Commit 644bf7b5 authored by Nitin Gupta's avatar Nitin Gupta Committed by Greg Kroah-Hartman

Staging: xvmalloc memory allocator

* 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.pdfSigned-off-by: default avatarNitin Gupta <ngupta@vflare.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent efdf83c1
This diff is collapsed.
/*
* xvmalloc memory allocator
*
* Copyright (C) 2008, 2009 Nitin Gupta
*
* This code is released using a dual license strategy: BSD/GPL
* You can choose the licence that better fits your requirements.
*
* Released under the terms of 3-clause BSD License
* Released under the terms of GNU General Public License Version 2.0
*/
#ifndef _XV_MALLOC_H_
#define _XV_MALLOC_H_
#include <linux/types.h>
struct xv_pool;
struct xv_pool *xv_create_pool(void);
void xv_destroy_pool(struct xv_pool *pool);
int xv_malloc(struct xv_pool *pool, u32 size, struct page **page,
u32 *offset, gfp_t flags);
void xv_free(struct xv_pool *pool, struct page *page, u32 offset);
u32 xv_get_object_size(void *obj);
u64 xv_get_total_size_bytes(struct xv_pool *pool);
#endif
/*
* xvmalloc memory allocator
*
* Copyright (C) 2008, 2009 Nitin Gupta
*
* This code is released using a dual license strategy: BSD/GPL
* You can choose the licence that better fits your requirements.
*
* Released under the terms of 3-clause BSD License
* Released under the terms of GNU General Public License Version 2.0
*/
#ifndef _XV_MALLOC_INT_H_
#define _XV_MALLOC_INT_H_
#include <linux/kernel.h>
#include <linux/types.h>
/* User configurable params */
/* Must be power of two */
#define XV_ALIGN_SHIFT 2
#define XV_ALIGN (1 << XV_ALIGN_SHIFT)
#define XV_ALIGN_MASK (XV_ALIGN - 1)
/* This must be greater than sizeof(link_free) */
#define XV_MIN_ALLOC_SIZE 32
#define XV_MAX_ALLOC_SIZE (PAGE_SIZE - XV_ALIGN)
/* Free lists are separated by FL_DELTA bytes */
#define FL_DELTA_SHIFT 3
#define FL_DELTA (1 << FL_DELTA_SHIFT)
#define FL_DELTA_MASK (FL_DELTA - 1)
#define NUM_FREE_LISTS ((XV_MAX_ALLOC_SIZE - XV_MIN_ALLOC_SIZE) \
/ FL_DELTA + 1)
#define MAX_FLI DIV_ROUND_UP(NUM_FREE_LISTS, BITS_PER_LONG)
/* End of user params */
enum blockflags {
BLOCK_FREE,
PREV_FREE,
__NR_BLOCKFLAGS,
};
#define FLAGS_MASK XV_ALIGN_MASK
#define PREV_MASK (~FLAGS_MASK)
struct freelist_entry {
struct page *page;
u16 offset;
u16 pad;
};
struct link_free {
struct page *prev_page;
struct page *next_page;
u16 prev_offset;
u16 next_offset;
};
struct block_header {
union {
/* This common header must be ALIGN bytes */
u8 common[XV_ALIGN];
struct {
u16 size;
u16 prev;
};
};
struct link_free link;
};
struct xv_pool {
ulong flbitmap;
ulong slbitmap[MAX_FLI];
spinlock_t lock;
struct freelist_entry freelist[NUM_FREE_LISTS];
/* stats */
u64 total_pages;
};
#endif
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