Reduce white space above chapter title, and reduce space between title and text, for unnumbered chapters

Question

How can I reduce the white space above the chapter heading?

How can I reduce the space between the heading and the text?

I want to be able to do this for selected chapters only, or after a given chapter (I want normal spacing from the Introduction chapter and outwards, but before that I want reduced spacing).

MWE:

\documentclass[b5paper, 11pt, twoside, openright]{report}
\usepackage{titlesec}
\begin{document}
\chapter*{Abstract}
This chapter should have less spacing
\chapter*{Preface}
This chapter should have less spacing
\tableofcontents %Less spacing
\listoffigures %Less spacing
\listoftables %Less spacing
\chapter*{Glossary}
Less spacing
\chapter{Introduction}
From this chapter, I want normal spacing
\end{document}

Answer 1

this answer directly modifies the command from report.cls that formats the headings of unnumbered chapters.

\documentclass[b5paper, 11pt, twoside, openright]{report}
\usepackage{titlesec}
\makeatletter
\renewcommand{\@makeschapterhead}[1]{%
%  \vspace*{50\p@}%
  \vspace*{20\p@}%
  {\parindent \z@ \raggedright
    \normalfont
    \interlinepenalty\@M
    \Huge \bfseries  #1\par\nobreak
%    \vskip 40\p@
    \vskip 20\p@
  }}
\makeatother

\begin{document}
\chapter*{Abstract}
This chapter should have less spacing
\chapter*{Preface}
This chapter should have less spacing
\tableofcontents %Less spacing
\listoffigures %Less spacing
\listoftables %Less spacing
\chapter*{Glossary}
Less spacing
\chapter{Introduction}
From this chapter, I want normal spacing
\end{document}

Answer 2

titlesec supports different spacing for numbered and unnumbered chapters:

\documentclass[b5paper, 11pt]{report}

%%% Add this %%%
\usepackage{titlesec}
\titleformat{\chapter}[display]
{\normalfont\huge\bfseries}{\chaptertitlename~\thechapter}{20pt}{\Huge}
\titlespacing*{\chapter}{0pt}{50pt}{40pt}
\titlespacing*{name=\chapter,numberless}{0pt}{-30pt}{10pt}
%%%   End   %%%


\begin{document}
\chapter*{Abstract}
This chapter should have less spacing
\chapter*{Preface}
This chapter should have less spacing
\tableofcontents %Less spacing
\listoffigures %Less spacing
\listoftables %Less spacing
\chapter*{Glossary}
Less spacing
\chapter{Introduction}
From this chapter, I want normal spacing
\end{document}