include/linux/pagemap.h

   1 #ifndef _LINUX_PAGEMAP_H
   2 #define _LINUX_PAGEMAP_H
   3
   4 /*
   5  * Copyright 1995 Linus Torvalds
   6  */
   7 #include <linux/mm.h>
   8 #include <linux/fs.h>
   9 #include <linux/list.h>
  10 #include <linux/highmem.h>
  11 #include <linux/compiler.h>
  12 #include <asm/uaccess.h>
  13 #include <linux/gfp.h>
  14 #include <linux/bitops.h>
  15 #include <linux/hardirq.h> /* for in_interrupt() */
  16
  17 /*
  18  * Bits in mapping->flags.  The lower __GFP_BITS_SHIFT bits are the page
  19  * allocation mode flags.
  20  */
  21 enum mapping_flags {
  22         AS_EIO          = __GFP_BITS_SHIFT + 0, /* IO error on async write */
  23         AS_ENOSPC       = __GFP_BITS_SHIFT + 1, /* ENOSPC on async write */
  24         AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
  25         AS_UNEVICTABLE  = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
  26 };
  27
  28 static inline void mapping_set_error(struct address_space *mapping, int error)
  29 {
  30         if (unlikely(error)) {
  31                 if (error == -ENOSPC)
  32                         set_bit(AS_ENOSPC, &mapping->flags);
  33                 else
  34                         set_bit(AS_EIO, &mapping->flags);
  35         }
  36 }
  37
  38 static inline void mapping_set_unevictable(struct address_space *mapping)
  39 {
  40         set_bit(AS_UNEVICTABLE, &mapping->flags);
  41 }
  42
  43 static inline void mapping_clear_unevictable(struct address_space *mapping)
  44 {
  45         clear_bit(AS_UNEVICTABLE, &mapping->flags);
  46 }
  47
  48 static inline int mapping_unevictable(struct address_space *mapping)
  49 {
  50         if (likely(mapping))
  51                 return test_bit(AS_UNEVICTABLE, &mapping->flags);
  52         return !!mapping;
  53 }
  54
  55 static inline gfp_t mapping_gfp_mask(struct address_space * mapping)
  56 {
  57         return (__force gfp_t)mapping->flags & __GFP_BITS_MASK;
  58 }
  59
  60 /*
  61  * This is non-atomic.  Only to be used before the mapping is activated.
  62  * Probably needs a barrier...
  63  */
  64 static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
  65 {
  66         m->flags = (m->flags & ~(__force unsigned long)__GFP_BITS_MASK) |
  67                                 (__force unsigned long)mask;
  68 }
  69
  70 /*
  71  * The page cache can done in larger chunks than
  72  * one page, because it allows for more efficient
  73  * throughput (it can then be mapped into user
  74  * space in smaller chunks for same flexibility).
  75  *
  76  * Or rather, it _will_ be done in larger chunks.
  77  */
  78 #define PAGE_CACHE_SHIFT        PAGE_SHIFT
  79 #define PAGE_CACHE_SIZE         PAGE_SIZE
  80 #define PAGE_CACHE_MASK         PAGE_MASK
  81 #define PAGE_CACHE_ALIGN(addr)  (((addr)+PAGE_CACHE_SIZE-1)&PAGE_CACHE_MASK)
  82
  83 #define page_cache_get(page)            get_page(page)
  84 #define page_cache_release(page)        put_page(page)
  85 void release_pages(struct page **pages, int nr, int cold);
  86
  87 /*
  88  * speculatively take a reference to a page.
  89  * If the page is free (_count == 0), then _count is untouched, and 0
  90  * is returned. Otherwise, _count is incremented by 1 and 1 is returned.
  91  *
  92  * This function must be called inside the same rcu_read_lock() section as has
  93  * been used to lookup the page in the pagecache radix-tree (or page table):
  94  * this allows allocators to use a synchronize_rcu() to stabilize _count.
  95  *
  96  * Unless an RCU grace period has passed, the count of all pages coming out
  97  * of the allocator must be considered unstable. page_count may return higher
  98  * than expected, and put_page must be able to do the right thing when the
  99  * page has been finished with, no matter what it is subsequently allocated
 100  * for (because put_page is what is used here to drop an invalid speculative
 101  * reference).
