MFC r319699

MFC r319699
  When allocating swap blocks, if the available number of free blocks in a
  subtree is already zero, then setting the "largest contiguous free block"
  hint for that subtree to anything other than zero makes no sense.  (To be
  clear, assigning a value to the hint that is too large is not a correctness
  problem, only a pessimization.)

MFC r319755
  blist_fill()'s return type is too narrow.  blist_fill() accepts a 64-bit
  quantity as the size of the range to fill, but returns a 32-bit quantity
  as the number of blocks that were allocated to fill that range.  This
  revision corrects that mismatch.

MFC r319793
  Remove an unnecessary field from struct blist.  (The comment describing
  what this field represented was also inaccurate.)

  In r178792, blist_create() grew a malloc flag, allowing M_NOWAIT to be
  specified.  However, blist_create() was not modified to handle the
  possibility that a malloc() call failed.  Address this omission.

  Increase the width of the local variable "radix" to 64 bits.  This
  matches the width of the corresponding field in struct blist.

git-svn-id: svn://svn.freebsd.org/base/stable/10@320622 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f