added initial slab code to the kernel. It is still unused, and there is still no VM interaction.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@20832 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/slab/Backend.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_BACKEND_H_
+#define _SLAB_BACKEND_H_
+
+#include <slab/Base.h>
+
+extern "C" {
+	status_t slab_area_backend_allocate(base_cache *cache, area_id *id,
+		void **pages, size_t byte_count, uint32_t flags);
+	void slab_area_backend_free(base_cache *cache, area_id id);
+}
+
+struct AreaBackend {
+	typedef area_id AllocationID;
+
+	static const size_t kPageSize = B_PAGE_SIZE;
+	static const size_t kMaximumAlignedLength = B_PAGE_SIZE;
+
+	static status_t AllocatePages(base_cache *cache, area_id *id, void **pages,
+		size_t byteCount, uint32_t flags)
+	{
+		return slab_area_backend_allocate(cache, id, pages, byteCount, flags);
+	}
+
+	static void FreePages(base_cache *cache, area_id id)
+	{
+		return slab_area_backend_free(cache, id);
+	}
+};
+
+#endif

headers/private/kernel/slab/Base.h

@@ -0,0 +1,111 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_BASE_SLAB_H_
+#define _SLAB_BASE_SLAB_H_
+
+#include <stdint.h>
+
+#include <OS.h>
+#include <util/list.h>
+
+#ifdef __cplusplus
+#include <utility> // pair<>
+
+extern "C" {
+#endif
+
+static const int kMinimumSlabItems = 32;
+
+typedef void (*base_cache_constructor)(void *cookie, void *object);
+typedef void (*base_cache_destructor)(void *cookie, void *object);
+
+/* base Slab implementation, opaque to the backend used. */
+
+typedef struct base_cache {
+	char name[32];
+	size_t object_size;
+	size_t cache_color_cycle;
+	struct list partial, full;
+	base_cache_constructor constructor;
+	base_cache_destructor destructor;
+	void *cookie;
+} base_cache;
+
+typedef struct cache_object_link {
+	struct cache_object_link *next;
+} cache_object_link;
+
+typedef struct cache_slab {
+	void *pages;
+	size_t count, size;
+	cache_object_link *free;
+	struct list_link link;
+} cache_slab;
+
+void base_cache_init(base_cache *cache, const char *name, size_t object_size,
+	size_t alignment, base_cache_constructor constructor,
+	base_cache_destructor destructor, void *cookie);
+
+cache_object_link *base_cache_allocate_object(base_cache *cache);
+int base_cache_return_object(base_cache *cache, cache_slab *slab,
+	cache_object_link *link);
+
+cache_slab *base_cache_construct_slab(base_cache *cache, cache_slab *slab,
+	void *pages, size_t byte_count, cache_object_link *(*get_link)(
+		void *parent, void *object), void *parent);
+void base_cache_destruct_slab(base_cache *cache, cache_slab *slab);
+
+#ifdef __cplusplus
+}
+
+typedef std::pair<cache_slab *, cache_object_link *> CacheObjectInfo;
+
+// Slab implementation, glues together the frontend, backend as
+// well as the Slab strategy used.
+template<typename Strategy>
+class Cache : protected base_cache {
+public:
+	typedef base_cache_constructor	Constructor;
+	typedef base_cache_destructor	Destructor;
+
+	Cache(const char *name, size_t objectSize, size_t alignment,
+		Constructor constructor, Destructor destructor, void *cookie)
+		: fStrategy(this)
+	{
+		base_cache_init(this, name, objectSize, alignment, constructor,
+			destructor, cookie);
+	}
+
+	void *AllocateObject(uint32_t flags)
+	{
+		if (list_is_empty(&partial)) {
+			cache_slab *newSlab = fStrategy.NewSlab(flags);
+			if (newSlab == NULL)
+				return NULL;
+			list_add_item(&partial, newSlab);
+		}
+
+		return fStrategy.Object(base_cache_allocate_object(this));
+	}
+
+	void ReturnObject(void *object)
+	{
+		CacheObjectInfo location = fStrategy.ObjectInformation(object);
+
+		if (base_cache_return_object(this, location.first, location.second))
+			fStrategy.ReturnSlab(location.first);
+	}
+
+private:
+	Strategy fStrategy;
+};
+
+#endif
+
+#endif

