cvs commit: src/lib/libc/stdlib malloc.c

[Jason Evans]

jasone      2007-03-23 05:05:48 UTC

  FreeBSD src repository

  Modified files:
    lib/libc/stdlib      malloc.c 
  Log:
  Use extents rather than binary buddies to track free pages within
  chunks.  This allows runs to be any multiple of the page size.  The
  primary advantage is that large objects are no longer constrained to be
  2^n pages, which can dramatically decrease internal fragmentation for
  large objects.  This also allows the sizes for runs that back small
  objects to be more finely tuned.
  
  Free runs are searched for linearly using the chunk page map (with the
  help of some heuristic optimizations).  This changes the allocation
  policy from "first best fit" to "first fit".  A prototype red-black tree
  implementation for tracking free runs that implemented "first best fit"
  did not cause a measurable speed or memory usage difference for
  realistic chunk sizes (though of course it is possible to construct
  benchmarks that favor one allocation policy over another).
  
  Refine the handling of fullness constraints for small runs to be more
  tunable.
  
  Restructure the per chunk page map to contain only two fields per entry,
  rather than four.  Also, increase each entry from 4 to 8 bytes, since it
  allows for 32-bit integers, without increasing the number of chunk
  header pages.
  
  Relax the maximum chunk size constraint.  This is of no practical
  interest; it is merely fallout from the chunk page map restructuring.
  
  Revamp statistics gathering and reporting to be faster, clearer and more
  informative.  Statistics gathering is fast enough now to have little
  to no impact on application speed, but it still requires approximately
  two extra pages of memory per arena (per process).  This memory overhead
  may be acceptable for most systems, but we still need to leave
  statistics gathering disabled by default in RELENG branches.
  
  Rename NO_MALLOC_EXTRAS to MALLOC_PRODUCTION in order to make its intent
  clearer (i.e. it should be defined in RELENG branches).
  
  Revision  Changes    Path
  1.142     +337 -328  src/lib/libc/stdlib/malloc.c