Increasing performance on low-RAM

Increase the performance of a low-RAM system by increasing swap space, swappiness and decreasing cache pressure. Basically, make it not hang.

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Oct 26, 2018
System Administration
4 minutes

tl;dr

 1# Increase swappiness & cache pressure
 2sudo echo "
 3# increase swappiness
 4# https://help.ubuntu.com/community/SwapFaq
 5vm.swappiness=100
 6
 7# Cache Pressure Setting
 8# https://www.digitalocean.com/community/tutorials/how-to-add-swap-space-on-ubuntu-18-04
 9vm.vfs_cache_pressure=50" >> /etc/sysctl.conf
10
11# Create a new swap file and delete the old one
12sudo fallocate -l 8G /swapfile8G # create new file
13sudo chmod 600 /swapfile8G # recommended permissions
14sudo mkswap /swapfile8G # format file as swap
15sudo swapon /swapfile8G # turn it on
16sudo swapoff /swapfile # turn off old swapfile
17sudo sudo rm -rf /swapfile # remove old swap file
18sudo swapon -s # verify 
19
20# After all edit your /etc/fstab, if you use it to turn on swap when reboot, to switch /swapfile to /swapfile8G
21sudo nano /etc/fstab
22# /var/swapfile8G none swap sw 0 0

background:

I have an old Acer Aspire 5742 with 4GB of RAM that i’m trying to use for dev work. But the darn thing hangs up after running out of memory. The stuff i’m running is not much - VS Code, npm, Chromium with 6 or so tabs, Sublime Text for note taking and File explorer.

The OS i have installed is Ubuntu Budgie 18.04.

The existing swap file was 2GB in size, which means i was running out on apprx. 6.5GB of memory+swap.

what i can’t do:

buy more RAM. this thing uses DDR3 1033MHz RAMs and can only support a max of 8GB. In order to upgrade i’d have to buy outdated technology that isn’t readily available and costs too much.

what i can do:

make OS tweaks like increasing swap size and swappiness
disable/remove processes i don’t need to free up RAM

swappiness

The swappiness parameter controls the tendency of the kernel to move processes out of physical memory and onto the swap disk.

1# check current cache presure value
2sudo sysctl vm.swappiness

1sudo nano /etc/sysctl.conf

Add the following to the end of file

vm.swappiness=100

100 is maximum. Since i have an SSD, i’m not too worried about moving processes onto disk, SSDs are fast enough to handle it.

increase swap file size

i don’t have a swap partition, i have a swap file (in the / dir) that is already in place. This file which is 2GB in size was created when i installed the OS. You can verify whether a swap os being used with sudo swapon --show, swapon --all or free -h

1sudo swapon --show

1NAME      TYPE SIZE USED PRIO
2/swapfile file   2G 1.6G   -2

No output means no swap file.

1free -h

              total        used        free      shared  buff/cache   available
Mem:           3.5G        2.7G        149M        353M        732M        308M
Swap:          2.0G

resize the old swap

 1# Turn all swap off
 2sudo swapoff -a
 3
 4# Resize the swapfile
 5sudo dd if=/dev/zero of=/swapfile bs=1M count=1024
 6
 7# Make swapfile usable
 8sudo mkswap /swapfile
 9
10# Make swapon again
11sudo swapon /swapfile

create and enable a new swap file and delete the old one

For 4GB RAM, i can add a maximum of 8GB swap file, i.e. double the size of the physical memory.

1sudo fallocate -l 8G /swapfile8G # create new file
2sudo chmod 600 /swapfile8G # recommended permissions
3sudo mkswap /swapfile8G # format file as swap
4sudo swapon /swapfile8G # turn it on
5sudo swapoff /swapfile # turn off old swapfile
6sudo sudo rm -rf /swapfile # remove old swap file
7sudo swapon -s # verify 
8# After all edit your /etc/fstab, if you use it to turn on swap when reboot, to switch /swapfile to /swapfile8G

1# After all edit your /etc/fstab, if you use it to turn on swap when reboot, to switch /swapfile to /swapfile8G
2sudo nano /etc/fstab

/var/swapfile8G none swap sw 0 0

Cache pressure setting

1# check current cache presure value
2sudo sysctl vm.vfs_cache_pressure

1sudo nano /etc/sysctl.conf

vm.vfs_cache_pressure=50

Decreasing vfs_cache_pressure causes the kernel to prefer to retain dentry and inode caches, which basically is access data about the file system and is requested frequently.

Notes