After this documentation was released in July 2003, I was approached by Prentice Hall and asked to write a book on the Linux VM under the Bruce Peren's Open Book Series.

The book is available and called simply "Understanding The Linux Virtual Memory Manager". There is a lot of additional material in the book that is not available here, including details on later 2.4 kernels, introductions to 2.6, a whole new chapter on the shared memory filesystem, coverage of TLB management, a lot more code commentary, countless other additions and clarifications and a CD with lots of cool stuff on it. This material (although now dated and lacking in comparison to the book) will remain available although I obviously encourge you to buy the book from your favourite book store :-) . As the book is under the Bruce Perens Open Book Series, it will be available 90 days after appearing on the book shelves which means it is not available right now. When it is available, it will be downloadable from http://www.phptr.com/perens so check there for more information.

To be fully clear, this webpage is not the actual book.

5.2 Managing the Address Space

The address space usable by the process is managed by a high level mm_struct which is roughly analogous to the vmspace struct in BSD [#!mckusick96!#].

Each address space consists of a number of page-aligned regions of memory that are in use. They never overlap and represent a set of addresses which contain pages that are related to each other in terms of protection and purpose. These regions are represented by a struct vm_area_struct and are roughly analogous to the vm_map_entry struct in BSD. For clarity, a region may represent the process heap for use with malloc(), a memory mapped file such as a shared library or a block of anonymous memory allocated with mmap(). The pages for this region may still have to be allocated, be active and resident or have been paged out.

If a region is backed by a file, its vm_file field will be set. By traversing vm_file$\rightarrow$f_dentry$\rightarrow$d_inode$\rightarrow$i_mapping, the associated address_space for the region may be obtained. The address_space has all the filesystem specific information required to perform page-based operations on disk.

A number of system calls are provided which affect the address space and regions. These are listed in Table 5.1

Table 5.1: System Calls Related to Memory Regions