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NAME | SYNOPSIS | DESCRIPTION | ATTRIBUTES | CONFORMING TO | BUGS | EXAMPLE | SEE ALSO | COLOPHON |
MALLINFO(3) Linux Programmer's Manual MALLINFO(3)
mallinfo - obtain memory allocation information
#include <malloc.h>
struct mallinfo mallinfo(void);
The mallinfo() function returns a copy of a structure containing
information about memory allocations performed by malloc(3) and
related functions. This structure is defined as follows:
struct mallinfo {
int arena; /* Non-mmapped space allocated (bytes) */
int ordblks; /* Number of free chunks */
int smblks; /* Number of free fastbin blocks */
int hblks; /* Number of mmapped regions */
int hblkhd; /* Space allocated in mmapped regions (bytes) */
int usmblks; /* Maximum total allocated space (bytes) */
int fsmblks; /* Space in freed fastbin blocks (bytes) */
int uordblks; /* Total allocated space (bytes) */
int fordblks; /* Total free space (bytes) */
int keepcost; /* Top-most, releasable space (bytes) */
};
The fields of the mallinfo structure 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 The "highwater mark" for allocated space—that is, the
maximum amount of space that was ever allocated. This
field is 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 │
└───────────┴───────────────┴──────────────────────────────┘
mallinfo() 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() is safe
enough, others modify with non-atomically maybe not.
This function is not specified by POSIX or the C standards. A
similar function exists on many System V derivatives, and was
specified in the SVID.
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 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 mallinfo() 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 "tlpi_hdr.h"
static void
display_mallinfo(void)
{
struct mallinfo mi;
mi = mallinfo();
printf("Total non-mmapped bytes (arena): %d\n", mi.arena);
printf("# of free chunks (ordblks): %d\n", mi.ordblks);
printf("# of free fastbin blocks (smblks): %d\n", mi.smblks);
printf("# of mapped regions (hblks): %d\n", mi.hblks);
printf("Bytes in mapped regions (hblkhd): %d\n", mi.hblkhd);
printf("Max. total allocated space (usmblks): %d\n", mi.usmblks);
printf("Free bytes held in fastbins (fsmblks): %d\n", mi.fsmblks);
printf("Total allocated space (uordblks): %d\n", mi.uordblks);
printf("Total free space (fordblks): %d\n", mi.fordblks);
printf("Topmost releasable block (keepcost): %d\n", mi.keepcost);
}
int
main(int argc, char *argv[])
{
#define MAX_ALLOCS 2000000
char *alloc[MAX_ALLOCS];
int numBlocks, j, freeBegin, freeEnd, freeStep;
size_t blockSize;
if (argc < 3 || strcmp(argv[1], "--help") == 0)
usageErr("%s num-blocks block-size [free-step [start-free "
"[end-free]]]\n", argv[0]);
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_mallinfo();
for (j = 0; j < numBlocks; j++) {
if (numBlocks >= MAX_ALLOCS)
fatal("Too many allocations");
alloc[j] = malloc(blockSize);
if (alloc[j] == NULL)
errExit("malloc");
}
printf("\n============== After allocating blocks ==============\n");
display_mallinfo();
for (j = freeBegin; j < freeEnd; j += freeStep)
free(alloc[j]);
printf("\n============== After freeing blocks ==============\n");
display_mallinfo();
exit(EXIT_SUCCESS);
}
mmap(2), malloc(3), malloc_info(3), malloc_stats(3), malloc_trim(3),
mallopt(3)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2015-12-05 MALLINFO(3)
Pages that refer to this page: malloc_hook(3), malloc_info(3), malloc_stats(3), mallopt(3)