This utility uses mmap() and mlock() to eat up RAM. This prevents the kernel from using RAM for more useful purposes, like page caching. The utility can be used as an alternative to the mem= kernel command-line, when page caching stands in the way of testing disk performance.
Building memeat from source code is very simple and only requires a C compiler and POSIX headers. On Ubuntu, the following command will suffice to install all dependencies:
sudo apt-get install build-essential
A Makefile is provided for convenience:
make
This example uses iozone to show how to make file-system operations disk-bound. The experiments have been conducted on a machine with 8GB of RAM and a Western Digital Caviar Blue Serial ATA disk. We first execute:
iozone -s 1g -r 256k -i 0 -i 2
This measures a random read throughput of 4.8 GB/s. Clearly, most reads have been served from RAM. If we now eat 5 GB of RAM
sudo ./memeat 5G
and re-run the same iozone command, we obtain a random read throughput of 22 MB/s. This is the expected random read throughput of the disk, thus, we can conclude that most of the reads have been served from disk.
The Linux kernel limits the amount of memory that can be mlock(). If you run this utility as an unprivileged (non-root) user, you will most likely get the following error:
mlock() failed: Cannot allocate memory
To fix this, either run memeat as root or change the resource limits by adding the following entries to /etc/security/limits.conf:
myuser soft memlock 16000000
myuser hard memlock 16000000
This will allow the user myuser to eat up to 16 GB of RAM.
Eating too much memory will freeze your system for a while, then, the OOM killer will kick in and most likely kill memeat.