is it possible to determine whether or not a specific app, user or system, is either leaking memory or not letting go? I'm currently rooted and am using CoolTool to stats, where one of them is free memory. After a fresh cold reboot, my free memory floats just a little over 300MB. Usually when I use an app that number drops below 300MB and always climbs back above after I close the app. Not exactly sure what it is yet, but sometimes that number keeps decreasing and decreasing until the phone is unusable. I'll kill all the running apps and that brings all the memory back temporarily. Less than two minutes later it would drop all the way back down to below 285MB free. Something is definitely grabbing the memory and not being caring by releasing. If I reboot, everything is back to normal. Any suggestions?

Are you using the Android OS? Maybe your question would be better answered here: http://www.androidquestions.org/forum.php

Aside from that, I think you need to tell us what app you are running when said memory leak occurs. Also it would be helpful to know what OS is on this device and what version of this OS you are running.

I'll give that site a try as well. To answer your questions, the most apparent time when the memory leak occurs is after using Google Maps or Endomondo. I'm not sure if it's the app themselves or if it's the Android OS and GPS as both those apps use GPS heavily. I've even used Google Maps after a fresh reboot to navigate me while driving for about an hour. After the navigation the device was sluggish with free RAM under 250MB. Force stopping Google Maps didn't bring the RAM back to normal or the system... Same with Endomondo as I used it yesterday to track my bike ride... had to reboot to get the system to a usable state.

The OS I'm using is 4.4.2 stock Touchwiz for a Samsung Galaxy S5.

Just to clarify, Touchwiz is the GUI, Kitkat 4.4.2 is the Android version. I had to look it up because I had never heard of Touchwiz being an Android version.
To the best of my knowledge, you would have to install the Eclipse Android development environment and use the Eclicpse Memory Analyzer on each application while it runs in a virtual Android device on your computer.

This is the way that I would do it. I am not really sure though if you will be able to test if the issue is related to the Touchwiz GUI or if it is related to the garbage collector that handles the opening and closing of apps in Kitkat 4.4.2. I am not really sure if Touchwiz can be installed in the development environment, since it looks like it is provided by Samsung, not Google.

I may be mistaken about this, and maybe someone more knowledgeable can verify this.

Here is an interesting discussion on the topic of android memory leaks.

Sorry, I should have been more specific... I've become too accustomed to Touchwiz being so meshed into the OS itself that I tend to forget they're separate. Anyway, I'll look into the Eclipse Memory Analyzer, however if I have to use it on every app on my device it might be quicker/easier to wipe and start fresh... unfortunately that's a mess in and of itself. One thing I notice on why the device gets so sluggish is that when the memory falls below 250MB, it begins swapping like crazy as evident by the kswapd0 process eating up CPU and causing insane amounts of I/O.

I'd like to exclude Touchwiz as being a culprit, since my friends with this device don't seem to have this issue =(