Calmar
The Commonwealth Graves Commission site shows his place of birth as Glasgow and parents as Alexander DRYSDALE and Elizabeth Barker DRYSDALE, altho' by 1918, they were living in Penwortham, whereever that is
You now need to spend a few bawbies by going onto the
www.scotslandspeople.gov.uk website, registering, buying a few credits, and looking for a birth of an Alexander DRYSDALE in the period 1898 to 1900. There's only 3, of which only one in Glasgow, who is your man (see Jean Jeanie's post =D> )
That birth register entry gives you the place and date of the marriage of his parents. That marriage register entry will give you the names of all 4 parents.
Simple looking directly for the marriages of those two sets of parents will take you back another generation, - guaranteed, - the records are there just waiting for you to access them. In others words these will give you the greatgrandparents of Second Lieutenant (Pilot) Alexander Drysdale, Royal Flying Corps. Not clear if he was killed in action in France/Flanders, or during training, but he is buried in Penwortham (St. Mary Churchyard)
It's probable that censuses, death register entries, and the IGI will take you back another couple of generations!
David