Optimizing Memory With Zram on Ubuntu Server 22.04
Recently at work, I had the pleasure of supporting a local university with their Linux infrastructure. I love working with universities: they are typically big open source users, and often operate at massive scale.
What’s particularly noteworthy though, is that, in my experience, most also contribute back to the community in one form or another - be it through purchasing support, code contributions, or other means.
And here’s a potentially controversial observation I’ve made over the years: there’s a distinct “academic mindset” that makes technical IT collaborations surprisingly smooth with academic circles, even with non-technical users. 🤓
Back to today’s topic.
One recent challenge we tackled involved a cluster of memory-constrained servers. These machines were working hard, running various research applications and services, but they needed a bit more breathing room in terms of RAM.
Enter one of my long-time favorites: zram.
It’s an elegant solution that I’ve relied on many times over the years, and I thought it worth documenting the implementation process for future reference.
What is zram and Why Use It?
zram creates a compressed block device in RAM, effectively creating a compressed swap space that exists in memory rather than on disk. Unlike traditional swap space that writes to disk (slow) or zswap that only acts as a compressed cache for swap, zram provides a fully compressed RAM disk.
The advantages are significant:
- Better compression ratios than
zswap - No disk I/O overhead like traditional swap
- Lower latency as everything stays in RAM
- Particularly effective for servers where memory pressure is an issue but disk swapping would be detrimental to performance - or even make issues worse
Implementation Guide
1. Verify Current Swap Configuration
First, check if any swap is currently enabled.
If swap is configured, you might see something like:
$ cat /proc/swaps
Filename Type Size Used Priority
/swapfile file 102400 102400 -2
You’ll need to first shut this down with swapoff -a, then commenting the swap out in your /etc/fstab config file, and (optinnaly) delete that swap file or partition.
If there’s no swap currently configured on this system.
2. Verify zswap Status
Make sure zswap isn’t enabled:
$ cat /sys/module/zswap/parameters/enabled
N
Command returner “N”. We are good to go.
3. Install zram
Ubuntu makes this straightforward with the zram-config package:
$ apt install util-linux zram-config
[... installation output ...]
4. Configure zram
The default configuration is in /usr/bin/init-zram-swapping. You might want to review or adjust the settings based on your needs.
By default, Ubuntu configures zram to use about 50% of your RAM. This is usually a good starting point, but you can adjust this based on your workload patterns.
5. Verify Implementation
After a reboot, you can verify your zram configuration:
$ free -hm
total used free shared buff/cache available
Mem: 62Gi 11Gi 36Gi 8.1Gi 14Gi 42Gi
Swap: 31Gi 0.0Ki 31Gi
As we can see, we now have 31GB of compressed swap space available in RAM, which effectively increases our memory capacity through compression.
Monitoring and Maintenance
Keep an eye on your zram usage through standard tools like free, htop, or zramctl.
> $ zramctl
NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lzo-rle 31.4G 4K 74B 12K 8 [SWAP]
In the present case, it’s pretty much unused - for now.
If you notice high utilization of the zram space, at some point your system will need more physical RAM.
Conclusion
zram provides an elegant solution for memory-constrained servers, offering better performance than traditional swap while being easier to configure than alternatives like zswap. While it’s not a replacement for adequate physical RAM, it can help optimize memory usage and improve system performance under pressure.
Remember that your mileage may vary depending on your specific workload and memory usage patterns. Be sure to monitor your system after implementation.
Hope this helps!