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.

9.6 Slab Allocator Initialisation

Here we will describe how the slab allocator initialises itself. When the slab allocator creates a new cache, it allocates the kmem_cache_t from the cache_cache or kmem_cache cache. This is an obvious chicken and egg problem so the cache_cache has to be statically initialised as

357 static kmem_cache_t cache_cache = {
358         slabs_full:     LIST_HEAD_INIT(cache_cache.slabs_full),
359         slabs_partial:  LIST_HEAD_INIT(cache_cache.slabs_partial),
360         slabs_free:     LIST_HEAD_INIT(cache_cache.slabs_free),
361         objsize:        sizeof(kmem_cache_t),
362         flags:          SLAB_NO_REAP,
363         spinlock:       SPIN_LOCK_UNLOCKED,
364         colour_off:     L1_CACHE_BYTES,
365         name:           "kmem_cache",
366 };

This code statically initialised the kmem_cache_t struct as follows:

358-360 Initialise the three lists as empty lists;

361 The size of each object is the size of a cache descriptor;

362 The creation and deleting of caches is extremely rare so do not consider it for reaping ever;

363 Initialise the spinlock unlocked;

364 Align the objects to the L1 cache;

365 Record the human readable name.

That statically defines all the fields that can be calculated at compile time. To initialise the rest of the struct, kmem_cache_init() is called from start_kernel().