Re: Buffer handling (setting PG_referenced on access)

Zlatko Calusic
1999-01-11T20:19:55Z

Linus Torvalds <torvalds@transmeta.com> writes:

> On 11 Jan 1999, Zlatko Calusic wrote:
> >
> > OK, implementation was easy and simple, much simpler than it was made
> > before (with BH_Touched copying...), but I must admit that even after
> > lots of testing I couldn't find any difference. Not in performance,
> > not in CPU usage, not in overall behaviour. Whatever results I have
> > accomplished, they were too much in the statistical noise, so I don't
> > have any useful data. Maybe, others can try and see.
>
> This was what I saw in my very very inconclusive tests too - which is why
> I decided that there was no point in doing buffer cache aging at all.

Yes, looks like we finished our tests with same results.

>
> > But, nevertheless, four lines added to the kernel look very correct to
> > me. My vote for including, if for nothing, then to make balance with
> > page cache. It won't harm anything, that's for sure.
>
> I can easily see it harming something - I actually think that not using
> the reference bit is "safer" in that it never allows the buffer cache to
> grow very aggressively for very long (and we definitely don't want to have
> an overlarge buffer cache - it's mostly used for temporary buffers for
> write-out anyway).
>
> Basically I don't want to enable the aging code unless somebody shows me
> that it makes a marked improvement under some (reasonably real-world)
> circumstances.. So far the jury seems to say that it doesn't.
>

OK, I got one more idea in the meantime, and I'll try it as the time
permits. In the meantime, I agree with you. If we can't prove it's
actually worthwhile to add those four lines, then we really don't need
them.

Regards,
--
Zlatko