MALLOC_STATS(3) Linux Programmer's Manual MALLOC_STATS(3)NAME
malloc_stats - print memory allocation statistics
SYNOPSIS
#include <malloc.h>
void malloc_stats(void);
DESCRIPTION
The malloc_stats() function prints (on standard error) statistics about memory allocated by malloc(3) and related functions. For each
arena (allocation area), this function prints the total amount of memory allocated and the total number of bytes consumed by in-use alloca-
tions. (These two values correspond to the arena and uordblks fields retrieved by mallinfo(3).) In addition, the function prints the sum
of these two statistics for all arenas, and the maximum number of blocks and bytes that were ever simultaneously allocated using mmap(2).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
+---------------+---------------+---------+
|Interface | Attribute | Value |
+---------------+---------------+---------+
|malloc_stats() | Thread safety | MT-Safe |
+---------------+---------------+---------+
CONFORMING TO
This function is a GNU extension.
NOTES
More detailed information about memory allocations in the main arena can be obtained using mallinfo(3).
SEE ALSO mmap(2), mallinfo(3), malloc(3), malloc_info(3), mallopt(3)COLOPHON
This page is part of release 4.15 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 2017-09-15 MALLOC_STATS(3)
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MALLINFO(3) Linux Programmer's Manual MALLINFO(3)NAME
mallinfo - obtain memory allocation information
SYNOPSIS
#include <malloc.h>
struct mallinfo mallinfo(void);
DESCRIPTION
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).
ATTRIBUTES
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.
CONFORMING TO
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.
BUGS
Information is returned for only the main memory allocation area. Allocations in other arenas are excluded. See malloc_stats(3) and mal-
loc_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.
EXAMPLE
The program below employs mallinfo() to retrieve memory allocation statistics before and after allocating and freeing some blocks of mem-
ory. 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_mallinfo(void)
{
struct mallinfo mi;
mi = mallinfo();
printf("Total non-mmapped bytes (arena): %d
", mi.arena);
printf("# of free chunks (ordblks): %d
", mi.ordblks);
printf("# of free fastbin blocks (smblks): %d
", mi.smblks);
printf("# of mapped regions (hblks): %d
", mi.hblks);
printf("Bytes in mapped regions (hblkhd): %d
", mi.hblkhd);
printf("Max. total allocated space (usmblks): %d
", mi.usmblks);
printf("Free bytes held in fastbins (fsmblks): %d
", mi.fsmblks);
printf("Total allocated space (uordblks): %d
", mi.uordblks);
printf("Total free space (fordblks): %d
", mi.fordblks);
printf("Topmost releasable block (keepcost): %d
", 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) {
fprintf(stderr, "%s num-blocks block-size [free-step "
"[start-free [end-free]]]
", 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 ==============
");
display_mallinfo();
for (j = 0; j < numBlocks; j++) {
if (numBlocks >= MAX_ALLOCS) {
fprintf(stderr, "Too many allocations
");
exit(EXIT_FAILURE);
}
alloc[j] = malloc(blockSize);
if (alloc[j] == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
}
printf("
============== After allocating blocks ==============
");
display_mallinfo();
for (j = freeBegin; j < freeEnd; j += freeStep)
free(alloc[j]);
printf("
============== After freeing blocks ==============
");
display_mallinfo();
exit(EXIT_SUCCESS);
}
SEE ALSO mmap(2), malloc(3), malloc_info(3), malloc_stats(3), malloc_trim(3), mallopt(3)COLOPHON
This page is part of release 4.15 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 2017-09-15 MALLINFO(3)