TeX Gyre Pagella Math Integral sign much too small

Simply adjust the DisplayOperatorMinHeight font parameter. That also indicates that the font is broken.

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{TeX Gyre Pagella Math}
\everydisplay{\Umathoperatorsize\displaystyle=5ex}
\begin{document}

\[\int_\gamma\frac{f(x)}{z-a}\]

\end{document}

with xelatex you get

but with lualatex you get

from

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{TeX Gyre Pagella Math}
\setmathfont{TeX Gyre Pagella Math}[range=\int,Scale=2]


\begin{document}

\[\int_\gamma\frac{f(x)}{z-a}\]

\end{document}

I'm not sure if the difference is in unicode-math or the underlying luatex math rendering, the scaled font for \int has caused the math parameters used for fraction spacing (and other things) to be scaled. I'll ping Will...

as Ulrike points out you can reset the parameters with an additional mathfont setting, resulting in

which doesn't produce quite the result xetex does but usable.

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{TeX Gyre Pagella Math}
\setmathfont{TeX Gyre Pagella Math}[range=\int,Scale=2]
\setmathfont{TeX Gyre Pagella Math}[range=\sum]


\begin{document}

\[\int_\gamma\frac{f(x)}{z-a}\]

\end{document}

\Uhextensible seems to work:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{TeX Gyre Pagella Math}


\begin{document}
\[\int _\gamma\frac{f(x)}{z-a}\]

\[ \Uhextensible width 2ex "0 "00222B_\gamma\frac{f(x)}{z-a}\]

\end{document}

But I have no idea why and which width is sensible.

After a bit digging in the context code I found also an (undocumented) \Uvextensible which looks more sensible:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{TeX Gyre Pagella Math}


\begin{document}
\[\int _\gamma\frac{f(x)}{z-a}\]

\[ \mathop{\Uvextensible height 15pt depth 15pt exact axis\Udelimiter "0 "0 "222B}\nolimits_\gamma\frac{f(x)}{z-a}\]

\end{document}