                 */
 704                pte = page_check_address(page, mm, address, &ptl, 0);
 705                if (!pte)
 706                        goto out;
 707
 708                if (vma->vm_flags & VM_LOCKED) {
 709                        pte_unmap_unlock(pte, ptl);
 710                        *mapcount = 0;  /* break early from loop */
 711                        *vm_flags |= VM_LOCKED;
 712                        goto out;
 713                }
 714
 715                if (ptep_clear_flush_young_notify(vma, address, pte)) {
 716                        /*
 717                         * Don't treat a reference through a sequentially read
 718                         * mapping as such.  If the page has been used in
 719                         * another mapping, we will catch it; if this other
 720                         * mapping is already gone, the unmap path will have
 721                         * set PG_referenced or activated the page.
 722                         */
 723                        if (likely(!(vma->vm_flags & VM_SEQ_READ)))
 724                                referenced++;
 725                }
 726                pte_unmap_unlock(pte, ptl);
 727        }
 728
 729        (*mapcount)--;
 730
 731        if (referenced)
 732                *vm_flags |= vma->vm_flags;
 733out:
 734        return referenced;
 735}
 736
 737static int page_referenced_anon(struct page *page,
 738                                struct mem_cgroup *memcg,
 739                                unsigned long *vm_flags)
 740{
 741        unsigned int mapcount;
 742        struct anon_vma *anon_vma;
 743        pgoff_t pgoff;
 744        struct anon_vma_chain *avc;
 745        int referenced = 0;
 746
 747        anon_vma = page_lock_anon_vma_read(page);
 748        if (!anon_vma)
 749                return referenced;
 750
 751        mapcount = page_mapcount(page);
 752        pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 753        anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
 754                struct vm_area_struct *vma = avc->vma;
 755                unsigned long address = vma_address(page, vma);
 756                /*
 757                 * If we are reclaiming on behalf of a cgroup, skip
 758                 * counting on behalf of references from different
 759                 * cgroups
 760                 */
 761                if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
 762                        continue;
 763                referenced += page_referenced_one(page, vma, address,
 764                                                  &mapcount, vm_flags);
 765                if (!mapcount)
 766                        break;
 767        }
 768
 769        page_unlock_anon_vma_read(anon_vma);
 770        return referenced;
 771}
 772
 773/**
 774 * page_referenced_file - referenced check for object-based rmap
 775 * @page: the page we're checking references on.
 776 * @memcg: target memory control group
 777 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
 778 *
 779 * For an object-based mapped page, find all the places it is mapped and
 780 * check/clear the referenced flag.  This is done by following the page->mapping
 781 * pointer, then walking the chain of vmas it holds.  It returns the number
 782 * of references it found.
 783 *
 784 * This function is only called from page_referenced for object-based pages.
 785 */
 786static int page_referenced_file(struct page *page,
 787                                struct mem_cgroup *memcg,
 788                                unsigned long *vm_flags)
 789{
 790        unsigned int mapcount;
 791        struct address_space *mapping = page->mapping;
 792        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 793        struct vm_area_struct *vma;
 794        int referenced = 0;
 795
 796        /*
 797         * The caller's checks on page->mapping and !PageAnon have made
 798         * sure that this is a file page: the check for page->mapping
 799         * excludes the case just before it gets set on an anon page.
 800         */
 801        BUG_ON(PageAnon(page));
 802
 803        /*
 804         * The page lock not only makes sure that page->mapping cannot
 805         * suddenly be NULLified by truncation, it makes sure that the
 806         * structure at mapping cannot be freed and reused yet,
 807         * so we can safely take mapping->i_mmap_mutex.
 808         */
 809        BUG_ON(!PageLocked(page));
 810
 811        mutex_lock(&mapping->i_mmap_mutex);
 812
 813        /*
 814         * i_mmap_mutex does not stabilize mapcount at all, but mapcount
 815         * is more likely to be accurate if we note it after spinning.
 816         */
 817        mapcount = page_mapcount(page);
 818
 819        vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
 820                unsigned long address = vma_address(page, vma);
 821                /*
 822                 * If we are reclaiming on behalf of a cgroup, skip
 823                 * counting on behalf of references from different
 824                 * cgroups
 825                 */
 826                if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
 827                        continue;
 828                referenced += page_referenced_one(page, vma, address,
 829                                                  &mapcount, vm_flags);
 830                if (!mapcount)
 831                        break;
 832        }
 833
 834        mutex_unlock(&mapping->i_mmap_mutex);
 835        return referenced;
 836}
 837
 838/**
 839 * page_referenced - test if the page was referenced
 840 * @page: the page to test
 841 * @is_locked: caller holds lock on the page
 842 * @memcg: target memory cgroup
 843 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
 844 *
 845 * Quick test_and_clear_referenced for all mappings to a page,
 846 * returns the number of ptes which referenced the page.
