hrStorageSize = 1.3.6.1.2.1.25.2.3.1.5
hrStorageUsed = 1.3.6.1.2.1.25.2.3.1.6
hrStorageAllocationUnits = 1.3.6.1.2.1.25.2.3.1.4
hrStorageDescr = 1.3.6.1.2.1.25.2.3.1.3
Based on polling results for these OIDs, the following calculations used to derive the value for FreeMemoryPct:
FreeMemoryPct = FreeMemory * 100 / (TotalMemory + 0.001)
TotalMemory = long(hrStorageSize * (float(hrStorageAllocationUnits) / 1024.0));
FreeMemory = long((hrStorageSize - hrStorageUsed) * (float(hrStorageAllocationUnits) / 1024.0));