9 Replies Latest reply on Aug 22, 2005 6:32 PM by JMills

    Disable Transparent Page Sharing?

    brightg Enthusiast

      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

        • 1. Re: Disable Transparent Page Sharing?
          kix1979 Champion

          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

          • 2. Re: Disable Transparent Page Sharing?
            JMills Master

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

            • 3. Re: Disable Transparent Page Sharing?
              kix1979 Champion

              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

              • 4. Re: Disable Transparent Page Sharing?
                JMills Master

                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).

                • 5. Re: Disable Transparent Page Sharing?
                  kix1979 Champion

                  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.

                  • 6. Re: Disable Transparent Page Sharing?
                    deadmetal Lurker

                    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

                    • 7. Re: Disable Transparent Page Sharing?
                      JMills Master

                      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

                      • 8. Re: Disable Transparent Page Sharing?
                        sherold Master

                        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

                        • 9. Re: Disable Transparent Page Sharing?
                          JMills Master

                          Agh.

                           

                          sched.mem.pshare = "FALSE"

                           

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