headers/private/kernel/slab/Depot.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_DEPOT_H_
+#define _SLAB_DEPOT_H_
+
+#include <stdint.h>
+
+#include <lock.h>
+#include <smp.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct depot_magazine {
+	struct depot_magazine *next;
+	uint16_t current_round, round_count;
+	void *rounds[0];
+} depot_magazine;
+
+
+typedef struct depot_cpu_store {
+	benaphore lock;
+	depot_magazine *loaded, *previous;
+} depot_cpu_store;
+
+
+typedef struct base_depot {
+	benaphore lock;
+	depot_magazine *full, *empty;
+	size_t full_count, empty_count;
+	depot_cpu_store *stores;
+
+	void (*return_object)(base_depot *depot, void *object);
+} base_depot;
+
+
+static inline depot_cpu_store *
+base_depot_cpu(base_depot *depot)
+{
+	return &depot->stores[smp_get_current_cpu()];
+}
+
+
+status_t base_depot_init(base_depot *depot,
+	void (*return_object)(base_depot *, void *));
+void base_depot_destroy(base_depot *depot);
+void *base_depot_obtain_from_store(base_depot *depot, depot_cpu_store *store);
+int base_depot_return_to_store(base_depot *depot, depot_cpu_store *store,
+	void *object);
+void base_depot_make_empty(base_depot *depot);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

headers/private/kernel/slab/HashStrategy.h

@@ -0,0 +1,192 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_HASH_STRATEGY_H_
+#define _SLAB_HASH_STRATEGY_H_
+
+#include <slab/Strategy.h>
+#include <slab/Utilities.h> // for TypedCache
+
+#include <KernelExport.h>
+#include <util/OpenHashTable.h>
+
+
+struct BaseHashCacheStrategy {
+	struct Link : cache_object_link, HashTableLink<Link> {
+		cache_slab *slab;
+		void *buffer;
+	};
+
+	struct HashTableDefinition {
+		typedef BaseHashCacheStrategy	ParentType;
+		typedef void *					KeyType;
+		typedef Link					ValueType;
+
+		HashTableDefinition(BaseHashCacheStrategy *_parent) : parent(_parent) {}
+
+		size_t HashKey(void *key) const
+		{
+			return (((uint8_t *)key) - ((uint8_t *)0)) >> parent->fLowerBoundary;
+		}
+
+		size_t Hash(Link *value) const { return HashKey(value->buffer); }
+
+		bool Compare(void *key, Link *value) const
+		{
+			return value->buffer == key;
+		}
+
+		HashTableLink<Link> *GetLink(Link *value) const { return value; }
+
+		BaseHashCacheStrategy *parent;
+	};
+
+	// for g++ 2.95
+	friend class HashTableDefinition;
+
+	typedef OpenHashTable<HashTableDefinition> HashTable;
+
+	static inline int
+	__Fls0(size_t value)
+	{
+		if (value == 0)
+			return -1;
+
+		int bit;
+		for (bit = 0; value != 1; bit++)
+			value >>= 1;
+		return bit;
+	}
+
+	BaseHashCacheStrategy(base_cache *parent)
+		: fHashTable(this), fLowerBoundary(__Fls0(parent->object_size)) {}
+
+	void *Object(cache_object_link *link) const
+	{
+		return ((Link *)link)->buffer;
+	}
+
+	CacheObjectInfo ObjectInformation(void *object) const
