92 lines
3.4 KiB
Markdown
92 lines
3.4 KiB
Markdown
# zram swap on hp-chell (KDE neon)
|
|
|
|
Set up **2026-03-05**, reconstructed on 2026-09-27 from `~/.bash_history`
|
|
and the live config. It replaces the disk swapfile with compressed swap
|
|
in RAM. That suits this machine: 15GiB RAM, and neon's root lives on a
|
|
slow microSD card in the built-in slot (`sda`) that you don't want to swap to or wear
|
|
out.
|
|
|
|
## Current state (2026-09-27)
|
|
|
|
```
|
|
$ zramctl
|
|
NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
|
|
/dev/zram0 zstd 8G 4K 59B 20K [SWAP]
|
|
$ swapon --show
|
|
NAME TYPE SIZE USED PRIO
|
|
/dev/zram0 partition 8G 0B 100
|
|
```
|
|
|
|
The zram device is the only swap. zswap is off
|
|
(`/sys/module/zswap/parameters/enabled` = `N`), and there's nothing
|
|
zram-related on the kernel command line.
|
|
|
|
## What was done
|
|
|
|
1. **Installed `zram-tools`** (Debian's simple `zramswap` service; not
|
|
`systemd-zram-generator`, which isn't installed):
|
|
`sudo apt install zram-tools`, `sudo systemctl enable --now zramswap`.
|
|
2. **Configured `/etc/default/zramswap`**. The file is still the
|
|
package's own conffile (`dpkg -V zram-tools` flags it as modified),
|
|
with these lines added at the end:
|
|
```
|
|
ENABLED=true
|
|
ALGO=zstd
|
|
SIZE=8192
|
|
PRIORITY=100
|
|
```
|
|
- `ALGO=zstd`: better compression than the default `lz4`, at some
|
|
CPU cost. Fine on this 4-core Core m7 for swap-sized traffic.
|
|
- `SIZE=8192`: an 8GiB zram device, a fixed size in MiB. `PERCENT`
|
|
isn't set; if set, it would override `SIZE`. That's the uncompressed
|
|
capacity; actual RAM used is the compressed size (`COMPR`/`TOTAL`
|
|
in `zramctl`).
|
|
- `PRIORITY=100`: above any disk swap, so zram is used first.
|
|
|
|
Tuned over several stop/edit/start rounds (the history shows
|
|
`systemctl stop zramswap` / `nano` / `start` three or four times).
|
|
Only the final values are known. Apply changes with
|
|
`sudo systemctl restart zramswap`.
|
|
3. **Disabled the disk swapfile**: in `/etc/fstab`,
|
|
```
|
|
# removed swapfile, using zram instead
|
|
#/swapfile swap swap defaults 0 0
|
|
```
|
|
then `sudo swapoff /swapfile`.
|
|
4. **Raised `vm.swappiness` to 100**, at runtime only
|
|
(`sudo sysctl vm.swappiness=100`). See the loose ends below.
|
|
|
|
## Loose ends (fixed 2026-09-27)
|
|
|
|
- **`vm.swappiness=100` hadn't been made persistent**: it had been set
|
|
with `sysctl` at runtime only and was back to the default 60. Now
|
|
persisted in `/etc/sysctl.d/99-zram.conf` (`vm.swappiness=100`) and
|
|
applied live. Swapping to zram is cheap, so a high swappiness is the
|
|
usual choice. Not changed: `vm.page-cluster` (still `3`). Some zram
|
|
guides set it to `0`, since zram has no seek cost and readahead just
|
|
wastes work.
|
|
- **The unused `/swapfile`** (512MiB, dated 2026-03-04, fstab line
|
|
commented out) was deleted. On 2026-09-28 a new **16GB `/swapfile`**
|
|
was added at priority 10 (below zram's 100) for hibernation. See
|
|
"Suspend-then-hibernate" in `NEON-CUSTOMIZATIONS.md`. zram is still
|
|
the everyday swap.
|
|
|
|
## Reapplying on a fresh neon install
|
|
|
|
```
|
|
sudo apt install zram-tools
|
|
sudo tee -a /etc/default/zramswap >/dev/null <<'EOF'
|
|
ENABLED=true
|
|
ALGO=zstd
|
|
SIZE=8192
|
|
PRIORITY=100
|
|
EOF
|
|
sudo systemctl enable --now zramswap
|
|
# comment out any /swapfile line in /etc/fstab, then:
|
|
sudo swapoff /swapfile
|
|
# persist swappiness
|
|
echo 'vm.swappiness=100' | sudo tee /etc/sysctl.d/99-zram.conf && sudo sysctl --system
|
|
```
|
|
|
|
Check with `zramctl` and `swapon --show`.
|