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@(#)appendix.t 5.1 (Berkeley) 4/16/91

.bp .H 1 "Appendix A - Implementation Details"

.vS
\h'\w' 'u-\w'/'u'/*\c\c
'+C

 * 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.
 *\h'\w' 'u-\w'/'u'/\c
'-C

\*(+K#define\*(-K MINBUCKET\h'|31n'4\h'|51n'\h'\w' 'u-\w'/'u'/*\c\c
'+C
 4 => min allocation of 16 bytes *\h'\w' 'u-\w'/'u'/\c
'-C

'FN MAXALLOCSAVE
\*(+K#define\*(-K MAXALLOCSAVE\h'|31n'(2 * CLBYTES)

\h'\w' 'u-\w'/'u'/*\c\c
'+C

 * Maximum amount of kernel dynamic memory.
 * Constraints: must be a multiple of the pagesize.
 *\h'\w' 'u-\w'/'u'/\c
'-C

'FN MAXKMEM
\*(+K#define\*(-K MAXKMEM\h'|31n'(1024 * PAGESIZE)

\h'\w' 'u-\w'/'u'/*\c\c
'+C

 * Arena for all kernel dynamic memory allocation.
 * This arena is known to start on a page boundary.
 *\h'\w' 'u-\w'/'u'/\c
'-C

\*(+Kextern\*(-K \*(+Kchar\*(-K kmembase[MAXKMEM];

\h'\w' 'u-\w'/'u'/*\c\c
'+C

 * Array of descriptors that describe the contents of each page
 *\h'\w' 'u-\w'/'u'/\c
'-C

\*(+Kstruct\*(-K kmemsizes \*(+K{\*(-K
\h'|11n'\*(+Kshort\*(-K\h'|21n'ks\*_indx;\h'|41n'\h'\w' 'u-\w'/'u'/*\c\c
'+C
 bucket index, size of small allocations *\h'\w' 'u-\w'/'u'/\c
'-C

\h'|11n'u\*_short\h'|21n'ks\*_pagecnt;\h'|41n'\h'\w' 'u-\w'/'u'/*\c\c
'+C
 for large allocations, pages allocated *\h'\w' 'u-\w'/'u'/\c
'-C

\*(+K}\*(-K\c\c
'-F
 kmemsizes[MAXKMEM \h'\w' 'u-\w'/'u'/ PAGESIZE];
'FC MAXALLOCSAVE

\h'\w' 'u-\w'/'u'/*\c\c
'+C

 * Set of buckets for each size of memory block that is retained
 *\h'\w' 'u-\w'/'u'/\c
'-C

\*(+Kstruct\*(-K kmembuckets \*(+K{\*(-K
\h'|11n'caddr\*_t kb\*_next;\h'|41n'\h'\w' 'u-\w'/'u'/*\c\c
'+C
 list of free blocks *\h'\w' 'u-\w'/'u'/\c
'-C

\*(+K}\*(-K\c\c
'-F
 bucket[MINBUCKET + 16];
.bp
\h'\w' 'u-\w'/'u'/*\c\c
'+C

 * Macro to convert a size to a bucket index. If the size is constant,
 * this macro reduces to a compile time constant.
 *\h'\w' 'u-\w'/'u'/\c
'-C

'FN MINALLOCSIZE
\*(+K#define\*(-K MINALLOCSIZE\h'|31n'(1 << MINBUCKET)
'FN BUCKETINDX
\*(+K#define\*(-K BUCKETINDX(size) \e
\h'|11n'(size) <= (MINALLOCSIZE * 128) \e
\h'|21n'? (size) <= (MINALLOCSIZE * 8) \e
\h'|31n'? (size) <= (MINALLOCSIZE * 2) \e
\h'|41n'? (size) <= (MINALLOCSIZE * 1) \e
\h'|51n'? (MINBUCKET + 0) \e
\h'|51n': (MINBUCKET + 1) \e
\h'|41n': (size) <= (MINALLOCSIZE * 4) \e
\h'|51n'? (MINBUCKET + 2) \e
\h'|51n': (MINBUCKET + 3) \e
\h'|31n': (size) <= (MINALLOCSIZE* 32) \e
\h'|41n'? (size) <= (MINALLOCSIZE * 16) \e
\h'|51n'? (MINBUCKET + 4) \e
\h'|51n': (MINBUCKET + 5) \e
\h'|41n': (size) <= (MINALLOCSIZE * 64) \e
\h'|51n'? (MINBUCKET + 6) \e
\h'|51n': (MINBUCKET + 7) \e
\h'|21n': (size) <= (MINALLOCSIZE * 2048) \e
\h'|31n'\h'\w' 'u-\w'/'u'/*\c\c
'+C
 etc ... *\h'\w' 'u-\w'/'u'/\c
'-C


\h'\w' 'u-\w'/'u'/*\c\c
'+C

 * Macro versions for the usual cases of malloc\h'\w' 'u-\w'/'u'/free
 *\h'\w' 'u-\w'/'u'/\c
'-C

'FN MALLOC
\*(+K#define\*(-K MALLOC(space, cast, size, flags) \*(+K{\*(-K \e
\h'|11n'\*(+Kregister\*(-K \*(+Kstruct\*(-K kmembuckets *kbp = &bucket[BUCKETINDX(size)]; \e
\h'|11n'\*(+Klong\*(-K s = splimp(); \e
\h'|11n'\*(+Kif\*(-K (kbp\*->kb\*_next == NULL) \*(+K{\*(-K \e
\h'|21n'(space) = (cast)malloc(size, flags); \e
\h'|11n'\*(+K}\*(-K \*(+Kelse\*(-K \*(+K{\*(-K \e
\h'|21n'(space) = (cast)kbp\*->kb\*_next; \e
\h'|21n'kbp\*->kb\*_next = *(caddr\*_t *)(space); \e
\h'|11n'\*(+K}\*(-K \e
\h'|11n'splx(s); \e
\*(+K}\*(-K\c\c
'-F

'FC BUCKETINDX

'FN FREE
\*(+K#define\*(-K FREE(addr) \*(+K{\*(-K \e
\h'|11n'\*(+Kregister\*(-K \*(+Kstruct\*(-K kmembuckets *kbp; \e
\h'|11n'\*(+Kregister\*(-K \*(+Kstruct\*(-K kmemsizes *ksp = \e
\h'|21n'&kmemsizes[((addr) \*- kmembase) \h'\w' 'u-\w'/'u'/ PAGESIZE]; \e
\h'|11n'\*(+Klong\*(-K s = splimp(); \e
\h'|11n'\*(+Kif\*(-K (1 << ksp\*->ks\*_indx > MAXALLOCSAVE) \*(+K{\*(-K \e
\h'|21n'free(addr); \e
\h'|11n'\*(+K}\*(-K \*(+Kelse\*(-K \*(+K{\*(-K \e
\h'|21n'kbp = &bucket[ksp\*->ks\*_indx]; \e
\h'|21n'*(caddr\*_t *)(addr) = kbp\*->kb\*_next; \e
\h'|21n'kbp\*->kb\*_next = (caddr\*_t)(addr); \e
\h'|11n'\*(+K}\*(-K \e
\h'|11n'splx(s); \e
\*(+K}\*(-K\c\c
'-F

'FC BUCKETINDX
.vE