+	{
+		Link *link = _Linkage(object);
+		return CacheObjectInfo(link->slab, link);
+	}
+
+protected:
+	Link *_Linkage(void *object) const
+	{
+		Link *link = fHashTable.Lookup(object);
+		if (link == NULL)
+			panic("slab: missing buffer link from hash table.");
+		return link;
+	}
+
+	static cache_object_link *_Linkage(void *_this, void *object)
+	{
+		return ((BaseHashCacheStrategy *)_this)->_Linkage(object);
+	}
+
+	HashTable fHashTable;
+	const size_t fLowerBoundary;
+};
+
+
+template<typename Backend>
+struct HashCacheStrategy : BaseCacheStrategy<Backend>, BaseHashCacheStrategy {
+	typedef typename BaseCacheStrategy<Backend>::Slab Slab;
+	typedef HashCacheStrategy<Backend> Strategy;
+
+	HashCacheStrategy(base_cache *parent)
+		: BaseCacheStrategy<Backend>(parent), BaseHashCacheStrategy(parent),
+			fSlabCache("slab cache", 0), fLinkCache("link cache", 0) {}
+
+	static size_t RequiredSpace(size_t objectSize)
+	{
+		return objectSize;
+	}
+
+	BaseSlab *NewSlab(uint32_t flags)
+	{
+		size_t byteCount = _SlabSize();
+
+		Slab *slab = fSlabCache.Alloc(flags);
+		if (slab == NULL)
+			return NULL;
+
+		void *pages;
+		if (Backend::AllocatePages(fParent, &slab->id, &pages, byteCount,
+				flags) < B_OK) {
+			fSlabCache.Free(slab);
+			return NULL;
+		}
+
+		if (_PrepareSlab(slab, pages, byteCount, flags) < B_OK) {
+			Backend::FreePages(fParent, slab->id);
+			fSlabCache.Free(slab);
+			return NULL;
+		}
+
+		// it's very important that we cast this to BaseHashCacheStrategy
+		// so we get the proper instance offset through void *
+		return BaseCacheStrategy<Backend>::_ConstructSlab(slab, pages, 0,
+			_Linkage, (BaseHashCacheStrategy *)this);
+	}
+
+	void ReturnSlab(BaseSlab *slab)
+	{
+		_ClearSlab(slab->pages, _SlabSize());
+		BaseCacheStrategy<Backend>::_DestructSlab(slab);
+		fSlabCache.Free((Slab *)slab);
+	}
+
+private:
+	size_t _SlabSize() const
+	{
+		return BaseCacheStrategy<Backend>::SlabSize(0);
+	}
+
+	status_t _PrepareSlab(Slab *slab, void *pages, size_t byteCount,
+		uint32_t flags)
+	{
+		uint8_t *data = (uint8_t *)pages;
+		for (uint8_t *it = data;
+				it < (data + byteCount); it += fParent->object_size) {
+			Link *link = fLinkCache.Alloc(flags);
+
+			if (link == NULL) {
+				_ClearSlabRange(data, it);
+				return B_NO_MEMORY;
+			}
+
+			link->slab = slab;
+			link->buffer = it;
+			fHashTable.Insert(link);
+		}
+
+		return B_OK;
+	}
+
+	void _ClearSlab(void *pages, size_t size)
+	{
+		_ClearSlabRange((uint8_t *)pages, ((uint8_t *)pages) + size);
+	}
+
+	void _ClearSlabRange(uint8_t *data, uint8_t *end)
+	{
+		for (uint8_t *it = data; it < end; it += fParent->object_size) {
+			Link *link = _Linkage(it);
+			fHashTable.Remove(link);
+			fLinkCache.Free(link);
+		}
+	}
+
+	TypedCache<Slab, Backend> fSlabCache;
+	TypedCache<Link, Backend> fLinkCache;
+};
+
+#endif

