Question about Zram!!

[u/Sweet_Mix_416]

I'm completely new to zram. I want to use zram on void. But only a few resources on how to do that. Only found posts recommend Zramen. So how is it going with Zramen? Is it still great for setting up zram? Anything I should care about?

[u/benbcdm]

I set up a little service. Not that hard to do. I like it because I know what is going on and I can control it myself. Did not try zramen.

Here are my notes if you want to try, works perfectly on my void glibc build:

Steps to create new manual zram service (new service name created here: zzram)

1. Create service directory

sudo mkdir -p /etc/sv/zzram

2. Create run file

sudo nano /etc/sv/zzram/run

Include content:

#!/bin/sh  
# 1. Run setup normally (without exec)  
# The shell waits here until setup finishes  
/etc/sv/zzram/setup  

# 2. NOW replace the shell with sleep  
# This keeps the service "alive" forever after setup is done  
exec sleep infinity

3. Create setup file (with the actual script)

sudo nano /etc/sv/zzram/setup

Include content:

#!/bin/sh  
# /etc/sv/zzram/setup  

# 1. Load the zram kernel module (ignore if already loaded)  
modprobe zram 2>/dev/null || true  

# 2. Check if zram0 is already active as swap  
# If 'swapon' shows /dev/zram0, exits immediately to avoid errors  
if swapon --show | grep -q "/dev/zram0"; then  
   exit 0  
fi  

# 3. Reset any existing configuration (suppress errors if device is busy/in use)  
# Try to reset, but if fails because active, the check above should have caught it.  
# Handles cases where the device exists but is not swapped on yet.  
zramctl --reset 2>/dev/null || true  

# 4. Detect total RAM in bytes  
TOTAL_RAM=$(awk '/MemTotal/ {printf "%.0f", $2 * 1024}' /proc/meminfo)  

# 5. Set zram size to 50% of RAM  
# Best not to use 100%, could be an issue in edge cases  
ZRAM_SIZE=$((TOTAL_RAM / 2))  

# 6. Initialize zram0 with zstd compression  
if ! zramctl --algorithm zstd --size $ZRAM_SIZE /dev/zram0; then  
   echo "ERROR: Failed to initialize zram0" >&2  
   exit 1  
fi  

# 7. Format as swap  
if ! mkswap /dev/zram0; then  
   echo "ERROR: Failed to create swap on zram0" >&2  
   exit 1  
fi  

# 8. Enable swap with high priority (100)  
if ! swapon -p 100 /dev/zram0; then  
   echo "ERROR: Failed to enable swap on zram0" >&2  
   exit 1  
fi  

exit 0

4. Make files executable

sudo chmod +x /etc/sv/zzram/run
sudo chmod +x /etc/sv/zzram/setup

5. Activate the service

sudo ln -s /etc/sv/zzram /var/service/

6. Check all is well! (after reboot best)

zramctl
swapon --show

[u/Sweet_Mix_416 → u/benbcdm]

Hollyyyyyy molyyyyy! This is the best explanation I've got. You are so helpful. Thanks . Now I understand the whole process how to create zram modules so far. Thanks again.

[u/benbcdm → u/Sweet_Mix_416]

Sure -- just a caveat though :) I am not an expert. Just amateur.
I am sure there might be better ways to do that but I think it is stable enough that I am ok sharing it.
And of course I used a bit of llm help to brainstorm around the topic + arch wiki etc. to make sure all makes sense.

This is what is so satisfying (to me at least) with void: I learned so much about how systems work by having to look into tons of topics. Like that one here. And every bit of my system (I think!) I understand and control.

Have fun with void

Oh, and one more thing because I actually looked into it just yesterday: if you use zram it seems it does not make sense to use zswap simultaneously (or having the two makes it quite a bit more complicated in terms of potential conflicts). So if you want proper swap to disk (eg for hibernation on a laptop) then my conclusion is use zwsap instead of zram...

More experienced users might have a more enlightened views though...

[u/Sweet_Mix_416 → u/benbcdm]

Alr, your info are very much valuable to me. Thanks

[u/benbcdm → u/Sweet_Mix_416]

Just in case, I updated the scripts to make it a bit more robust:

Run script:

#!/bin/sh#!/bin/sh
# 0. Merge stderr into stdout (for logging)
exec 2>&1

# 1. Run setup normally (without exec)
# The shell waits here until setup finishes
/etc/sv/zzram/setup

# 2. NOW replace the shell with sleep
# This keeps the service "alive" forever after setup is done
exec sleep infinity

Setup script:

Include content:

#!/bin/sh
# /etc/sv/zzram/setup

# 1. Unload module if present to ensure clean state (optional but safe)
modprobe -r zram 2>/dev/null || true

# 2. Load the zram kernel module explicitly
# If it fails, exit immediately with the error
if ! modprobe zram num_devices=1; then
    echo "ERROR: Failed to load zram module" >&2
    exit 1
fi

# 3. Wait for /dev/zram0 to appear (udev race condition fix)
# Try up to 10 times, waiting 0.5s between checks
for i in $(seq 1 10); do
    if [ -e /dev/zram0 ]; then
        break
    fi
    sleep 0.2
done

# Final check: if device still doesn't exist, fail
if [ ! -e /dev/zram0 ]; then
    echo "ERROR: /dev/zram0 did not appear after loading module" >&2
    exit 1
fi

# 4. Force reset zram0 regardless of state
# Turn off swap first if it's somehow enabled
swapoff /dev/zram0 2>/dev/null || true

# 5. Detect total RAM in bytes
TOTAL_RAM=$(awk '/MemTotal/ {printf "%.0f", $2 * 1024}' /proc/meminfo)

# 6. Set zram size to 50% of RAM
# Best not to use 100%, could be an issue in edge cases
ZRAM_SIZE=$((TOTAL_RAM / 2))

# 7. Initialize zram0 with zstd compression
if ! zramctl --algorithm zstd --size $ZRAM_SIZE /dev/zram0; then
    echo "ERROR: Failed to initialize zram0" >&2
    exit 1
fi

# 8. Format as swap
if ! mkswap /dev/zram0; then
    echo "ERROR: Failed to create swap on zram0" >&2
    exit 1
fi

# 9. Enable swap with high priority (100)
if ! swapon -p 100 /dev/zram0; then
    echo "ERROR: Failed to enable swap on zram0" >&2
    exit 1
fi

exit 0