1. A method for selecting virtual machines to be migrated, the method comprising: monitoring page consumption by each virtual machine running on a physical machine as a function of time, wherein said page consumption comprises an amount of virtual memory accessed; recording said page consumption by each virtual machine running on said physical machine at sample points in time within an observation window of time; computing a gradient of page consumption for each virtual machine running on said physical machine at each sample interval within said observation window of time, wherein each said sample interval is a time duration between two consecutive sample points in time within said observation window of time; identifying those virtual machines with a positive computed gradient of page consumption that is less than a threshold to be placed in a list of virtual machines to be ranked, wherein said threshold comprises a percentage of sample intervals within said observation window of time that have a positive gradient of page consumption; computing a relative page consumption value for each virtual machine in said list of virtual machines to be ranked for each said sample interval within said observation window of time, wherein said relative page consumption value indicates a change in a rate of said page consumption; ranking said virtual machines in said list of virtual machines based on an increasing order of said relative page consumption value at each said sample interval within said observation window of time; computing, by a processor, a final rank for each virtual machine in said list of virtual machines based on averaging its ranking across each said sample interval within said observation window of time; and selecting one or more virtual machines to be migrated from said list of virtual machines that have a lowest final ranking.