FreeBSD vice OS X memory management

[RW]

On Thu, 26 Apr 2012 08:32:39 +0000 (UTC)
jb wrote:

> Adam Vande More <amvandemore <at> gmail.com> writes:
> 
> > ... 
> > http://workstuff.tumblr.com/post/19036310553/two-things-that-really-helped-
> > speed-up-my-mac-and
> > http://dywypi.org/2012/02/back-on-linux.html
> > 
> 
> "2) Inactive memory (which is memory that has been recently used but
> is no longer) is supposed to be seamlessly reclaimed automatically by
> the OS when needed for new programs. In practice, I’ve found that
> this isn’t the case, and my system slows to a crawl and starts paging
> out to disk when free memory drops to zero, even as half of the
> available RAM (which is a lot) is marked as inactive. ..."

That's not a good description of inactive memory, most of which
contains useful data. The situation described is undesirable, but not
abnormal. It can happen when your physical memory is spread thinly, but
most of it isn't being frequently accessed. In that case the inactive
queue can be dominated by dirty swap-backed pages. 


> The above and the past FreeBSD thread here, both I referred to, have
> something in common - the system seems to progressively come under
> stress due to what one user experienced as "missing memory",

The FreeBSD link involved ZFS which manages its own disk caching and
is relatively new. My guess is that if there is a problem it's ZFS
specific. If it were a more general problem I think we'd see a lot more
complaints, whereas  ZFS already has a reputation for needing lots of
memory.