headers/private/kernel/slab/MergedStrategy.h

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_MERGED_STRATEGY_H_
+#define _SLAB_MERGED_STRATEGY_H_
+
+#include <slab/Strategy.h>
+
+
+namespace Private {
+	static inline const void *
+	LowerBoundary(void *object, size_t byteCount)
+	{
+		const uint8_t *null = (uint8_t *)NULL;
+		return null + ((((uint8_t *)object) - null) & ~(byteCount - 1));
+	}
+}
+
+
+// This slab strategy includes the ObjectLink at the end of each object and the
+// slab at the end of the allocated pages. It uses aligned allocations to
+// provide object to slab mapping with zero storage, thus there is only one
+// word of overhead per object. This is optimized for small objects.
+template<typename Backend>
+class MergedLinkCacheStrategy : public BaseCacheStrategy<Backend> {
+public:
+	typedef typename BaseCacheStrategy<Backend>::Slab Slab;
+	typedef cache_object_link Link;
+
+	MergedLinkCacheStrategy(base_cache *parent)
+		: BaseCacheStrategy<Backend>(parent) {}
+
+	static size_t RequiredSpace(size_t objectSize)
+	{
+		return objectSize + sizeof(Link);
+	}
+
+	void *Object(Link *link) const
+	{
+		return ((uint8_t *)link) - (fParent->object_size - sizeof(Link));
+	}
+
+	CacheObjectInfo ObjectInformation(void *object) const
+	{
+		Slab *slab = _SlabInPages(Private::LowerBoundary(object, _SlabSize()));
+		return CacheObjectInfo(slab, _Linkage(object));
+	}
+
+	BaseSlab *NewSlab(uint32_t flags)
+	{
+		typename Backend::AllocationID id;
+		void *pages;
+
+		size_t byteCount = _SlabSize();
+		if (byteCount > Backend::kMaximumAlignedLength)
+			byteCount = Backend::kMaximumAlignedLength;
+
+		// in order to save a pointer per object or a hash table to
+		// map objects to slabs we required this set of pages to be
+		// aligned in a (pageCount * PAGE_SIZE) boundary.
+		if (Backend::AllocatePages(fParent, &id, &pages, byteCount,
+				CACHE_ALIGN_TO_TOTAL | flags) < B_OK)
+			return NULL;
+
+		_SlabInPages(pages)->id = id;
+
+		return BaseCacheStrategy<Backend>::_ConstructSlab(_SlabInPages(pages),
+			pages, sizeof(Slab), _Linkage, this);
+	}
+
+	void ReturnSlab(BaseSlab *slab)
+	{
+		BaseCacheStrategy<Backend>::_DestructSlab(slab);
+	}
+
+private:
+	size_t _SlabSize() const
+	{
+		return BaseCacheStrategy<Backend>::SlabSize(sizeof(Slab));
+	}
+
+	Link *_Linkage(void *object) const
+	{
+		return (Link *)(((uint8_t *)object)
+			+ (fParent->object_size - sizeof(Link)));
+	}
+
+	Slab *_SlabInPages(const void *pages) const
+	{
+		return (Slab *)(((uint8_t *)pages) + _SlabSize() - sizeof(Slab));
+	}
+
+	static Link *_Linkage(void *_this, void *object)
+	{
+		return ((MergedLinkCacheStrategy *)_this)->_Linkage(object);
+	}
+};
+
+#endif

headers/private/kernel/slab/Slab.h

@@ -0,0 +1,103 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_SLAB_H_
+#define _SLAB_SLAB_H_
+
+#ifdef __cplusplus
+
+#include <slab/Backend.h>
+#include <slab/Base.h>
+#include <slab/Depot.h>
+#include <slab/MergedStrategy.h>
+#include <slab/HashStrategy.h>
+#include <slab/Utilities.h>
+
+
+extern "C" {
+#endif
+
+enum {
+	CACHE_DONT_SLEEP		= 1 << 0,
+	CACHE_ALIGN_TO_TOTAL	= 1 << 16,
+};
+
+typedef void *object_cache_t;
+
+
+object_cache_t
+object_cache_create(const char *name, size_t object_size, size_t alignment,
+	void (*_constructor)(void *, void *), void (*_destructor)(void *, void *),
+	void *cookie);
+void *object_cache_alloc(object_cache_t cache);
+void *object_cache_alloc_etc(object_cache_t cache, uint32_t flags);
+void object_cache_free(object_cache_t cache, void *object);
+void object_cache_destroy(object_cache_t cache);
+
+#ifdef __cplusplus
+}
+
+
+template<typename CacheType>
+class LocalCache : public CacheType, protected base_depot {
+public:
+	typedef LocalCache<CacheType> ThisType;
+	typedef typename CacheType::Constructor Constructor;
+	typedef typename CacheType::Destructor Destructor;
+
+	LocalCache(const char *name, size_t objectSize, size_t alignment,
+		Constructor _constructor, Destructor _destructor, void *_cookie)
+		: CacheType(name, objectSize, alignment, _constructor, _destructor,
+			_cookie)
+	{
+		fStatus = base_depot_init(this, _ReturnObject);
+	}
+
+	~LocalCache()
+	{
+		base_depot_destroy(this);
+	}
+
+	status_t InitCheck() const { return fStatus; }
+
+	void *Alloc(uint32_t flags)
+	{
+		void *object = base_depot_obtain_from_store(this, base_depot_cpu(this));
+		if (object == NULL)
+			object = CacheType::AllocateObject(flags);
+		return object;
+	}
+
+	void Free(void *object)
+	{
+		if (!base_depot_return_to_store(this, base_depot_cpu(this), object))
+			CacheType::ReturnObject(object);
+	}
+
+	void Destroy()
+	{
+		base_depot_make_empty(this);
+	}
+
+private:
+	void ReturnObject(void *object)
+	{
+		CacheType::ReturnObject(object);
+	}
+
+	static void _ReturnObject(base_depot *self, void *object)
+	{
+		static_cast<ThisType *>(self)->ReturnObject(object);
+	}
+
+	status_t fStatus;
+};
+
+#endif /* __cplusplus */
+
+#endif

