Googled a bit about sui dynasty's population at this time and it says around 35 millions, it seems really incredible for me that the sui dynasty drafted more than 10% of its population into the direct war effort, and in contrast, numbers in European battles are really low compared to it cos it's few hundred here few hundred there and if some one has a gigantic army it's 30k...
These numbers appear to be accurate. Victor Cunrui Xiong, an expert on the era, identifies the size of the Sui dynasty's first Korean expeditionary force as 1,133,800 soldiers supported by "a labor force twice as large" (Emperor Yang of the Sui Dynasty, p. 56). For what it's worth, the failures of Emperor Yang's campaigns contributed to far greater domestic tumult than failed campaigns in later dynasties (e.g. Emperor Taizong of Song's misadventures against the Liao, which are documented in great detail by the historian Peter Lorge in The Reunification of China). Given the massive size of the invading force and the extent to which conscription impacted everyday life in China, both the size of the ensuing anti-Sui rebellions and the government's manpower issues in combating the revolts make a lot of sense.