 847 */
 848int page_referenced(struct page *page,
 849                    int is_locked,
 850                    struct mem_cgroup *memcg,
 851                    unsigned long *vm_flags)
 852{
 853        int referenced = 0;
 854        int we_locked = 0;
 855
 856        *vm_flags = 0;
 857        if (page_mapped(page) && page_rmapping(page)) {
 858                if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
 859                        we_locked = trylock_page(page);
 860                        if (!we_locked) {
 861                                referenced++;
 862                                goto out;
 863                        }
 864                }
 865                if (unlikely(PageKsm(page)))
 866                        referenced += page_referenced_ksm(page, memcg,
 867                                                                vm_flags);
 868                else if (PageAnon(page))
 869                        referenced += page_referenced_anon(page, memcg,
 870                                                                vm_flags);
 871                else if (page->mapping)
 872                        referenced += page_referenced_file(page, memcg,
 873                                                                vm_flags);
 874                if (we_locked)
 875                        unlock_page(page);
 876
 877                if (page_test_and_clear_young(page_to_pfn(page)))
 878                        referenced++;
 879        }
 880out:
 881        return referenced;
 882}
 883
 884static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
 885                            unsigned long address)
 886{
 887        struct mm_struct *mm = vma->vm_mm;
 888        pte_t *pte;
 889        spinlock_t *ptl;
 890        int ret = 0;
 891
 892        pte = page_check_address(page, mm, address, &ptl, 1);
 893        if (!pte)
 894                goto out;
 895
 896        if (pte_dirty(*pte) || pte_write(*pte)) {
 897                pte_t entry;
 898
 899                flush_cache_page(vma, address, pte_pfn(*pte));
 900                entry = ptep_clear_flush(vma, address, pte);
 901                entry = pte_wrprotect(entry);
 902                entry = pte_mkclean(entry);
 903                set_pte_at(mm, address, pte, entry);
 904                ret = 1;
 905        }
 906
 907        pte_unmap_unlock(pte, ptl);
 908
 909        if (ret)
 910                mmu_notifier_invalidate_page(mm, address);
 911out:
 912        return ret;
 913}
 914
 915static int page_mkclean_file(struct address_space *mapping, struct page *page)
 916{
 917        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 918        struct vm_area_struct *vma;
 919        int ret = 0;
 920
 921        BUG_ON(PageAnon(page));
 922
 923        mutex_lock(&mapping->i_mmap_mutex);
 924        vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
 925                if (vma->vm_flags & VM_SHARED) {
 926                        unsigned long address = vma_address(page, vma);
 927                        ret += page_mkclean_one(page, vma, address);
 928                }
 929        }
 930        mutex_unlock(&mapping->i_mmap_mutex);
 931        return ret;
 932}
 933
 934int page_mkclean(struct page *page)
 935{
 936        int ret = 0;
 937
 938        BUG_ON(!PageLocked(page));
 939
 940        if (page_mapped(page)) {
 941                struct address_space *mapping = page_mapping(page);
 942                if (mapping)
 943                        ret = page_mkclean_file(mapping, page);
 944        }
 945
 946        return ret;
 947}
 948EXPORT_SYMBOL_GPL(page_mkclean);
 949
 950/**
 951 * page_move_anon_rmap - move a page to our anon_vma
 952 * @page:       the page to move to our anon_vma
 953 * @vma:        the vma the page belongs to
 954 * @address:    the user virtual address mapped
 955 *
 956 * When a page belongs exclusively to one process after a COW event,
 957 * that page can be moved into the anon_vma that belongs to just that
 958 * process, so the rmap code will not search the parent or sibling
 959 * processes.
 960 */
 961void page_move_anon_rmap(struct page *page,
 962        struct vm_area_struct *vma, unsigned long address)
 963{
 964        struct anon_vma *anon_vma = vma->anon_vma;
 965
 966        VM_BUG_ON(!PageLocked(page));
 967        VM_BUG_ON(!anon_vma);
 968        VM_BUG_ON(page->index != linear_page_index(vma, address));
 969
 970        anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
 971        page->mapping = (struct address_space *) anon_vma;
 972}
 973
 974/**
 975 * __page_set_anon_rmap - set up new anonymous rmap
 976 * @page:       Page to add to rmap     
 977 * @vma:        VM area to add page to.
 978 * @address:    User virtual address of the mapping     
 979 * @exclusive:  the page is exclusively owned by the current process
 980 */
 981static void __page_set_anon_rmap(struct page *page,
 982        struct vm_area_struct *vma, unsigned long address, int exclusive)
 983{
 984        struct anon_vma *anon_vma = vma->anon_vma;
 985
 986        BUG_ON(!anon_vma);
 987
 988        if (PageAnon(page))
 989                return;
 990
 991        /*
 992         * If the page isn't exclusively mapped into this vma,
 993         * we must use the _oldest_ possible anon_vma for the
 994         * page mapping!
