Re: 2.6.0-test9 - poor swap performance on low end machines

Roger Luethi
2003-12-17T19:51:00Z

On Wed, 17 Dec 2003 13:53:28 -0500, Rik van Riel wrote:
> On Tue, 16 Dec 2003, Roger Luethi wrote:
>
> > One potential problem with the benchmarks is that my test box has
> > just one bar with 256 MB RAM. The kbuild and efax tests were run with
> > mem=64M and mem=32M, respectively. If the difference between mem=32M
>
> OK, I found another difference with 2.4.
>
> Try "echo 256 > /proc/sys/vm/min_free_kbytes", I think
> that should give the same free watermarks that 2.4 has.

I played around with that knob after wli posted his findings in the
"mem=16MB laptop testing" thread. IIRC tweaking min_free_kbytes didn't
help nearly as much as I had hoped. I'm running the efax benchmark
right now just to make sure. It's going to take a couple of hours,
I'll follow up with results.

FWIW akpm posted a patch to initialize min_free_kbytes depending on
available RAM which seemed to make sense but it hasn't made it into
mainline yet.

> Using 1MB as the min free watermark for lowmem is bound
> to result in more free (and less used) memory on systems
> with less than 128 MB RAM ... significantly so on smaller
> systems.

Possibly. If memory pressure is high enough, though, the allocator
ignores the watermarks. And on the other end kswapd seems to be pretty
busy anyway during the benchmarks.

Roger