# 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`.