freebsd-dev/share/doc/papers/kernmalloc/appendix.t

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1994-05-30 19:09:18 +00:00
.\" Copyright (c) 1988 The Regents of the University of California.
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
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.\" notice, this list of conditions and the following disclaimer in the
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.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
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.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" @(#)appendix.t 5.1 (Berkeley) 4/16/91
.\"
.bp
.H 1 "Appendix A - Implementation Details"
.LP
.nf
.vS
/*
* Constants for setting the parameters of the kernel memory allocator.
*
* 2 ** MINBUCKET is the smallest unit of memory that will be
* allocated. It must be at least large enough to hold a pointer.
*
* Units of memory less or equal to MAXALLOCSAVE will permanently
* allocate physical memory; requests for these size pieces of memory
* are quite fast. Allocations greater than MAXALLOCSAVE must
* always allocate and free physical memory; requests for these size
* allocations should be done infrequently as they will be slow.
* Constraints: CLBYTES <= MAXALLOCSAVE <= 2 ** (MINBUCKET + 14)
* and MAXALLOCSIZE must be a power of two.
*/
#define MINBUCKET 4 /* 4 => min allocation of 16 bytes */
#define MAXALLOCSAVE (2 * CLBYTES)
/*
* Maximum amount of kernel dynamic memory.
* Constraints: must be a multiple of the pagesize.
*/
#define MAXKMEM (1024 * PAGESIZE)
/*
* Arena for all kernel dynamic memory allocation.
* This arena is known to start on a page boundary.
*/
extern char kmembase[MAXKMEM];
/*
* Array of descriptors that describe the contents of each page
*/
struct kmemsizes {
short ks_indx; /* bucket index, size of small allocations */
u_short ks_pagecnt; /* for large allocations, pages allocated */
} kmemsizes[MAXKMEM / PAGESIZE];
/*
* Set of buckets for each size of memory block that is retained
*/
struct kmembuckets {
caddr_t kb_next; /* list of free blocks */
} bucket[MINBUCKET + 16];
.bp
/*
* Macro to convert a size to a bucket index. If the size is constant,
* this macro reduces to a compile time constant.
*/
#define MINALLOCSIZE (1 << MINBUCKET)
#define BUCKETINDX(size) \
(size) <= (MINALLOCSIZE * 128) \
? (size) <= (MINALLOCSIZE * 8) \
? (size) <= (MINALLOCSIZE * 2) \
? (size) <= (MINALLOCSIZE * 1) \
? (MINBUCKET + 0) \
: (MINBUCKET + 1) \
: (size) <= (MINALLOCSIZE * 4) \
? (MINBUCKET + 2) \
: (MINBUCKET + 3) \
: (size) <= (MINALLOCSIZE* 32) \
? (size) <= (MINALLOCSIZE * 16) \
? (MINBUCKET + 4) \
: (MINBUCKET + 5) \
: (size) <= (MINALLOCSIZE * 64) \
? (MINBUCKET + 6) \
: (MINBUCKET + 7) \
: (size) <= (MINALLOCSIZE * 2048) \
/* etc ... */
/*
* Macro versions for the usual cases of malloc/free
*/
#define MALLOC(space, cast, size, flags) { \
register struct kmembuckets *kbp = &bucket[BUCKETINDX(size)]; \
long s = splimp(); \
if (kbp->kb_next == NULL) { \
(space) = (cast)malloc(size, flags); \
} else { \
(space) = (cast)kbp->kb_next; \
kbp->kb_next = *(caddr_t *)(space); \
} \
splx(s); \
}
#define FREE(addr) { \
register struct kmembuckets *kbp; \
register struct kmemsizes *ksp = \
&kmemsizes[((addr) - kmembase) / PAGESIZE]; \
long s = splimp(); \
if (1 << ksp->ks_indx > MAXALLOCSAVE) { \
free(addr); \
} else { \
kbp = &bucket[ksp->ks_indx]; \
*(caddr_t *)(addr) = kbp->kb_next; \
kbp->kb_next = (caddr_t)(addr); \
} \
splx(s); \
}
.vE