Re: 2.4.0test9 vm: disappointing streaming i/o under load

Chris Evans
2000-10-11T20:59:10Z

On Wed, 11 Oct 2000, Eric Lowe wrote:

> > Unfortunately, 2.4.0test9 exhibits poor streaming i/o performance when
> > under a bit of memory pressure.

[...]

> Would you try setting /proc/sys/vm/page-cluster to 8 or 16 and let
> me know the results? I think one _part_ of the problem is that
> when the swapper isn't agressive enough, it causes too much disk
> thrashing which gets in the way of normal I/O... my experience
> has been that with modern disks with 512K+ cache you have to
> write in 64K clusters to get optimum throughput.

Raising the cluster size didn't seem to do much apart from generally slow
down interactive response. Lowering it, however, seemed to make playback
less jittery. I guess that's to be expected; faulting in large chunks of
sequential i/o won't help much when under memory pressure because the
pages will get thrown out again before they get a chance to be
used. Especially with drop_behind.

Rik what do you think.

Cheers
Chris