A discussion of Pool Resources and Pool Resource Depletion. First of all - what are Pool Resources? When a machine boots up, the Memory Manager creates two dynamically sized memory pools that kernel-mode components use to allocate system memory. These two pools are known as the Paged Pool and NonPaged Pool. Each of these pools start at an initial size that is based upon the amount of physical memory present in the system. Pool memory is a subset of available memory and is not necessarily contiguous. If necessary, these pools can grow up to a maximum size that is determined by the system at boot time.
So - what distinguishes Paged Pool and NonPaged Pool memory? The first difference is that Paged Pool is exactly what its name implies - it can be paged out. The NonPaged Pool cannot be paged out. Drivers use the NonPaged Pool for many of their requirements because they can be accessed at any Interrupt Request Level (IRQL). The IRQL defines the hardware priority at which a processor operates at any given time (there's a link to a document covering Scheduling, Thread Context and IRQL's in the Additional Resources section at the end of this post).
Getting back to our Pool Resources, it is important to remember that these resources are finite. The table below outlines some sample maximum values for Paged / NonPaged Pool on x86 systems that are not configured with the /3GB switch in the system's boot.ini file. We'll cover /3GB and its effects on memory in a future post. We'll also cover Kernel Changes to Windows Vista separately. It's important to note that x64 systems don't suffer from these limitations!
|System RAM||NonPaged Max||Paged Max||Paged Max (TS)|
|512 MB||131 MB||264 MB||160 MB *|
|1024 MB||212 MB||268 MB||160 MB *|
|1536 MB||256 MB||340 MB||160 MB *|
|2048 MB||256 MB||340 MB||160 MB *|
* If Terminal Services is installed on Windows 2000, Paged Pool is lowered down to 160 MB unless a registry change is made to the server to set the Paged Pool Size to its maximum value (see below).
Windows 2003 SP1
|System RAM||NonPaged Max||Paged Max|
|512 MB||125 MB||184 MB|
|1024 MB||202 MB||168 MB|
|1536 MB||254 MB||352 MB|
|2048 MB||252 MB||352 MB|
On Windows 2003 systems, Terminal Services are enabled by default.
On both Windows 2000 and Windows 2003, the HKLM\System\CurrentControlSet\Control\Session Management\Memory Management\PagedPoolSize value can be set to 0xFFFFFFFF (or resetting the value to 0) to ensure that the Virtual Address Space used for Paged Pool is maximized.
Also - here's the theoretical maximums for pre-Vista Operating Systems:
|Process Address Space||7152 GB||8192 GB||2 to 3 GB*|
|Paged Pool||128 GB||128 GB||470 to 650 MB|
|NonPaged Pool||128 GB||128 GB||256 MB|
* depends on whether or not /3GB is enabled
Now that we know what the maximum value ranges should look like, here's how to verify what those values look like on your own system using Process Explorer:
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