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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.
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Next: 13. Out Of Memory Up: 12. Swap Management Previous: 12.8 Swapping Out Pages   Contents   Index

12.9 Reading/Writing the Swap Area

The top-level function for reading and writing to the swap area is rw_swap_page(). This function ensures that all operations are performed through the swap cache to prevent lost updates. rw_swap_page_base() is the core function which performs the real work.

It begins by checking if the operation is a read. If it is, it clears the uptodate flag with ClearPageUptodate(). This flag will be set again if the page is successfully read from disk. It then calls get_swaphandle_info() to acquire the device for the swap partition of the inode for the file. These are needed before block IO operations may be performed.

If the swap area is a file, bmap() is used to fill a local array with a list of all blocks in the filesystem which contain the page being operated on. Remember that filesystems may have their own method of storing files and disk and it is not as simple as the swap partition where information may be written directly to disk.

Once that is complete, a normal block IO operation takes place with brw_page(). The function of block IO is beyond the scope of this document.

next up previous contents index
Next: 13. Out Of Memory Up: 12. Swap Management Previous: 12.8 Swapping Out Pages   Contents   Index
Mel 2004-02-15

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