From: Jim C. Nasby <jnasby@pervasive.com>
To: Alex Hayward <xelah-pgsql@xelah.com>
Cc: Mark Kirkwood <markir@paradise.net.nz>
Cc: Vivek Khera <vivek@khera.org>
Cc: Postgresql Performance <pgsql-performance@postgresql.org>
Subject: Re: Best OS & Configuration for Dual Xeon w/4GB & Adaptec
Date: Tue, 21 Mar 2006 06:34:17 -0600
Message-ID: <20060321123417.GW15742@pervasive.com> (raw)
In-Reply-To: <Pine.LNX.4.58.0603211217420.27598@sphinx.mythic-beasts.com>
References: <20060317221116.GA14661@juniper.net>
<8F6490E1-64E2-406B-A559-7DA8BA1EB197@khera.org>
<20060321103219.GD15742@pervasive.com>
<441FDD7E.7050106@paradise.net.nz>
<20060321114658.GK15742@pervasive.com>
<Pine.LNX.4.58.0603211217420.27598@sphinx.mythic-beasts.com>
On Tue, Mar 21, 2006 at 12:22:31PM +0000, Alex Hayward wrote:
> On Tue, 21 Mar 2006, Jim C. Nasby wrote:
>
> > On Tue, Mar 21, 2006 at 11:03:26PM +1200, Mark Kirkwood wrote:
> > >
> > > So its really all about accounting, in a sense - whether pages end up in
> > > the 'Buf' or 'Inactive' queue, they are still cached!
> >
> > So what's the difference between Buf and Active then? Just that active
> > means it's a code page, or that it's been directly mapped into a
> > processes memory (perhaps via mmap)?
>
> I don't think that Buf and Active are mutually exclusive. Try adding up
> Active, Inactive, Cache, Wired, Buf and Free - it'll come to more than
> your physical memory.
>
> Active gives an amount of physical memory. Buf gives an amount of
> kernel-space virtual memory which provide the kernel with a window on to
> pages in the other categories. In fact, I don't think that 'Buf' really
> belongs in the list as it doesn't represent a 'type' of page at all.
Ahhh, I get it... a KVM (what's that stand for anyway?) is required any
time the kernel wants to access a page that doesn't belong to it, right?
And actually, I just checked 4 machines and adding all the queues plus
buf together didn't add up to total memory except on one of them (there
adding just the queues came close; 1507.6MB on a 1.5GB machine).
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, xelah-pgsql@xelah.com, markir@paradise.net.nz, vivek@khera.org
Subject: Re: Best OS & Configuration for Dual Xeon w/4GB & Adaptec
In-Reply-To: <20060321123417.GW15742@pervasive.com>
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