nmbclusters

[Bosko Milekic]

It's always only been boot-time tunable (well, "always" is of course
relative to my time with FreeBSD -- Dag-Erling has been around longer
and therefore recounts its more comprehensive history).  In
6.0-CURRENT there was an intention to make it sysctl (runtime)
tunable, as it finally became at least theoretically possible to do
so.

I have recently seen a patch floating around from Paul Saab (ps@) who
has finally made it runtime tunable -- at least enough so that it can
be _increased_.  Not sure if he has committed it, yet.  Note that
_decreasing_ nmbclusters at run-time will probably never be possible
-- implementing is too difficult for what it would be worth.

Cheers,
Bosko

On 3/29/06, Dag-Erling Smørgrav <des at des.no> wrote:
> "Conrad J. Sabatier" <conrads at cox.net> writes:
> > Chris <chrcoluk at gmail.com> wrote:
> > > so [kern.ipc.nmbclusters] has no affect, has this become a read only
> > > tunable again only settable in loader.conf?
> > To the best of my knowledge, this has *always* been a loader tunable,
> > not configurable on-the-fly.
>
> kern.ipc.nmbclusters is normally computed at boot time.  A compile-
> time option to override it was introduced in 2.0-CURRENT.  At that
> time, it was defined in param.c.  A read-only sysctl was introduced in
> 3.0-CURRENT.  It moved from param.c to uipc_mbuf.c in 4.0-CURRENT,
> then to subr_mbuf.c when mballoc was introduced in 5.0-CURRENT; became
> a tunable at some point after that; then moved again to kern_mbuf.c
> when mballoc was replaced with mbuma in 6.0-CURRENT.  That is the
> point where it became read-write, for no good reason that I can see;
> setting it at runtime has no effect, because the size of the mbuf zone
> is determined at boot time.  Perhaps Bosko (who wrote both mballoc and
> mbuma, IIRC) knows.
>
> DES
> --
> Dag-Erling Smørgrav - des at des.no
>


--
Bosko Milekic <bosko.milekic at gmail.com>

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