(I'm using bold words to refer to 'free -h' columns)

I have Arch Linux installed on my laptop with 4GB RAM. When I'm copying a large file (or doing anything involving file operations), I can see the Mem: buff/cache increasing using 'free -h'. Regardless of how much RAM I'm using at the moment, buff/cache grows up until there's only about 100mb of Mem: free memory. Then, when the value of Mem: free goes below 100mb, the system starts swapping. Usually about 35mb of data gets swapped, and it stays around that number. Then, as the file is still being copied, the data amount in Swap: used fluctuates between 1-2 megabytes. If 35mb are swapped, it becomes 36mb after a few seconds, and then after another few seconds it returns to 35mb. This fluctuation affects the performance as it continues swapping in and out until the file is copied. I've experienced this behaviour on Arch, PopOS and Elementary OS. So I thought this was normal for linux until...

I recently installed Linux Mint and noticed that this doesn't happen on it. No matter how large a file I try to copy, Mem: buff/cache grows until Mem: free goes below 100mb, and then it stabilizes. Mem: free value fluctuates slightly by about 10 megabytes. In Mint, swapping doesn't occur while copying files.

How does this happen? Does Mint have special settings that prevent unnecessary swapping? If it does how do I apply them to Arch or any other distro?

PS: Sorry for my bad English and the terrible structure of the question. I tried my best to put this together.

What you need to read is the linux kernel documentation on swapping, if you're going to rebuild the kernel. Usually it's in the Documentation directory of the kernel source. Otherwise do what the rest of us do: use your computer without fixating on figures.

Linux isn't windows. No BSOD in linux! It can run hundreds of processes any of which can want a chunk of ram to avoid crashing, and linux might give them the same chunk of ram. Then when one of them actually starts writing to that ram, it has to juggle things around, and tries to keep blocks contiguous (=together), rather than spread all over. It never wants to use the last byte, and does different things depending on the pressure it's under. Programs may have asked for a buffer, and they fill unpredictably. So if youi can figure what it's up to with free -h, you're smarter than me.

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probably you will find it interesting: www.linuxatemyram.com

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Thanks for the replies! I found out that the unresponsiveness during swapping data is caused by a bug in the linux kernel starting from 5.3.0

The problem doesn't occur on Linux Mint because it uses kernel 5.0