2.2.0-pre[56] swap performance poor with > 1 thrashing task

[Dax Kelson <dkelson@inconnect.com>]

On 7 Jan 1999, Zlatko Calusic wrote:

> 2.2.0-pre5 works very good, indeed, but it still has some not
> sufficiently explored nuisances:
> 
> 1) Swap performance in pre-5 is much worse compared to pre-4 in
> *certain* circumstances. I'm using quite stupid and unintelligent
> program to check for raw swap speed (attached below). With 64 MB of
> RAM I usually run it as 'hogmem 100 3' and watch for result which is
> recently around 6 MB/sec. But when I lately decided to start two
> instances of it like "hogmem 50 3 & hogmem 50 3 &" in pre-4 I got 2 x
> 2.5 MB/sec and in pre-5 it is only 2 x 1 MB/sec and disk is making
> very weird and frightening sounds. My conclusion is that now (pre-5)
> system behaves much poorer when we have more than one thrashing
> task. *Please*, check this, it is a quite serious problem.

I just tried this on 2.2.0-pre6 PentiumII 412Mhz, 128MB SDRAM, one IDE
disk (/ & swap).

./hogmem 100 3  (no swapping)
Memory speed: 167.60 MB/sec

./hogmem 200 3
Memory speed: 9.01 MB/sec

./hogmem 100 3 & ./hogmem 100 3
Memory speed: 0.96 MB/sec
Memory speed: 0.96 MB/sec

./hogmem 100 3 (no swap)
Memory speed: 180.18 MB/sec

./hogmem 200 3
Memory speed: 8.68 MB/sec

I then tried 

./hogmem 200 3 &

find / (on about 1.5GB of data on ext2 and vfat and nfs repeatedly) 

And launched netscape.  After 45 mins, I didn't restart the find, and
about 3 mins later the hogmem completed at 0.75MB/sec.  Netscape was
surprisingly responsive however.

Dax Kelson



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