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Whilst I've seem some similar questions, I can't troubleshoot the problem I am having as they tend to be specific to that user asking.
When I run my PC > 24 hours (I have reasons why I do this), my RAM usage creeps up. I had my PC on all weekend, and my ram was maxed out at 100%.
When I check in task manager, the usage is not accounted for at all. I have 32GB RAM, and usually the highest usage on the RAM will be a Google Chrome process with half a gig usage, a handful of processes over 100MB total, then others with smaller amounts. Never enough to account for the actual usage.
After looking through other answers I downloaded Process Explorer, and looked at the Working Set column. There is a process there called "memory Compression", with 6,344K private byes but a working set of 2,6922,748K. Thats at time of writing, where my PC hasn't been on as long as I noramlly would let it run in total before a reboot. Total RAM usage currently sits at 50%.
Some people suggested it might be a driver with a memory leak, but I am unsure how to diagnose a problem further here. Theres an image of some of what I'm seeing. In 1-3 days, I would expect to see that at 32 GB, but with seemingly no extra processes using RAM etc.