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Comment by nisa | Hacker News Reader

If you are on the experimental side:

There is also zram (just swap in memory lz4/lzo compressed) and zswap (compressed cache in memory for swap pages before hitting disk) that needs a real swap device but compresses pages beforehand.

I run zswap on my Desktop and on a few servers and it gives you some more time before the oom killer comes and the system feels a bit longer responsive.

zram is a nice idea but quite a beast in practice (at least on MIPS with 32mb RAM) sys constantly at 100% if you need it and other quirks. Maybe it got better or I did something wrong.

But if you need an in-memory compressed block-device it's pretty great - you can just format it with ext4 and have a lz4 compressed tmpfs.

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From what I understand, zram results in LRU cache inversion whereas zswap does not (as it intercepts calls to the kernel frontswap API). Although, if you have a workload that would benefit from MRU then I guess this is just a bonus :)

Zswap maintains default kernel memory allocation behaviour, with the tradeoff that it needs a backing swap device to push old pages out to (which is why zram tends to be used more often in embedded devices that only have a single volatile memory store, of devices with limited non-volatile storage).

I use zram rather than a regular swap partition on all my laptops (because I'd rather not swap on SSDs) and desktops (same reason and/or there is an absurd amount of RAM to begin with). I also hear that most chromebooks use zram too (you really don't want to be swapping on that eMMC memory).

I set it up with one zram device per CPU core for a total space of ~20% available RAM.

No performance issues w/ zram so far so I haven't felt the need to change the compression algorithm.

zram has worked fine on my chromebooks. This is with running multiple chroots - and I have hit the oom killer a number of times (when even zram swap wasn't enough).

Until you actually run out of memory, zram seems very much a set-and-forget type of thing. No babysitting required.

tl;dr: it does what it says on the tin, and ... with minimal cpu impact.

First I've heard of either. How would I set these up?

You can setup zram like this. Typically you'll want to make a service for it since it needs to run on every boot.

  # modprobe zram num_devices=1
  # echo 1G > /sys/block/zram0/disksize
  # mkswap zram0 /dev/zram0 -L zram0
  # swapon -p 100 /dev/zram0

Official documentation here: https://www.kernel.org/doc/Documentation/blockdev/zram.txt

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