Hello,
My SSD, mounted only to my home dir, is getting roughly 100GB of writes per day. I'm at a loss for how this could be. I'm using only very normal SW, mail-client (I turned off the shred function some time ago), webbrowser, etc. The filesystem is NILFS2, which is designed for SSDs. I also setup fstrim without an effect on how much data is being written.

Does anyone have an idea how I can figure out what is going on?
For example, is there a way to track writes? I know about iotop, but it often just lists kernel processes, not what is causing the kernel to perform a write.

Thanks!

Website cache, most certainly. Video stream writes cache on your drive and deletes cache from your drive dynamically.
So you'll never see the cache directory inflate too much, but youtube for example does write quite a lot of that.
That said, everything's using disk as a cache dump these days, see: mesa shader cache, mozilla sqlite database.. etc..

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I moved the browser's complete folder to an HDD. Now I'm getting about 6GB of writes to the SSD per day.
Thanks guys!

Interesting...
If someone has spare ram, then, is it worth putting ~/.cache in a ramdisk?
How big would it need to be?

Sure, what I did couple of years ago well I mounted tmp as tmpfs (in fstab) according to some advice I was given around here. It was 2G of 4G RAM, so half by default, configurable.
After that I'd just create /tmp/cache1 on boot with a rc.local, and then use the browser about:config to point default cache dir at /tmp/cache1
For another browser, I'd use /tmp/cache2 and so forth. After grasping the concept, I've done also an extraction of full browser profile archive to /tmp on boot, which is a bit more advanced.
I could also recommend squid if you're into caching web stuff locally, takes a while to configure and has huge documentation, but works nice in my experience.
If you have a LOT of big files, iso images, videos etc. it's probably better to have a mechanical storage disk or something. I do have some SSDs but for systems only, not for storage.

Wouldn't a symlink from ~/.cache to /tmp/cache1 do it? That even saves farting about with default locations. Is that stuff ever read?

Probably worth mentioning it's ~/.cache/mozilla (if you're using firefox) and not ~/.cache (you'd likely want to keep the shader cache, and thumbnails for example).
If all of it is on tmpfs, on next boot you're basically recreating it all. Causing thumbnails to load slow, and forcing shaders to recompile.
But if you want to be thorough, sure, it can all go to tmpfs, even /home (where you might want to make some major changes in /etc/skel).

Yes, that would work fine.

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Something I discovered was that apparently there's an option browser.cache.disk.enable that will turn off caching on your disk. You might have to toggle something more than that. I'm not personally interested in the option, so I did not research it further.

Thanks for the reply. I'm not going to go with that option if I can find a better one, as I'm told the mesa shader cache will have to be recompiled constantly.

Looking at tmpfs, it's got 1.6G and nothing used according to 'df -h'. Tmpfs has a line in fstab So I've created a directory /dev/shm/chromium-ungoogled and put a symlink to it from ~/.cache/chromium-ungoogled, which seems to work. It's holding 51M at the moment because I rsync'ed the existing cache. That all vanishes of course if I umount tmpfs, either shutting it down or unmounting. I'll check it later.