headers/private/kernel/slab/Strategy.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_STRATEGY_H_
+#define _SLAB_STRATEGY_H_
+
+#include <slab/Base.h>
+
+
+template<typename Backend>
+class BaseCacheStrategy {
+protected:
+	typedef cache_object_link	ObjectLink;
+	typedef cache_slab			BaseSlab;
+
+	BaseCacheStrategy(base_cache *parent)
+		: fParent(parent) {}
+
+	size_t SlabSize(size_t tailSpace) const
+	{
+		size_t pageCount = (kMinimumSlabItems * fParent->object_size
+			+ tailSpace) / Backend::kPageSize;
+		if (pageCount < 1)
+			pageCount = 1;
+		return pageCount * Backend::kPageSize;
+	}
+
+	struct Slab : BaseSlab {
+		typename Backend::AllocationID id;
+	};
+
+	BaseSlab *_ConstructSlab(Slab *slab, void *pages, size_t tailSpace,
+		ObjectLink *(*getLink)(void *parent, void *object), void *parent)
+	{
+		return base_cache_construct_slab(fParent, slab, pages,
+			SlabSize(tailSpace) - tailSpace, getLink, parent);
+	}
+
+	void _DestructSlab(BaseSlab *slab)
+	{
+		base_cache_destruct_slab(fParent, slab);
+		Backend::FreePages(fParent, ((Slab *)slab)->id);
+	}
+
+	base_cache *fParent;
+};
+
+#endif

headers/private/kernel/slab/Utilities.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#ifndef _SLAB_UTILITIES_H_
+#define _SLAB_UTILITIES_H_
+
+#include <slab/Base.h>
+#include <slab/MergedStrategy.h>
+
+
+template<typename Type, typename Backend>
+class TypedCache : public Cache< MergedLinkCacheStrategy<Backend> > {
+public:
+	typedef MergedLinkCacheStrategy<Backend> Strategy;
+	typedef Cache<Strategy> BaseType;
+
+	TypedCache(const char *name, size_t alignment)
+		: BaseType(name, sizeof(Type), alignment, _ConstructObject,
+			_DestructObject, this) {}
+	virtual ~TypedCache() {}
+
+	Type *Alloc(uint32_t flags) { return (Type *)BaseType::AllocateObject(flags); }
+	void Free(Type *object) { BaseType::ReturnObject(object); }
+
+private:
+	static void _ConstructObject(void *cookie, void *object)
+	{
+		((TypedCache *)cookie)->ConstructObject((Type *)object);
+	}
+
+	static void _DestructObject(void *cookie, void *object)
+	{
+		((TypedCache *)cookie)->DestructObject((Type *)object);
+	}
+
+	virtual void ConstructObject(Type *object) {}
+	virtual void DestructObject(Type *object) {}
+};
+
+#endif

src/system/kernel/Jamfile

@@ -61,6 +61,7 @@ KernelLd kernel_$(TARGET_ARCH) :
 	kernel_util.o
 	kernel_messaging.o
 	kernel_debug.o
+	kernel_slab.o
 
 	lib$(TARGET_ARCH).a
 	kernel_platform_$(TARGET_BOOT_PLATFORM).o
@@ -91,6 +92,7 @@ KernelLd kernel.so :
 	kernel_util.o
 	kernel_messaging.o
 	kernel_debug.o
+	kernel_slab.o
 
 	lib$(TARGET_ARCH).a
 	kernel_platform_$(TARGET_BOOT_PLATFORM).o
@@ -124,6 +126,7 @@ SubInclude HAIKU_TOP src system kernel disk_device_manager ;
 SubInclude HAIKU_TOP src system kernel fs ;
 SubInclude HAIKU_TOP src system kernel lib ;
 SubInclude HAIKU_TOP src system kernel messaging ;
+SubInclude HAIKU_TOP src system kernel slab ;
 SubInclude HAIKU_TOP src system kernel util ;
 SubInclude HAIKU_TOP src system kernel vm ;
 

src/system/kernel/slab/Jamfile

@@ -0,0 +1,9 @@
+SubDir HAIKU_TOP src system kernel slab ;
+
+UsePrivateHeaders [ FDirName kernel slab ] ;
+
+KernelMergeObject kernel_slab.o :
+	Slab.cpp
+
+	: $(TARGET_KERNEL_PIC_CCFLAGS) -Wno-unused
+	;

