ZFS kmem_map too small.

Ali Mashtizadeh mashtizadeh at gmail.com
Wed Oct 31 09:57:07 PDT 2007

For ZFS KVA_PAGES=512 seems to run very stable so it's unfortunate that we
have to give up our VA space in the userland. I would personally like to see
a move to a 4-4 Memory model or at least have it as a compile time option.
Does anyone know if that's been attempted on FreeBSD?


On 10/9/07, Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
> On Tue, Oct 09, 2007 at 12:28:09PM -0700, Darren Reed wrote:
> > Pawel Jakub Dawidek wrote:
> > >...
> > >
> > >For i386 one has to set, eg. 'options KVA_PAGES=512' to the kernel
> > >config to be able to define kmem larger than ~700MB. I guess you're
> > >running amd64, maybe there is similar requirement?
> > >
> >
> > Given how much RAM PCs have these days, why isn't this a default for
> >
> > Or why isn't it at least a tunable rather than an option?
> This may be a good reason - today's PCs have a lot of RAM and KVA_PAGES
> splits address space between userland and kernel - the more address
> space for the kernel, the less address space for the userland.
> KVA_PAGES=512 splits 4GB address space in half, so userland processes
> can address at most 2GB of memory.
> --
> Pawel Jakub Dawidek                       http://www.wheel.pl
> pjd at FreeBSD.org                           http://www.FreeBSD.org
> FreeBSD committer                         Am I Evil? Yes, I Am!

Ali Mashtizadeh
علی مشتی زاده

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