XALLOC(10.2)                                         XALLOC(10.2)

          xalloc, xspanalloc, xfree - basic memory management

          void* xalloc(ulong size)

          void* xspanalloc(ulong size, int align, ulong span)

          void  xfree(void *p)

          Xalloc and xfree are primitives used by higher-level memory
          allocators in the kernel, such as malloc(10.2). They are not
          intended for use directly by most kernel routines.  The main
          exceptions are routines that permanently allocate large
          structures, or need the special alignment properties guaran-
          teed by xspanalloc.

          Xalloc returns a pointer to a range of size bytes of memory.
          The memory will be zero filled and aligned on a 8 byte
          (BY2V) address. If the memory is not available, xalloc
          returns a null pointer.

          Xspanalloc allocates memory given alignment and spanning
          constraints.  The block returned will contain size bytes,
          aligned on a boundary that is 0 mod align, in such a way
          that the memory in the block does not span an address that
          is 0 mod span.  Xspanalloc is intended for use allocating
          hardware data structures (eg, page tables) or I/O buffers
          that must satisfy specific alignment restrictions.  If
          xspanalloc cannot allocate memory to satisfy the given con-
          straints, it will panic(10.2). The technique it uses can
          sometimes cause memory to be wasted.  Consequently,
          xspanalloc should be used sparingly.

          Xfree frees the block of memory at p, which must be an
          address previously returned by xalloc (not xspanalloc).

        Allocation status
          Some memory allocation statistics are written to the console
          in response to the debugging sequence `control-T control-T
          x'.  The output includes the total free space, the number of
          free holes, and a summary of active holes.  Each line shows
          `address top size'.