Wednesday, June 16, 2010

Disabling compcache for good

If a Ubuntu is installe from a CD or DVD chances are that along with the swap disk which physically exists on the hard drive Ubuntu also uses a RAM SWAP. This is a most annoying behavior because it leads to serious slowdowns and locks ups of the system.
If you are one of those poor souls whose Firefox freezes up regularly after prolonged use even when not too many tabs are open then you are a victim of the Compcache. Even though it is boon for Live CDs it becomes the unwanted child in an installed Linux distribution.

What do Compcache do ?
I quote the webpage dedicated to Compcache (https://wiki.ubuntu.com/Compcache)
"Compcache provides a possibility of using parts of the memory as virtual compressed swapdevice." 

So Compcache creates a virtual drive in memory called the ramzswapfound at /dev/ramzswap0 and makes programs trick into storing their swap data there.
This is not at all needed if a dedicated swap partition exists in a system. It interferes with the swapping mechanism of the kernel and causes slowdowns.

To see if Compcache is doing its stuff type the fgollowing command. It shows what swap devices are on.

$ swapon -s

If there is an output like


Filename                Type        Size    Used    Priority
/dev/sda9                               partition    2104472    358796    -1
/dev/ramzswap0                          partition       1299996 186680  100


then the RAM SWAP in ON.

To disable RAM SWAP temporarily do the following --

$ swapoff /dev/ramzswap0

Now see the improvement in the performance of the PC.

To turn off Compcache permanently

$ cd usr/share/initramfs-tools/conf.d/
$ sudo mv compcache old-compcache 

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