chunk_mmap.c revision 245ae6036c09cc11a72fab4335495d95cddd5beb 
1#define	JEMALLOC_CHUNK_MMAP_C_
2#include "jemalloc/internal/jemalloc_internal.h"
3
4/******************************************************************************/
5
6static void *
7chunk_alloc_mmap_slow(size_t size, size_t alignment, bool *zero, bool *commit)
8{
9	void *ret;
10	size_t alloc_size;
11
12	alloc_size = size + alignment;
13	/* Beware size_t wrap-around. */
14	if (alloc_size < size)
15		return (NULL);
16	do {
17		void *pages;
18		size_t leadsize;
19		pages = pages_map(NULL, alloc_size);
20		if (pages == NULL)
21			return (NULL);
22		leadsize = ALIGNMENT_CEILING((uintptr_t)pages, alignment) -
23		    (uintptr_t)pages;
24		ret = pages_trim(pages, alloc_size, leadsize, size);
25	} while (ret == NULL);
26
27	assert(ret != NULL);
28	*zero = true;
29	if (!*commit)
30		*commit = pages_decommit(ret, size);
31	return (ret);
32}
33
34void *
35chunk_alloc_mmap(void *new_addr, size_t size, size_t alignment, bool *zero,
36    bool *commit)
37{
38	void *ret;
39	size_t offset;
40
41	/*
42	 * Ideally, there would be a way to specify alignment to mmap() (like
43	 * NetBSD has), but in the absence of such a feature, we have to work
44	 * hard to efficiently create aligned mappings.  The reliable, but
45	 * slow method is to create a mapping that is over-sized, then trim the
46	 * excess.  However, that always results in one or two calls to
47	 * pages_unmap().
48	 *
49	 * Optimistically try mapping precisely the right amount before falling
50	 * back to the slow method, with the expectation that the optimistic
51	 * approach works most of the time.
52	 */
53
54	assert(alignment != 0);
55	assert((alignment & chunksize_mask) == 0);
56
57	ret = pages_map(new_addr, size);
58	if (ret == NULL || ret == new_addr)
59		return (ret);
60	assert(new_addr == NULL);
61	offset = ALIGNMENT_ADDR2OFFSET(ret, alignment);
62	if (offset != 0) {
63		pages_unmap(ret, size);
64		return (chunk_alloc_mmap_slow(size, alignment, zero, commit));
65	}
66
67	assert(ret != NULL);
68	*zero = true;
69	if (!*commit)
70		*commit = pages_decommit(ret, size);
71	return (ret);
72}
73
74bool
75chunk_dalloc_mmap(void *chunk, size_t size)
76{
77
78	if (config_munmap)
79		pages_unmap(chunk, size);
80
81	return (!config_munmap);
82}
83