On Wed, Jul 26, 2006 at 07:07:49PM +0200, Mark Perry wrote:
> Rob van der Heij wrote:
> >On 7/26/06, Brian France <[EMAIL PROTECTED]> wrote:
> >
> >> I have an image that is 1280m. It's swap space is 464m. Is that a
> >>good ratio? The image has chewed up according to Perftoolkit 75% of
> >>it. I was thinking a bigger swap space as opposed to more memory
> >>which is what I being pressured to do.
> >
> >Little rules of thumb or golden ratio. The total of swap space and
> >'real' memory relates to how much virtual memory Linux can hand out.
> >If the sum of that is too low then you get Out-of-Memory terminations.
> >Whether the ratio is 1:1 or 10:1.
> >The algorithm for allocating swap space makes it use fresh pages
> >rather than re-use old ones. This means that the "used" portion will
> >grow until all has been used. You can prevent that by using multiple
> >vdisks for swapping. When they have different priority you force Linux
> >to reuse free space in the first before using fresh pages in the
> >second.
> >You should compare the internal memory measurements in Linux with the
> >VM side to draw conclusions.
> When considering z/VM VDISKs for Linux swap you should refer to:
> http://www.vm.ibm.com/perf/tips/linuxper.html
>
> Specifically note VDISK advantage only when z/VM has plenty of REAL
> storage available, and that idle Linux guests can prevent the z/VM page
> stealing alg. from working efficiently (Steals from other guests first.)
>
For the decision whether you need more swap or more memory start
vmstat 5 500
and look at the coloums si and so to see how the system uses the swap.
regards
Ihno
"Never trust a computer you can lift."
--
Ihno Krumreich [EMAIL PROTECTED]
SUSE LINUX Products GmbH Projectmanager S390 & zSeries
Maxfeldstr. 5 +49-911-74053-439
D-90409 Nürnberg http://www.suse.de
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