Summary: RE: How to disable round robin paging

From: <george.done_at_dutchtone.nl>
Date: Wed Sep 05 2001 - 06:44:37 EDT
	I've got a lot of interesting messages to the question below. The
most important ones were that:
	1. There is a solution to this as suggested by Lieven Marchand and
this was to change the value of swap_maxcontig from the default 1 Mb to 2GB
and 
	have as a secondary effect round robin paging disabled. However, he
also pointed out that this is highly experimental and the ones willing to
try this on their production systems are on their own. I was not willing to
try hence I still have no feedback on this solution.
	2. The second (indirect) answer is that applications tend to reserve
upfront large quantities of memory upfront from which often a half or even
one third actually use. So, the fact that swap apear to be used means that
in fact that virtual memory was reserved, not necesarilly used. Of course,
because of the above, there will not actually be disk paging activity and
subsequently no performance problems. Adrian Cockroft personally pointed me
that a lot of memory shortage problems can be solved by just configuring
more swap (taking care if 32 bit kernel is used, that none of them is larger
than 2GB). In that way, applications which reserves virtual memory will
reserve not physical memory but disk swap space. This makes sense.
	Thanks everybody who bottered to respond !
	Best Regards,
	George DONE 


> I ran in the following annoying "feature" of Solaris: Round Robin paging.
> This are the facts:
> 1) the space over 2 GB in a swap device is ignored
> 2) if you have more than one swap device, Solaris use them all in a round
> robin fashion, several pages on each swap device.
> Now this is good if you put each swap device on a separate
> volume/metadevice, because spreads the disk load. But if you need 12GB of
> swap, that means you should use 12 separate disks to create 6 mirrored
> chunks of 2GB. This is way too many disks used for that.
> Alternativelly, you could place more than one swap metadevice/volume on
> the
> same pair of mirrored disks but you will soon notice bad performance
> because
> of long disk seeks.
> Now the question is:
> How can I disable this round robin and force Solaris to do paging on only
> one volume/metadevice and only when the first one is all used to turn to
> the
> second one ? The gotcha here is that most of the time I use only 1 GB or
> so
> of swap for paging and I need to configure 12 GB only to insure I will not
> run out of virtual memory in worst case batch run-scenario. The machine is
> already filled up with physical memory at full capacity.
> 
> Regards,
> George DONE
> http://www.sunmanagers.org/mailman/listinfo/sunmanagers
> 
> 
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Received on Sun Sep 9 00:02:58 2001

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