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/*
* 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 ();
fa = __heap_free (&__malloc_heap, mem, size);
/* Now we check to see if FA has grown big enough that it should be
unmapped. */
if (HEAP_FREE_AREA_SIZE (fa) < MALLOC_UNMAP_THRESHOLD)
/* Nothing left to do, just release the lock. */
__malloc_unlock ();
else
/* Try to unmap FA. */
{
unsigned long start, end;
#ifndef MALLOC_USE_SBRK
unsigned long unmap_start, unmap_end;
#endif
end = (unsigned long)HEAP_FREE_AREA_END (fa);
#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",
(unsigned long)HEAP_FREE_AREA_START (fa),
(unsigned long)HEAP_FREE_AREA_END (fa),
fa->size);
__malloc_unlock_sbrk ();
__malloc_unlock ();
return;
}
#endif
start = (unsigned long)HEAP_FREE_AREA_START (fa);
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)
munmap ((void *)unmap_start, unmap_end - unmap_start);
#endif /* MALLOC_USE_SBRK */
}
}
}
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