haiku/headers/private/kernel/slab/MergedStrategy.h
Hugo Santos 81423c91c7 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
2007-04-26 03:41:24 +00:00

105 lines
2.6 KiB
C++

/*
* 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