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5,010 Views 9 Replies Last post: Aug 22, 2005 6:32 PM by JMills RSS
brightg Enthusiast
brightg
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Mar 22, 2005
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Aug 22, 2005 10:23 AM

Disable Transparent Page Sharing?

Does anyone one know if you can Disable Transparent Page Sharing?

 

Just wondered if it was per VM or per ESX server, that is if you can do it at all?

 

Sorry for ramdom question revising for VCP and wondered?

 

Gary

kix1979 Champion
kix1979
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1. Aug 22, 2005 10:34 AM in response to: brightg
Re: Disable Transparent Page Sharing?

You can disable it per server.

 

From the command line

echo 0 > /proc/vmware/config/Mem/ShareScanTotal

echo 0 > /proc/vmware/config/Mem/ShareScanVM

Save the changes in the file /etc/vmware/vmkconfig, otherwise it will not hold after a reboot.

 

 

Message was edited by: kix1979

Thomas H. Bryant III Director, Advanced Technology & Products [Vizioncore, Inc.|http://www.vizioncore.com] VMware Communities User Moderator
JMills Master
JMills
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2. Aug 22, 2005 11:07 AM in response to: kix1979
Re: Disable Transparent Page Sharing?

And it can also be done on a per-VM basis using a sched.mem.* hierarchy .VMX option.

kix1979 Champion
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3. Aug 22, 2005 11:16 AM in response to: brightg
Re: Disable Transparent Page Sharing?

Thanks JMills, that is really good to know!  I actually have had to setup a server with no TPS for a client because of their request based on a few of the VMs.  Looks like I can call them back

Thomas H. Bryant III Director, Advanced Technology & Products [Vizioncore, Inc.|http://www.vizioncore.com] VMware Communities User Moderator
JMills Master
JMills
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4. Aug 22, 2005 11:18 AM in response to: kix1979
Re: Disable Transparent Page Sharing?

Part of the DMZ/Firewall VM KB I'm writing will include things like disabling TPS.

 

Could you find out from them why they need it disabled? I'm collecting various business cases where one might want to temporarily or permanently disable it... typically they're related to either performance under extreme duress, or standards certification (i.e., performance under worst-case scenario resource overcommit).

kix1979 Champion
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5. Aug 22, 2005 11:22 AM in response to: JMills
Re: Disable Transparent Page Sharing?

I know the reason, which is absurd to me.  The senior server admin loves the idea of VMWare for reducing hardware costs, but he had in his mind that sharing memory pages could create serious instability in his web servers, they do about $300M via web orders annually.  His contention is that if multiple servers are sharing the same page and that page gets corrupted it could kill all of the servers accessing it.  I tried to demonstrate differently, but at the end of the day he would not believe me.

Thomas H. Bryant III Director, Advanced Technology & Products [Vizioncore, Inc.|http://www.vizioncore.com] VMware Communities User Moderator
deadmetal Lurker
deadmetal
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6. Aug 22, 2005 12:47 PM in response to: JMills
Re: Disable Transparent Page Sharing?

Thanks for the reply's

 

Is it these options you spoke about in the vmx files?

 

sched.mem.pshare.enable

sched.mem.pshare.debug

sched.mem.pshare.scanRate

sched.mem.pshare.checkRate

JMills Master
JMills
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7. Aug 22, 2005 6:33 PM in response to: deadmetal
Re: Disable Transparent Page Sharing?

Yes, but there are some boundary conditions which alter the behavior of scanRate / checkRate.

 

sched.mem.pshare = "FALSE"

 

should shut off TPS for an ESX Server VM. You'll need to do this while the VM is powered off, nat'ch.

 

*****

Fixed typo.

Message was edited by: JMills

sherold Master vExpert
sherold
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8. Aug 22, 2005 6:20 PM in response to: kix1979
Re: Disable Transparent Page Sharing?

He must be a developer of sorts...

 

The great thing about TPS is that it constantly keeps track of identical (and typically static) memory pages across the VMs.  When the memory is no longer identical (ie: it gets corrupted, lets say...due to bad code) the mapping from Virtual Page Numbers of that guest to Machine Page Numbers on the host are removed from the Shadow Page Table in the VMkernel.  Have him pick up Carl Waldspurger's paper, its a good read

 

Scott

-Scott ________________________ http://www.vmguru.com http://www.thevesi.org
JMills Master
JMills
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9. Aug 22, 2005 6:32 PM in response to: JMills
Re: Disable Transparent Page Sharing?

Agh.

 

sched.mem.pshare = "FALSE"

 

is the correct one for ESX Server 2.x ... mybad.

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