Linux: TCMalloc does not release free memory when requested

[martyngigg]

There are calls to TCMalloc's ReleaseFreeMemory both before and after algorithm execution and also when calling FrameworkManager::clear.

It would appear that these calls do not always do what is expected. For example, the system test performance reports seem to suggest alot of memory loss in many tests:

https://builds.sns.gov/view/All/job/ornl_test_rhel6_develop/System_tests_performance/?

whereas the Windows servers do not show this:

https://builds.sns.gov/view/All/job/ornl_test_windows7_develop/System_tests_performance/?

Investigate what is happening here. The script below (data in systemtests/Data) should leave memory around when the clear should have freed it up:

#!python
import mantid
from mantid.kernel import MemoryStats
from mantid.simpleapi import *
mantid.api.FrameworkManager.clear()

## TEST ##
memory_before = MemoryStats().residentMem()/1024
wish_ws = Load(Filename='WISH00016748.raw',OutputWorkspace='wish_ws')
mantid.api.FrameworkManager.clear()

heldMemory = MemoryStats().residentMem()/1024 - memory_before

print "Memory held:",heldMemory

[martyngigg]

This issue was originally trac ticket 7798