desfree

Description

Amount of memory desired to be free at all times on the system.

Data Type

Unsigned integer

Default

lotsfree / 2

Range

The minimum value is 256 Kbytes or 1/128th of physical memory, whichever is greater, expressed as pages using the page size returned by getpagesize(3C).

The maximum is the number of physical memory pages. The maximum value should be no more than 15% of physical memory. The system does no enforcement of this range other than that described in the Validation section.

Units

Pages

Dynamic?

Yes, unless dynamic reconfiguration operations that add or delete memory occur. At that point, the value is reset to whatever was provided in the /etc/system file or was calculated from the new physical memory value.

Validation

If desfree is greater than lotsfree, desfree is set to lotsfree / 2. No message is displayed.

Implicit

The relationship of cachefree is greater than or equal to lotsfree, which is greater than desfree, which is greater than minfree, should be maintained at all times.

Side Effects

Several side effects can arise from increasing the value of this variable. When the new value nears or exceeds the amount of available memory on the system:

• Asynchronous I/O requests are not processed unless available memory exceeds desfree. Increasing the value of desfree can result in rejection of requests that otherwise would succeed.

• NFS Version 3 asynchronous writes are executed as synchronous writes.

• The swapper is awakened earlier, and the behavior of the swapper is biased towards more aggressive actions.

• The system might not prefault as many executable pages into the system. This side effect results in applications potentially running slower than they otherwise would.

When to Change

For systems with relatively static workloads and large amounts of memory, adjust this value downwards. The minimum acceptable value is 256 Kbytes expressed as pages using the page size returned by getpagesize(3C).

Commitment Level

Unstable