 102  *
 103  * This is the interesting part of the lockless pagecache (and lockless
 104  * get_user_pages) locking protocol, where the lookup-side (eg. find_get_page)
 105  * has the following pattern:
 106  * 1. find page in radix tree
 107  * 2. conditionally increment refcount
 108  * 3. check the page is still in pagecache (if no, goto 1)
 109  *
 110  * Remove-side that cares about stability of _count (eg. reclaim) has the
 111  * following (with tree_lock held for write):
 112  * A. atomically check refcount is correct and set it to 0 (atomic_cmpxchg)
 113  * B. remove page from pagecache
 114  * C. free the page
 115  *
 116  * There are 2 critical interleavings that matter:
 117  * - 2 runs before A: in this case, A sees elevated refcount and bails out
 118  * - A runs before 2: in this case, 2 sees zero refcount and retries;
 119  *   subsequently, B will complete and 1 will find no page, causing the
 120  *   lookup to return NULL.
 121  *
 122  * It is possible that between 1 and 2, the page is removed then the exact same
 123  * page is inserted into the same position in pagecache. That's OK: the
 124  * old find_get_page using tree_lock could equally have run before or after
 125  * such a re-insertion, depending on order that locks are granted.
 126  *
 127  * Lookups racing against pagecache insertion isn't a big problem: either 1
 128  * will find the page or it will not. Likewise, the old find_get_page could run
 129  * either before the insertion or afterwards, depending on timing.
 130  */
 131 static inline int page_cache_get_speculative(struct page *page)
 132 {
 133         VM_BUG_ON(in_interrupt());
 134
 135 #if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
 136 # ifdef CONFIG_PREEMPT
 137         VM_BUG_ON(!in_atomic());
 138 # endif
 139         /*
 140          * Preempt must be disabled here - we rely on rcu_read_lock doing
 141          * this for us.
 142          *
 143          * Pagecache won't be truncated from interrupt context, so if we have
 144          * found a page in the radix tree here, we have pinned its refcount by
 145          * disabling preempt, and hence no need for the "speculative get" that
 146          * SMP requires.
 147          */
 148         VM_BUG_ON(page_count(page) == 0);
 149         atomic_inc(&page->_count);
 150
 151 #else
 152         if (unlikely(!get_page_unless_zero(page))) {
 153                 /*
 154                  * Either the page has been freed, or will be freed.
 155                  * In either case, retry here and the caller should
 156                  * do the right thing (see comments above).
 157                  */
 158                 return 0;
 159         }
 160 #endif
 161         VM_BUG_ON(PageTail(page));
 162
 163         return 1;
 164 }
 165
 166 /*
 167  * Same as above, but add instead of inc (could just be merged)
 168  */
 169 static inline int page_cache_add_speculative(struct page *page, int count)
 170 {
 171         VM_BUG_ON(in_interrupt());
 172
 173 #if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
 174 # ifdef CONFIG_PREEMPT
 175         VM_BUG_ON(!in_atomic());
 176 # endif
 177         VM_BUG_ON(page_count(page) == 0);
 178         atomic_add(count, &page->_count);
 179
 180 #else
 181         if (unlikely(!atomic_add_unless(&page->_count, count, 0)))
 182                 return 0;
 183 #endif
 184         VM_BUG_ON(PageCompound(page) && page != compound_head(page));
 185
 186         return 1;
 187 }
 188
 189 static inline int page_freeze_refs(struct page *page, int count)
 190 {
 191         return likely(atomic_cmpxchg(&page->_count, count, 0) == count);
 192 }
 193
 194 static inline void page_unfreeze_refs(struct page *page, int count)
 195 {
 196         VM_BUG_ON(page_count(page) != 0);
 197         VM_BUG_ON(count == 0);
 198
 199         atomic_set(&page->_count, count);
 200 }
 201
 202 #ifdef CONFIG_NUMA
 203 extern struct page *__page_cache_alloc(gfp_t gfp);
 204 #else
 205 static inline struct page *__page_cache_alloc(gfp_t gfp)
 206 {
 207         return alloc_pages(gfp, 0);
 208 }
 209 #endif
 210
 211 static inline struct page *page_cache_alloc(struct address_space *x)
 212 {
 213         return __page_cache_alloc(mapping_gfp_mask(x));
 214 }
 215
 216 static inline struct page *page_cache_alloc_cold(struct address_space *x)
 217 {
 218         return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD);
 219 }
 220
 221 typedef int filler_t(void *, struct page *);
 222
 223 extern struct page * find_get_page(struct address_space *mapping,
 224                                 pgoff_t index);
 225 extern struct page * find_lock_page(struct address_space *mapping,
 226                                 pgoff_t index);
 227 extern struct page * find_or_create_page(struct address_space *mapping,
 228                                 pgoff_t index, gfp_t gfp_mask);
 229 unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
 230                         unsigned int nr_pages, struct page **pages);
 231 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
 232                                unsigned int nr_pages, struct page **pages);
 233 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
 234                         int tag, unsigned int nr_pages, struct page **pages);
 235
 236 struct page *grab_cache_page_write_begin(struct address_space *mapping,
 237                         pgoff_t index, unsigned flags);
 238
 239 /*
 240  * Returns locked page at given index in given cache, creating it if needed.
