Hugo Santos
5d6551d69f
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@20841 a95241bf-73f2-0310-859d-f6bbb57e9c96
82 lines
2.3 KiB
C++
82 lines
2.3 KiB
C++
/*
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* Copyright 2007, Hugo Santos. All Rights Reserved.
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* Distributed under the terms of the MIT License.
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*
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* Authors:
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* Hugo Santos, [email protected]
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*/
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#ifndef _SLAB_MERGED_STRATEGY_H_
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#define _SLAB_MERGED_STRATEGY_H_
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#include <slab/Strategy.h>
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// This slab strategy includes the ObjectLink at the end of each object and the
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// slab at the end of the allocated pages. It uses aligned allocations to
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// provide object to slab mapping with zero storage, thus there is only one
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// word of overhead per object. This is optimized for small objects.
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template<typename Backend>
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class MergedLinkCacheStrategy : public BaseCacheStrategy<Backend> {
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public:
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typedef typename BaseCacheStrategy<Backend>::BaseSlab BaseSlab;
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typedef typename BaseCacheStrategy<Backend>::Slab Slab;
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MergedLinkCacheStrategy(base_cache *parent)
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: BaseCacheStrategy<Backend>(parent) {}
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static inline const void *
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LowerBoundary(void *object, size_t byteCount)
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{
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const uint8_t *null = (uint8_t *)NULL;
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return null + ((((uint8_t *)object) - null) & ~(byteCount - 1));
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}
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BaseSlab *ObjectSlab(void *object) const
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{
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return _SlabInPages(LowerBoundary(object, _SlabSize()));
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}
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BaseSlab *NewSlab(uint32_t flags)
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{
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typename Backend::AllocationID id;
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void *pages;
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size_t byteCount = _SlabSize();
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// in order to save a pointer per object or a hash table to
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// map objects to slabs we required this set of pages to be
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// aligned in a (pageCount * PAGE_SIZE) boundary.
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if (Backend::AllocatePages(Parent(), &id, &pages, byteCount,
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CACHE_ALIGN_TO_TOTAL | flags) < B_OK)
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return NULL;
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_SlabInPages(pages)->id = id;
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return BaseCacheStrategy<Backend>::_ConstructSlab(_SlabInPages(pages),
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pages, byteCount - sizeof(Slab), this, NULL, NULL);
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}
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void ReturnSlab(BaseSlab *slab)
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{
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BaseCacheStrategy<Backend>::_DestructSlab(slab, NULL, NULL);
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}
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private:
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size_t _SlabSize() const
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{
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size_t byteCount = BaseCacheStrategy<Backend>::SlabSize(sizeof(Slab));
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if (byteCount > Backend::kMaximumAlignedLength)
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byteCount = Backend::kMaximumAlignedLength;
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return byteCount;
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}
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base_cache *Parent() const { return BaseCacheStrategy<Backend>::Parent(); }
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Slab *_SlabInPages(const void *pages) const
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{
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return (Slab *)(((uint8_t *)pages) + _SlabSize() - sizeof(Slab));
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}
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};
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#endif
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