How to determine the appropriate page file size for 64-bit versions of Windows
Summary
64-bit versions of Windows and Windows Server support more physical memory (RAM) than 32-bit versions support. However, the reason to configure the page file size has not changed. It has always been about supporting a system crash dump, if it is necessary, or extending the system commit limit, if it is necessary. For example, when a lot of physical memory is installed, a page file might not be required to back the system commit charge during peak usage. The available physical memory alone might be large enough to do this. However, a page file or a dedicated dump file might still be required to back a system crash dump.
Use the following considerations for page file sizing for all versions of Windows and Windows Server:
- Crash dump setting: If you want a crash dump file to be created during a system crash, a page file or a dedicated dump file must exist and be large enough to back the system crash dump setting. Otherwise, a system memory dump file is not created.
- Peak system commit charge: The system commit charge cannot exceed the system commit limit. This limit is the sum of physical memory (RAM) and all page files combined. If no page files exist, the system commit limit is slightly less than the physical memory installed. Peak system-committed memory usage can vary greatly between systems. Therefore, physical memory and page file sizing also varies.
- Quantity of infrequently accessed pages: The purpose of a page file is to back infrequently accessed modified pages so that they can be removed from physical memory. This provides more available space for more frequently accessed pages. The "\Memory\Modified Page List Bytes" performance counter measures, in part, the number of infrequently accessed modified pages that are destined for the hard disk. However, be aware that not all the memory on the modified page list is written out to disk. Typically, several hundred megabytes of memory remains resident on the modified list. Therefore, consider extending or adding a page file if all the following conditions are true:
- More available physical memory (\Memory\Available MBytes) is required.
- The modified page list contains a significant amount of memory.
- The existing page files are fairly full (\Paging Files(*)\% Usage).
Notes- Some products or services may require a page file for reasons other than those discussed here. For more information, check your product documentation. For example, Windows Server domain controllers and DFS replication, certificate, and LDS servers (also Client editions) are not supported without a configured page file. The algorithm of the database cache for ESENT (ESE, in Microsoft Exchange Server) depends on the "\Memory\Transition Pages RePurposed/sec" performance monitor counter. A page file is required to make sure that the database cache can release memory if memory is requested by other services or applications. In summary, page file sizing depends on the system crash dump setting requirements and the system commit charge peak usage or expected usage. Both considerations are unique to each system, even for systems that are identical to other systems. This means that page file sizing is unique to each system and cannot be generalized.
- For Windows Server 2012 Hyper-V and Windows Server 2012 R2 Hyper-V, the page file of the management OS (commonly called the host OS) should be left at the default of setting of "System Managed." This is per the Hyper-V product group.
More information
System committed memory
The system commit limit is the sum of physical memory and all page files combined. It represents the maximum system-committed memory (known as the “system commit charge”) that the system can back. The system commit charge is the total committed or “promised” memory of all committed virtual memory in the system. If the system commit charge reaches the system commit limit, the system and processes might not obtain committed memory. This condition can cause hangs, crashes, and other malfunctions. Therefore, make sure that you set the system commit limit large enough to back the system commit charge during peak usage.The system commit charge and system commit limit can be measured on the Performance tab in Task Manager or by using "\Memory\Committed Bytes" and "\Memory\Commit Limit" performance counters. The "\Memory\% Committed Bytes In Use" counter is a ratio of the "\Memory\Committed Bytes" to "\Memory\Commit Limit" values.
Note System-managed page files automatically grow up to three times physical memory or 4 GB (whichever is larger) when the system commit charge reaches 90 percent of the system commit limit. This assumes that enough free disk space is available to accommodate the growth.
System crash dumps
A system crash (also known as a “bug check” or a "Stop error") occurs when the system cannot run correctly. The dump file that is produced from this event is called a system crash dump. A page file or dedicated dump file is used to write a crash dump file (memory.dmp) to disk. Therefore, a page file or a dedicated dump file must be large enough to back the kind of crash dump selected. Otherwise, the system cannot create the crash dump file.Note During startup, system-managed page files are sized respective to the system crash dump settings. This assumes that enough free disk space exists.
| System crash dump setting | Minimum page file size requirement |
|---|---|
| Small memory dump (256 KB) | 1 MB |
| Kernel memory dump | Depends on kernel virtual memory usage |
| Complete memory dump | 1 x RAM plus 257 MB* |
| Automatic memory dump | Depends on kernel virtual memory usage. For details, see Automatic memory dump on MSDN. |
* 1 MB of header data and device drivers can total 256 MB of secondary crash dump data.
Automatic memory dump
Windows 8 and Windows Server 2012 introduced the “Automatic memory dump” feature. This feature is enabled by default. This is a new setting, not a new kind of crash dump. This setting automatically selects the best page file size, depending on the frequency of system crashes.The Automatic memory dump setting at first selects a small paging file size, would accommodate the kernel memory most of the time. If the system crashes again within four weeks, the Automatic memory dump feature selects the page file size as either the RAM size or 32 GB, whichever is smaller.
