include/linux/page-flags.h

   1 /*
   2  * Macros for manipulating and testing page->flags
   3  */
   4
   5 #ifndef PAGE_FLAGS_H
   6 #define PAGE_FLAGS_H
   7
   8 #include <linux/types.h>
   9 #ifndef __GENERATING_BOUNDS_H
  10 #include <linux/mm_types.h>
  11 #include <linux/bounds.h>
  12 #endif /* !__GENERATING_BOUNDS_H */
  13
  14 /*
  15  * Various page->flags bits:
  16  *
  17  * PG_reserved is set for special pages, which can never be swapped out. Some
  18  * of them might not even exist (eg empty_bad_page)...
  19  *
  20  * The PG_private bitflag is set on pagecache pages if they contain filesystem
  21  * specific data (which is normally at page->private). It can be used by
  22  * private allocations for its own usage.
  23  *
  24  * During initiation of disk I/O, PG_locked is set. This bit is set before I/O
  25  * and cleared when writeback _starts_ or when read _completes_. PG_writeback
  26  * is set before writeback starts and cleared when it finishes.
  27  *
  28  * PG_locked also pins a page in pagecache, and blocks truncation of the file
  29  * while it is held.
  30  *
  31  * page_waitqueue(page) is a wait queue of all tasks waiting for the page
  32  * to become unlocked.
  33  *
  34  * PG_uptodate tells whether the page's contents is valid.  When a read
  35  * completes, the page becomes uptodate, unless a disk I/O error happened.
  36  *
  37  * PG_referenced, PG_reclaim are used for page reclaim for anonymous and
  38  * file-backed pagecache (see mm/vmscan.c).
  39  *
  40  * PG_error is set to indicate that an I/O error occurred on this page.
  41  *
  42  * PG_arch_1 is an architecture specific page state bit.  The generic code
  43  * guarantees that this bit is cleared for a page when it first is entered into
  44  * the page cache.
  45  *
  46  * PG_highmem pages are not permanently mapped into the kernel virtual address
  47  * space, they need to be kmapped separately for doing IO on the pages.  The
  48  * struct page (these bits with information) are always mapped into kernel
  49  * address space...
  50  *
  51  * PG_buddy is set to indicate that the page is free and in the buddy system
  52  * (see mm/page_alloc.c).
  53  *
  54  */
  55
  56 /*
  57  * Don't use the *_dontuse flags.  Use the macros.  Otherwise you'll break
  58  * locked- and dirty-page accounting.
  59  *
  60  * The page flags field is split into two parts, the main flags area
  61  * which extends from the low bits upwards, and the fields area which
  62  * extends from the high bits downwards.
  63  *
  64  *  | FIELD | ... | FLAGS |
  65  *  N-1           ^       0
  66  *               (NR_PAGEFLAGS)
  67  *
  68  * The fields area is reserved for fields mapping zone, node (for NUMA) and
  69  * SPARSEMEM section (for variants of SPARSEMEM that require section ids like
  70  * SPARSEMEM_EXTREME with !SPARSEMEM_VMEMMAP).
  71  */
  72 enum pageflags {
  73         PG_locked,              /* Page is locked. Don't touch. */
  74         PG_error,
  75         PG_referenced,
  76         PG_uptodate,
  77         PG_dirty,
  78         PG_lru,
  79         PG_active,
  80         PG_slab,
  81         PG_owner_priv_1,        /* Owner use. If pagecache, fs may use*/
  82         PG_arch_1,
  83         PG_reserved,
  84         PG_private,             /* If pagecache, has fs-private data */
  85         PG_writeback,           /* Page is under writeback */
  86 #ifdef CONFIG_PAGEFLAGS_EXTENDED
  87         PG_head,                /* A head page */
  88         PG_tail,                /* A tail page */
  89 #else
  90         PG_compound,            /* A compound page */
  91 #endif
  92         PG_swapcache,           /* Swap page: swp_entry_t in private */
  93         PG_mappedtodisk,        /* Has blocks allocated on-disk */
  94         PG_reclaim,             /* To be reclaimed asap */
  95         PG_buddy,               /* Page is free, on buddy lists */
  96 #ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
