Ubuntu 11.04 headless omap with / without SWAP

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1

Dear all,

for those who have the similar sluggish start-up problem with ubuntu
11.04 headless on beagleboard xM, you could try to comment out the
following line in /tec/fstab:

'/SWAP.swap none swap sw 0 0'

This is to bring up the 512MB swap file on the SD card at each bootup.
But it takes about 180 s for swapon to finished the IO process, during
which the system becomes very sluggish.

After commenting out the swap file in /etc/fstab, the whole bootup
process can be finished within 85 s (traced with bootchart).

However, there is still some questions from me on the swap of embedded
linux:
- It seems Angstrom (the demo distribution coming with BB-xM Rec. C)
does not use any swap:

root@beagleboard:~# free
             total used free shared buffers
cached
Mem: 496660 134180 362480 0 4836
64920
-/+ buffers/cache: 64424 432236
Swap: 0 0 0

- Why does Ubuntu headless still need 512 MB Swap? Is it safe to
disable swap, given I am only using the BB without X-server?

Best regards,
Hans

2

Hi Hans,

for those who have the similar sluggish start-up problem with ubuntu
11.04 headless on beagleboard xM, you could try to comment out the
following line in /tec/fstab:

'/SWAP.swap none swap sw 0 0'

This is to bring up the 512MB swap file on the SD card at each bootup.
But it takes about 180 s for swapon to finished the IO process, during
which the system becomes very sluggish.

After commenting out the swap file in /etc/fstab, the whole bootup
process can be finished within 85 s (traced with bootchart).

Wouldn't it have been quicker if they created a partition just for
swap on the SDCard (by marking it as swap in the partition table) and
then using it instead of a swap "file" ?. It seems that bringing up a
512MB file each time would be quite slow.

However, there is still some questions from me on the swap of embedded
linux:
- It seems Angstrom (the demo distribution coming with BB-xM Rec. C)
does not use any swap:

root@beagleboard:~# free
total used free shared buffers
cached
Mem: 496660 134180 362480 0 4836
64920
-/+ buffers/cache: 64424 432236
Swap: 0 0 0

- Why does Ubuntu headless still need 512 MB Swap? Is it safe to
disable swap, given I am only using the BB without X-server?

There are systems that work without any problems with no swap at all.
Most pages in memory are backed by a disk file. I don't forsee a
problem but I think it also depends on how much memory your
application is dynamically allocating. If its just the X-server, I
don't think it would be a problem.

thanks,
Joel

3

'/SWAP.swap none swap sw 0 0'

This is to bring up the 512MB swap file on the SD card at each bootup.
But it takes about 180 s for swapon to finished the IO process, during
which the system becomes very sluggish.

After commenting out the swap file in /etc/fstab, the whole bootup
process can be finished within 85 s (traced with bootchart).

Wouldn't it have been quicker if they created a partition just for
swap on the SDCard (by marking it as swap in the partition table) and
then using it instead of a swap "file" ?. It seems that bringing up a
512MB file each time would be quite slow.

This also seems to be the approach that the AlwaysInnovating guys have
taken for Ubuntu in their AIOS demo.

thanks,
Joel

4

Thanks Joel! 512 BM ram is sufficient for our application. So I would
prefer to keep the swap off.

The ubutun 11.04 demo image from Robert looks as a better option. By
default, it has no swap file created unless one uses the --swap_file
<swap file size in MB's> option with the script:

http://elinux.org/BeagleBoardUbuntu#Demo_Image

Regards,
Hans