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Date: Sun, 30 May 2004 00:34:13 -0700
From: David Schultz <das@FreeBSD.ORG>
To: Geert Hendrickx <geert.hendrickx@ua.ac.be>
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References: <20040529200748.GA87145@lori.mine.nu>
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cc: freebsd-hackers@FreeBSD.ORG
Subject: Re: documentation on sysctl vm.defer_swapspace_pageouts?
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On Sat, May 29, 2004, Geert Hendrickx wrote:
> where can I find documentation on the vm.defer_swapspace_pageouts
> sysctl?  LINT only mentions it, without explaining, man sysctl doesn't 
> mention it at all, and even Google yields very few useful results...  

vm.defer_swapspace_pageouts causes the system to avoid using swap,
if possible.  With the option enabled, the VM system will still
evict clean pages and read them in again from the filesystem when
necessary, but it will only write dirty pages to the swap
partition as a last resort.

> I was looking for a way to tune swap-usage a bit, I heard Linux has a
> "swappiness" setting (telling the kernel how easy it should go with 
> paging out), and I hoped FreeBSD would have something similar.
> vm.defer_swapspace_pageouts might do the trick, but so it seems to be 
> poorly documented...  

Take a look at vm.swap_idle_enabled.  With that option enabled,
the VM system is more proactive in swapping out idle processes,
rather than waiting for a low-memory situation to materialize
before taking action.