DietPi-Swapfile auto-sizing can try to create it larger than available free space

[Jaffa]

Details:

• Date | Sat 1 Sep 12:16:01 BST 2018
• Bug report | N/A
• DietPi version | v6.14
• Img creator | DietPi Core Team
• Pre-image | Raspbian Lite
• SBC device | RPi Zero W (armv6l) (index=1)
• Kernel version | #1134 Tue Aug 14 16:58:07 BST 2018
• Distro | stretch (index=4)
• Command | fallocate -l 1567M /var/swap
• Exit code | 1
• Software title | DietPi-Swapfile

Steps to reproduce:

1. Leave default AUTO_SETUP_SWAPFILE_SIZE=1 in dietpi.txt
2. Install v6.13 on to 2GB SD card using Etcher
3. Configure AUTO_SETUP_AUTOMATED.
4. Wait

Expected behaviour:

DietPi-Swapfile configures swap size to take into account free space on device.

Actual behaviour:

According to the comment in dietpi.txt, AUTO_SETUP_SWAPFILE_SIZE=1 tries to set the swap file to 2GB - _RAM_. On a Raspberry Pi Zero W, this explains why it's trying to create a 1.5GB swap file.

However, on a 2GB SD card, which Etcher/the default image has partioned into a 1.8GB / partition, and ~500MB has been used by the base install, the swap size should probably be maxed out at about half of the free space (~500-600MB).

Additional logs:

[  OK  ] DietPi-Software | Free space check: path=/ | available=1207 MB | required=500 MB
...
[  OK  ] DietPi-Swapfile | swapoff -a
[ INFO ] DietPi-Swapfile | Deleting existing swapfile (/var/swap)
[ SUB1 ] DietPi-Swapfile > Generating new swapfile
[ INFO ] DietPi-Swapfile | Size     = 1567 MB
[ INFO ] DietPi-Swapfile | Location = /var/swap
[FAILED] DietPi-Swapfile | fallocate -l 1567M /var/swap
fallocate: fallocate failed: No space left on device

[Jaffa]

/DietPi/dietpi/func/dietpi-set_dphys-swapfile currently does:

SWAP_SIZE_TARGET=$(( 2048 - $(free -m | grep -m1 'Mem:' | awk '{print $2}') ))

We can get the disk space available in MB for $SWAP_LOCATION with, and half it, with:

MAX_SWAP_SIZE=$(( $(df --output=avail /var/opt | tail -n 1) / 1024 / 2))
if (( $SWAP_SIZE_TARGET > $MAX_SWAP_SIZE )); then
  SWAP_SIZE_TARGET=$MAX_SWAP_SIZE
fi

[Jaffa]

Confirmed the following works:

        MAX_SWAP_SIZE=$(( $(df --output=avail $(dirname "$SWAP_LOCATION") | tail -n 1) / 1024 / 2))
        if (( $SWAP_SIZE_TARGET > $MAX_SWAP_SIZE )); then

            SWAP_SIZE_TARGET=$MAX_SWAP_SIZE

        fi

[MichaIng]

@Jaffa
Many thanks for your report and providing already the solution 👍.

We already have a free space check function ([ OK ] DietPi-Software | Free space check: path=/ | available=1207 MB | required=500 MB), but the 500M is just checked as default on dietpi-software start, but is not used/checked on swapfile creation. We will fix this for v6.15.

[Jaffa]

Ah, cool. Great stuff!

[Fourdee]

@Jaffa @MichaIng

Resolved for v6.15 (ETA: few days release):

root@DietPi:~# /DietPi/dietpi/func/dietpi-set_dphys-swapfile 1000000 /var/swap
[  OK  ] Root access verified.
[FAILED] DietPi-Swapfile | Free space check: path=/var/swap | available=12996 MB | required=1000000 MB
[FAILED] DietPi-Swapfile | Unable to generate swapfile due to insufficient disk space. Swap will be disabled.

 DietPi-Swapfile
─────────────────────────────────────────────────────
 Mode: Disable swapfile

[  OK  ] DietPi-Swapfile | swapoff -a
[ INFO ] DietPi-Swapfile | Deleting existing swapfile (/var/swap)
[ INFO ] DietPi-Swapfile | Setting /tmp tmpfs size: 1006M
[  OK  ] DietPi-Swapfile | mount -o remount,size=1006M tmpfs /tmp

Completed.

[Jaffa]

@Fourdee, thanks. That works great when you've explicitly requested a size (i.e. >= 2). When it's set to 1 (AUTO), should it be more intelligent (as I suggest above) in selecting a size? Or should it just give up, as you've done?

[Fourdee]

@Jaffa

That works great when you've explicitly requested a size (i.e. >= 2). When it's set to 1 (AUTO), should it be more intelligent (as I suggest above) in selecting a size?

Regardless of the size input (auto or manual), if the required space is lower than what is available, the swapfile will simply be removed (if it exists), then disabled.

Please bear in mind, this fix will be only be available in v6.15 release. Which has been delayed a few days due to RL.

[Jaffa]

@Fourdee, understood.

if the required space is lower than what is available, the swapfile will simply be removed (if it exists), then disabled.

Sorry I wasn't clear: my suggestion for auto was that the calculation of the "required space" takes into account the "available space".

Currently auto results in "required space" of:

2GB - $RAM

However, above, I propose changing auto to have a "required space" for the swap file of:

min(2GB - $RAM, $AVAILABLE / 2)

Then, if you have swap enabled & in auto size mode, you'll end up with a size appropriate to the space and RAM available.

[MichaIng]

@Jaffa
Makes sense, although $AVAILABLE / 2 is perhaps a bid random and still dangerous if the available space is already small. Maybe better $AVAILABLE - 500M, as 500M is what we check before starting up dietpi-software, and block creation completely if result is negative, thus less then 500M is available?

Maybe also 200M free is sufficient for daily work + some software install. dietpi-software could be adjusted for this, also since downloads are not placed inside RAM and auto removed after extraction. Of course can always fail, if you just select too much software at once, thus would put more responsibility to end user. But actually this is another topic 😄.

[Jaffa]

Yep, $AVAILABLE - 500M (or similar) would be smarter.