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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | ATTRIBUTES | STANDARDS | HISTORY | BUGS | EXAMPLES | SEE ALSO |
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mallinfo(3) Library Functions Manual mallinfo(3)
mallinfo, mallinfo2 - obtain memory allocation information
Standard C library (libc, -lc)
#include <malloc.h>
struct mallinfo mallinfo(void);
struct mallinfo2 mallinfo2(void);
These functions return a copy of a structure containing
information about memory allocations performed by malloc(3) and
related functions. The structure returned by each function
contains the same fields. However, the older function,
mallinfo(), is deprecated since the type used for the fields is
too small (see BUGS).
Note that not all allocations are visible to these functions; see
BUGS and consider using malloc_info(3) instead.
The mallinfo2 structure returned by mallinfo2() is defined as
follows:
struct mallinfo2 {
size_t arena; /* Non-mmapped space allocated (bytes) */
size_t ordblks; /* Number of free chunks */
size_t smblks; /* Number of free fastbin blocks */
size_t hblks; /* Number of mmapped regions */
size_t hblkhd; /* Space allocated in mmapped regions
(bytes) */
size_t usmblks; /* See below */
size_t fsmblks; /* Space in freed fastbin blocks (bytes) */
size_t uordblks; /* Total allocated space (bytes) */
size_t fordblks; /* Total free space (bytes) */
size_t keepcost; /* Top-most, releasable space (bytes) */
};
The mallinfo structure returned by the deprecated mallinfo()
function is exactly the same, except that the fields are typed as
int.
The structure fields contain the following information:
arena The total amount of memory allocated by means other than
mmap(2) (i.e., memory allocated on the heap). This figure
includes both in-use blocks and blocks on the free list.
ordblks
The number of ordinary (i.e., non-fastbin) free blocks.
smblks The number of fastbin free blocks (see mallopt(3)).
hblks The number of blocks currently allocated using mmap(2).
(See the discussion of M_MMAP_THRESHOLD in mallopt(3).)
hblkhd The number of bytes in blocks currently allocated using
mmap(2).
usmblks
This field is unused, and is always 0. Historically, it
was the "highwater mark" for allocated space—that is, the
maximum amount of space that was ever allocated (in
bytes); this field was maintained only in nonthreading
environments.
fsmblks
The total number of bytes in fastbin free blocks.
uordblks
The total number of bytes used by in-use allocations.
fordblks
The total number of bytes in free blocks.
keepcost
The total amount of releasable free space at the top of
the heap. This is the maximum number of bytes that could
ideally (i.e., ignoring page alignment restrictions, and
so on) be released by malloc_trim(3).
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────┬───────────────┬─────────────────────────────────┐
│ Interface │ Attribute │ Value │
├─────────────┼───────────────┼─────────────────────────────────┤
│ mallinfo(), │ Thread safety │ MT-Unsafe init const:mallopt │
│ mallinfo2() │ │ │
└─────────────┴───────────────┴─────────────────────────────────┘
mallinfo()/ mallinfo2() would access some global internal
objects. If modify them with non-atomically, may get
inconsistent results. The identifier mallopt in const:mallopt
mean that mallopt() would modify the global internal objects with
atomics, that make sure mallinfo()/ mallinfo2() is safe enough,
others modify with non-atomically maybe not.
None.
mallinfo()
glibc 2.0. SVID.
mallinfo2()
glibc 2.33.
Information is returned for only the main memory allocation area.
Allocations in other arenas are excluded. See malloc_stats(3)
and malloc_info(3) for alternatives that include information
about other arenas.
The fields of the mallinfo structure that is returned by the
older mallinfo() function are typed as int. However, because
some internal bookkeeping values may be of type long, the
reported values may wrap around zero and thus be inaccurate.
The program below employs mallinfo2() to retrieve memory
allocation statistics before and after allocating and freeing
some blocks of memory. The statistics are displayed on standard
output.
The first two command-line arguments specify the number and size
of blocks to be allocated with malloc(3).
The remaining three arguments specify which of the allocated
blocks should be freed with free(3). These three arguments are
optional, and specify (in order): the step size to be used in the
loop that frees blocks (the default is 1, meaning free all blocks
in the range); the ordinal position of the first block to be
freed (default 0, meaning the first allocated block); and a
number one greater than the ordinal position of the last block to
be freed (default is one greater than the maximum block number).
