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.

13.1 Selecting a Process

The function select_bad_process() is responsible for choosing a process to kill. It decides by stepping through each running task and calculating how suitable it is for killing with the function badness(). The badness is calculated as follows, note that the square roots are integer approximations calculated with int_sqrt();

$$\mathrm{badness\_for\_task} = \frac{\mathrm{total\_vm\_for\_t... ...me\_in\_seconds}) * \sqrt[4](\mathrm{cpu\_time\_in\_minutes})}$$

This has been chosen to select a process that is using a large amount of memory but is not that long lived. Processes which have been running a long time are unlikely to be the cause of memory shortage so this calculation is likely to select a process that uses a lot of memory but has not been running long. If the process is a root process or has CAP_SYS_ADMIN capabilities, the points are divided by four as it is assumed that root privilege processes are well behaved. Similarly, if it has CAP_SYS_RAWIO capabilities (access to raw devices) privileges, the points are further divided by 4 as it is undesirable to kill a process that has direct access to hardware.