ZRAM Swap Activation

[Forum Admin SamK]

This is rescued from the defunct antiX forum for the benefit of new users who cannot access that old forum and others who might not have seen the original topic. It deals with starting, and checking, zram and tweaking related performance on an old system manufactured around 2009.

Wed Nov 04, 2015 6:45 am #5
quote SamK

Wed Nov 04, 2015 quote
rokytnji:
Can I get the command syntax to run zram at boot as user root for AntiX/icewm startup?

Try the steps outlined in zram file

sudo cp /usr/local/bin/zram  / etc/init.d/
sudo update-rc.d zram defaults

Reboot

Check whether zram loaded

lsmod | grep zram
sudo swapon --summary

Wed Nov 04, 2015
quote rokytnji:

$ harry@biker:~
lsmod | grep zram
zram                   24576  2
lz4_compress           16384  1 zram
harry@biker:~
$ sudo swapon --summary
[sudo] password for harry:
Filename Type Size Used Priority
/dev/zram0                             partition 257172 0 100
/dev/zram1                             partition 257172 0 100

Thank you very much SamK. Readout is after a reboot on this netbook.

$ linuxinfo
Linux biker 4.2.1-antix.2-486-smp #5 SMP Wed Sep 30 15:14:04 EEST 2015
Two Intel Unknown 1600MHz processors, 6383.92 total bogomips, 2009M RAM
System library 2.19.0

$ free
            total       used       free     shared    buffers     cached
Mem:       2057400     564356    1493044      35036      29436     247932
-/+ buffers/cache:     286988    1770412
Swap:       514344          0     514344

$ sudo parted -l
Model: ATA KingSpec KSD-ZF1 (scsi)
Disk /dev/sda: 63.3GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type     File system  Flags
1      1049kB  8914MB  8913MB  primary  ext4
2      8914MB  63.3GB  54.4GB  primary  ext4

Model: Unknown (unknown)
Disk /dev/zram0: 263MB
Sector size (logical/physical): 4096B/4096B
Partition Table: loop
Disk Flags:

Number  Start  End    Size   File system     Flags
1      0.00B  263MB  263MB  linux-swap(v1)

Model: Unknown (unknown)
Disk /dev/zram1: 263MB
Sector size (logical/physical): 4096B/4096B
Partition Table: loop
Disk Flags:

Number  Start  End    Size   File system     Flags
1      0.00B  263MB  263MB  linux-swap(v1)

I love learning something new every day. 🙂

Thu Nov 05, 2015 7:36 am #7
SamK:

rokytnji wrote:
I love learning something new every day.

With zram working there are plenty of opportunities for that.

Things to explore…

If the amount of swap space created by zram is not large enough for your needs you might partner zram swap with a conventional swap file. You have the choice of starting them manually and individually after boot-up, or automatically during boot-up (zram via /etc/init.d/zram and swap file via /etc/rc.local).

If you use zram and a swap file in partnership, you might want to manage the order in which they are used. A swap space in RAM is faster than a swap file in conventional storage. Consider whether there is any benefit to your local system in assigning the zram swap space a higher priority than the swap file. zram space is usually created with a priority of 100. Assign a lower priority to the swap file (e.g. 90) when activating via the swapon command.

The way in which your system handles any and all swap spaces can be tuned with plenty of scope for experimentaion. The following are entries that I have used for some years as starting points in /etc/sysctl.d/local.conf. They are then adjusted to suit the characteristics of the particular system.

# Uncomment the following two values to improve percieved system performance
# Threshold at which swapping starts
# Values lower than default favour filling physical RAM before begining to use a swap area 
# Default vm.swappiness=60
vm.swappiness=10
#
# Threshold at which the directory and inode caches are reclaimed
# Values lower than default favour retaining them rather than recovering the memory they occupy
# Default vm.vfs_cache_pressure=100
vm.vfs_cache_pressure=50

A related matter…

I know you are moving to newer kit than previously. I mention the following just in case you try zram on older kit.

The basic action of zram is to create a swap space per CPU in the local system (zram0, zram1…). In a modern system with multiple CPUs the shipped zram script does this OK. In an older single CPU system the shipped zram script calculates the number incorrectly and therefore creates an incorrect number of swap spaces. It still works but just with the wrong number of swap spaces.

Because antiX is aimed at both modern and older kit I found the shipped zram script disappointing and unsatisfactory. Eventually I decided to do something about it and rewrote my own version of the zram script which works correctly with both single and multiple CPU systems.

[Anonymous]

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::

v— paraphrased instructions found in 2012 oldforums topic

To have zRam start at bootup:

• cp /usr/local/bin/zram /etc/init.d/zram
• ensure owner and group are root:root
• ensure permissions are rwxr-xr-x
• run the command update-rc.d zram defaults
• reboot the system

To check that it has loaded, look at the size of the swap reported by conky (if you use conky). Alternatively, a command such as blkid -o list should list a /dev/zram0 mounted as swap

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