gpl2016 / mlcache

MLCache: A Multi-Armed Bandit Policy for an Operating System Page Cache

MLCache: A Multi-Armed Bandit Policy for an Operating System Page Cache

by Renato Costa ([e-mail]) and Jose Pazos ([e-mail])

MLCache is a Linux page cache replacement policy that uses the UCB1 algorithm to calculate a score for each page in the page cache.

Project Structure

• linux/src: Snapshot of the Linux kernel source tree used for this project (4.14.0-rc7). MLCache adds a new driver (drivers/mlcache), a new tracepoint event (include/trace/events/mlcache.h), as well as other in place changes.

• linux/qemu: Scripts are available in order to create a Debian disk image (using debootstrap) with a previously built kernel image; and to run a QEMU virtual machine.

• proposal, report: the proposal and report for this project, respectively.

Testing MLCache

When building the kernel, two configuration options are required:

CONFIG_MLCACHE=y
CONFIG_MLCACHE_ACTIVE=y

The first the enables MLCache driver; the second allows MLCache to actively collect and update page data (see usage instructions below). If MLCache is enabled but not active, it will just collect page hit/miss ratios, without affecting the standard LRU eviction policy in Linux.

Usage

In a kernel with MLCache enabled, there should be a /proc/mlcache/filter file in the system. Writing to that file controls MLCache's operation:

# Checking the status of the MLCache driver
root@mlcache:~# cat /proc/mlcache/filter
[Active] MLCache is currently not enabled.

# Requesting MLCache to monitor the process tree under the running shell
root@mlcache:~# echo tree:$$ >/proc/mlcache/filter

# Check the status of the driver after the command above
root@mlcache:~# cat /proc/mlcache/filter
[Active] MLCache is watching the tree under process 1675

# Triggering some file system activity
root@mlcache:~# ls
fs.sh  linux  pg.sh  vanilla.fs.sh  vanilla.pg.sh

# Reading hit ratio statistics for the monitored processes
root@mlcache:~# cat /proc/mlcache/1675
Hits: 23 | Misses: 1