ZFS committed to the FreeBSD base.

Bruce Evans brde at optusnet.com.au
Thu May 24 05:03:03 UTC 2007

On Wed, 23 May 2007, Kris Kennaway wrote:

> On Wed, May 23, 2007 at 05:32:31AM -0400, Kris Kennaway wrote:
>> I would actually be interested to know how Solaris gets away with
>> this.  It sounds like there must be less of a distinction between
>> memory allocated to the kernel and to userland, and the ability for
>> memory to flow between these two with some form of backpressure when
>> userland wants memory that is currently gobbled by up solaris ZFS.
>> This kind of system probably makes good sense (although maybe there
>> are trade-offs), but anyway it's not how FreeBSD does it.
> After some further thought I guess the difference is just that on a
> 64-bit kernel you don't have KVA issues and can indeed map all of
> physical RAM into the kernel for caching.

This should probably happen for 64-bit kernels in FreeBSD too.  FreeBSD
sizes the buffer map part of KVA in the same way on all arches, to squeeze
it into the limited available space on i386's, and has large complexity
and some loss of performance in the buffer cache in order to work with
the limited KVA.  (Very old versions had less complexity and a large loss
of performance.)


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