Linux/PROCESSOR-SDK-AM335X: Unable to use swapfile on Linux kernel 3.12

Ankur Tank

Expert 2985 points

Part Number: PROCESSOR-SDK-AM335X

Tool/software: Linux

Hello experts,

We are using Beaglbone Black based custom board, with 256MB RAM and 4GB eMMC, with kernel 3.12

I wanted to test swapfile on the board, I followed following steps to create swap file and mount it as swap partition.

Added following lines in /etc/fstab

/var/eventlog/swap/swapfile none swap sw,pri=32767 0 0

Then followed steps.

mkdir -p /var/eventlog/swap/
dd if=/dev/zero of=/var/eventlog/swap/swapfile bs=1M count=256
chmod 0600 /var/eventlog/swap/swapfile
mkswap /var/eventlog/swap/swapfile
swapon /var/eventlog/swap/swapfile

After that I in free command I see following output

# free 
             total         used         free       shared      buffers
Mem:        251324       132244       119080            0         5668
-/+ buffers:             126576       124748
Swap:       262140            0       262140

Following is output of /proc/swaps

# cat /proc/swaps 
Filename				Type		Size	Used	Priority
/var/eventlog/swap/swapfile             file		262140	0	-1

So swap seems to be enabled,

Then I ran memory intensive tasks in the system (tar extraction), I see free memory going low but pages are not swapped out to swapfile

I don't know what is going wrong,

Any suggestion, pointer ?

Thank you,

Regards,

Ankur

over 8 years ago

0 Cvetolin Shulev-XID over 8 years ago

TI__Guru 65405 points

Hi Anhur,

Are you using an official TI'a Linux release?
Do you have writing permissions?

BR
Tsvetolin Shulev

0 Ankur Tank over 8 years ago in reply to Cvetolin Shulev-XID

Expert 2985 points

Thank you for reply Tsvetolin Shulev,

Yes I do have write permission,

# ls -lrt /var/eventlog/swap/swapfile

-rw-rw-rw-    1 root     root     268435456 Jun 22 07:43 /var/eventlog/swap/swapfile

It is from timesys and it is based TI SDK on

http://software-dl.ti.com/sitara_linux/esd/AM335xSDK/07_00_00_00/index_FDS.html

even swapiness is set to 60

# cat /proc/sys/vm/swappiness
60

Thank you,

Regards,

Ankur

0 Cvetolin Shulev-XID over 8 years ago in reply to Ankur Tank

TI__Guru 65405 points

Ankur,

Try to enable swap file usage via "swapon" command as it is described at:
processors.wiki.ti.com/.../Talk:Creating_a_Root_File_System_for_Linux_on_OMAP35x
You can find more details about "swapon" command at:
man7.org/.../swapon.8.html
www.computerhope.com/.../swapon.htm

BR
Tsvetolin Shulev

0 Ankur Tank over 8 years ago in reply to Cvetolin Shulev-XID

Expert 2985 points

Hi Tsvetolin,

I followed the steps and it seems to work now.

I think problem was in the /etc/fsctab entry.

When I ran below command kernel starting using swap space.

swapon /var/eventlog/swap/swapfile

I see swapfile being used, However it was not effective as kernel was moving very little data to swap, may be because of swap is on eMMC and it might be slow compare to RAM.

Then on similar line I enabled SWAP on ZRAM using following commands,

# echo 64M > /sys/block/zram0/disksize 

# mkswap /dev/zram0 65536
Setting up swapspace version 1, size = 67104768 bytes
UUID=b0db8b82-214f-45bd-8783-8525fb0ddbe6

# swapon /dev/zram0 
# 
# 
# free
             total         used         free       shared      buffers
Mem:        251324       157044        94280            0         5784
-/+ buffers:             151260       100064
Swap:        65532            0        65532

Again I see ZRAM based swap enabled however when I run memory intensive task, I see free going low but kernel is not swapping out pages to ZRAM Swap.

Any suggestion to fix that ?

My supposition is if ZRAM swap works, kernel would move(compress) more pages to ZRAM based swap, as RAM is faster and we can take advantage of it in our system.

Thank you,

Regards,

Ankur

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Linux/PROCESSOR-SDK-AM335X: Unable to use swapfile on Linux kernel 3.12