 995         */
 996        if (!exclusive)
 997                anon_vma = anon_vma->root;
 998
 999        anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1000        page->mapping = (struct address_space *) anon_vma;
1001        page->index = linear_page_index(vma, address);
1002}
1003
1004/**
1005 * __page_check_anon_rmap - sanity check anonymous rmap addition
1006 * @page:       the page to add the mapping to
1007 * @vma:        the vm area in which the mapping is added
1008 * @address:    the user virtual address mapped
1009 */
1010static void __page_check_anon_rmap(struct page *page,
1011        struct vm_area_struct *vma, unsigned long address)
1012{
1013#ifdef CONFIG_DEBUG_VM
1014        /*
1015         * The page's anon-rmap details (mapping and index) are guaranteed to
1016         * be set up correctly at this point.
1017         *
1018         * We have exclusion against page_add_anon_rmap because the caller
1019         * always holds the page locked, except if called from page_dup_rmap,
1020         * in which case the page is already known to be setup.
1021         *
1022         * We have exclusion against page_add_new_anon_rmap because those pages
1023         * are initially only visible via the pagetables, and the pte is locked
1024         * over the call to page_add_new_anon_rmap.
1025         */
1026        BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
1027        BUG_ON(page->index != linear_page_index(vma, address));
1028#endif
1029}
1030
1031/**
1032 * page_add_anon_rmap - add pte mapping to an anonymous page
1033 * @page:       the page to add the mapping to
1034 * @vma:        the vm area in which the mapping is added
1035 * @address:    the user virtual address mapped
1036 *
1037 * The caller needs to hold the pte lock, and the page must be locked in
1038 * the anon_vma case: to serialize mapping,index checking after setting,
1039 * and to ensure that PageAnon is not being upgraded racily to PageKsm
1040 * (but PageKsm is never downgraded to PageAnon).
1041 */
1042void page_add_anon_rmap(struct page *page,
1043        struct vm_area_struct *vma, unsigned long address)
1044{
1045        do_page_add_anon_rmap(page, vma, address, 0);
1046}
1047
1048/*
1049 * Special version of the above for do_swap_page, which often runs
1050 * into pages that are exclusively owned by the current process.
1051 * Everybody else should continue to use page_add_anon_rmap above.
1052 */
1053void do_page_add_anon_rmap(struct page *page,
1054        struct vm_area_struct *vma, unsigned long address, int exclusive)
1055{
1056        int first = atomic_inc_and_test(&page->_mapcount);
1057        if (first) {
1058                if (!PageTransHuge(page))
1059                        __inc_zone_page_state(page, NR_ANON_PAGES);
1060                else
1061                        __inc_zone_page_state(page,
1062                                              NR_ANON_TRANSPARENT_HUGEPAGES);
1063        }
1064        if (unlikely(PageKsm(page)))
1065                return;
1066
1067        VM_BUG_ON(!PageLocked(page));
1068        /* address might be in next vma when migration races vma_adjust */
1069        if (first)
1070                __page_set_anon_rmap(page, vma, address, exclusive);
1071        else
1072                __page_check_anon_rmap(page, vma, address);
1073}
1074
1075/**
1076 * page_add_new_anon_rmap - add pte mapping to a new anonymous page
1077 * @page:       the page to add the mapping to
1078 * @vma:        the vm area in which the mapping is added
1079 * @address:    the user virtual address mapped
1080 *
1081 * Same as page_add_anon_rmap but must only be called on *new* pages.
1082 * This means the inc-and-test can be bypassed.
1083 * Page does not have to be locked.
1084 */
1085void page_add_new_anon_rmap(struct page *page,
1086        struct vm_area_struct *vma, unsigned long address)
1087{
1088        VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
1089        SetPageSwapBacked(page);
1090        atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
1091        if (!PageTransHuge(page))
1092                __inc_zone_page_state(page, NR_ANON_PAGES);
1093        else
1094                __inc_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
1095        __page_set_anon_rmap(page, vma, address, 1);
1096        if (!mlocked_vma_newpage(vma, page)) {
1097                SetPageActive(page);
1098                lru_cache_add(page);
1099        } else
1100                add_page_to_unevictable_list(page);
1101}
1102
1103/**
1104 * page_add_file_rmap - add pte mapping to a file page
1105 * @page: the page to add the mapping to
1106 *
1107 * The caller needs to hold the pte lock.
1108 */
1109void page_add_file_rmap(struct page *page)
1110{
1111        bool locked;
1112        unsigned long flags;
1113
1114        mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1115        if (atomic_inc_and_test(&page->_mapcount)) {
1116                __inc_zone_page_state(page, NR_FILE_MAPPED);
1117                mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
1118        }
1119        mem_cgroup_end_update_page_stat(page, &locked, &flags);
1120}
1121
1122/**
1123 * page_remove_rmap - take down pte mapping from a page
1124 * @page: page to remove mapping from
1125 *
1126 * The caller needs to hold the pte lock.
1127 */
1128void page_remove_rmap(struct page *page)
1129{
1130        bool anon = PageAnon(page);
1131        bool locked;
1132        unsigned long flags;
1133
1134        /*
1135         * The anon case has no mem_cgroup page_stat to update; but may
1136         * uncharge_page() below, where the lock ordering can deadlock if
1137         * we hold the lock against page_stat move: so avoid it on anon.
