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Oracle Solaris 11.1 Tunable Parameters Reference Manual     Oracle Solaris 11.1 Information Library
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Document Information

Preface

1.  Overview of Oracle Solaris System Tuning

2.  Oracle Solaris Kernel Tunable Parameters

Where to Find Tunable Parameter Information

General Kernel and Memory Parameters

physmem

default_stksize

lwp_default_stksize

logevent_max_q_sz

segkpsize

noexec_user_stack

fsflush and Related Parameters

fsflush

tune_t_fsflushr

autoup

dopageflush

doiflush

Process-Sizing Parameters

maxusers

reserved_procs

pidmax

max_nprocs

maxuprc

ngroups_max

Paging-Related Parameters

lotsfree

desfree

minfree

throttlefree

pageout_reserve

pages_pp_maximum

tune_t_minarmem

fastscan

slowscan

min_percent_cpu

handspreadpages

pages_before_pager

maxpgio

Swapping-Related Parameters

swapfs_reserve

swapfs_minfree

Kernel Memory Allocator

kmem_flags

kmem_stackinfo

General Driver Parameters

moddebug

ddi_msix_alloc_limit

Network Driver Parameters

igb Parameters

mr_enable

intr_force

ixgbe Parameters

tx_queue_number

rx_queue_number

intr_throttling

rx_limit_per_intr

tx_ring_size

rx_ring_size

tx_copy_threshold

rx_copy_threshold

General I/O Parameters

maxphys

rlim_fd_max

rlim_fd_cur

General File System Parameters

ncsize

dnlc_dir_enable

dnlc_dir_min_size

dnlc_dir_max_size

dnlc_dircache_percent

TMPFS Parameters

tmpfs:tmpfs_maxkmem

tmpfs:tmpfs_minfree

Pseudo Terminals

pt_cnt

pt_pctofmem

pt_max_pty

STREAMS Parameters

nstrpush

strmsgsz

strctlsz

System V Message Queues

System V Semaphores

System V Shared Memory

segspt_minfree

Scheduling

disp_rechoose_interval

Timers

hires_tick

timer_max

SPARC System Specific Parameters

tsb_alloc_hiwater_factor

default_tsb_size

enable_tsb_rss_sizing

tsb_rss_factor

Locality Group Parameters

lpg_alloc_prefer

lgrp_mem_pset_aware

3.  Oracle Solaris ZFS Tunable Parameters

4.  NFS Tunable Parameters

5.  Internet Protocol Suite Tunable Parameters

6.  System Facility Parameters

A.  Tunable Parameters Change History

B.  Revision History for This Manual

Index

fsflush and Related Parameters

This section describes fsflush and related tunables.

fsflush

The system daemon, fsflush, runs periodically to do three main tasks:

  1. On every invocation, fsflush flushes dirty file system pages over a certain age to disk.

  2. On every invocation, fsflush examines a portion of memory and causes modified pages to be written to their backing store. Pages are written if they are modified and if they do not meet one of the following conditions:

    • Pages are kernel page

    • Pages are free

    • Pages are locked

    • Pages are associated with a swap device

    • Pages are currently involved in an I/O operation

    The net effect is to flush pages from files that are mapped with mmap with write permission and that have actually been changed.

    Pages are flushed to backing store but left attached to the process using them. This will simplify page reclamation when the system runs low on memory by avoiding delay for writing the page to backing store before claiming it, if the page has not been modified since the flush.

  3. fsflush writes file system metadata to disk. This write is done every nth invocation, where n is computed from various configuration variables. See tune_t_fsflushr and autoup for details.

The following features are configurable:

For most systems, memory scanning and file system metadata synchronizing are the dominant activities for fsflush. Depending on system usage, memory scanning can be of little use or consume too much CPU time.

tune_t_fsflushr

Description

Specifies the number of seconds between fsflush invocations

Data Type

Signed integer

Default

1

Range

1 to MAXINT

Units

Seconds

Dynamic?

No

Validation

If the value is less than or equal to zero, the value is reset to 1 and a warning message is displayed. This check is done only at boot time.

When to Change

See the autoup parameter.

Commitment Level

Unstable

autoup

Description

Along with tune_t_flushr, autoup controls the amount of memory examined for dirty pages in each invocation and frequency of file system synchronizing operations.

The value of autoup is also used to control whether a buffer is written out from the free list. Buffers marked with the B_DELWRI flag (which identifies file content pages that have changed) are written out whenever the buffer has been on the list for longer than autoup seconds. Increasing the value of autoup keeps the buffers in memory for a longer time.

Data Type

Signed integer

Default

30

Range

1 to MAXINT

Units

Seconds

Dynamic?

No

Validation

If autoup is less than or equal to zero, it is reset to 30 and a warning message is displayed. This check is done only at boot time.

Implicit

autoup should be an integer multiple of tune_t_fsflushr. At a minimum, autoup should be at least 6 times the value of tune_t_fsflushr. If not, excessive amounts of memory are scanned each time fsflush is invoked.

The total system pages multiplied by tune_t_fsflushr should be greater than or equal to autoup to cause memory to be checked if dopageflush is non-zero.

When to Change

Here are several potential situations for changing autoup, tune_t_fsflushr, or both:

  • Systems with large amounts of memory – In this case, increasing autoup reduces the amount of memory scanned in each invocation of fsflush.

  • Systems with minimal memory demand – Increasing both autoup and tune_t_fsflushr reduces the number of scans made. autoup should be increased also to maintain the current ratio of autoup / tune_t_fsflushr.

  • Systems with large numbers of transient files (for example, mail servers or software build machines) – If large numbers of files are created and then deleted, fsflush might unnecessarily write data pages for those files to disk.

Commitment Level

Unstable

dopageflush

Description

Controls whether memory is examined for modified pages during fsflush invocations. In each invocation of fsflush, the number of physical memory pages in the system is determined. This number might have changed because of a dynamic reconfiguration operation. Each invocation scans by using this algorithm: total number of pages x tune_t_fsflushr / autoup pages

Data Type

Signed integer

Default

1 (enabled)

Range

0 (disabled) or 1 (enabled)

Units

Toggle (on/off)

Dynamic?

Yes

Validation

None

When to Change

If the system page scanner rarely runs, which is indicated by a value of 0 in the sr column of vmstat output.

Commitment Level

Unstable

doiflush

Description

Controls whether file system metadata syncs will be executed during fsflush invocations. This synchronization is done every Nth invocation of fsflush where N= (autoup / tune_t_fsflushr). Because this algorithm is integer division, if tune_t_fsflushr is greater than autoup, a synchronization is done on every invocation of fsflush because the code checks to see if its iteration counter is greater than or equal to N. Note that N is computed once on invocation of fsflush. Later changes to tune_t_fsflushr or autoup have no effect on the frequency of synchronization operations.

Data Type

Signed integer

Default

1 (enabled)

Range

0 (disabled) or 1 (enabled)

Units

Toggle (on/off)

Dynamic?

Yes

Validation

None

When to Change

When files are frequently modified over a period of time and the load caused by the flushing perturbs system behavior.

Files whose existence, and therefore consistency of state, does not matter if the system reboots are better kept in a TMPFS file system (for example, /tmp). Inode traffic can be reduced on systems by using the mount -noatime option. This option eliminates inode updates when the file is accessed.

For a system engaged in realtime processing, you might want to disable this option and use explicit application file synchronizing to achieve consistency.

Commitment Level

Unstable