RE: [PATCH 0/8] zcache: page cache compression support

Dan Magenheimer
2010-07-21T17:39:23Z

> > Maybe the best solution is to make the threshold a sysfs
> > settable? Or maybe BOTH the single-page threshold and
> > the average threshold as two different sysfs settables?
> > E.g. throw away a put page if either it compresses poorly
> > or adding it to the pool would push the average over.
>
> Considering overall compression average instead of bothering about
> individual page compressibility seems like a good point. Still, I think
> storing completely incompressible pages isn't desirable.
>
> So, I agree with the idea of separate sysfs tunables for average and
> single-page
> compression thresholds with defaults conservatively set to 50% and
> PAGE_SIZE/2
> respectively. I will include these in "v2" patches.

Unless the single-page compression threshold is higher than the
average, the average is useless. IMHO I'd suggest at least
5*PAGE_SIZE/8 as the single-page threshold, possibly higher.