How to Limit the Size of the tmpfs File System

How to Limit the Size of the `tmpfs` File System

To edit the vfstab file, you must become an administrator who is assigned the solaris.admin.edit/etc/vfstab authorization. To read the changes into the OS, you must be assigned the Service Configuration rights profile. The root role has all of these rights. For more information, see Using Your Assigned Administrative Rights in Securing Users and Processes in Oracle Solaris 11.4.

In this procedure, you base the size of the tmpfs file system on a percentage of system memory. You might try several values to achieve best system performance.

Determine the amount of memory on your system.hardwareSPARC T series serversSPARC T series serversTMPFS configuration example

Note:

The SPARC T7 series system that is used for the following example has 32 disks. The system has around 500 GB of memory.

% prtconf | head
System Configuration:  Oracle Corporation  sun4v
Memory size: 523776 Megabytes
System Peripherals (Software Nodes):

ORCL,SPARC-T7-1
    scsi_vhci, instance #0
        disk, instance #28
        disk, instance #29
        disk, instance #6
        disk, instance #5
        disk, instance #32
        ...

Compute a memory limit for tmpfs.

Depending on the size of the system memory, you might want to compute a memory limit of around 20 percent for large systems and around 30 percent for smaller systems.
- For a larger system, use .20 as the multiplier.
```
523776M x .20 ≈ 104755M
```
- For a smaller system, use .30 as the multiplier.
```
260352M x .30 ≈ 78105M
```

Modify the swap entry in the /etc/vfstab file with the size limit.

# pfedit /etc/vfstab
#device     device       mount       FS      fsck    mount mount
#to mount   to fsck      point       type    pass    at boot options
#
...
#swap       -            /tmp        tmpfs   -       yes     -
swap        -            /tmp        tmpfs   -       yes     size=104700m
/dev/zvol/dsk/rpool/swap   -      -  swap    -       no      -

Restart the svc:/system/filesystem/local:default service.
```
# svcadm restart filesystem/local
```

Verify that the size limit is in effect.

% mount -v
swap on /system/volatile type tmpfs
read/write/setuid/devices/rstchown/xattr/dev=89c0006 on Thurs Feb 4 14:07:27 2016
swap on /tmp type tmpfs
read/write/setuid/devices/rstchown/xattr/size=104700m/dev=89c0006 on Thurs ...

Monitor the memory usage and adjust it to the requirements of your site.
The df command is somewhat useful. The swap command provides the most useful statistics.
```
% df -h /tmp
Filesystem Size Used Available Capacity Mounted on
swap          7.  4G     44M    7.4G 1%       /tmp

% swap -s
total: 190248k bytes allocated + 30348k reserved = 220596k used,
7743780k available
```
For more information, see the tmpfs(4FS), mount_tmpfs(8), df(8), and swap(8) man pages.