Latest revision as of 17:47, 15 August 2010

WARNING: THIS MIGHT KILL YOUR SD CARD, since there might be alot of read/writes on the same spot. The Freerunner has only 128mb ram, when this is used up applications get killed.

Please note that the above warning do not apply to microSD (including microSDHC) card with wear-levelling algorithms/microcontrollers. (See #References)

Please note that you can change the swappiness setting (low value, default 60) so the swap partition or swap file will be used as little as possible. (See #References)

[edit] Make swap when you are connected to your openmoko with ssh

64M byte of swap just as an example

dd if=/dev/zero of=/swapfile bs=1024 count=65536

Next time you boot there will be swap

echo "/swapfile               swap                    swap    defaults        0 0">> /etc/fstab 

Make swap

mkswap /swapfile

Make the swap file work now:

swapon /swapfile

[edit] Make swap when microSD card is in a card reader

The uSD card is booted on /boot. To use this, we need to make sure that the microsd card is booted, and the Swap can be turned on.

Create the swapfile on the uSD card.

 # dd if=/dev/zero of=/boot/swapfile bs=1024k count=128
 # mkswap /boot/swapfile

Now, we can put in an init script for Fyp which does this for us everytime we boot.

 # touch /etc/init.d/extswap.sh
 # chmod +x /etc/init.d/extswap.sh
 # cat > /etc/init.d/extswap.sh
 #! /bin/sh
 ### BEGIN INIT INFO
 # Provides:          extswap
 # Required-Start:    mountall
 # Required-Stop: 
 # Default-Start:     S
 # Default-Stop:
 # Short-Description: Uses Additional Swap If Available. works on SHR distro
 # Description:
 ### END INIT INFO
 
 PATH=/sbin:/bin
 
 do_start() {
         modprobe loop
         echo 10 > /proc/sys/vm/swappiness
         if [ -e /boot/swapfile ] ; then
                for loopdev in `ls /dev/loop* 2>/dev/null` ; do
 		losetup $loopdev /boot/swapfile && swapon $loopdev && echo $loopdev > /var/extswapfile && break
                done
         fi
 }
 
 do_stop() {
       	loopdev=`cat /var/extswapfile 2>/dev/null`
         swapoff $loopdev 2>/dev/null && rm -f /var/extswapfile && losetup -d $loopdev
 }
 
 case "$1" in
   start|"")
 	do_start
 	;;
   restart|reload|force-reload)
 	do_stop
         do_start
 	;;
   stop)
 	do_stop
 	;;
   *)
 	echo "Usage: extswap.sh [start|stop|restart]" >&2
 	exit 3
 	;;
 esac
 # update-rc.d extswap.sh defaults

[edit] References

• 2/17/2008, notebookreview.com: SDHC Cards vs Hard Drive vs SSD Quote: "...That sounds like an absolutely manditory thing to have in flash storage ... and luckily "high-performance" SDHC cards such as the 16GB A-DATA SDHC card and many other class 6 cards from other manufacturers incorportate wear-leveling [Please check before you buy!]..."
• MicroSD(HC) cards are a sort of a SSD: December 7, 2008, robert.penz.name: No SWAP Partition, Journaling Filesystems, … on a SSD? Quote: "...They assume perfect wear leveling...We stay also with the 2 million cycles and assume a 16GB SSD *With 50 MByte/sec we get 20 years! *With 2 MByte/sec we get 519 years! *And even if we reduce the write cycles to 100.000 and write with 2 MByte/sec all the time we’re at 26 years!!...1. Never choose to use a journaling file system on the SSD partitions: Bullshit, you’re just risking data security. Stay with ext3...7. One more thing to consider is that flash-devices handle their space in blocks. The blocksize typically varies between 16KB and 512 KB. Therefore writing one byte may cause erase and rewrite of up to 512KB..."
• fosswire.com: Speed up your system by avoiding the swap file Quote: "...the Linux kernel provides a tweakable setting that controls how often the swap file is used, called swappiness. A swappiness setting of zero means that the disk will be avoided unless absolutely necessary (you run out of memory), while a swappiness setting of 100 means that programs will be swapped to disk almost instantly..."

[edit] Links

• http://www.google.dk/search?q=linux+swap+partition+vs+file+speed
• http://shr-project.org/trac/wiki/swap