  97         PG_uncached,            /* Page has been mapped as uncached */
  98 #endif
  99         __NR_PAGEFLAGS
 100 };
 101
 102 #ifndef __GENERATING_BOUNDS_H
 103
 104 /*
 105  * Macros to create function definitions for page flags
 106  */
 107 #define TESTPAGEFLAG(uname, lname)                                      \
 108 static inline int Page##uname(struct page *page)                        \
 109                         { return test_bit(PG_##lname, &page->flags); }
 110
 111 #define SETPAGEFLAG(uname, lname)                                       \
 112 static inline void SetPage##uname(struct page *page)                    \
 113                         { set_bit(PG_##lname, &page->flags); }
 114
 115 #define CLEARPAGEFLAG(uname, lname)                                     \
 116 static inline void ClearPage##uname(struct page *page)                  \
 117                         { clear_bit(PG_##lname, &page->flags); }
 118
 119 #define __SETPAGEFLAG(uname, lname)                                     \
 120 static inline void __SetPage##uname(struct page *page)                  \
 121                         { __set_bit(PG_##lname, &page->flags); }
 122
 123 #define __CLEARPAGEFLAG(uname, lname)                                   \
 124 static inline void __ClearPage##uname(struct page *page)                \
 125                         { __clear_bit(PG_##lname, &page->flags); }
 126
 127 #define TESTSETFLAG(uname, lname)                                       \
 128 static inline int TestSetPage##uname(struct page *page)                 \
 129                 { return test_and_set_bit(PG_##lname, &page->flags); }
 130
 131 #define TESTCLEARFLAG(uname, lname)                                     \
 132 static inline int TestClearPage##uname(struct page *page)               \
 133                 { return test_and_clear_bit(PG_##lname, &page->flags); }
 134
 135
 136 #define PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname)               \
 137         SETPAGEFLAG(uname, lname) CLEARPAGEFLAG(uname, lname)
 138
 139 #define __PAGEFLAG(uname, lname) TESTPAGEFLAG(uname, lname)             \
 140         __SETPAGEFLAG(uname, lname)  __CLEARPAGEFLAG(uname, lname)
 141
 142 #define PAGEFLAG_FALSE(uname)                                           \
 143 static inline int Page##uname(struct page *page)                        \
 144                         { return 0; }
 145
 146 #define TESTSCFLAG(uname, lname)                                        \
 147         TESTSETFLAG(uname, lname) TESTCLEARFLAG(uname, lname)
 148
 149 struct page;    /* forward declaration */
 150
 151 PAGEFLAG(Locked, locked) TESTSCFLAG(Locked, locked)
 152 PAGEFLAG(Error, error)
 153 PAGEFLAG(Referenced, referenced) TESTCLEARFLAG(Referenced, referenced)
 154 PAGEFLAG(Dirty, dirty) TESTSCFLAG(Dirty, dirty) __CLEARPAGEFLAG(Dirty, dirty)
 155 PAGEFLAG(LRU, lru) __CLEARPAGEFLAG(LRU, lru)
 156 PAGEFLAG(Active, active) __CLEARPAGEFLAG(Active, active)
 157 __PAGEFLAG(Slab, slab)
 158 PAGEFLAG(Checked, owner_priv_1)         /* Used by some filesystems */
 159 PAGEFLAG(Pinned, owner_priv_1) TESTSCFLAG(Pinned, owner_priv_1) /* Xen */
 160 PAGEFLAG(Reserved, reserved) __CLEARPAGEFLAG(Reserved, reserved)
 161 PAGEFLAG(Private, private) __CLEARPAGEFLAG(Private, private)
 162         __SETPAGEFLAG(Private, private)
 163
 164 /*
 165  * Only test-and-set exist for PG_writeback.  The unconditional operators are
 166  * risky: they bypass page accounting.
 167  */
 168 TESTPAGEFLAG(Writeback, writeback) TESTSCFLAG(Writeback, writeback)
 169 __PAGEFLAG(Buddy, buddy)
 170 PAGEFLAG(MappedToDisk, mappedtodisk)
 171
 172 /* PG_readahead is only used for file reads; PG_reclaim is only for writes */
 173 PAGEFLAG(Reclaim, reclaim) TESTCLEARFLAG(Reclaim, reclaim)
 174 PAGEFLAG(Readahead, reclaim)            /* Reminder to do async read-ahead */
 175
 176 #ifdef CONFIG_HIGHMEM
 177 /*
 178  * Must use a macro here due to header dependency issues. page_zone() is not
 179  * available at this point.