 241  */
 242 static inline struct page *grab_cache_page(struct address_space *mapping,
 243                                                                 pgoff_t index)
 244 {
 245         return find_or_create_page(mapping, index, mapping_gfp_mask(mapping));
 246 }
 247
 248 extern struct page * grab_cache_page_nowait(struct address_space *mapping,
 249                                 pgoff_t index);
 250 extern struct page * read_cache_page_async(struct address_space *mapping,
 251                                 pgoff_t index, filler_t *filler,
 252                                 void *data);
 253 extern struct page * read_cache_page(struct address_space *mapping,
 254                                 pgoff_t index, filler_t *filler,
 255                                 void *data);
 256 extern struct page * read_cache_page_gfp(struct address_space *mapping,
 257                                 pgoff_t index, gfp_t gfp_mask);
 258 extern int read_cache_pages(struct address_space *mapping,
 259                 struct list_head *pages, filler_t *filler, void *data);
 260
 261 static inline struct page *read_mapping_page_async(
 262                                                 struct address_space *mapping,
 263                                                      pgoff_t index, void *data)
 264 {
 265         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
 266         return read_cache_page_async(mapping, index, filler, data);
 267 }
 268
 269 static inline struct page *read_mapping_page(struct address_space *mapping,
 270                                              pgoff_t index, void *data)
 271 {
 272         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
 273         return read_cache_page(mapping, index, filler, data);
 274 }
 275
 276 /*
 277  * Return byte-offset into filesystem object for page.
 278  */
 279 static inline loff_t page_offset(struct page *page)
 280 {
 281         return ((loff_t)page->index) << PAGE_CACHE_SHIFT;
 282 }
 283
 284 static inline pgoff_t linear_page_index(struct vm_area_struct *vma,
 285                                         unsigned long address)
 286 {
 287         pgoff_t pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
 288         pgoff += vma->vm_pgoff;
 289         return pgoff >> (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 290 }
 291
 292 extern void __lock_page(struct page *page);
 293 extern int __lock_page_killable(struct page *page);
 294 extern void __lock_page_nosync(struct page *page);
 295 extern void unlock_page(struct page *page);
 296
 297 static inline void __set_page_locked(struct page *page)
 298 {
 299         __set_bit(PG_locked, &page->flags);
 300 }
 301
 302 static inline void __clear_page_locked(struct page *page)
 303 {
 304         __clear_bit(PG_locked, &page->flags);
 305 }
 306
 307 static inline int trylock_page(struct page *page)
 308 {
 309         return (likely(!test_and_set_bit_lock(PG_locked, &page->flags)));
 310 }
 311
 312 /*
 313  * lock_page may only be called if we have the page's inode pinned.
 314  */
 315 static inline void lock_page(struct page *page)
 316 {
 317         might_sleep();
 318         if (!trylock_page(page))
 319                 __lock_page(page);
 320 }
 321
 322 /*
 323  * lock_page_killable is like lock_page but can be interrupted by fatal
 324  * signals.  It returns 0 if it locked the page and -EINTR if it was
 325  * killed while waiting.
