Re: Linux-2.1.129..

Stephen C. Tweedie
1998-11-24T15:49:04Z

Hi,

On 24 Nov 1998 00:28:16 -0600, ebiederm+eric@ccr.net (Eric
W. Biederman) said:

> Imagine a machine with 1 Gigabyte of RAM and 8 Gigabyte of swap,
> in heavy use. Swapping but not thrashing.

> You can't swap out several hundred megabytes all at once.

Sure you can! It's a tradeoff between moment-to-moment predictability
and overall throughput. Swapping loads at once gives unpredictable
short-term behaviour but great throughput. Performance is nearly
always about trading of throughput for things like predictability or
fairness.

> You can handle a suddne flurry of network traffic much better this way
> for example.

As long as you have got enough clean pages around, you can deal with
this anyway: kswapd can find free memory very rapidly as long as it
doesn't have to spend time writing things to swap.

> As far as fixed percentages. It's a loose every time, and I won't
> drop a working feature for an older lesser design. Having tuneable
> fixed percentages is only a win on a 1 application, 1 load pattern
> box.

<Nods head vigorously.> Try running with a big ramdisk on a 2.1.125
box, for example: the precomputed page cache limits no longer work and
performance falls apart.

--Stephen