Re: kswapd taking 100% CPU - only there's no swap?

[Tom Sightler <ttsig tuxyturvy com>]

On Tue, 2006-03-07 at 14:04 -0800, Don MacAskill wrote:
> There was a big discussion about this problem on taroon-list a few years 
> ago.   We all spent quite a bit of time trying to tune the swap 
> parameters and couldn't do it.  Turning of swap fixed the problem 100%.

Correct, but Taroon is quite different from Nahant, use completely
different kernels and generally have quite different behaviors with
regards to VM.  I wouldn't have given you the same response had you said
you were running Taroon.

> Fact:  There was major brokenness under DB loads with swap enabled.  It 
> *is* broken.

It may be a fact in certain setups, but it's not a general fact.  I
manage a large number of systems with DB loads and have swap enabled on
all of them although, under their normal load, they see practically no
swap activity.

> Fact:  As soon as we disabled swap, our DB boxes saw a 2X boost in 
> performance.

I can believe this, since the system is now forced to live with the
memory it has and can't swap.   As long as you fully understand the
impact of that decision, I doubt it's a major problem.

Later,
Tom