To view the list of page files, look in the registry at HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PagingFiles. This entry contains the paging file configuration settings modified through the Advanced System Settings dialog box. Open Control Panel, click System And Security, and then System. This is the System Properties dialog box, also reachable by right-clicking on Computer in Explorer and selecting Properties. From there, click Advanced System Settings, then Settings in the Performance area. In the Performance Options dialog box, click the Advanced tab, and then click Change in the Virtual Memory area.
To add a new page file, Control Panel uses the (internal only)
Commit Charge and the System Commit Limit
We are now in a position to more thoroughly discuss the concepts of commit charge and the system commit limit.
Whenever virtual address space is created, for example by a
All other virtual allocations rely for storage on system-managed shared resources: RAM and the paging file(s). The purpose of the system commit limit and commit charge is to track all uses of these resources to ensure that they are never overcommitted—that is, that there is never more virtual address space defined than there is space to store its contents, either in RAM or in backing store (on disk).
Note
This section makes frequent references to paging files. It is possible, though not generally recommended, to run Windows without any paging files. Every reference to paging files here may be considered to be qualified by “if one or more paging files exist.”
Conceptually, the system commit limit represents the total virtual address space that can be created in addition to virtual allocations that are associated with their own backing store—that is, in addition to sections mapped to files. Its numeric value is simply the amount of RAM available to Windows plus the current sizes of any page files. If a page file is expanded, or new page files are created, the commit limit increases accordingly. If no page files exist, the system commit limit is simply the total amount of RAM available to Windows.
Commit charge is the systemwide total of all “committed” memory allocations that must be kept in either RAM or in a paging file. From the name, it should be apparent that one contributor to commit charge is process-private committed virtual address space. However, there are many other contributors, some of them not so obvious.
Windows also maintains a per-process counter called the
The following types of memory allocations contribute to the system commit charge and, in many cases, to the process page file quota. (Some of these will be described in detail in later sections of this chapter.)
Private committed memory is memory allocated with the
Page-file-backed mapped memory is memory allocated with a
Copy-on-write regions of mapped memory, even if it is associated with ordinary mapped files. The mapped file provides backing store for its own unmodified content, but should a page in the copy-on-write region be modified, it can no longer use the original mapped file for backing store. It must be kept in RAM or in a paging file. These allocations are not charged to the process page file quota.