If these three arguments are omitted, then the defaults cause all
allocated blocks to be freed.
In the following example run of the program, 1000 allocations of
100 bytes are performed, and then every second allocated block is
freed:
$ ./a.out 1000 100 2
============== Before allocating blocks ==============
Total non-mmapped bytes (arena): 0
# of free chunks (ordblks): 1
# of free fastbin blocks (smblks): 0
# of mapped regions (hblks): 0
Bytes in mapped regions (hblkhd): 0
Max. total allocated space (usmblks): 0
Free bytes held in fastbins (fsmblks): 0
Total allocated space (uordblks): 0
Total free space (fordblks): 0
Topmost releasable block (keepcost): 0
============== After allocating blocks ==============
Total non-mmapped bytes (arena): 135168
# of free chunks (ordblks): 1
# of free fastbin blocks (smblks): 0
# of mapped regions (hblks): 0
Bytes in mapped regions (hblkhd): 0
Max. total allocated space (usmblks): 0
Free bytes held in fastbins (fsmblks): 0
Total allocated space (uordblks): 104000
Total free space (fordblks): 31168
Topmost releasable block (keepcost): 31168
============== After freeing blocks ==============
Total non-mmapped bytes (arena): 135168
# of free chunks (ordblks): 501
# of free fastbin blocks (smblks): 0
# of mapped regions (hblks): 0
Bytes in mapped regions (hblkhd): 0
Max. total allocated space (usmblks): 0
Free bytes held in fastbins (fsmblks): 0
Total allocated space (uordblks): 52000
Total free space (fordblks): 83168
Topmost releasable block (keepcost): 31168
Program source
#include <malloc.h>
#include <stdlib.h>
#include <string.h>
static void
display_mallinfo2(void)
{
struct mallinfo2 mi;
mi = mallinfo2();
printf("Total non-mmapped bytes (arena): %zu\n", mi.arena);
printf("# of free chunks (ordblks): %zu\n", mi.ordblks);
printf("# of free fastbin blocks (smblks): %zu\n", mi.smblks);
printf("# of mapped regions (hblks): %zu\n", mi.hblks);
printf("Bytes in mapped regions (hblkhd): %zu\n", mi.hblkhd);
printf("Max. total allocated space (usmblks): %zu\n", mi.usmblks);
printf("Free bytes held in fastbins (fsmblks): %zu\n", mi.fsmblks);
printf("Total allocated space (uordblks): %zu\n", mi.uordblks);
printf("Total free space (fordblks): %zu\n", mi.fordblks);
printf("Topmost releasable block (keepcost): %zu\n", mi.keepcost);
}
int
main(int argc, char *argv[])
{
#define MAX_ALLOCS 2000000
char *alloc[MAX_ALLOCS];
size_t blockSize, numBlocks, freeBegin, freeEnd, freeStep;
if (argc < 3 || strcmp(argv[1], "--help") == 0) {
fprintf(stderr, "%s num-blocks block-size [free-step "
"[start-free [end-free]]]\n", argv[0]);
exit(EXIT_FAILURE);
}
numBlocks = atoi(argv[1]);
blockSize = atoi(argv[2]);
freeStep = (argc > 3) ? atoi(argv[3]) : 1;
freeBegin = (argc > 4) ? atoi(argv[4]) : 0;
freeEnd = (argc > 5) ? atoi(argv[5]) : numBlocks;
printf("============== Before allocating blocks ==============\n");
display_mallinfo2();
for (size_t j = 0; j < numBlocks; j++) {
if (numBlocks >= MAX_ALLOCS) {
fprintf(stderr, "Too many allocations\n");
exit(EXIT_FAILURE);
}
alloc[j] = malloc(blockSize);
if (alloc[j] == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
}
printf("\n============== After allocating blocks ==============\n");
display_mallinfo2();
for (size_t j = freeBegin; j < freeEnd; j += freeStep)
free(alloc[j]);
printf("\n============== After freeing blocks ==============\n");
display_mallinfo2();
exit(EXIT_SUCCESS);
}
mmap(2), malloc(3), malloc_info(3), malloc_stats(3),
malloc_trim(3), mallopt(3)
Linux man-pages (unreleased) (date) mallinfo(3)
Pages that refer to this page: malloc_hook(3), malloc_info(3), malloc_stats(3), mallopt(3)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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