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As you run Firefox, it leaks memory. This is well known by now, I am sure, and it should go away by closing and reopening it right, because a process's memory is freed on closing, right? That's what I thought, but Process Explorer, and my computer's pop-ups saying "Close programs to prevent information loss", disagree with me. Notice the System Commit in the following two screenshots below (my understanding is that this is equivalent to amount of space consumed on the allocated page file) - it is far higher than the combined sum of all memory usage by all processes Process Explorer shows, even after closing and re-opening Firefox:

Showing that the system commit is high. (You can't see it in this screenshot, but it's larger than the combined memory usage of all processes by about half an order of magnitude. It increases over time the longer firefox runs and leaks memory.) More global memory usage information

When I close and re-open Firefox, instead of all of the System Commit leak it has produced being removed, it only removes the amount of memory it has at that point in time - up to about 3 gigabytes at worst, but it can leak 30+ gigabytes of System Commit. In this case I only get back about 0.9GB, barely enough to run Firefox again:

Now I close Firefox. This is the dent it makes in system commit - not the total amount of system commit it has leaked all time, but only the amount of memory it was using at that point in time. I would like to know how to recover the rest of the system commit Firefox has used in the past but clearly is not using anymore without restarting my computer.

Since Firefox leaks more System Commit than it has memory at any point in time, this eventually leads to a state of being unable to run anything new until I restart my computer, which fixes the problem.

I have tried increasing the page file, no good - Firefox just consumes however extra amount of System Commit I let it have! (And you could just say, 'Swap to another browser' - but what if that browser also has a System Commit leak, or what if I experience it with a different program entirely for which there is no alternative? So I am looking for a general solution.)

What steps can I take to restore System Commit to normal levels, without restarting my computer? (I do not need Firefox's memory leak itself to be fixed - I am fine with having to restart it every now and again, because it does so very promptly, so this is distinct from asking about fixing Firefox itself.)

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I don't think your problem has anything to do with FF - all the memory it takes is released when closed. Run Sysinternals' RAMMap, and see what holds you memory (I think it shows the pagefile as well). – EliadTech Jun 10 '14 at 10:34
If restarting Firefox does not fix the "memory leak" then its not a Firefox's memory leak. – Ramhound Jun 10 '14 at 10:52
@EliadTech Thanks for the RAMMap shoutout, this looks like exactly the tool I need to explore further. If I end up solving this myself I will self-answer. – Patashu Jun 10 '14 at 11:06
Do you get the same issue if you perform a clean boot? – and31415 Jun 11 '14 at 7:05

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