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Date: Tue, 20 Oct 2009 20:12:58 +0100
From: Vincent Hoffman <vince@unsane.co.uk>
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To: Christopher Hilton <chris@vindaloo.com>
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Cc: freebsd-questions@freebsd.org
Subject: Re: /tmp on mfs
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Christopher Hilton wrote:
> Reading the list yesterday I came across a little controversy about
> swap backed /tmp filesystems. I've been using this in my /etc/rc.conf
>
> tmpmfs="YES"            # Set to YES to always create an mfs /tmp, NO
> to never
> tmpsize="1g"            # Size of mfs /tmp if created
> tmpmfs_flags="-S -o async,noexec"       # Extra mdmfs options for the
> mfs /tmp
>
> To mount /tmp on a swap backed filesystem. I've been assuming that
> data stored in the /tmp directory was held in RAM and then written to
> the swap space only when the system had a more pressing need for the
> RAM. I typically configure my systems with swap == 2 * RAM or more.
> And on the systems in question I have at least 1Gb of RAM. I was
> hoping to  use this trick to enhance the performance of the postgresql
> database (temp_tablespace=/tmp/pgsql/....) Is my assumption about
> where the data in a temporary file is stored incorrect?
>
Thats certainly always been my interpretation of the manpage.
                      "Storage for this type of memory disk is allocated
from
                      buffer memory.  Pages get pushed out to the swap when
                      the system is under memory pressure, otherwise
they stay
                      in the operating memory."

If thats not the case I'd be interested to know how it does work.

Vince
> -- Chris
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