Git log command doesn't run as expected.

Hi,
	I’m using following command to do some search work:
	git log --all -G 'some regexp' -p — path/to/my/file.
But the output could miss some commit. (For example, I grep a little piece of code from a commit diff message(properly handled for regexp), but when I use the command above to search that code, I could not get that commit.)
	I wonder that it is because I use it in a wrong way? Then what should I do to correct it.

																							Thanks!