1. A global memory sharing method, wherein the method comprises: counting, by a sub-operating system, a page replacement rate in a task scheduling period of a predetermined quantity of times, and a memory residence time ratio in a page replacement period; calculating, by the sub-operating system, a memory pressure index according to the page replacement rate and the memory residence time ratio; and sending, by the sub-operating system, an application to a global memory management service module when the memory pressure index is greater than a memory pressure threshold, wherein the application is used for applying for allocation of currently acquirable memory from global sharing memory.