[SOLVED] How "to clear" memory swap?

afreitascs · 05-09-2010, 11:43 PM

I have 2G of physical memory and 1G of memory swap. Very rarely the memory swap is used and when usage is around 1% while, then gets a lot of free physical memory...

My question is:
It is possible to "clean up" the memory swap. Or better still (I think). It is possible to spend
physical memory for data that is in memory swap?

let me know ...

many thanks

evo2 · 05-09-2010, 11:48 PM

I guess the following would "clean up" swap:

Code:

swapoff -a && swapon -a

I don't really understand why you want to do this though.

Evo2.

dh2k · 05-10-2010, 07:49 AM

have you tried to reduce swappiness?

I use swappiness in a vice-versa way to your needs as I have old hardware on some boxes.
Currently set swappiness to 95 (0-100) on 256MB and system is much more repsonsive.

(0 - 100) == 0 never use swap;

You might want to try swap off as above post or swappiness 05 (0-100) - maybe -
or with your hardware even swappiness of 01.

For on-the-fly - Use:
Does not stay after a reboot;

Code:

sysctl -w vm.swappiness=05

I would test swappiness first 'on-the-fly' then with successful testing and to make permanent after reboots with;

Code:

cp /etc/sysctl.conf /etc/sysctl.conf_ORIGINAL

if you already have a 'sysctl.conf'

then change the last line below in /etc/sysctl.conf

Code:

# as root use 
# 'cat /proc/sys/vm/swappiness'
# to view system swappiness
###
# default is 60
###
# as root use
# 'sysctl -w vm.swappiness=10'
# to change the swappiness on the fly
###
# change the following decimal integer 
# 0 - 100 where 0 is NEVER use swap - not an altogether fantastic idea!!!
vm.swappiness=05

I agree with 'evo2':

I don't really understand why you want to do this though.

..more effort required than increased performance with your hardware..

catkin · 05-10-2010, 08:12 AM

But the default swap behaviour is usually no problem. Can you describe the symptoms more fully and explain why you think there is a need to change?

dh2k · 05-10-2010, 09:12 AM

Quote:

Originally Posted by afreitascs

My question is:
It is possible to "clean up" the memory swap. Or better still (I think). It is possible to spend
physical memory for data that is in memory swap?

let me know ...

many thanks

In a nut shell, - Yes it is - is it worth it? - well, we'll put our own value on that I guess - for learning - a defo yes.

afreitascs · 05-11-2010, 12:20 AM

First, many thanks for answers :-)

Right now I'm out of time to provide feedback. My understanding of English is poor and time consuming in my case ...

I am very interested in the answer!

I have a case with 700M of memory and another with 2G. The first, when I use KDE
quicker to swap memory is used and pc is slow ... In the second case (2G) happens
to get the memory swap around 1% (which does not change the performace)

Thank you very much

ps: I use very Google translator

Richard Cranium · 05-11-2010, 05:11 PM

Quote:

Originally Posted by afreitascs

First, many thanks for answers :-)

Right now I'm out of time to provide feedback. My understanding of English is poor and time consuming in my case ...

I am very interested in the answer!

I have a case with 700M of memory and another with 2G. The first, when I use KDE
quicker to swap memory is used and pc is slow ... In the second case (2G) happens
to get the memory swap around 1% (which does not change the performace)

Thank you very much

ps: I use very Google translator

OK.

In general, Linux will move a program's memory to swap space if it believes that the program hasn't been doing anything useful in a period of time.

For instance, if I were to launch Netbeans and then minimize the window that comes up, then after a period of time the operating system (OS) would decide to save all the Netbeans state to swap so that other programs could use the RAM for whatever I was really doing.

If I were to bring up the Netbeans window, I would have to wait whilst the SO loaded all the Netbeans pages from swap.

afreitascs · 05-11-2010, 10:45 PM

Quote:

Originally Posted by Richard Cranium

OK.

In general, Linux will move a program's memory to swap space if it believes that the program hasn't been doing anything useful in a period of time.

For instance, if I were to launch Netbeans and then minimize the window that comes up, then after a period of time the operating system (OS) would decide to save all the Netbeans state to swap so that other programs could use the RAM for whatever I was really doing.

If I were to bring up the Netbeans window, I would have to wait whilst the SO loaded all the Netbeans pages from swap.

Please
In your example with the minimized program, I type

swapoff -a && swapon -a (answered by EVO2 up ,thanks )

what happens with the program? The system is "smart" enough to save the data?

thanks

afreitascs · 05-11-2010, 11:00 PM

Quote:

Originally Posted by dh2k

.......................
..........................

Code:

cp /etc/syscrl.conf /etc/sysctl.conf_ORIGINAL

if you already have a 'sysctrl.conf'
.......................
........................

I did not find this file in slack ...

/etc/sysctl.conf

thanks

Richard Cranium · 05-11-2010, 11:23 PM

Quote:

Originally Posted by afreitascs

Please
In your example with the minimized program, I type

swapoff -a && swapon -a (answered by EVO2 up ,thanks )

what happens with the program? The system is "smart" enough to save the data?

thanks

Did you really mean to ask if the system was smart enough to read the data out of a swap partition before turning it off?

I don't know and really have no interest in finding out since I turn my swap partitions on and leave them that way.

(I do know that if your swap device fails, Bad Things Happen. That's why some people actually use a mirrored raid array for their swap partition.)

afreitascs · 05-11-2010, 11:32 PM

Quote:

Originally Posted by Richard Cranium

Did you really mean to ask if the system was smart enough to read the data out of a swap partition before turning it off?

I don't know and really have no interest in finding out since I turn my swap partitions on and leave them that way.

(I do know that if your swap device fails, Bad Things Happen. That's why some people actually use a mirrored raid array for their swap partition.)

Otherwise :
With the system running, data is lost when "cleaning" swap ?

thanks

lumak · 05-12-2010, 12:45 PM

if you are concerned about private data that may be on the swap partition, you could always use a random generator on the swap partition.

Please double check this before performing:
swapoff -a
dd of=/dev/swap/partition if=/dev/urandom bs=512
mkswap /dev/swap/partition
swapon -a

There are also other things you can do like using cryptsetup to encrypt the swap partition and using a key file that auto unlocks it on boot.

dh2k · 05-12-2010, 12:51 PM

Quote:

Originally Posted by afreitascs

I did not find this file in slack ...

/etc/syscrl.conf

thanks

I typo'ed - I have edited correctly to:

Code:

/etc/sysctl.conf

syg00 · 05-12-2010, 04:53 PM

This all seems pointless if you don't understand the functions and workings of the paging system.
Swapoff forces all pages back into backing RAM. If there is insufficient the swapoff fails, an the swap extent remains in use.

afreitascs · 05-12-2010, 11:15 PM

@lumak

Quote:

if you are concerned about private data that may be on the swap partition, you could always use a random generator on the swap partition.

Please double check this before performing:

Quote:

swapoff -a
dd of=/dev/swap/partition if=/dev/urandom bs=512
mkswap /dev/swap/partition
swapon -a

There are also other things you can do like using cryptsetup to encrypt the swap partition and using a key file that auto unlocks it on boot.

Although not want to encrypt my data, my bad English and his patience,caused me to learn something more ...

@dh2k

Quote:

/etc/sysctl.conf

Sorry, I do not understand, but I did not find this file in Slackware ...

@syg00

Quote:

[This all seems pointless if you don't understand the functions and workings of the paging system.

You're right!

Quote:

Swapoff forces all pages back into backing RAM. If there is insufficient the swapoff fails, an the swap extent remains in use.

I think that this answers my question.

many thanks to you all