Sparse-matrix vector product A*x for general ghosts in x

[fverdugo]

functio spmv(A,x;reuse)
      cols = partition(axes(A,2))
      x_with_ghost, cachex = consistent(x,cols;reuse=true) |> fetch
      b = A*x_with_ghost
      cache = (x_with_ghost,cachex)
      b, cache
end

function spmv!(b,A,x,cache)
     consistent!(x_with_ghost,x,cachex) |> wait
     mul!(b,A,x_with_ghost)
end

Explore if cache can be hidden in the matrix.