allocate_fs_swapmap.5 (2010 09)

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allocate_fs_swapmap(5) allocate_fs_swapmap(5)

(Tunable Kernel Parameters)

NAME

allocate_fs_swapmap - determines when swapmap structures are allocated for ﬁlesystem swap

VALUES

Failsafe

0 (off)

Default

0 (off)

Allowed values

1 (on) or 0 (off)

DESCRIPTION

The

allocate_fs_swapmap

tunable is used to determine whether to allocate all needed ﬁlesystem

swap structures during the initialization of the ﬁlesystem swap device or wait until they are needed.

Pre-allocation of all ﬁlesystem swap structures upon initialization saves time during later usage of the

ﬁlesystem swap, and prevents later allocation failure due to physical memory contention.

Dynamic allocation decreases the memory footprint of the ﬁlesystem swap system.

Who is Expected to Change This Tunable?

Anyone.

Restrictions on Changing

Changes to this tunable take effect at the next reboot.

When Should the Value of This Tunable Be Raised?

Systems under heavy memory load may not be able to acquire enough memory to hold the swap mapping

structures for an addition of ﬁle system swap. These calls to add swap would fail with the error

[ENOMEM], though presumably they would be retried. Frequent failure on ﬁle system swap addition

with [ENOMEM] would merit enabling this tunable.

What Are the Side Effects of Raising the Value?

All the swap map structures for each ﬁle system swap device would be preallocated during swap initiali-

zation at kernel boot, increasing the memory footprint of the kernel. The amount of increase depends on

the number and size of ﬁle system swap devices.

When Should the Value of This Tunable Be Lowered?

Systems with limited memory available to the kernel that also have limited use of ﬁle system swap dev-

ices should disable this tunable to decrease kernel memory usage.

What Are the Side Effects of Lowering the Value?

File system swap additions may fail with [ENOMEM] when memory contention is high.

What Other Tunable Values Should Be Changed at the Same Time?

None.

WARNINGS

All HP-UX kernel tunable parameters are release speciﬁc. This parameter may be removed or have its

meaning changed in future releases of HP-UX.

Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parame-

ter values. After installation, some tunable parameters may no longer be at the default or recommended

values. For information about the effects of installation on tunable values, consult the documentation for

the kernel software being installed. For information about optional kernel software that was factory

installed on your system, see HP-UX Release Notes at

http://www.hp.com/go/hpux-core-docs.

AUTHOR

allocate_fs_swapmap was developed by HP.

Summary of content (2 pages)

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allocate_fs_swapmap(5) allocate_fs_swapmap(5) (Tunable Kernel Parameters) NAME allocate_fs_swapmap - determines when swapmap structures are allocated for filesystem swap VALUES Failsafe 0 (off) Default 0 (off) A Allowed values 1 (on) or 0 (off) DESCRIPTION The allocate_fs_swapmap tunable is used to determine whether to allocate all needed filesystem swap structures during the initialization of the filesystem swap device or wait until they are needed.
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(Notes) A (Notes) aA 2 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010