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Re: Swappiness and Virtual Memory Management



On Wednesday 27 April 2005 22:31, Ow Mun Heng wrote:
> I've got a question regarding VM management in Linux.
>
> I've got 512MB of RAM on my laptop and at times it can still be slow esp
> when the RAM is used up and starts accessing the swap.
>
> Setting swappiness to 10 doesn't really make a difference at all.
>
> However, (what I've heard) users of FreeBSD has attested that hitting
> swap on those BSD system does not make any noticeable effect on their
> system. Even when there's up to like 700MB of swap in use.
>
> On Linux, it seems that the opposite is true, when we hit swap, and then
> the disk starts to thrash violently and I get slow load-up of programs
> and even switching between virtual Desktops can be a real pain.
>
> Does anyone has more insight to this? I know the solution is to add more
> RAM but is that really a solution? I mean, it's like storage, is there
> really such a thing as "I've got enough storage?"

I do some work where I can't ever get enough ram - My current system is about 
14GB in swap and I don't feel any real issue with that... 

It mostly depends on your workload. If you run a lot of server tasks you 
notice paging less then if you run interactive stuff. Worst is, if you try to 
work with a huge picture in gimp - a few meg in swap can already drag you 
down consierably... 

Also, you're running a laptop - laptop drives are horribly slow. We did the 
same work on desktops and laptops - both with 2GB ram, 3.2GHz desktop P4 and 
otherwise also almost the same - difference was the disk... our ram usage was 
about 2.5GB and the resulting performance panelty was about 40%... 

Other than that, yes FreeBSD I can agree acts a little nicer when it comes to 
swapping - but in all honesty, the difference is so little that you really 
have to test the system and create the swapping on purpose and then time the 
apps to notice any difference. 

Peter.


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