"China agreed . . . to give North Korea 500,000 tons of grain"

 

 500,000 tonnes = 500,000,000 kg

 

Likely all the grain is rice. Rounding down the population of the DPRK to 25,000,000, this means 20 kg of rice for each. Supposing each person eats 200 g of rice a day ( I estimate consumption per person high to offset a low population estimate), 20 kg of rice will feed one person for 100 days.

 

This means China has given the DPRK enough food to survive the winter until the early harvests in May.