5.2. Tuning the Page Cache

Page cache is a disk cache which holds data of files and executable programs, for example pages with actual contents of files or block devices. Page cache (disk cache) is used to reduce the number of disk reads. To control the percentage of total memory used for page cache in Red Hat Enterprise Linux 5, change the pagecache kernel parameter. The lower the percentage, the more the system favors reclaiming unmapped pagecache memory over mapped memory. High values (like the default value of 100) are not recommended for databases.

The pagecache parameters can be changed in the proc file system without reboot:

echo "40" > /proc/sys/vm/pagecache

# echo "40" > /proc/sys/vm/pagecache

Alternatively, you can use sysctl(8) to change it:

sysctl -w vm.pagecache="40"

# sysctl -w vm.pagecache="40"

To make the change permanent, add the following line to the file /etc/sysctl.conf. This file is used during the boot process.

echo "vm.pagecache=40" >> /etc/sysctl.conf

# echo "vm.pagecache=40" >> /etc/sysctl.conf

You can also adjust the minimum free pages using the following command:

echo 1024 > /proc/sys/vm/min_free_kbytes

# echo 1024 > /proc/sys/vm/min_free_kbytes

To make this change permanent, add the following line to the file /etc/sysctl.conf:

echo vm.min_free_kbytes=1024 >> /etc/sysctl.conf

# echo vm.min_free_kbytes=1024 >> /etc/sysctl.conf