src/system/kernel/slab/Slab.cpp

@@ -0,0 +1,448 @@
+/*
+ * Copyright 2007, Hugo Santos. All Rights Reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *      Hugo Santos, hugosantos@gmail.com
+ */
+
+#include <Slab.h>
+
+#include <string.h>
+
+#include <KernelExport.h>
+#include <util/AutoLock.h>
+
+#include <algorithm> // swap
+#include <new>
+
+// TODO all of the small allocations we perform here will fallback
+//      to the internal allocator which in the future will use this
+//      same code. We'll have to resolve all of the dependencies
+//      then, for now, it is still not required.
+
+
+// TODO this value should be dynamically tuned per cache.
+static const int kMagazineCapacity = 32;
+
+static const size_t kCacheColorPeriod = 8;
+
+static depot_magazine *_AllocMagazine();
+static void _FreeMagazine(depot_magazine *magazine);
+
+template<typename Type> static Type *
+SListPop(Type* &head)
+{
+	Type *oldHead = head;
+	head = head->next;
+	return oldHead;
+}
+
+
+template<typename Type> static inline void
+SListPush(Type* &head, Type *object)
+{
+	object->next = head;
+	head = object;
+}
+
+
+status_t
+slab_area_backend_allocate(base_cache *cache, area_id *id, void **pages,
+	size_t byteCount, uint32_t flags)
+{
+	if (flags & CACHE_ALIGN_TO_TOTAL && byteCount > B_PAGE_SIZE)
+		return NULL;
+
+	dprintf("AreaBackend::AllocatePages(%lu, 0x%lx)\n", byteCount, flags);
+
+	area_id areaId = create_area(cache->name, pages,
+		B_ANY_KERNEL_ADDRESS, byteCount, B_NO_LOCK, B_READ_AREA | B_WRITE_AREA);
+	if (areaId < 0)
+		return areaId;
+
+	dprintf("  AreaBackend::AllocatePages() = { %ld, %p }\n", areaId, *pages);
+
+	*id = areaId;
+	return B_OK;
+}
+
+void
+slab_area_backend_free(base_cache *cache, area_id area)
+{
+	dprintf("AreaBackend::DeletePages(%ld)\n", area);
+	delete_area(area);
+}
+
+
+void
+base_cache_init(base_cache *cache, const char *name, size_t objectSize,
+	size_t alignment, base_cache_constructor constructor,
+	base_cache_destructor destructor, void *cookie)
+{
+	strlcpy(cache->name, name, sizeof(cache->name));
+
+	if (alignment > 0 && (objectSize & (alignment - 1)))
+		cache->object_size = objectSize + alignment
+			- (objectSize & (alignment - 1));
+	else
+		cache->object_size = objectSize;
+
+	cache->cache_color_cycle = 0;
+
+	list_init_etc(&cache->partial, offsetof(cache_slab, link));
+	list_init_etc(&cache->full, offsetof(cache_slab, link));
+}
+
+
+cache_object_link *
+base_cache_allocate_object(base_cache *cache)
+{
+	cache_slab *slab = (cache_slab *)list_get_first_item(&cache->partial);
+
+	dprintf("BaseCache::AllocateObject() from %p, %lu remaining\n",
+		slab, slab->count);
+
+	cache_object_link *link = SListPop(slab->free);
+	slab->count--;
+	if (slab->count == 0) {
+		// move the partial slab to the full list
+		list_remove_item(&cache->partial, slab);
+		list_add_item(&cache->full, slab);
+	}
+
+	return link;
+}
+
+
+int
+base_cache_return_object(base_cache *cache, cache_slab *slab,
+	cache_object_link *link)
+{
+	// We return true if the slab is completely unused.
+
+	SListPush(slab->free, link);
+	slab->count++;
+	if (slab->count == slab->size) {
+		list_remove_item(&cache->partial, slab);
+		return 1;
+	} else if (slab->count == 1) {
+		list_remove_item(&cache->full, slab);
+		list_add_item(&cache->partial, slab);
+	}
+
+	return 0;
+}
+
+
+cache_slab *
+base_cache_construct_slab(base_cache *cache, cache_slab *slab, void *pages,
+	size_t byteCount, cache_object_link *(*getLink)(void *parent, void *object),