1138         */
1139        if (!anon)
1140                mem_cgroup_begin_update_page_stat(page, &locked, &flags);
1141
1142        /* page still mapped by someone else? */
1143        if (!atomic_add_negative(-1, &page->_mapcount))
1144                goto out;
1145
1146        /*
1147         * Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
1148         * and not charged by memcg for now.
1149         */
1150        if (unlikely(PageHuge(page)))
1151                goto out;
1152        if (anon) {
1153                mem_cgroup_uncharge_page(page);
1154                if (!PageTransHuge(page))
1155                        __dec_zone_page_state(page, NR_ANON_PAGES);
1156                else
1157                        __dec_zone_page_state(page,
1158                                              NR_ANON_TRANSPARENT_HUGEPAGES);
1159        } else {
1160                __dec_zone_page_state(page, NR_FILE_MAPPED);
1161                mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
1162                mem_cgroup_end_update_page_stat(page, &locked, &flags);
1163        }
1164        if (unlikely(PageMlocked(page)))
1165                clear_page_mlock(page);
1166        /*
1167         * It would be tidy to reset the PageAnon mapping here,
1168         * but that might overwrite a racing page_add_anon_rmap
1169         * which increments mapcount after us but sets mapping
1170         * before us: so leave the reset to free_hot_cold_page,
1171         * and remember that it's only reliable while mapped.
1172         * Leaving it set also helps swapoff to reinstate ptes
1173         * faster for those pages still in swapcache.
1174         */
1175        return;
1176out:
1177        if (!anon)
1178                mem_cgroup_end_update_page_stat(page, &locked, &flags);
1179}
1180
1181/*
1182 * Subfunctions of try_to_unmap: try_to_unmap_one called
1183 * repeatedly from try_to_unmap_ksm, try_to_unmap_anon or try_to_unmap_file.
1184 */
1185int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
1186                     unsigned long address, enum ttu_flags flags)
1187{
1188        struct mm_struct *mm = vma->vm_mm;
1189        pte_t *pte;
1190        pte_t pteval;
1191        spinlock_t *ptl;
1192        int ret = SWAP_AGAIN;
1193
1194        pte = page_check_address(page, mm, address, &ptl, 0);
1195        if (!pte)
1196                goto out;
1197
1198        /*
1199         * If the page is mlock()d, we cannot swap it out.
1200         * If it's recently referenced (perhaps page_referenced
1201         * skipped over this mm) then we should reactivate it.
1202         */
1203        if (!(flags & TTU_IGNORE_MLOCK)) {
1204                if (vma->vm_flags & VM_LOCKED)
1205                        goto out_mlock;
1206
1207                if (TTU_ACTION(flags) == TTU_MUNLOCK)
1208                        goto out_unmap;
1209        }
1210        if (!(flags & TTU_IGNORE_ACCESS)) {
1211                if (ptep_clear_flush_young_notify(vma, address, pte)) {
1212                        ret = SWAP_FAIL;
1213                        goto out_unmap;
1214                }
1215        }
1216
1217        /* Nuke the page table entry. */
1218        flush_cache_page(vma, address, page_to_pfn(page));
1219        pteval = ptep_clear_flush(vma, address, pte);
1220
1221        /* Move the dirty bit to the physical page now the pte is gone. */
1222        if (pte_dirty(pteval))
1223                set_page_dirty(page);
1224
1225        /* Update high watermark before we lower rss */
1226        update_hiwater_rss(mm);
1227
1228        if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
1229                if (!PageHuge(page)) {
1230                        if (PageAnon(page))
1231                                dec_mm_counter(mm, MM_ANONPAGES);
1232                        else
1233                                dec_mm_counter(mm, MM_FILEPAGES);
1234                }
1235                set_pte_at(mm, address, pte,
1236                           swp_entry_to_pte(make_hwpoison_entry(page)));
1237        } else if (PageAnon(page)) {
1238                swp_entry_t entry = { .val = page_private(page) };
1239                pte_t swp_pte;
1240
1241                if (PageSwapCache(page)) {
1242                        /*
1243                         * Store the swap location in the pte.
1244                         * See handle_pte_fault() ...
1245                         */
1246                        if (swap_duplicate(entry) < 0) {
1247                                set_pte_at(mm, address, pte, pteval);
1248                                ret = SWAP_FAIL;
1249                                goto out_unmap;
1250                        }
1251                        if (list_empty(&mm->mmlist)) {
1252                                spin_lock(&mmlist_lock);
1253                                if (list_empty(&mm->mmlist))
1254                                        list_add(&mm->mmlist, &init_mm.mmlist);
1255                                spin_unlock(&mmlist_lock);
1256                        }
1257                        dec_mm_counter(mm, MM_ANONPAGES);
1258                        inc_mm_counter(mm, MM_SWAPENTS);
1259                } else if (IS_ENABLED(CONFIG_MIGRATION)) {
1260                        /*
1261                         * Store the pfn of the page in a special migration
1262                         * pte. do_swap_page() will wait until the migration
1263                         * pte is removed and then restart fault handling.
