nofscache

A loadable kernel moduel trying to eliminating page caching effects for user applications.

Requirements

• Linux kernel version >= 4.12
• Having CONFIG_ADVISE_SYSCALLS=y in /boot/config-$(shell uname -r)
• This module affects only 64-bit userspace programs since we didn't patch the compatibility version of system calls (compat_sys_xyzzy()).

Installation

git clone https://github.com/ljishen/nofscache.git
cd nofscache
make install

If you keep seeing processes under

[INFO] Checking transition state for module no_fscache (update every 2s)...

[INFO] 2 tasks are not in patched state:
USER       PID   TID CMD
root      1040  1131 /usr/bin/lxcfs /var/lib/lxcfs/
root      1040  1133 /usr/bin/lxcfs /var/lib/lxcfs/

...

You may need to manually kill these processes because they are stopping the module from finishing the transition state from unpatched to patched. See livepatch consistency model for more details.

To uninstall the kernel module, use

make uninstall

Again, you may need to kill processes to help the module finish the transition state from patched to unpatched.

Limitations and Performance Results

See https://ljishen.github.io/nofscache/ for more details.

How to start the Vagrant testing environment

This repository contains a Vagrantfile used to start an Ubuntu 18.04.3 LTS environment for testing.

1. Download and install Vagrant

   curl -s https://releases.hashicorp.com/vagrant/2.2.5/vagrant_2.2.5_x86_64.deb -o /tmp/vagrant_x86_64.deb
   sudo dpkg -i /tmp/vagrant_x86_64.deb

2. This Vagrant environment uses the libvirt provider. We need to have all the build dependencies installed in order to use vagrant-libvirt

   sudo apt-get update
   sudo apt-get -y install qemu libvirt-bin ebtables dnsmasq-base
   sudo apt-get -y install libxslt-dev libxml2-dev libvirt-dev zlib1g-dev ruby-dev

3. Add your user to the "libvirt" group. Remember that you will have to log out and back in for this to take effect!

   sudo usermod -aG libvirt $USER

4. You're ready to install vagrant-libvirt using standard Vagrant plugin installation methods

   vagrant plugin install vagrant-libvirt

5. Install NFS server since we use NFS to set up synced folders

   sudo apt-get -y install nfs-kernel-server

6. Start the Vagrant environment

   git clone https://github.com/ljishen/nofscache
   cd nofscache
   vagrant up

7. Connect to the virtual machine via SSH

   vagrant [-X] ssh

   or via serial console

   virsh console "$(virsh list --state-running --name | grep nofscache)"

   • Use vagrant -X ssh to connect with X11 forwarding enabled.
   • The default user is vagrant with password vagrant. To exit a virsh console session, type Ctrl+].

Troubleshooting

• If you see something like the following error during vagrant up:

  ==> default: Mounting NFS shared folders...
  The following SSH command responded with a non-zero exit status.
  Vagrant assumes that this means the command failed!
  
  mount -o vers=3,udp,rw,vers=3,tcp,actimeo=2 192.168.121.1:/users/ljishen/nofscache /vagrant
  
  Stdout from the command:
  
  
  
  Stderr from the command:
  
  mount.nfs: access denied by server while mounting 192.168.121.1:/users/ljishen/nofscache

  Try to add this rule to file /etc/hosts.allow

  $ echo "rpcbind: 192.168.121." >> /etc/hosts.allow

  As the default management_network_address used by vagrant-libvirt is 192.168.121.0/24. See management_network_address for more details.

Miscellaneous

• How to change the directory where Vagrant boxes are stored?

  Set the VAGRANT_HOME environmental variable.

• How to change the default libvirt storage pool?

  • Related Posts:
    • Configure default KVM virtual storage on Redhat Linux
    • How to change the default Storage Pool from libvirt?
    • Storage Management
  • The permission denied error:
    • qemu-kvm: could not open disk image ' ': Permission denied
    • permission denied error for NFS image, should libvirt error message mention virt_use_nfs?