+	void *parent)
+{
+	dprintf("BaseCache::ConstructSlab(%p, %p, %lu, %p, %p)\n", slab, pages,
+		byteCount, getLink, parent);
+
+	slab->pages = pages;
+	slab->count = slab->size = byteCount / cache->object_size;
+	slab->free = NULL;
+
+	size_t spareBytes = byteCount - (slab->size * cache->object_size);
+	size_t cycle = cache->cache_color_cycle;
+
+	if (cycle > spareBytes)
+		cache->cache_color_cycle = cycle = 0;
+	else
+		cache->cache_color_cycle += kCacheColorPeriod;
+
+	dprintf("  %lu objects, %lu spare bytes, cycle %lu\n",
+		slab->size, spareBytes, cycle);
+
+	uint8_t *data = ((uint8_t *)pages) + cycle;
+
+	for (size_t i = 0; i < slab->size; i++) {
+		if (cache->constructor)
+			cache->constructor(cache->cookie, data);
+		SListPush(slab->free, getLink(parent, data));
+		data += cache->object_size;
+	}
+
+	return slab;
+}
+
+
+void
+base_cache_destruct_slab(base_cache *cache, cache_slab *slab)
+{
+	if (cache->destructor == NULL)
+		return;
+
+	uint8_t *data = (uint8_t *)slab->pages;
+
+	for (size_t i = 0; i < slab->size; i++) {
+		cache->destructor(cache->cookie, data);
+		data += cache->object_size;
+	}
+}
+
+
+static inline bool
+_IsMagazineEmpty(depot_magazine *magazine)
+{
+	return magazine->current_round == 0;
+}
+
+
+static inline bool
+_IsMagazineFull(depot_magazine *magazine)
+{
+	return magazine->current_round == magazine->round_count;
+}
+
+
+static inline void *
+_PopMagazine(depot_magazine *magazine)
+{
+	return magazine->rounds[--magazine->current_round];
+}
+
+
+static inline bool
+_PushMagazine(depot_magazine *magazine, void *object)
+{
+	if (_IsMagazineFull(magazine))
+		return false;
+	magazine->rounds[magazine->current_round++] = object;
+	return true;
+}
+
+
+static bool
+_ExchangeWithFull(base_depot *depot, depot_magazine* &magazine)
+{
+	BenaphoreLocker _(depot->lock);
+
+	if (depot->full == NULL)
+		return false;
+
+	depot->full_count--;
+	depot->empty_count++;
+
+	SListPush(depot->empty, magazine);
+	magazine = SListPop(depot->full);
+	return true;
+}
+
+
+static bool
+_ExchangeWithEmpty(base_depot *depot, depot_magazine* &magazine)
+{
+	BenaphoreLocker _(depot->lock);
+
+	if (depot->empty == NULL) {
+		depot->empty = _AllocMagazine();
+		if (depot->empty == NULL)
+			return false;
+	} else {
+		depot->empty_count--;
+	}
+
+	if (magazine) {
+		SListPush(depot->full, magazine);
+		depot->full_count++;
+	}
+
+	magazine = SListPop(depot->empty);
+	return true;
+}
+
+
+static depot_magazine *
+_AllocMagazine()
+{
+	depot_magazine *magazine = (depot_magazine *)malloc(sizeof(depot_magazine)
+		+ kMagazineCapacity * sizeof(void *));
+	if (magazine) {
+		magazine->next = NULL;
+		magazine->current_round = 0;
+		magazine->round_count = kMagazineCapacity;
+	}
+
+	return magazine;
+}
+
+
+static void
+_FreeMagazine(depot_magazine *magazine)
+{
+	free(magazine);
+}
+
+
+static void
+_EmptyMagazine(base_depot *depot, depot_magazine *magazine)
+{
+	for (uint16_t i = 0; i < magazine->current_round; i++)
+		depot->return_object(depot, magazine->rounds[i]);
+	_FreeMagazine(magazine);
+}
+
+
+status_t
+base_depot_init(base_depot *depot,
+	void (*return_object)(base_depot *depot, void *object))
+{
+	depot->full = NULL;
+	depot->empty = NULL;
+	depot->full_count = depot->empty_count = 0;
+
+	status_t status = benaphore_init(&depot->lock, "depot");
+	if (status < B_OK)
+		return status;
+
+	depot->stores = new (std::nothrow) depot_cpu_store[smp_get_num_cpus()];
+	if (depot->stores == NULL) {