1264                         */
1265                        BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
1266                        entry = make_migration_entry(page, pte_write(pteval));
1267                }
1268                swp_pte = swp_entry_to_pte(entry);
1269                if (pte_soft_dirty(pteval))
1270                        swp_pte = pte_swp_mksoft_dirty(swp_pte);
1271                set_pte_at(mm, address, pte, swp_pte);
1272                BUG_ON(pte_file(*pte));
1273        } else if (IS_ENABLED(CONFIG_MIGRATION) &&
1274                   (TTU_ACTION(flags) == TTU_MIGRATION)) {
1275                /* Establish migration entry for a file page */
1276                swp_entry_t entry;
1277                entry = make_migration_entry(page, pte_write(pteval));
1278                set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
1279        } else
1280                dec_mm_counter(mm, MM_FILEPAGES);
1281
1282        page_remove_rmap(page);
1283        page_cache_release(page);
1284
1285out_unmap:
1286        pte_unmap_unlock(pte, ptl);
1287        if (ret != SWAP_FAIL)
1288                mmu_notifier_invalidate_page(mm, address);
1289out:
1290        return ret;
1291
1292out_mlock:
1293        pte_unmap_unlock(pte, ptl);
1294
1295
1296        /*
1297         * We need mmap_sem locking, Otherwise VM_LOCKED check makes
1298         * unstable result and race. Plus, We can't wait here because
1299         * we now hold anon_vma->rwsem or mapping->i_mmap_mutex.
1300         * if trylock failed, the page remain in evictable lru and later
1301         * vmscan could retry to move the page to unevictable lru if the
1302         * page is actually mlocked.
1303         */
1304        if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1305                if (vma->vm_flags & VM_LOCKED) {
1306                        mlock_vma_page(page);
1307                        ret = SWAP_MLOCK;
1308                }
1309                up_read(&vma->vm_mm->mmap_sem);
1310        }
1311        return ret;
1312}
1313
1314/*
1315 * objrmap doesn't work for nonlinear VMAs because the assumption that
1316 * offset-into-file correlates with offset-into-virtual-addresses does not hold.
1317 * Consequently, given a particular page and its ->index, we cannot locate the
1318 * ptes which are mapping that page without an exhaustive linear search.
1319 *
1320 * So what this code does is a mini "virtual scan" of each nonlinear VMA which
1321 * maps the file to which the target page belongs.  The ->vm_private_data field
1322 * holds the current cursor into that scan.  Successive searches will circulate
1323 * around the vma's virtual address space.
1324 *
1325 * So as more replacement pressure is applied to the pages in a nonlinear VMA,
1326 * more scanning pressure is placed against them as well.   Eventually pages
1327 * will become fully unmapped and are eligible for eviction.
1328 *
1329 * For very sparsely populated VMAs this is a little inefficient - chances are
1330 * there there won't be many ptes located within the scan cluster.  In this case
1331 * maybe we could scan further - to the end of the pte page, perhaps.
1332 *
1333 * Mlocked pages:  check VM_LOCKED under mmap_sem held for read, if we can
1334 * acquire it without blocking.  If vma locked, mlock the pages in the cluster,
1335 * rather than unmapping them.  If we encounter the "check_page" that vmscan is
1336 * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
1337 */
1338#define CLUSTER_SIZE    min(32*PAGE_SIZE, PMD_SIZE)
1339#define CLUSTER_MASK    (~(CLUSTER_SIZE - 1))
1340
1341static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
1342                struct vm_area_struct *vma, struct page *check_page)
1343{
1344        struct mm_struct *mm = vma->vm_mm;
1345        pmd_t *pmd;
1346        pte_t *pte;
1347        pte_t pteval;
1348        spinlock_t *ptl;
1349        struct page *page;
1350        unsigned long address;
1351        unsigned long mmun_start;       /* For mmu_notifiers */
1352        unsigned long mmun_end;         /* For mmu_notifiers */
1353        unsigned long end;
1354        int ret = SWAP_AGAIN;
1355        int locked_vma = 0;
1356
1357        address = (vma->vm_start + cursor) & CLUSTER_MASK;
1358        end = address + CLUSTER_SIZE;
1359        if (address < vma->vm_start)
1360                address = vma->vm_start;
1361        if (end > vma->vm_end)
1362                end = vma->vm_end;
1363
1364        pmd = mm_find_pmd(mm, address);
1365        if (!pmd)
1366                return ret;
1367
1368        mmun_start = address;
1369        mmun_end   = end;
1370        mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
1371
1372        /*
1373         * If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
1374         * keep the sem while scanning the cluster for mlocking pages.
