| Subject: /3GB and /PAE |
| Group: microsoft.public.winternals |
| Date: 11/2/2007 2:46:03 PM |
| From: Megan Kielman [Email Address Protection] |
I have a Windows 2003 Ent system with 16GB of RAM. I have the /3GB and /PAE switch enabled. I am running into system resource problems and have determined that it is because there aren't enough page table entires. I found the following information from the link http://technet2.microsoft.com/windowsserver/en/library/00284c8d-7a42-40f2-8a01-8de61dccd8c91033.mspx?mfr=true. Can someone explain what can cause the system to run out of page table entries before the system attempts to use 16GB of RAM? ---------- PAE X86 and 4GT 4GT is another technology that makes more physical memory available to user applications. PAE X86 and 4GT can be combined to provide applications large amounts of virtual memory and provide a significant performance boost. However, using 4GT reduces the amount of PTEs available to the kernel, while using PAE X86 dramatically increases the amount of memory that must be indexed and translated by the memory manager. This combination will exhaust system kernel space much earlier than normal. Because of this, the memory manager imposes a virtual memory limit of 16 GB on a system with both 4GT and PAE X86 enabled. Even if a system has 32 GB or more of physical memory, if both options are enabled, only 16 GB of memory will be recognized. Thus, if PAE X86 is enabled on a system with more that 16 GB of physical memory, 4GT should not be used. Note � Even though the memory manager imposes a hard limit of 16 GB when both 4GT and PAE X86 are enabled, it is possible to encounter problems with lesser amount of memory, such as 8 GB or 12 GB. Therefore, the kernel should be given as much memory as possible. -------- I also don't understand the following excerpt: -------- In a standard configuration (without 4GT), there are typically 80,000 to 140,000 PTEs available. This is reduced to only 40,000 PTEs when using 4GT. The next section describes the implications of this change. -------- I thought each PTE could map 4KB of memory. If there are typically 140,000 free, then that is only 500+MB. That number seems really low. What am I missing? |
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| Subject: Re: /3GB and /PAE |
| Group: microsoft.public.winternals |
| Date: 11/2/2007 6:37:25 PM |
| From: DevilsPGD [Email Address Protection] |
In message <O5gAFnZHIHA.284@TK2MSFTNGP02.phx.gbl> Megan Kielman <megan.kielman@gmaildotcom> wrote: >� Even though the memory manager imposes a hard limit of 16 GB when both >4GT and PAE X86 are enabled, it is possible to encounter problems with >lesser amount of memory, such as 8 GB or 12 GB. Therefore, the kernel >should be given as much memory as possible. In other words, turn off the /3GB switch. -- You can get more with a kind word and a 2x4 than just a kind word. |
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| Subject: Re: /3GB and /PAE |
| Group: microsoft.public.winternals |
| Date: 11/5/2007 3:34:04 AM |
| From: "Edwin vMierlo [MVP]" [Email Address Protection] |
> > Can someone explain what can cause the system to run out of page table > entries before the system attempts to use 16GB of RAM? > The Kernel uses 2GB of RAM, or 1GB of ram without /3GB, it uses 2GB of RAM with the /3GB it uses 1GB of RAM the /PAE switch allows applications (!!) which are AWE compliant to use above the 4GB. But you kernel still runs in 1 or 2 GB.... hope this explains it, if not, do a searh on google you will find lots of documentation on /PAE and AWE rgds, Edwin. |
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| Subject: Re: /3GB and /PAE |
| Group: microsoft.public.winternals |
| Date: 11/6/2007 4:54:22 PM |
| From: Megan Kielman [Email Address Protection] |
I apologize for not being very clear with my question. I understand what happens when the /3GB switched is used, what I don't understand is the following: --------below taking from technet article------------------------------- In a standard configuration (without 4GT), there are typically 80,000 to 140,000 PTEs available. This is reduced to only 40,000 PTEs when using 4GT. The next section describes the implications of this change. ----------------------------------------------------------------------- I thought each PTE could map 4KB of memory. If there are typically 140,000 free, then that is only 500+MB. That number seems really low. What am I missing? Edwin vMierlo [MVP] wrote: >> Can someone explain what can cause the system to run out of page table >> entries before the system attempts to use 16GB of RAM? >> > > The Kernel uses 2GB of RAM, or 1GB of ram > > without /3GB, it uses 2GB of RAM > with the /3GB it uses 1GB of RAM > > the /PAE switch allows applications (!!) which are AWE compliant to use > above the 4GB. > But you kernel still runs in 1 or 2 GB.... > > hope this explains it, > if not, do a searh on google you will find lots of documentation on /PAE and > AWE > > rgds, > Edwin. > > |
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