arc cache: pagesize and/or power of 2 constraints?

[Andriy Gapon]

on 29/07/2010 10:31 Alexander Leidinger said the following:
> Hi,
> 
> while writting some acceptance tests for the Solaris machines at work I
> wondered if the size of the arc cache should be a multiple of the page
> size and/or a power of 2. I searched the net, but was not able to find
> some info regarding this.

I suppose you mean ZFS ARC, not an ARC concept in general.
I wonder why you came at this question.

> I would expect that it does not make sense to have an arc cache size
> which is not a multiple of the page size.

Why?

> And depending on how the arc
> cache is implemented, it would make sense to have it even as a power of
> 2 size (even if it is able to handle non-power-of-2 sizes).

Why?

> Did someone had a look at this in FreeBSD?

ARC size is almost arbitrary.
It's a collection of malloc/uma allocated buffers of various sizes, individual
sizes are various multiples of 512.

-- 
Andriy Gapon