FreeBSD 5.1-R kernel panic

Terry Lambert tlambert2 at mindspring.com
Thu Jul 24 23:09:46 PDT 2003


Stephane Raimbault wrote:
> I recently realized that I was miss-understanding how much free memory I had
> on the system, and I doubt I even need the full 4Gig's.
> 
> Perhaps I can re-confirm how to check how much free real memory is available
> on the system.

For 4G of physical RAM, with 3G of KVA and 1G of UVA, you have
enough memory to hold the kernel and the page mappings for all
of KVA + the pages dedicated to the kernel, plust the defaults
for buffers (if you *do not* autotune) for ~2G of mbufs and
tuning for approximately 280,000 socket connections and open
files, *IF* you disable IPSEC, AND you intend to run one or
two processes in user space and use mode of the 1G of address
space there.

If you autotune, the numbers of connections you can run drops
sharply.

Also note that the default UVA/KVA plist is *not* 1G/3G, it's
2G/2G, and it used to be 3G/1G.  For 4G server systems, the
very first thing I always recommend, if you want the highest
load capacity possible, is to reduce the UVA and increse the
KVA so you have enough space in the KVA to map and store the
resources you'll need for a high load.  The most common thing
to run out of, in everything but database servers, is KVA
space ("panic: kmem_map too small").

For databases with large data sets, you have to artificially
restrict the amount of total KVA that everything added together
can consume to keep it under the 2G ceiling.  This usually
means a tradeoff between number of connections and database
size.

-- Terry


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