WM_COMPACTING
wCompactRatio = wParam; /* compacting ratio */The WM_COMPACTING message is sent to all top-level windows when Windows detects that more than 12.5 percent of system time over a 30- to 60-second interval is being spent compacting memory. This indicates that system memory is low.
wCompactRatio
Value of wParam. Specifies the ratio of central processing unit (CPU) time currently spent by Windows compacting memory to CPU time currently spent by Windows performing other operations. For example, 0x8000 represents 50 percent of CPU time spent compacting memory.
An application should return zero if it processes this message.
When an application receives this message, it should free as much memory as possible, taking into account the current level of activity of the application and the total number of applications running with Windows. The application can call the GetNumTasks function to determine how many applications are running.