1375         */
1376        if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
1377                locked_vma = (vma->vm_flags & VM_LOCKED);
1378                if (!locked_vma)
1379                        up_read(&vma->vm_mm->mmap_sem); /* don't need it */
1380        }
1381
1382        pte = pte_offset_map_lock(mm, pmd, address, &ptl);
1383
1384        /* Update high watermark before we lower rss */
1385        update_hiwater_rss(mm);
1386
1387        for (; address < end; pte++, address += PAGE_SIZE) {
1388                if (!pte_present(*pte))
1389                        continue;
1390                page = vm_normal_page(vma, address, *pte);
1391                BUG_ON(!page || PageAnon(page));
1392
1393                if (locked_vma) {
1394                        mlock_vma_page(page);   /* no-op if already mlocked */
1395                        if (page == check_page)
1396                                ret = SWAP_MLOCK;
1397                        continue;       /* don't unmap */
1398                }
1399
1400                if (ptep_clear_flush_young_notify(vma, address, pte))
1401                        continue;
1402
1403                /* Nuke the page table entry. */
1404                flush_cache_page(vma, address, pte_pfn(*pte));
1405                pteval = ptep_clear_flush(vma, address, pte);
1406
1407                /* If nonlinear, store the file page offset in the pte. */
1408                if (page->index != linear_page_index(vma, address)) {
1409                        pte_t ptfile = pgoff_to_pte(page->index);
1410                        if (pte_soft_dirty(pteval))
1411                                pte_file_mksoft_dirty(ptfile);
1412                        set_pte_at(mm, address, pte, ptfile);
1413                }
1414
1415                /* Move the dirty bit to the physical page now the pte is gone. */
1416                if (pte_dirty(pteval))
1417                        set_page_dirty(page);
1418
1419                page_remove_rmap(page);
1420                page_cache_release(page);
1421                dec_mm_counter(mm, MM_FILEPAGES);
1422                (*mapcount)--;
1423        }
1424        pte_unmap_unlock(pte - 1, ptl);
1425        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
1426        if (locked_vma)
1427                up_read(&vma->vm_mm->mmap_sem);
1428        return ret;
1429}
1430
1431bool is_vma_temporary_stack(struct vm_area_struct *vma)
1432{
1433        int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
1434
1435        if (!maybe_stack)
1436                return false;
1437
1438        if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
1439                                                VM_STACK_INCOMPLETE_SETUP)
1440                return true;
1441
1442        return false;
1443}
1444
1445/**
1446 * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
1447 * rmap method
1448 * @page: the page to unmap/unlock
1449 * @flags: action and flags
1450 *
1451 * Find all the mappings of a page using the mapping pointer and the vma chains
1452 * contained in the anon_vma struct it points to.
1453 *
1454 * This function is only called from try_to_unmap/try_to_munlock for
1455 * anonymous pages.
1456 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1457 * where the page was found will be held for write.  So, we won't recheck
1458 * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1459 * 'LOCKED.
1460 */
1461static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
1462{
1463        struct anon_vma *anon_vma;
1464        pgoff_t pgoff;
1465        struct anon_vma_chain *avc;
1466        int ret = SWAP_AGAIN;
1467
1468        anon_vma = page_lock_anon_vma_read(page);
1469        if (!anon_vma)
1470                return ret;
1471
1472        pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1473        anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1474                struct vm_area_struct *vma = avc->vma;
1475                unsigned long address;
1476
1477                /*
1478                 * During exec, a temporary VMA is setup and later moved.
1479                 * The VMA is moved under the anon_vma lock but not the
1480                 * page tables leading to a race where migration cannot
1481                 * find the migration ptes. Rather than increasing the
1482                 * locking requirements of exec(), migration skips
1483                 * temporary VMAs until after exec() completes.
1484                 */
1485                if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
1486                                is_vma_temporary_stack(vma))
1487                        continue;
1488
1489                address = vma_address(page, vma);
1490                ret = try_to_unmap_one(page, vma, address, flags);
1491                if (ret != SWAP_AGAIN || !page_mapped(page))
1492                        break;
1493        }
1494
1495        page_unlock_anon_vma_read(anon_vma);
1496        return ret;
1497}
1498
1499/**
1500 * try_to_unmap_file - unmap/unlock file page using the object-based rmap method
1501 * @page: the page to unmap/unlock
1502 * @flags: action and flags
1503 *
1504 * Find all the mappings of a page using the mapping pointer and the vma chains
1505 * contained in the address_space struct it points to.
1506 *
1507 * This function is only called from try_to_unmap/try_to_munlock for
1508 * object-based pages.
1509 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma
1510 * where the page was found will be held for write.  So, we won't recheck
1511 * vm_flags for that VMA.  That should be OK, because that vma shouldn't be
1512 * 'LOCKED.
1513 */
1514static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
1515{
1516        struct address_space *mapping = page->mapping;
1517        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1518        struct vm_area_struct *vma;
1519        int ret = SWAP_AGAIN;
1520        unsigned long cursor;
1521        unsigned long max_nl_cursor = 0;
1522        unsigned long max_nl_size = 0;
1523        unsigned int mapcount;
1524
1525        if (PageHuge(page))
1526                pgoff = page->index << compound_order(page);
1527
1528        mutex_lock(&mapping->i_mmap_mutex);
1529        vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1530                unsigned long address = vma_address(page, vma);
1531                ret = try_to_unmap_one(page, vma, address, flags);
1532                if (ret != SWAP_AGAIN || !page_mapped(page))
1533                        goto out;
1534        }
1535
1536        if (list_empty(&mapping->i_mmap_nonlinear))
1537                goto out;
1538
1539        /*
1540         * We don't bother to try to find the munlocked page in nonlinears.