Note In Windows 8.1 and Windows Server 2012 R2, the initial minimum size of the page file or the dedicated dump file is 1 GB.
Kernel memory crash dumps require enough page file space or dedicated dump file space to accommodate the kernel mode side of virtual memory usage. If the system crashes again within four weeks of the previous crash, aComplete memory dump is selected at restart. This requires a page file or dedicated dump file of at least the size of physical memory (RAM) plus 1 MB for header information plus 256 MB for potential driver data to support all the potential data that is dumped from memory. Again, the system-managed page file will be increased to back this kind of crash dump. If the system is configured to have a page file or a dedicated dump file of a specific size, make sure that the size is sufficient to back the crash dump setting that is listed in the table earlier in this section together with and the peak system commit charge.
For more information about system crash dumps, click the following article number to go to the article in the Microsoft Knowledge Base:
969028 How to generate a kernel or a complete memory dump file in Windows Server 2008 and Windows Server 2008 R2
Dedicated dump files
Computers that are running Microsoft Windows or Microsoft Windows Server usually must have a page file to back a system crash dump. System administrators now have the option to create a dedicated dump file instead by using the following software packages to start with:- Windows 7 Service Pack 1 with hotfix 2716542 applied
- Windows Server 2008 R2 Service Pack 1 with hotfix 2716542 applied
For more information about dedicated dump files, click the following article numbers to go to the articles in the Microsoft Knowledge Base:
969028 How to generate a kernel or a complete memory dump file in Windows Server 2008 and Windows Server 2008 R2
950858 Dedicated dump files are unexpectedly truncated to 4 GB on a computer that is running Windows Server 2008 or Windows Vista and that has more than 4 GB of physical memory
System-managed page files
By default, page files are system-managed. This means that the page files increase and decrease based on many factors, such as the amount of physical memory installed, the process of accommodating the system commit charge, and the process of accommodating a system crash dump.For example, when the system commit charge is more than 90 percent of the system commit limit, the page file is increased to back it. This continues to occur until the page file reaches three times the size of physical memory or 4 GB, whichever is larger. This all assumes that the logical disk that is hosting the page file is large enough to accommodate the growth.
The following table lists the minimum and maximum page file sizes of system-managed page files.
| Operating system | Minimum page file size | Maximum page file size |
|---|---|---|
| Windows XP and Windows Server 2003 with less than 1 GB of RAM | 1.5 x RAM | 3 x RAM or 4 GB, whichever is larger |
| Windows XP and Windows Server 2003 with more than 1 GB of RAM | 1 x RAM | 3 x RAM or 4 GB, whichever is larger |
| Windows Vista and Windows Server 2008 | 1 x RAM | 3 x RAM or 4 GB, whichever is larger |
| Windows 7 and Windows Server 2008 R2 | 1 x RAM | 3 x RAM or 4 GB, whichever is larger |
| Windows 8 and Windows Server 2012 | Depends on crash dump setting* | 3 x RAM or 4 GB, whichever is larger |
| Windows 8.1 and Windows Server 2012 R2 | Depends on crash dump setting* | 3 x RAM or 4 GB, whichever is larger |
* See system crash dumps.
Performance counters
Several performance counters are related to page files. This section describes the counters and what they measure.\Memory\Page/sec and other hard page fault counters
The following performance counters measure hard page faults (which include, but are not limited to, page file reads):- \Memory\Page/sec
- \Memory\Page Reads/sec
- \Memory\Page Inputs/sec
- \Memory\Page Writes/sec
- \Memory\Page Output/sec
- Parts of image files (.dll and .exe files) as they are used
- Memory-mapped files
- A page file
Therefore, we recommend that you monitor the disk performance of the logical disks that host a page file in correlation with these counters. Be aware that a system that has a sustained 100 hard page faults per second experiences 400 KB per second disk transfers. Most 7200 RPM disk drives can handle about 5 MB per second at an IO size of 16 KB or 800 KB per second at an IO size of 4 KB. No performance counter directly measures which logical disk the hard page faults are resolved for.
\Paging File(*)\% Usage
The \Paging File(*)\% Usage performance counter measures the percentage of usage of each page file. 100 percent usage of a page file does not indicate a performance problem as long as the system commit limit is not reached by the system commit charge, and if a significant amount of memory is not waiting to be written to a page file.Note The size of the Modified Page List (\Memory\Modified Page List Bytes) is the total of modified data that is waiting to be written to disk.
If the Modified Page List (a list of physical memory pages that are the least frequently accessed) contains a lot of memory, and if the % Usage value of all page files is greater than 90, you can make more physical memory available for more frequently access pages by increasing or adding a page file.
Note Not all the memory on the modified page list is written out to disk. Typically, several hundred megabytes of memory remains resident on the modified list.
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