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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>
86 lines
1.7 KiB
C
86 lines
1.7 KiB
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_INT_H_
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#define _XV_MALLOC_INT_H_
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#include <linux/kernel.h>
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#include <linux/types.h>
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/* User configurable params */
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/* Must be power of two */
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#define XV_ALIGN_SHIFT 2
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#define XV_ALIGN (1 << XV_ALIGN_SHIFT)
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#define XV_ALIGN_MASK (XV_ALIGN - 1)
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/* This must be greater than sizeof(link_free) */
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#define XV_MIN_ALLOC_SIZE 32
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#define XV_MAX_ALLOC_SIZE (PAGE_SIZE - XV_ALIGN)
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/* Free lists are separated by FL_DELTA bytes */
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#define FL_DELTA_SHIFT 3
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#define FL_DELTA (1 << FL_DELTA_SHIFT)
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#define FL_DELTA_MASK (FL_DELTA - 1)
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#define NUM_FREE_LISTS ((XV_MAX_ALLOC_SIZE - XV_MIN_ALLOC_SIZE) \
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/ FL_DELTA + 1)
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#define MAX_FLI DIV_ROUND_UP(NUM_FREE_LISTS, BITS_PER_LONG)
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/* End of user params */
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enum blockflags {
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BLOCK_FREE,
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PREV_FREE,
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__NR_BLOCKFLAGS,
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};
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#define FLAGS_MASK XV_ALIGN_MASK
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#define PREV_MASK (~FLAGS_MASK)
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struct freelist_entry {
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struct page *page;
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u16 offset;
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u16 pad;
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};
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struct link_free {
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struct page *prev_page;
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struct page *next_page;
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u16 prev_offset;
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u16 next_offset;
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};
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struct block_header {
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union {
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/* This common header must be ALIGN bytes */
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u8 common[XV_ALIGN];
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struct {
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u16 size;
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u16 prev;
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};
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};
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struct link_free link;
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};
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struct xv_pool {
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ulong flbitmap;
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ulong slbitmap[MAX_FLI];
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spinlock_t lock;
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struct freelist_entry freelist[NUM_FREE_LISTS];
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/* stats */
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u64 total_pages;
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};
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#endif
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