1541         * It's costly. Instead, later, page reclaim logic may call
1542         * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.
1543         */
1544        if (TTU_ACTION(flags) == TTU_MUNLOCK)
1545                goto out;
1546
1547        list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1548                                                        shared.nonlinear) {
1549                cursor = (unsigned long) vma->vm_private_data;
1550                if (cursor > max_nl_cursor)
1551                        max_nl_cursor = cursor;
1552                cursor = vma->vm_end - vma->vm_start;
1553                if (cursor > max_nl_size)
1554                        max_nl_size = cursor;
1555        }
1556
1557        if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
1558                ret = SWAP_FAIL;
1559                goto out;
1560        }
1561
1562        /*
1563         * We don't try to search for this page in the nonlinear vmas,
1564         * and page_referenced wouldn't have found it anyway.  Instead
1565         * just walk the nonlinear vmas trying to age and unmap some.
1566         * The mapcount of the page we came in with is irrelevant,
1567         * but even so use it as a guide to how hard we should try?
1568         */
1569        mapcount = page_mapcount(page);
1570        if (!mapcount)
1571                goto out;
1572        cond_resched();
1573
1574        max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
1575        if (max_nl_cursor == 0)
1576                max_nl_cursor = CLUSTER_SIZE;
1577
1578        do {
1579                list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
1580                                                        shared.nonlinear) {
1581                        cursor = (unsigned long) vma->vm_private_data;
1582                        while ( cursor < max_nl_cursor &&
1583                                cursor < vma->vm_end - vma->vm_start) {
1584                                if (try_to_unmap_cluster(cursor, &mapcount,
1585                                                vma, page) == SWAP_MLOCK)
1586                                        ret = SWAP_MLOCK;
1587                                cursor += CLUSTER_SIZE;
1588                                vma->vm_private_data = (void *) cursor;
1589                                if ((int)mapcount <= 0)
1590                                        goto out;
1591                        }
1592                        vma->vm_private_data = (void *) max_nl_cursor;
1593                }
1594                cond_resched();
1595                max_nl_cursor += CLUSTER_SIZE;
1596        } while (max_nl_cursor <= max_nl_size);
1597
1598        /*
1599         * Don't loop forever (perhaps all the remaining pages are
1600         * in locked vmas).  Reset cursor on all unreserved nonlinear
1601         * vmas, now forgetting on which ones it had fallen behind.
1602         */
1603        list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.nonlinear)
1604                vma->vm_private_data = NULL;
1605out:
1606        mutex_unlock(&mapping->i_mmap_mutex);
1607        return ret;
1608}
1609
1610/**
1611 * try_to_unmap - try to remove all page table mappings to a page
1612 * @page: the page to get unmapped
1613 * @flags: action and flags
1614 *
1615 * Tries to remove all the page table entries which are mapping this
1616 * page, used in the pageout path.  Caller must hold the page lock.
1617 * Return values are:
1618 *
1619 * SWAP_SUCCESS - we succeeded in removing all mappings
1620 * SWAP_AGAIN   - we missed a mapping, try again later
1621 * SWAP_FAIL    - the page is unswappable
1622 * SWAP_MLOCK   - page is mlocked.
1623 */
1624int try_to_unmap(struct page *page, enum ttu_flags flags)
1625{
1626        int ret;
1627
1628        BUG_ON(!PageLocked(page));
1629        VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
1630
1631        if (unlikely(PageKsm(page)))
1632                ret = try_to_unmap_ksm(page, flags);
1633        else if (PageAnon(page))
1634                ret = try_to_unmap_anon(page, flags);
1635        else
1636                ret = try_to_unmap_file(page, flags);
1637        if (ret != SWAP_MLOCK && !page_mapped(page))
1638                ret = SWAP_SUCCESS;
1639        return ret;
1640}
1641
1642/**
1643 * try_to_munlock - try to munlock a page
1644 * @page: the page to be munlocked
1645 *
1646 * Called from munlock code.  Checks all of the VMAs mapping the page
1647 * to make sure nobody else has this page mlocked. The page will be
1648 * returned with PG_mlocked cleared if no other vmas have it mlocked.
1649 *
1650 * Return values are:
1651 *
1652 * SWAP_AGAIN   - no vma is holding page mlocked, or,
1653 * SWAP_AGAIN   - page mapped in mlocked vma -- couldn't acquire mmap sem
1654 * SWAP_FAIL    - page cannot be located at present
1655 * SWAP_MLOCK   - page is now mlocked.
