TMPFS-Related Error Messages

The following message is displayed if a page could not be allocated when writing a file. This problem can occur when TMPFS tries to write more than it is allowed or if currently executed programs are using a lot of memory.

directory: File system full, swap space limit exceeded

The following message means TMPFS ran out of physical memory while attempting to create a new file or directory.

directory: File system full, memory allocation failed

For information on recovering from the TMPFS-related error messages, see TMPFS(7FS).

How Swap Space Is Allocated

Initially, swap space is allocated as part of the Solaris installation process. If you use the installation program's automatic layout of disk slices and do not manually change the size of the swap slice, the Solaris installation program allocates a default swap area of 512 Mbytes.

Starting in the Solaris 9 release, the installation program allocates swap space starting at the first available disk cylinder (typically cylinder 0). This placement provides maximum space for the root (/) file system during the default disk layout and enables the growth of the root (/) file system during an upgrade.

For general guidelines on allocating swap space, see Planning for Swap Space.

You can allocate additional swap space to the system by creating a swap file. For information about creating a swap file, see Adding More Swap Space.

The /etc/vfstab File

After the system is installed, swap slices and swap files are listed in the /etc/vfstab file. They are activated by the /sbin/swapadd script when the system is booted.

An entry for a swap device in the /etc/vfstab file contains the following:

• The full path name of the swap slice or swap file

• File system type of swap

The file system that contains a swap file must be mounted before the swap file is activated. So, in the /etc/vfstab file, make sure that the entry that mounts the file system comes before the entry that activates the swap file.

Planning for Swap Space

The most important factors in determining swap space size are the requirements of the system's software applications. For example, large applications such as computer-aided-design simulators, database-management products, transaction monitors, and geologic analysis systems can consume as much as 200-1000 Mbytes of swap space.

Consult your application vendor for swap space requirements for their applications.

If you are unable to determine swap space requirements from your application vendor, use the following general guidelines based on your system type to allocate swap space:

In addition to the general guidelines, consider allocating swap or disk space for the following:

• A dedicated dump device.

• Determine whether large applications (like compilers) will be using the /tmp directory. Then allocate additional swap space to be used by TMPFS. For information about TMPFS, see Swap Space and the TMPFS File System.

Monitoring Swap Resources

The /usr/sbin/swap command is used to manage swap areas. Two options, -l and -s, display information about swap resources.

Use the swap -l command to identify a system's swap areas. Activated swap devices or files are listed under the swapfile column.

# swap -l
swapfile             dev  swaplo blocks   free
/dev/dsk/c0t0d0s1   136,1      16 1638608 1600528

Use the swap -s command to monitor swap resources.

# swap -s
total: 57416k bytes allocated + 10480k reserved = 67896k used, 
833128k available

The used value plus the available value equals the total swap space on the system, which includes a portion of physical memory and swap devices (or files).

You can use the amount of available and used swap space (in the swap -s output) as a way to monitor swap space usage over time. If a system's performance is good, use swap -s to see how much swap space is available. When the performance of a system slows down, check the amount of available swap space to see if it has decreased. Then you can identify what changes to the system might have caused swap space usage to increase.

When using this command, keep in mind that the amount of physical memory available for swap usage changes dynamically as the kernel and user processes lock down and release physical memory.

Note - The swap -l command displays swap space in 512-byte blocks and the swap -s command displays swap space in 1024-byte blocks. If you add up the blocks from swap -l and convert them to Kbytes, the result will be less than used + available (in the swap -s output) because swap -l does not include physical memory in its calculation of swap space.

The output from the swap -s command is summarized in the following table.

Table 42-1 Output of the swap -s Command

Adding More Swap Space

As system configurations change and new software packages are installed, you might need to add more swap space. The easiest way to add more swap space is to use the mkfile and swap commands to designate a part of an existing UFS or NFS file system as a supplementary swap area. These commands, described in the following sections, enable you to add more swap space without repartitioning a disk.

Alternative ways to add more swap space are to repartition an existing disk or add another disk. For information on how to repartition a disk, see Chapter 32, Managing Disks (Overview).

Creating a Swap File

The following general steps are involved in creating a swap file:

• Creating a swap file with the mkfile command

• Activating the swap file with the swap command

• Adding an entry for the swap file in the /etc/vfstab file so that the swap file is activated automatically when the system is booted.

The mkfile Command

The mkfile command creates a file that is suitable for use as either an NFS-mounted or a local swap area. The sticky bit is set, and the file is filled with zeros. You can specify the size of the swap file in bytes (the default) or in Kbytes, blocks, or Mbytes by using the k, b, or m suffixes, respectively.

The following table shows the mkfile command options.

Table 42-2 Options to the mkfile Command

Caution - Use the -n option only when you create an NFS swap file.