Swapping-Related Parameters

Swapping in the Oracle Solaris OS is accomplished by the swapfs pseudo file system. The combination of space on swap devices and physical memory is treated as the pool of space available to support the system for maintaining backing store for anonymous memory. The system attempts to allocate space from disk devices first, and then uses physical memory as backing store. When swapfs is forced to use system memory for backing store, limits are enforced to ensure that the system does not deadlock because of excessive consumption by swapfs.

swapfs_reserve

Description

Defines the amount of system memory that is reserved for use by system (UID = 0) processes.

Data Type

Unsigned long

Default

The smaller of 4 MB and 1/16th of physical memory

Range

The minimum value is 4 MB or 1/16th of physical memory, whichever is smaller, expressed as pages using the page size returned by getpagesize.

The maximum value is the number of physical memory pages. The maximum value should be no more than 10 percent of physical memory. The system does not enforce this range, other than that described in the Validation section.

Units

Pages

Dynamic?

No

Validation

None

When to Change

Generally not necessary. Only change when recommended by a software provider, or when system processes are terminating because of an inability to obtain swap space. A much better solution is to add physical memory or additional swap devices to the system.

Commitment Level

Unstable

swapfs_minfree

Description

Defines the desired amount of physical memory to be kept free for the rest of the system. Attempts to reserve memory for use as swap space by any process that causes the system's perception of available memory to fall below this value are rejected. Pages reserved in this manner can only be used for locked-down allocations by the kernel or by user-level processes.

Data Type

Unsigned long

Default

The larger of 2 MB and 12.5% of physical memory

Range

1 to amount of physical memory

Units

Pages

Dynamic?

No

Validation

None

When to Change

Consider reducing this parameter value when processes are failing because of an inability to obtain swap space, yet the system has memory available. For example, change this value to use no more than 6.25% of system memory, but do not reduce it below 5% of system memory.

On SPARC systems, the value should be at least 2 times the value of tsb_alloc_hiwater_factor. For more information, see tsb_alloc_hiwater_factor.

Commitment Level

Unstable

Change History

For information, see swapfs_minfree.