Setting up the DSM 6.1 Tool Chain

Synology has provided excellent documentation on how to compile kernel modules. You should follow their tutorial on how to setup the toolkit to compile the kernel.

Steps for the DS212j are roughly:

Setup toolkit: mkdir -p /toolkit

cd /toolkit

git clone https://github.com/SynologyOpenSource/pkgscripts-ng.git

cd /toolkit/pkgscripts-ng/

./EnvDeploy -v 6.1 -p 6281

Compiling the 2.6.32 Kernel

You will need to follow the Synology documentation to compile kernel modules here in order to build the LZO kernel module. This is a dependent kernel module for zRAM.

Steps are roughly:

Download the kernel source for the closest branch that is currently deployed on your Synology: https://sourceforge.net/projects/dsgpl/files/Synology%20NAS%20GPL%20Source/

Extract the source to /toolkit/build_env/ds.x64-6.1/root/

Enter the tool chain chroot: chroot /toolkit/build_env/ds.x64-6.1 /bin/bash

cd root/linux-2.6.32

cp synoconfigs/88f6281 .config

export ARCH="arm"

export CROSS_COMPILE="/usr/local/arm-marvell-linux-gnueabi/bin/arm-marvell-linux-gnueabi-"

make oldconfig

make menuconfig

Build LZO modules because they’re dependencies for zRAM. Enter Cryptographic API to select LZO compression algorithm as a module. Exit and save.

make prepare

make modules

Copy lzo_compress.ko, lzo_decompress.ko, lzo.ko to your Synology

Compiling the Compcache Kernel Module

I have successfully compiled the Compcache 0.6.2 kernel module and gotten it to work with the stock 2.6.32 kernel. The latest version doesn’t seem to work so we’re going to stick with 0.6.2 where we will follow the Compcache documentation here.

cd /root/

Download Compcache 0.6.2 module source: wget https://storage.googleapis.com/google-code-archive-downloads/v2/code.google.com/compcache/compcache-0.6.2.tar.gz

tar -xzf compcache-0.6.2.tar.gz

cd compcache-0.6.2

export KERNEL_BUILD_PATH=/root/linux-2.6.32

make

Copy ramzswap.ko to your Synology

Installation

Copy kernel modules to Synology DSM

Test kernels by inserting them

/sbin/insmod /lib/modules/lzo_decompress.ko /sbin/insmod /lib/modules/lzo_compress.ko /sbin/insmod /lib/modules/lzo.ko /sbin/insmod /lib/modules/ramzswap.ko disksize_kb=131072 /sbin/swapon /dev/ramzswap0 -p 5

Enable swap with: /sbin/swapon /dev/ramzswap0 -p 5

Verify everything worked by checking dmesg for errors

nschimme@NilsDiskStation:~$ dmesg | grep -E "(ramzswap|lzo)" [ 100.500000] alg: No test for lzo (lzo-generic) [ 100.550000] ramzswap: num_devices not specified. Using default: 1 [ 100.550000] ramzswap: /dev/ramzswap0 initialized: disksize_kb=131072 [ 100.560000] ramzswap: Invalid ioctl 21297 [ 101.560000] Adding 131064k swap on /dev/ramzswap0. Priority:5 extents:1 across:131064k SS nschimme@NilsDiskStation:~$

Add above insmod/swapon commands to /etc/rc.local to make the changes permanent

zRAM Results

It’s super effective! I’ve noticed that there was roughly ~100MB of paged memory usually and I’ve managed to get it all to fit within ~30MB of compressed memory space rather than going down to the hard drive. Responsiveness in the DSM OS has greatly improved as a result.