freebsd stable - Dec 2006 - kern.ipc.nsfbufs Max Value?

I have an extremely busy web server here serving mostly static html pages
and images using apache 2.2.3 with sendfile enabled. It's a Dual Xeon
server with 4 GB RAM and I've tweaked many sysctl variables to help the
system chug along. At peak, apache is running nearly 1,500 child
processes.

To my question, what is the max value of kern.ipc.nsfbufs and does it
depend on any other values? I had originally increased it to 32768 however
sfbufs got maxed out slowing the server. Then I increased it to 65536 and
currently have these results:

45348/48844/65536 sfbufs in use (current/peak/max)

To me that's too close for comfort so I further tried to increase it to
131072 however with that setting the system would not boot. The kernel
page faulted with an error in the swapper process until I decreased
kern.ipc.nsfbufs back to 65536.

Is there anyway to increase this value even higher? The server has nearly
2.5 GB of free ram out of the 4 GB installed and the load averages are
very low 0.07, 0.15, 0.34 so hopefully it's possible to tweak this some
more.

Any ideas?

Thank You,

Holt G.


 
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On Sun, Dec 10, 2006 at 08:23:00AM -0800, Holtor wrote:
> I have an extremely busy web server here serving mostly static html pages
> and images using apache 2.2.3 with sendfile enabled. It's a Dual Xeon
> server with 4 GB RAM and I've tweaked many sysctl variables to help the
> system chug along. At peak, apache is running nearly 1,500 child
> processes.
> 
Have a look at ports/www/nginx for the alternative web server.
> To my question, what is the max value of kern.ipc.nsfbufs and does it
> depend on any other values? I had originally increased it to 32768 however
> sfbufs got maxed out slowing the server. Then I increased it to 65536 and
> currently have these results:
> 
> 45348/48844/65536 sfbufs in use (current/peak/max)
> 
> To me that's too close for comfort so I further tried to increase it to
> 131072 however with that setting the system would not boot. The kernel
> page faulted with an error in the swapper process until I decreased
> kern.ipc.nsfbufs back to 65536.
> 
> Is there anyway to increase this value even higher? The server has nearly
> 2.5 GB of free ram out of the 4 GB installed and the load averages are
> very low 0.07, 0.15, 0.34 so hopefully it's possible to tweak this some
> more.
> 
> Any ideas?
> 
On i386, the sfbufs are allocated from kernel_map which is basically
limited by the amount of KVA.  Try increasing KVA_PAGES to give more
virtual space for the kernel (at the cost of reducing the virtual
address space for userland); see the comments regarding this option
in sys/i386/conf/NOTES.  On amd64, you wouldn't have this problem as
sf_bufs are only opaque objects there and don't consume real memory.


Cheers,
-- 
Ruslan Ermilov
ru@FreeBSD.org
FreeBSD committer
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