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Old 11-30-2011, 08:05 AM   #1
arvindk.monu
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Registered: Aug 2009
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Problem with swap space


Hello Folks ,

I am facing a problem ,my swap space is not working on my system.even when i am using heavy process and services.

System
root@Troy:~# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 10.10
Release: 10.10
Codename: maverick

root@Troy:~# free -m
total used free shared buffers cached
Mem: 1001 979 21 0 51 645
-/+ buffers/cache: 282 719
Swap: 4290 0 4290

cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
# / was on /dev/sda1 during installation
UUID=7c6e437d-fcee-4182-a887-5c3d89b570f8 / ext4 errors=remount-ro 0 1
# swap was on /dev/sda5 during installation
UUID=bb76de4b-32db-42dc-8672-ff90fc2444fc none swap sw 0 0
/dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0


root@Troy:~# blkid
/dev/sda1: UUID="7c6e437d-fcee-4182-a887-5c3d89b570f8" TYPE="ext4"
/dev/sda5: UUID="bb76de4b-32db-42dc-8672-ff90fc2444fc" TYPE="swap"

root@Troy:~# swapon -s
Filename Type Size Used Priority
/dev/sda5 partition 4393980 0 -1


please help me in this, UUID for swap is correctly mapped into fstab inspite of that Swap doesnt start working.



Please help.

Last edited by arvindk.monu; 11-30-2011 at 08:06 AM.
 
Old 11-30-2011, 08:34 AM   #2
_bsd
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1GB is still a lot of RAM, most of the new Android devices come with less than that.
I have a 2GB system that doesn't swap.

Your /etc/fstab looks correct and swapping is on.

Use top, or htop to see which apps are using memory and how much.

as an experiment, you could
Code:
cat /proc/sys/vm/swappiness
see what that says, save the echo'd value to restore later.

Code:
echo 100 > /proc/sys/vm/swappiness #(100 is max)
see how swapping behaves after that.
If swapping works when needed, and you have no performance issue what are you worried about?
 
Old 11-30-2011, 08:49 AM   #3
johnsfine
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Quote:
Originally Posted by arvindk.monu View Post
I am facing a problem ,my swap space is not working on my system.even when i am using heavy process and services.
I don't see any problem in those numbers. I think you are simply misunderstanding the reasons a Linux system uses swap space and expecting use of swap space when the system has not needed any.

Quote:
Originally Posted by _bsd View Post
as an experiment, you could ...
I wouldn't bet that experiment would produce any informative results and if it happened to produce such results, I'd bet against the OP understanding those results.

Given "memory pressure", which might or might not exist in the OP's system, Linux might displace certain kinds of memory use that can be read back later from the same file it came from originally. That is an important activity very similar to what a user thinks of as swapping, but it doesn't use any swap space.
Alternately, Linux might displace other kinds of memory use out to swap space.

Which of those it will do depends on which kind of memory use is present but not recently accessed. Swappiness affects that decision (which of those two kinds of memory to displace) in borderline cases where the two are roughly equal). A normal Swappiness value makes Linux prefer (in borderline cases) to displace memory use that doesn't take swap space. Swappiness 100 makes it treat the two equally, which is a bad idea, because displacing memory use back to the original file is in the long run half as expensive displacing memory to swap.

If none of the uses of "anonymous memory" are "stale" then changing swappiness would have no effect. Linux might choose to displace the kind of memory use that goes to the original file even if it is making the decision on an equal basis.

Last edited by johnsfine; 11-30-2011 at 09:04 AM.
 
Old 11-30-2011, 08:14 PM   #4
arvindk.monu
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Registered: Aug 2009
Posts: 22

Original Poster
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Thanks johnsfine,_bsd it start using swap space when i start heavy numerous process to small extent..i think my understanding to swapping was wrong,i was thinking unused pages from RAM to swap space whether RAM is not fully occupied(not using 100%),but in current scenario it seems to me swap space is only used when RAM become full.if you guys can enlighten some more information this i will be very thankful to you.
 
Old 11-30-2011, 08:58 PM   #5
frankbell
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My understanding is that Linux swaps only when it needs to; if it doesn't need to, it won't. The more RAMs, the less swapping.

The one I'm using right now has 4 GB RAM and is not swapping at all.

Here's one interesting article I found:

http://www.xenotime.net/linux/doc/swap-mini-howto.txt
 
  


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