Understanding Virtual Memory Manager Interfaces

The virtual memory manager supports functions that allow a wide range of kernel extension data operations.

Virtual Memory Objects
A virtual memory object is an abstraction for the contiguous data that can be mapped into a region of an address space. As a data object, it is independent of any address space. The data it represents can be in memory or on an external storage device. The data represented by the virtual memory object can be shared by mapping the virtual memory object into each address space sharing the access, with the access capability of each mapping represented in that address space map.
Addressing Data
This section describes how data can be addressed in a virtual memory object.
Moving Data to or from a Virtual Memory Object
Moving data to or from a virtual memory object is an operation on the virtual memory object, not an address space range.
Data Flushing
A kernel extension uses the vm_write or vm_writep kernel services depending on the addressability to the data area.
Discarding Data
The virtual memory manager interface discards data using the vm_release and vm_releasep services.
Protecting Data
The service that is listed in this section can change the storage protect keys in a page range.
Executable Data
If the data moved is to become executable, any data remaining in processor cache must be guaranteed to be moved from cache to memory.
Installing Pager Backends
The kernel-extension data providers must provide appropriate routines to be called by the virtual memory manager. These routines move a page-sized block of data into or out of a specified page. These services are also referred to as pager backends.
Thread Page-I/O Strategy Routine
Pager backends have their strategy routines run at the interrupt level of the Virtual Memory Manager (VMM). Some file systems, however, require that their strategy routines run in the context of the thread that directly causes the page I/O to occur. The VMM accommodates the difference with a blocking, or thread page-I/O strategy routine. If no thread directly causes page I/O to occur, for example, in the case of page replacement, then the strategy routine is invoked in the context of a worker thread from a pool of worker threads that are managed by the VMM.
Referenced Routines
The virtual memory manager exports these routines exported to kernel extensions.
Services that Support 64-bit Processes
The following section lists the services that support 64-bit processes.

Parent topic: Kernel Services