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* Features: - Low metadata overhead (just 4 bytes per object) - O(1) Alloc/Free - except when we have to call system page allocator to get additional memory. - Very low fragmentation: In all tests, xvmalloc memory usage is within 12% of "Ideal". - Pool based allocator: Each pool can grow and shrink. - It maps pages only when required. So, it does not hog vmalloc area which is very small on 32-bit systems. SLUB allocator could not be used due to fragmentation issues: http://code.google.com/p/compcache/wiki/AllocatorsComparison Data here shows kmalloc using ~43% more memory than TLSF and xvMalloc is showed ~2% more space efficiency than TLSF (due to smaller metadata). Creating various kmem_caches can reduce space efficiency gap but still problem of being limited to low memory exists. Also, it depends on allocating higher order pages to reduce fragmentation - this is not acceptable for ramzswap as it is used under memory crunch (its a swap device!). SLOB allocator could not be used do to reasons mentioned here: http://lkml.org/lkml/2009/3/18/210 * Implementation: It uses two-level bitmap search to find free list containing block of correct size. This idea is taken from TLSF (Two-Level Segregate Fit) allocator and is well explained in its paper (see [Links] below). * Limitations: - Poor scalability: No per-cpu data structures (work in progress). [Links] 1. Details and Performance data: http://code.google.com/p/compcache/wiki/xvMalloc http://code.google.com/p/compcache/wiki/xvMallocPerformance 2. TLSF memory allocator: home: http://rtportal.upv.es/rtmalloc/ paper: http://rtportal.upv.es/rtmalloc/files/MRBC_2008.pdf Signed-off-by: Nitin Gupta <ngupta@vflare.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
30 lines
768 B
C
30 lines
768 B
C
/*
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* xvmalloc memory allocator
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*
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* Copyright (C) 2008, 2009 Nitin Gupta
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*
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* This code is released using a dual license strategy: BSD/GPL
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* You can choose the licence that better fits your requirements.
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*
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* Released under the terms of 3-clause BSD License
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* Released under the terms of GNU General Public License Version 2.0
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*/
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#ifndef _XV_MALLOC_H_
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#define _XV_MALLOC_H_
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#include <linux/types.h>
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struct xv_pool;
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struct xv_pool *xv_create_pool(void);
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void xv_destroy_pool(struct xv_pool *pool);
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int xv_malloc(struct xv_pool *pool, u32 size, struct page **page,
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u32 *offset, gfp_t flags);
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void xv_free(struct xv_pool *pool, struct page *page, u32 offset);
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u32 xv_get_object_size(void *obj);
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u64 xv_get_total_size_bytes(struct xv_pool *pool);
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#endif
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