= 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 con‐
straints.   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 can‐
not allocate memory to satisfy the given constraints, it will
panic(10.2).   The technique it uses can sometimes cause mem‐
ory 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 The output includes the
total free space, the number of free holes, and a summary  of
active holes.  Each line shows `address top size'.

== see ALSO
malloc(10.2)