1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
|
/*
* libc/stdlib/malloc/free.c -- free function
*
* Copyright (C) 2002 NEC Corporation
* Copyright (C) 2002 Miles Bader <miles@gnu.org>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License. See the file COPYING.LIB in the main
* directory of this archive for more details.
*
* Written by Miles Bader <miles@gnu.org>
*/
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>
#include "malloc.h"
#include "heap.h"
void
free (void *mem)
{
if (mem)
{
size_t size;
struct heap_free_area *fa;
mem -= MALLOC_ALIGNMENT;
size = *(size_t *)mem;
MALLOC_DEBUG ("free: 0x%lx (base = 0x%lx, total_size = %d)\n",
(long)mem + MALLOC_ALIGNMENT, (long)mem, size);
__malloc_lock ();
/* Put MEM back in the heap, and get the free-area it was placed in. */
fa = __heap_free (&__malloc_heap, mem, size);
/* See if the free-area FA has grown big enough that it should be
unmapped. */
if (HEAP_FREE_AREA_SIZE (fa) < MALLOC_UNMAP_THRESHOLD)
/* Nope, nothing left to do, just release the lock. */
__malloc_unlock ();
else
/* Yup, try to unmap FA. */
{
unsigned long start = (unsigned long)HEAP_FREE_AREA_START (fa);
unsigned long end = (unsigned long)HEAP_FREE_AREA_END (fa);
#ifndef MALLOC_USE_SBRK
unsigned long unmap_start, unmap_end;
#endif
#ifdef MALLOC_USE_SBRK
/* Get the sbrk lock so that the two possible calls to sbrk below
are guaranteed to be contiguous. */
__malloc_lock_sbrk ();
/* When using sbrk, we only shrink the heap from the end. It would
be possible to allow _both_ -- shrinking via sbrk when possible,
and otherwise shrinking via munmap, but this results in holes in
memory that prevent the brk from every growing back down; since
we only ever grow the heap via sbrk, this tends to produce a
continuously growing brk (though the actual memory is unmapped),
which could eventually run out of address space. Note that
`sbrk(0)' shouldn't normally do a system call, so this test is
reasonably cheap. */
if ((void *)end != sbrk (0))
{
MALLOC_DEBUG (" not unmapping: 0x%lx - 0x%lx (%d bytes)\n",
start, end, end - start);
__malloc_unlock_sbrk ();
__malloc_unlock ();
return;
}
#endif
MALLOC_DEBUG (" unmapping: 0x%lx - 0x%lx (%ld bytes)\n",
start, end, end - start);
/* Remove FA from the heap. */
__heap_unlink_free_area (&__malloc_heap, fa);
if (!fa->next && !fa->prev)
/* We want to avoid the heap from losing all memory, so reserve
a bit. This test is only a heuristic -- the existance of
another free area, even if it's smaller than
MALLOC_MIN_SIZE, will cause us not to reserve anything. */
{
/* Put the reserved memory back in the heap; we asssume that
MALLOC_UNMAP_THRESHOLD is greater than MALLOC_MIN_SIZE, so
we use the latter unconditionally here. */
__heap_free (&__malloc_heap, (void *)start, MALLOC_MIN_SIZE);
start += MALLOC_MIN_SIZE;
}
#ifdef MALLOC_USE_SBRK
/* Release the main lock; we're still holding the sbrk lock. */
__malloc_unlock ();
/* Lower the brk. */
sbrk (start - end);
/* Release the sbrk lock too; now we hold no locks. */
__malloc_unlock_sbrk ();
#else /* !MALLOC_USE_SBRK */
/* MEM/LEN may not be page-aligned, so we have to page-align them,
and return any left-over bits on the end to the heap. */
unmap_start = MALLOC_ROUND_UP_TO_PAGE_SIZE (start);
unmap_end = MALLOC_ROUND_DOWN_TO_PAGE_SIZE (end);
/* We have to be careful that any left-over bits are large enough to
return. Note that we _don't check_ to make sure there's room to
grow/shrink the start/end by another page, we just assume that
the unmap threshold is high enough so that this is always safe
(i.e., it should probably be at least 3 pages). */
if (unmap_start > start)
{
if (unmap_start - start < HEAP_MIN_FREE_AREA_SIZE)
unmap_start += MALLOC_PAGE_SIZE;
__heap_free (&__malloc_heap, (void *)start, unmap_start - start);
}
if (end > unmap_end)
{
if (end - unmap_end < HEAP_MIN_FREE_AREA_SIZE)
unmap_end -= MALLOC_PAGE_SIZE;
__heap_free (&__malloc_heap, (void *)unmap_end, end - unmap_end);
}
/* Release the malloc lock before we do the system call. */
__malloc_unlock ();
if (unmap_end > unmap_start)
/* Finally, actually unmap the memory. */
munmap ((void *)unmap_start, unmap_end - unmap_start);
#endif /* MALLOC_USE_SBRK */
}
}
}
|