1656 */
1657int try_to_munlock(struct page *page)
1658{
1659        VM_BUG_ON(!PageLocked(page) || PageLRU(page));
1660
1661        if (unlikely(PageKsm(page)))
1662                return try_to_unmap_ksm(page, TTU_MUNLOCK);
1663        else if (PageAnon(page))
1664                return try_to_unmap_anon(page, TTU_MUNLOCK);
1665        else
1666                return try_to_unmap_file(page, TTU_MUNLOCK);
1667}
1668
1669void __put_anon_vma(struct anon_vma *anon_vma)
1670{
1671        struct anon_vma *root = anon_vma->root;
1672
1673        if (root != anon_vma && atomic_dec_and_test(&root->refcount))
1674                anon_vma_free(root);
1675
1676        anon_vma_free(anon_vma);
1677}
1678
1679#ifdef CONFIG_MIGRATION
1680/*
1681 * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
1682 * Called by migrate.c to remove migration ptes, but might be used more later.
1683 */
1684static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
1685                struct vm_area_struct *, unsigned long, void *), void *arg)
1686{
1687        struct anon_vma *anon_vma;
1688        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1689        struct anon_vma_chain *avc;
1690        int ret = SWAP_AGAIN;
1691
1692        /*
1693         * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read()
1694         * because that depends on page_mapped(); but not all its usages
1695         * are holding mmap_sem. Users without mmap_sem are required to
1696         * take a reference count to prevent the anon_vma disappearing
1697         */
1698        anon_vma = page_anon_vma(page);
1699        if (!anon_vma)
1700                return ret;
1701        anon_vma_lock_read(anon_vma);
1702        anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
1703                struct vm_area_struct *vma = avc->vma;
1704                unsigned long address = vma_address(page, vma);
1705                ret = rmap_one(page, vma, address, arg);
1706                if (ret != SWAP_AGAIN)
1707                        break;
1708        }
1709        anon_vma_unlock_read(anon_vma);
1710        return ret;
1711}
1712
1713static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
1714                struct vm_area_struct *, unsigned long, void *), void *arg)
1715{
1716        struct address_space *mapping = page->mapping;
1717        pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
1718        struct vm_area_struct *vma;
1719        int ret = SWAP_AGAIN;
1720
1721        if (!mapping)
1722                return ret;
1723        mutex_lock(&mapping->i_mmap_mutex);
1724        vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
1725                unsigned long address = vma_address(page, vma);
1726                ret = rmap_one(page, vma, address, arg);
1727                if (ret != SWAP_AGAIN)
1728                        break;
1729        }
1730        /*
1731         * No nonlinear handling: being always shared, nonlinear vmas
1732         * never contain migration ptes.  Decide what to do about this
1733         * limitation to linear when we need rmap_walk() on nonlinear.
1734         */
1735        mutex_unlock(&mapping->i_mmap_mutex);
1736        return ret;
1737}
1738
1739int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
1740                struct vm_area_struct *, unsigned long, void *), void *arg)
1741{
1742        VM_BUG_ON(!PageLocked(page));
1743
1744        if (unlikely(PageKsm(page)))
1745                return rmap_walk_ksm(page, rmap_one, arg);
1746        else if (PageAnon(page))
1747                return rmap_walk_anon(page, rmap_one, arg);
1748        else
1749                return rmap_walk_file(page, rmap_one, arg);
1750}
1751#endif /* CONFIG_MIGRATION */
1752
1753#ifdef CONFIG_HUGETLB_PAGE
1754/*
1755 * The following three functions are for anonymous (private mapped) hugepages.
1756 * Unlike common anonymous pages, anonymous hugepages have no accounting code
1757 * and no lru code, because we handle hugepages differently from common pages.
1758 */
1759static void __hugepage_set_anon_rmap(struct page *page,
1760        struct vm_area_struct *vma, unsigned long address, int exclusive)
1761{
1762        struct anon_vma *anon_vma = vma->anon_vma;
1763
1764        BUG_ON(!anon_vma);
1765
1766        if (PageAnon(page))
1767                return;
1768        if (!exclusive)
1769                anon_vma = anon_vma->root;
1770
1771        anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
1772        page->mapping = (struct address_space *) anon_vma;
1773        page->index = linear_page_index(vma, address);
1774}
1775
1776void hugepage_add_anon_rmap(struct page *page,
1777                            struct vm_area_struct *vma, unsigned long address)
1778{
1779        struct anon_vma *anon_vma = vma->anon_vma;
1780        int first;
1781
1782        BUG_ON(!PageLocked(page));
1783        BUG_ON(!anon_vma);
1784        /* address might be in next vma when migration races vma_adjust */
1785        first = atomic_inc_and_test(&page->_mapcount);
1786        if (first)
1787                __hugepage_set_anon_rmap(page, vma, address, 0);
1788}
1789
1790void hugepage_add_new_anon_rmap(struct page *page,
1791                        struct vm_area_struct *vma, unsigned long address)
1792{
1793        BUG_ON(address < vma->vm_start || address >= vma->vm_end);
1794        atomic_set(&page->_mapcount, 0);
1795        __hugepage_set_anon_rmap(page, vma, address, 1);
1796}
1797#endif /* CONFIG_HUGETLB_PAGE */
1798
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