[SOLVED] Swap keeps growing after hibernation restore

m1m · 10-13-2015, 01:41 PM

Hi,
I use Slackware 14.1 x64 with default kernel (3.10.17). I have 8GB ram and 10GB swap partition. I mainly use Opera 12 and I try to keep as much as I can in the ram. In normal conditions Opera takes ~3GB (I have many tabs opened) and total system usage is ~3,5GB-4,5GB. I also use ramdisk which is ~1GB.

When I boot system for the first time I have 0 swap usage. But when I hibernate & restore, swap usage goes +1,5GB, later it goes down 200-300 MB but after another hibernate & restore it goes up another 1,5GB and so on. I never goes back to 0 despite there is 4,5GB of free ram.

I thought that after restore from hibernation all swap is loaded back to ram and cleared (because there was nothing in swap before hibernation). I have set swappiness to 10. I use standard XFCE panel button to hibernate.

For example, this is memory usage after 3 hibernations with runnig opera:

Code:

free -m
             total       used       free     shared    buffers     cached
Mem:          7923       4782       3141          0        216        970
-/+ buffers/cache:       3595       4328
Swap:        10237       2540       7697

I run

Code:

vmstat 1

for a while and it dosen't show any swap usage.

lazydog · 10-13-2015, 02:29 PM

There will always be residual pages left in SWAP that don't get cleared. The only thing that gets loaded back into RAM are what is needed or most frequently used. Items that are not frequently used don't have to be read back into memory.

And swappiness is only used to instruct the system when to swap as the memory starts to become fully utilized.

m1m · 10-13-2015, 02:34 PM

OK, so what should I do then? After few more hibernations I'll run out of swap space...

Hangaber · 10-13-2015, 04:55 PM

Quote:

Originally Posted by lazydog

[...]The only thing that gets loaded back into RAM are what is needed or most frequently used. Items that are not frequently used don't have to be read back into memory.[...]

My thoughts exactly.

I suspect what is happening is;
When you hibernate-to-disk, it sounds like your 'used' + 'cached' memory is being stored.
Upon the restore, the 'used' is read, but the 'cached' remains in swap. If the system needs anything from that cached data, it'll fetch it.

So I also suspect that; Just like if you run out of actual RAM, the unneeded 'cached' data will be dumped first from RAM. Likewise, if your swap gets full, the unneeded 'cached' data in that swap file will be discarded.

m1m · 10-13-2015, 05:18 PM

Thanks for answers, now it's more clear to me, but I think it's a bit ineffective - why use swap when there are loads of free ram? Anyway, is there any command to "move" swap back to ram?

syg00 · 10-13-2015, 07:46 PM

Why swap it back in if it's never referenced ?. That would be a much more inefficient use of memory.

"swapoff" followed by "swapon" will clear swap.
If you have insufficient RAM, the swapoff will fail - then you'll know you really do have an issue.

All unnecessary IMHO, but it's your machine.

lazydog · 10-16-2015, 07:46 AM

A thing to remember is SWAP will take care of itself. The only time you have to worry about it is when you are working and it fills to capacity then you have a problem.