 326  */
 327 static inline int lock_page_killable(struct page *page)
 328 {
 329         might_sleep();
 330         if (!trylock_page(page))
 331                 return __lock_page_killable(page);
 332         return 0;
 333 }
 334
 335 /*
 336  * lock_page_nosync should only be used if we can't pin the page's inode.
 337  * Doesn't play quite so well with block device plugging.
 338  */
 339 static inline void lock_page_nosync(struct page *page)
 340 {
 341         might_sleep();
 342         if (!trylock_page(page))
 343                 __lock_page_nosync(page);
 344 }
 345
 346 /*
 347  * This is exported only for wait_on_page_locked/wait_on_page_writeback.
 348  * Never use this directly!
 349  */
 350 extern void wait_on_page_bit(struct page *page, int bit_nr);
 351
 352 /*
 353  * Wait for a page to be unlocked.
 354  *
 355  * This must be called with the caller "holding" the page,
 356  * ie with increased "page->count" so that the page won't
 357  * go away during the wait..
 358  */
 359 static inline void wait_on_page_locked(struct page *page)
 360 {
 361         if (PageLocked(page))
 362                 wait_on_page_bit(page, PG_locked);
 363 }
 364
 365 /*
 366  * Wait for a page to complete writeback
 367  */
 368 static inline void wait_on_page_writeback(struct page *page)
 369 {
 370         if (PageWriteback(page))
 371                 wait_on_page_bit(page, PG_writeback);
 372 }
 373
 374 extern void end_page_writeback(struct page *page);
 375
 376 /*
 377  * Add an arbitrary waiter to a page's wait queue
 378  */
 379 extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
 380
 381 /*
 382  * Fault a userspace page into pagetables.  Return non-zero on a fault.
 383  *
 384  * This assumes that two userspace pages are always sufficient.  That's
 385  * not true if PAGE_CACHE_SIZE > PAGE_SIZE.
 386  */
 387 static inline int fault_in_pages_writeable(char __user *uaddr, int size)
 388 {
 389         int ret;
 390
 391         if (unlikely(size == 0))
 392                 return 0;
 393
 394         /*
 395          * Writing zeroes into userspace here is OK, because we know that if
 396          * the zero gets there, we'll be overwriting it.
 397          */
 398         ret = __put_user(0, uaddr);
 399         if (ret == 0) {
 400                 char __user *end = uaddr + size - 1;
 401
 402                 /*
 403                  * If the page was already mapped, this will get a cache miss
 404                  * for sure, so try to avoid doing it.
 405                  */
 406                 if (((unsigned long)uaddr & PAGE_MASK) !=
 407                                 ((unsigned long)end & PAGE_MASK))
 408                         ret = __put_user(0, end);
 409         }
 410         return ret;
 411 }
 412
 413 static inline int fault_in_pages_readable(const char __user *uaddr, int size)
 414 {
 415         volatile char c;
 416         int ret;
 417
 418         if (unlikely(size == 0))
 419                 return 0;
 420
 421         ret = __get_user(c, uaddr);
 422         if (ret == 0) {
 423                 const char __user *end = uaddr + size - 1;
 424
 425                 if (((unsigned long)uaddr & PAGE_MASK) !=
 426                                 ((unsigned long)end & PAGE_MASK))
 427                         ret = __get_user(c, end);
 428         }
 429         return ret;
 430 }
 431
 432 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
 433                                 pgoff_t index, gfp_t gfp_mask);
 434 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
 435                                 pgoff_t index, gfp_t gfp_mask);
 436 extern void remove_from_page_cache(struct page *page);
 437 extern void __remove_from_page_cache(struct page *page);
 438
 439 /*
 440  * Like add_to_page_cache_locked, but used to add newly allocated pages:
 441  * the page is new, so we can just run __set_page_locked() against it.
 442  */
 443 static inline int add_to_page_cache(struct page *page,
 444                 struct address_space *mapping, pgoff_t offset, gfp_t gfp_mask)
 445 {
 446         int error;
 447
 448         __set_page_locked(page);
 449         error = add_to_page_cache_locked(page, mapping, offset, gfp_mask);
 450         if (unlikely(error))
 451                 __clear_page_locked(page);
 452         return error;
 453 }
 454
 455 #endif /* _LINUX_PAGEMAP_H */