deps/gc/include/gc_tiny_fl.h

   1 /*
   2  * Copyright (c) 1999-2005 Hewlett-Packard Development Company, L.P.
   3  *
   4  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
   5  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
   6  *
   7  * Permission is hereby granted to use or copy this program
   8  * for any purpose,  provided the above notices are retained on all copies.
   9  * Permission to modify the code and to distribute modified code is granted,
  10  * provided the above notices are retained, and a notice that the code was
  11  * modified is included with the above copyright notice.
  12  */
  13
  14 #ifndef GC_TINY_FL_H
  15 #define GC_TINY_FL_H
  16 /*
  17  * Constants and data structures for "tiny" free lists.
  18  * These are used for thread-local allocation or in-lined allocators.
  19  * Each global free list also essentially starts with one of these.
  20  * However, global free lists are known to the GC.  "Tiny" free lists
  21  * are basically private to the client.  Their contents are viewed as
  22  * "in use" and marked accordingly by the core of the GC.
  23  *
  24  * Note that inlined code might know about the layout of these and the constants
  25  * involved.  Thus any change here may invalidate clients, and such changes should
  26  * be avoided.  Hence we keep this as simple as possible.
  27  */
  28
  29 /*
  30  * We always set GC_GRANULE_BYTES to twice the length of a pointer.
  31  * This means that all allocation requests are rounded up to the next
  32  * multiple of 16 on 64-bit architectures or 8 on 32-bit architectures.
  33  * This appears to be a reasonable compromise between fragmentation overhead
  34  * and space usage for mark bits (usually mark bytes).
  35  * On many 64-bit architectures some memory references require 16-byte
  36  * alignment, making this necessary anyway.
  37  * For a few 32-bit architecture (e.g. x86), we may also need 16-byte alignment
  38  * for certain memory references.  But currently that does not seem to be the
  39  * default for all conventional malloc implementations, so we ignore that
  40  * problem.
  41  * It would always be safe, and often useful, to be able to allocate very
  42  * small objects with smaller alignment.  But that would cost us mark bit
  43  * space, so we no longer do so.
  44  */
  45 #ifndef GC_GRANULE_BYTES
  46   /* GC_GRANULE_BYTES should not be overridden in any instances of the GC */
  47   /* library that may be shared between applications, since it affects    */
  48   /* the binary interface to the library.                                 */
  49 # if defined(__LP64__) || defined (_LP64) || defined(_WIN64) \
  50         || defined(__s390x__) || defined(__x86_64__) \
  51         || defined(__alpha__) || defined(__powerpc64__) \
  52         || defined(__arch64__)
  53 #  define GC_GRANULE_BYTES 16
  54 #  define GC_GRANULE_WORDS 2
  55 # else
  56 #  define GC_GRANULE_BYTES 8
  57 #  define GC_GRANULE_WORDS 2
  58 # endif
  59 #endif /* !GC_GRANULE_BYTES */
  60
  61 #if GC_GRANULE_WORDS == 2
  62 #  define GC_WORDS_TO_GRANULES(n) ((n)>>1)
  63 #else
  64 #  define GC_WORDS_TO_GRANULES(n) ((n)*sizeof(void *)/GC_GRANULE_BYTES)
  65 #endif
  66
  67 /* A "tiny" free list header contains TINY_FREELISTS pointers to        */
  68 /* singly linked lists of objects of different sizes, the ith one       */
  69 /* containing objects i granules in size.  Note that there is a list    */
  70 /* of size zero objects.                                                */
  71 #ifndef GC_TINY_FREELISTS
  72 # if GC_GRANULE_BYTES == 16
  73 #   define GC_TINY_FREELISTS 25
  74 # else
  75 #   define GC_TINY_FREELISTS 33 /* Up to and including 256 bytes */
  76 # endif
  77 #endif /* !GC_TINY_FREELISTS */
  78
  79 /* The ith free list corresponds to size i*GC_GRANULE_BYTES     */
  80 /* Internally to the collector, the index can be computed with  */
  81 /* ROUNDED_UP_GRANULES.  Externally, we don't know whether      */
  82 /* DONT_ADD_BYTE_AT_END is set, but the client should know.     */
  83
  84 /* Convert a free list index to the actual size of objects      */
  85 /* on that list, including extra space we added.  Not an        */
  86 /* inverse of the above.                                        */
  87 #define GC_RAW_BYTES_FROM_INDEX(i) ((i) * GC_GRANULE_BYTES)
  88
  89 #endif /* GC_TINY_FL_H */