Re: Tuning Question

In message <44odnziewr.fsf@xxxxxxxxxxxxxxx>, Lowell Gilbert writes:
Cy Schubert <Cy.Schubert@xxxxxxxxxxxx> writes:

I have a question about tuning FreeBSD systems, specifically in regard to
memory. At one time on Solaris systems it was recommended to keep scan rate

below 200 pages per second. (Today it's 300 pages per second, dependent on
the amount of memory, class of system.) Are there any recommendations or
rules of thumb a person can use to determine when a memory upgrade is
required? My machines are only busy during port builds when the scan rate
can vary greatly and the page out rate could reach as high as two pages per

second during brief periods. What kind of memory and paging metrics should
I use on FreeBSD systems?

I'm not convinced that such a simple algorithm makes sense these days.
If the system is normally pretty quiet, then it is unlikely you'll see
any difference from optimizing memory behaviour further.

I believe that when top(1) gives memory sizes, they are in bytes
rather than pages as the manual indicates.

Top's output, as is free memory on all O/S's these days, is bogus. It's the
size of the free memory pool which is available for immediate allocation.
Used memory is just as useless. It doesn't matter how much is swapped out,
what matters is how much I/O is being performed to support VM. I know at
work, which is an Oracle ghetto, paging should be kept at a minimum,
especially the SGA. Other apps can afford more. In the case of an average
FreeBSD system it's been guesswork.

I should also mention that even though Sun recommended certain metrics for
their systems. In a previous life as an MVS (IBM mainframe) systems
programmer, IBM recommended that no more than 5% of system resources should
be used for paging, otherwise you're paging too much. I suppose this might
be a good paper for someone to write. (As I'm already writing a book, I
probably don't have time to research and write yet another subject.)


--
Cheers,
Cy Schubert <Cy.Schubert@xxxxxxxxxxxx>
FreeBSD UNIX: <cy@xxxxxxxxxxx> Web: http://www.FreeBSD.org

e**(i*pi)+1=0


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