+		benaphore_destroy(&depot->lock);
+		return B_NO_MEMORY;
+	}
+
+	for (int i = 0; i < smp_get_num_cpus(); i++) {
+		benaphore_init(&depot->stores[i].lock, "cpu store");
+		depot->stores[i].loaded = depot->stores[i].previous = NULL;
+	}
+
+	depot->return_object = return_object;
+
+	return B_OK;
+}
+
+
+void
+base_depot_destroy(base_depot *depot)
+{
+	base_depot_make_empty(depot);
+
+	for (int i = 0; i < smp_get_num_cpus(); i++) {
+		benaphore_destroy(&depot->stores[i].lock);
+	}
+
+	delete [] depot->stores;
+
+	benaphore_destroy(&depot->lock);
+}
+
+
+void *
+base_depot_obtain_from_store(base_depot *depot, depot_cpu_store *store)
+{
+	BenaphoreLocker _(store->lock);
+
+	// To better understand both the Alloc() and Free() logic refer to
+	// Bonwick's ``Magazines and Vmem'' [in 2001 USENIX proceedings]
+
+	// In a nutshell, we try to get an object from the loaded magazine
+	// if it's not empty, or from the previous magazine if it's full
+	// and finally from the Slab if the magazine depot has no full magazines.
+
+	if (store->loaded == NULL)
+		return NULL;
+
+	while (true) {
+		if (!_IsMagazineEmpty(store->loaded))
+			return _PopMagazine(store->loaded);
+
+		if (store->previous && (_IsMagazineFull(store->previous)
+			|| _ExchangeWithFull(depot, store->previous)))
+			std::swap(store->previous, store->loaded);
+		else
+			return NULL;
+	}
+}
+
+
+int
+base_depot_return_to_store(base_depot *depot, depot_cpu_store *store,
+	void *object)
+{
+	BenaphoreLocker _(store->lock);
+
+	// We try to add the object to the loaded magazine if we have one
+	// and it's not full, or to the previous one if it is empty. If
+	// the magazine depot doesn't provide us with a new empty magazine
+	// we return the object directly to the slab.
+
+	while (true) {
+		if (store->loaded && _PushMagazine(store->loaded, object))
+			return 1;
+
+		if ((store->previous && _IsMagazineEmpty(store->previous))
+			|| _ExchangeWithEmpty(depot, store->previous))
+			std::swap(store->loaded, store->previous);
+		else
+			return 0;
+	}
+}
+
+
+void
+base_depot_make_empty(base_depot *depot)
+{
+	// TODO locking
+
+	for (int i = 0; i < smp_get_num_cpus(); i++) {
+		if (depot->stores[i].loaded)
+			_EmptyMagazine(depot, depot->stores[i].loaded);
+		if (depot->stores[i].previous)
+			_EmptyMagazine(depot, depot->stores[i].previous);
+		depot->stores[i].loaded = depot->stores[i].previous = NULL;
+	}
+
+	while (depot->full)
+		_EmptyMagazine(depot, SListPop(depot->full));
+
+	while (depot->empty)
+		_EmptyMagazine(depot, SListPop(depot->empty));
+}
+
+
+typedef MergedLinkCacheStrategy<AreaBackend> AreaMergedCacheStrategy;
+typedef Cache<AreaMergedCacheStrategy> AreaMergedCache;
+typedef LocalCache<AreaMergedCache> AreaLocalCache;
+
+object_cache_t
+object_cache_create(const char *name, size_t object_size, size_t alignment,
+	void (*_constructor)(void *, void *), void (*_destructor)(void *, void *),
+	void *cookie)
+{
+	return new (std::nothrow) AreaLocalCache(name, object_size, alignment,
+		_constructor, _destructor, cookie);
+}
+
+
+void *
+object_cache_alloc(object_cache_t cache)
+{
+	return ((AreaLocalCache *)cache)->Alloc(0);
+}
+
+
+void *
+object_cache_alloc_etc(object_cache_t cache, uint32_t flags)
+{
+	return ((AreaLocalCache *)cache)->Alloc(flags);
+}
+
+
+void
+object_cache_free(object_cache_t cache, void *object)
+{
+	((AreaLocalCache *)cache)->Free(object);
+}
+
+
+void
+object_cache_destroy(object_cache_t cache)
+{
+	delete (AreaLocalCache *)cache;
+}
+