Re: FSI TX200 S2 and main memory > 4 GB

On Thu, 2007-06-21 at 09:29 -0300, Herman.Maseberglomanegra.com.ar
wrote:
> 
> Oh, Interesting !! 
> 
> I have the same configuration (64bit and 16GB RAM), the
script from
> metalink note 401749.1recommend me: 
> 
> lnrsdb0:~ # ./hugepages_settings.sh 
> Recommended setting: vm.nr_hugepages = 3996 
> 
> And my SGA is: 
> 
> SQL> show sga 
> 
> Total System Global Area 4414479016 bytes 
> Fixed Size                   748200 bytes 
> Variable Size             738197504 bytes 
> Database Buffers         3674210304 bytes 
> Redo Buffers                1323008 bytes 
> 
Well, assuming SuSE uses 2048MB Hugepages (I'm mostly a
Redhat person,
sorry) then 3996 huge pages is reasonably close to 8GB, but
you only
have a 4.5GB SGA.  That means that 3.5GB of your RAM is
likely going to
waste right now.  When you allocate hugepages, the system
reserves them
immediately and that memory can only be used by programs
which
specifically requrest hugepage memory.  You can verify this
by running
"cat /proc/meminfo" and looking at the last few
lines which show your
"hugepages" allocation.  My guess is you'll se
something like:

HugePages_Total:     3996
HugePages_Free:      1891
Hugepagesize:     2048 kB

If so, that would mean that Oracle is using 2105 hugepages
and the other
1891 (about 3.6GB) are basically going to waste.  If you
have memory
going to waste then this is one of the places where huge
pages can work
against you.  If it turns out that you have huge pages going
to waste
you should either increase your SGA to allow Oracle to use
them, or
decrease your allocation of huge pages to the kernel so that
it can use
the memory for other things.

The above is just a guess based on the information you've
provided, feel
free to post the actual HugePages numbers so that we can
know for sure.

Later,
Tom


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