 180  */
 181 #define PageHighMem(__p) is_highmem(page_zone(__p))
 182 #else
 183 PAGEFLAG_FALSE(HighMem)
 184 #endif
 185
 186 #ifdef CONFIG_SWAP
 187 PAGEFLAG(SwapCache, swapcache)
 188 #else
 189 PAGEFLAG_FALSE(SwapCache)
 190 #endif
 191
 192 #ifdef CONFIG_IA64_UNCACHED_ALLOCATOR
 193 PAGEFLAG(Uncached, uncached)
 194 #else
 195 PAGEFLAG_FALSE(Uncached)
 196 #endif
 197
 198 static inline int PageUptodate(struct page *page)
 199 {
 200         int ret = test_bit(PG_uptodate, &(page)->flags);
 201
 202         /*
 203          * Must ensure that the data we read out of the page is loaded
 204          * _after_ we've loaded page->flags to check for PageUptodate.
 205          * We can skip the barrier if the page is not uptodate, because
 206          * we wouldn't be reading anything from it.
 207          *
 208          * See SetPageUptodate() for the other side of the story.
 209          */
 210         if (ret)
 211                 smp_rmb();
 212
 213         return ret;
 214 }
 215
 216 static inline void __SetPageUptodate(struct page *page)
 217 {
 218         smp_wmb();
 219         __set_bit(PG_uptodate, &(page)->flags);
 220 #ifdef CONFIG_S390
 221         page_clear_dirty(page);
 222 #endif
 223 }
 224
 225 static inline void SetPageUptodate(struct page *page)
 226 {
 227 #ifdef CONFIG_S390
 228         if (!test_and_set_bit(PG_uptodate, &page->flags))
 229                 page_clear_dirty(page);
 230 #else
 231         /*
 232          * Memory barrier must be issued before setting the PG_uptodate bit,
 233          * so that all previous stores issued in order to bring the page
 234          * uptodate are actually visible before PageUptodate becomes true.
 235          *
 236          * s390 doesn't need an explicit smp_wmb here because the test and
 237          * set bit already provides full barriers.
 238          */
 239         smp_wmb();
 240         set_bit(PG_uptodate, &(page)->flags);
 241 #endif
 242 }
 243
 244 CLEARPAGEFLAG(Uptodate, uptodate)
 245
 246 extern void cancel_dirty_page(struct page *page, unsigned int account_size);
 247
 248 int test_clear_page_writeback(struct page *page);
 249 int test_set_page_writeback(struct page *page);
 250
 251 static inline void set_page_writeback(struct page *page)
 252 {
 253         test_set_page_writeback(page);
 254 }
 255
 256 #ifdef CONFIG_PAGEFLAGS_EXTENDED
 257 /*
 258  * System with lots of page flags available. This allows separate
 259  * flags for PageHead() and PageTail() checks of compound pages so that bit
 260  * tests can be used in performance sensitive paths. PageCompound is
 261  * generally not used in hot code paths.
 262  */
 263 __PAGEFLAG(Head, head)
 264 __PAGEFLAG(Tail, tail)
 265
 266 static inline int PageCompound(struct page *page)
 267 {
 268         return page->flags & ((1L << PG_head) | (1L << PG_tail));
 269
 270 }
 271 #else
 272 /*
 273  * Reduce page flag use as much as possible by overlapping
 274  * compound page flags with the flags used for page cache pages. Possible
 275  * because PageCompound is always set for compound pages and not for
 276  * pages on the LRU and/or pagecache.
 277  */
 278 TESTPAGEFLAG(Compound, compound)
 279 __PAGEFLAG(Head, compound)
 280
 281 /*
 282  * PG_reclaim is used in combination with PG_compound to mark the
 283  * head and tail of a compound page. This saves one page flag
 284  * but makes it impossible to use compound pages for the page cache.
 285  * The PG_reclaim bit would have to be used for reclaim or readahead
 286  * if compound pages enter the page cache.
 287  *
 288  * PG_compound & PG_reclaim     => Tail page
 289  * PG_compound & ~PG_reclaim    => Head page
 290  */
 291 #define PG_head_tail_mask ((1L << PG_compound) | (1L << PG_reclaim))
 292
 293 static inline int PageTail(struct page *page)
 294 {
 295         return ((page->flags & PG_head_tail_mask) == PG_head_tail_mask);
 296 }
 297
 298 static inline void __SetPageTail(struct page *page)
 299 {
 300         page->flags |= PG_head_tail_mask;
 301 }
 302
 303 static inline void __ClearPageTail(struct page *page)
 304 {
 305         page->flags &= ~PG_head_tail_mask;
 306 }
 307
 308 #endif /* !PAGEFLAGS_EXTENDED */
 309 #endif /* !__GENERATING_BOUNDS_H */
 310 #endif  /* PAGE_FLAGS_H */