Linux FAQ Items Post: 302088226

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Operating Systems Linux Gentoo Linux FAQ Items Post 302088226 by prashant_ohol on Sunday 10th of September 2006 05:02:25 PM

09-10-2006

Registered User

Linux FAQ Items

Hello Guys,

Sometimes it is necessary to add more swap space after installation. For example, you may upgrade the amount of RAM in your system from 64 MB to 128 MB, but there is only 128 MB of swap space. It might be advantageous to increase the amount of swap space to 256 MB if you perform memory-intense operations or run applications that require a large amount of memory.

You have two options: add a swap partition or add a swap file. The easiest way to achieve this it to through swap file.

To add a swap file:

Determine the size of the new swap file and multiple by 1024 to determine the block size. For example, the block size of a 64 MB swap file is 65536.

At a shell prompt as root, type the following command with count being equal to the desired block size:

dd if=/dev/zero of=/swapfile bs=1024 count=65536

then

mkswap /swapfile

To enable the swap file immediately but not automatically at boot time:

swapon /swapfile

To enable it at boot time, edit /etc/fstab to include:

/swapfile swap swap defaults 0 0

The next time the system boots, it will enable the new swap file.

After adding the new swap file and enabling it, make sure it is enabled by viewing the output of the command cat /proc/swaps or free.

bingo Smilie

Let me know if you have any questions.

Prashant,
prashant ohol - System Administrator,

Last edited by prashant_ohol; 09-11-2006 at 04:50 PM..

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LEARN ABOUT HPUX

allocate_fs_swapmap

allocate_fs_swapmap(5)						File Formats Manual					    allocate_fs_swapmap(5)

NAME

       allocate_fs_swapmap - determines when swapmap structures are allocated for filesystem swap

VALUES

   Failsafe
   Default
   Allowed values
       or

DESCRIPTION

       The 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 though presumably they would be retried.  Frequent failure  on	file  system  swap
       addition with 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 initialization 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 devices 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 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  parameter  values.   After  installation,
       some  tunable  parameters may no longer be at the default or recommended values.  For information about the effects of installation on tun-
       able values, consult the documentation for the kernel software being installed.	For information about optional kernel  software  that  was
       factory installed on your system, see at

AUTHOR

       was developed by HP.

							     Tunable Kernel Parameters					    allocate_fs_swapmap(5)