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e9dec93f4b
This patch changes the organization of the slab blocks within the slab allocator. Originally, blocks were kept in a list sorted by the number of free entries. However, it turned out that the maintenance of this invariant involves a lot of overhead in the presence of a large number of blocks. The new implementation manages blocks within a ring in no particular order and maintains a pointer to the block where the next allocation is attempted. This alleviates the need for sorting blocks when allocating and deallocating. Fixes #1908
150 lines
3.1 KiB
C++
150 lines
3.1 KiB
C++
/*
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* \brief Slab allocator
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* \author Norman Feske
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* \date 2006-04-18
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*/
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/*
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* Copyright (C) 2006-2013 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU General Public License version 2.
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*/
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#ifndef _INCLUDE__BASE__SLAB_H_
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#define _INCLUDE__BASE__SLAB_H_
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#include <base/allocator.h>
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#include <base/stdint.h>
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namespace Genode { class Slab; }
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/**
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* Transitional type definition, for API compatibility only
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*
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* \deprecated To be removed once all Slab users are updated.
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*/
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namespace Genode { typedef void Slab_block; }
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/**
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* Slab allocator
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*/
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class Genode::Slab : public Allocator
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{
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private:
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struct Block;
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struct Entry;
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size_t const _slab_size; /* size of one slab entry */
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size_t const _block_size; /* size of slab block */
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size_t const _entries_per_block; /* number of slab entries per block */
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Block *_initial_sb; /* initial (static) slab block */
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bool _nested; /* indicator for nested call of alloc */
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size_t _num_blocks = 0;
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size_t _total_avail = 0;
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/**
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* Block used for attempting the next allocation
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*/
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Block *_curr_sb = nullptr;
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Allocator *_backing_store;
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/**
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* Allocate and initialize new slab block
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*/
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Block *_new_slab_block();
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/*****************************
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** Methods used by 'Block' **
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*****************************/
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void _release_backing_store(Block *);
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/**
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* Insert block into slab block ring
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*
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* \noapi
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*/
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void _insert_sb(Block *);
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/**
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* Release slab block
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*/
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void _free_curr_sb();
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/**
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* Free slab entry
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*/
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void _free(void *addr);
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public:
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/**
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* Constructor
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*
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* At construction time, there exists one initial slab
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* block that is used for the first couple of allocations,
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* especially for the allocation of the second slab
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* block.
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*/
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Slab(size_t slab_size, size_t block_size, void *initial_sb,
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Allocator *backing_store = 0);
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/**
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* Destructor
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*/
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~Slab();
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/**
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* Add new slab block as backing store
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*
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* The specified 'ptr' has to point to a buffer with the size of one
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* slab block.
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*/
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void insert_sb(void *ptr);
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/**
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* Return a used slab element, or nullptr if empty
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*/
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void *any_used_elem();
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/**
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* Define/request backing-store allocator
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*
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* \noapi
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*/
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void backing_store(Allocator *bs) { _backing_store = bs; }
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/**
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* Request backing-store allocator
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*
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* \noapi
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*/
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Allocator *backing_store() { return _backing_store; }
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/*************************
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** Allocator interface **
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*************************/
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/**
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* Allocate slab entry
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*
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* The 'size' parameter is ignored as only slab entries with
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* preconfigured slab-entry size are allocated.
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*/
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bool alloc(size_t size, void **addr) override;
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void free(void *addr, size_t) override { _free(addr); }
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size_t consumed() const override;
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size_t overhead(size_t) const override { return _block_size/_entries_per_block; }
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bool need_size_for_free() const override { return false; }
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};
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#endif /* _INCLUDE__BASE__SLAB_H_ */
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