* Change the offset alignment in vn_rdwe_inchunks()

*	Change the offset alignment in vn_rdwe_inchunks()
	This is primarily used by the ELF image activator.

FreeBSD src repository

  Modified files:
    sys/kern             vfs_vnops.c
  Log:
  Align the offset in vn_rdwr_inchunks() so that at most the first and
  the last chunk are misaligned relative to a MAXBSIZE byte boundary.
  vn_rdwr_inchunks() is used mainly for elf core dumps, and elf sections
  are usually perfectly misaligned relative to MAXBSIZE, and chunking
  prevents the file system from doing much realigning.

  This gives a surprisingly large speedup for core dumps -- from 50 to
  13 seconds for a 512MB core dump here.  The pessimization was mostly
  from an interaction of the misalignment with IO_DIRECT.  It increased
  the number of i/o's for each chunk by a factor of 5 (3 writes and 2
  read-before-writes instead of 1 write).