adding more ram
thomas.sparrevohn at eds.com
Wed Dec 10 16:26:33 PST 2003
The same was true for 10.20 and 11 Versions of HPUX - I believe there once
was I very long going debate when the "new" FreeBSD vm was made on the
issue. The fundamental question at the time was what to do when you run out
of swap/vm space. The 1-1 backing of swap space was seen as a way to avoid
that you have resort to kill random processes in order to free up space and
the tradition with the 2-1 swap ratio used to have "a performance reason" in
the initial Unix Swap and paging implementations. I can't seem to recall the
From: owner-freebsd-hackers at freebsd.org
[mailto:owner-freebsd-hackers at freebsd.org] On Behalf Of Bill Vermillion
Sent: 10 December 2003 14:41
To: freebsd-isp at freebds.org
Cc: nbari at unixmexico.com; freebsd-isp at freebsd.org;
freebsd-hackers at freebsd.org
Subject: Re: adding more ram
While normally not able to pour water out of a boot with instructions on the
heel, on Wed, Dec 10, 2003 at 02:41
our dear friend Mike Silbersack uttered this load of codswallop:
Just one slight addendum here.
> I'm replying because I want to answer your real question.
> <g> The notion of swap = 2 x ram is an old one, and is no longer
> applicable. (Some) older VM systems used very simplistic swapping
> mechanisms, which required entire processes to be swapped, thereby
> requiring large amounts of swap space. FreeBSD (and other modern OSes)
> page out to the swap file in increments of 4K pages, and do so in a
> flexible manner. As a result, you should always have *some* swap space
> to handle overload cases, but it's not necessary to keep any specific
> ram to swap ratio.
Systems such as the Irix I used before moving the servers to FBSD around
1996 - reserverd swap space for applications when the application started up
so those needed large swap space. Often it was never used, but the design
allocated it anyway.
Bill Vermillion - bv @ wjv . com
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