I got a cheap netbook style laptop for traveling some weeks ago (HP Stream 11" with 4 GB of RAM and a N4120). Didn't expect much more from this hardware than opening a few browser tabs and doing some retro gaming via Steam.
Shared RAM with graphics card means that 3.64 GB of RAM are effectively usable for the OS. This was even too little RAM to open a handful of tabs w/o having tabs being unresponsive for seconds sometimes in a very annoying way. Another thing which made trouble was the Wifi - I guess it went into power saving, was swapped and didn't load fast enough to provide a good experience. (Of course I wasted an hour checking for Wifi drivers/support.)
In short: Even for my low expectations for this laptop it was an underwhelming experience.
First step was to look at my vm.swappiness and set it to 10, which already helped, but still the machine had hiccups and annoying timeouts.
In a last, desperate effort I enabled ZRAM on the laptop... and literally WTF: Saying it is a night and day difference doesn't do the experience justice. Typing this words now on the Stream, which I use exactly the same way as my much more beefy other machines (my next worst computer has 8G of RAM and an Intel Core i3), browsing with 10 open tabs, e-mail client open on another virtual desktop... it is crazy, it makes the Stream fun to use and I use it at home for everything which isn't heavily CPU/IO bound.
What surprised me the most: No hiccups, no timeouts and it even fixed the Wifi issues on this little machine. Didn't expect this would be possible, especially with a N4120 and 3.64 GB of RAM.
In short, my laptop changed from not even reaching my low/realistic expectations to being my favorite technical purchase of the last years, thanks to ZRAM.
Besides making this a ZRAM appreciation post, I really want to spread the word about it. Especially for old hardware and limited RAM situations, IMHO it should be the first thing which comes to mind/is recommended.
Fedora and PopOS use it by default, so it is well tested and should IMHO again, be a default at least for desktop setups.
Give it a try - supposedly it even improved the experience on much more beefy computers for gaming etc.
I am using Debian 12 and I am pretty sure zswap is not enabled by default.
With zstd the compression ratio is better than 3 in all experiments I saw. (Of course you won't get this numbers for random/encrypted data). Right now I have 12MB compressed to 2MB via ZRAM (fresh reboot) which is a factor of 6.
So, taking 3 as factor learned from others and my experience, with 1.8 GB of ZRAM I can store 5.4 GB of memory, adding the 1.8 GB of usual RAM, I end up with 7.2 GB of RAM which is double my 3.6 GB RAM I started with. (All this is backed by 4 GB of physical SWAP.)
Sorry, I cannot really answer your questions concerning zswap vs ZRAM, I just follow the herd and trust that the Fedora people usually have good reasons for their technical choices and are deploying ZRAM by default for several years now.
Just btw, while zstd's compression ratio might be stronger, it will not be as fast as something like lzo-rle. When it comes to RAM you will definitely want to prefer speed unless you have a strict space usage requirement.
A valid point and hard to find an objectively right answer (I searched for some information regarding this topic and found for example [this](https://www.reddit.com/r/Fedora/comments/mzun99/new_zram_tuning_benchmarks/ thread on reddit).
In my totally not scientific benchmark of running my backup script with time, LZ4 clearly outperformed ZSTD and no ZRAM at all, when I was generating some CPU load in the background. (LZ4 was 14% faster compared with ZSTD, 19% faster compared to no ZRAM).
I am thinking about switching to LZ4 or even lzo-rle for some time and observe, if I hit the physical swap. If not, I hope to get some speed advantage and perhaps a few minutes longer battery life.