memTracker.hpp is included by 846 out of 971 .o files in the HotSpot build:

$ cd build/linux-x64
$ find hotspot -name \*.o | wc -l
971
$ find hotspot -name \*.d | grep -v LIBJVM.d | xargs cat | wc -l
259927
$ find hotspot -name \*.d | grep -v LIBJVM.d | xargs grep -l memTracker.hpp | wc -l
846

After fixing the excessive includes, the number has reduced significantly:
$ find hotspot -name \*.d | grep -v LIBJVM.d | xargs cat | wc -l
252033
$ find hotspot -name \*.d | grep -v LIBJVM.d | xargs grep -l memTracker.hpp | wc -l
94

The total number of included header files has reduced for about 3% (259927 / 252033 = 1.0313).