Problems reclaiming VM cache = XFree86 startup annoyance

David G. Lawrence dg at
Sat Dec 20 13:56:25 PST 2003

> As you can probably gather, all this manual intervention is a bit of a
> hassle.  So, my question is this: is there a way explicitly to force
> the kernel to flush its VM cache (to move it to "Free").  Failing
> that, are there any sysctls to tune to help alleviate the problem?
> The only sysctls I change in /etc/sysctl.conf are as follows:

   I don't know what is causing your problem, but 'cache' pages in FreeBSD
are free pages - they can be allocated directly in the page allocation code.
They only differ from "free" pages in that they contain cached file data.
   So the number of pages 'cache' vs. 'free' isn't the cause of the problem.
> net.inet.tcp.sendspace=65536

   You might want to use 65535 there instead to avoid the system having to
use large-window TCP extensions.

> kern.ipc.shmmax=67108864
> kern.ipc.shmall=32768
> The latter two were in response to an installation message of a port I
> installed quite some time ago (xine, perhaps?).

   Uh, yeah. You might want to take that out and see if it affects the
problem. shmall of 32768 could potentially result in up to 134MB of virtual
memory being consumed, and in most FreeBSD kernel configurations, this would
cause it to run out.


David G. Lawrence
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